Proteins offer a diversity of self-assembly pathways: not only of the amino acid-based polymer itself, but in biomineralization, a protein matrix directs crystal phase and orientation of inorganic materials. The rich sequence diversity of proteins, however, has not been demonstrated for synthetic three-dimensional (3-D), continuous frameworks. Block copolymers offer long range periodic order of 0-D to 3-D structures through self-assembly and have been utilized to template high-surface area inorganic materials. Nevertheless, control has primarily been spatial while direction of crystal type and crystallographic orientation has remained challenging. By combining the long-range periodic structure direction of block copolymers with the chemical and sequence specificity of peptides, new highly-controlled composite materials might be created. Here we demonstrate the synthesis of peptide and peptoid functionalized block copolymers. By altering the amino acid content and order, we investigate the role of peptide/peptoid sequence on polymer self-assembly and on directed and templated inorganic materials growth.

Crosslinked polymers are ubiquitous in medical devices, so understanding the physiochemical processes which underlie network formation is highly pertinent to predicting their properties and % extractables. For example, the poly(ethylene) used in artificial joints is crosslinked by gamma radiation, which causes simultaneous chain scission and coupling reactions. To gain insight into this class of materials we synthesized a model copolymer and studied its response to light stimuli under various conditions. Its architecture was designed to satisfy two functionality requirements not present in commercially available materials. One chemical subunit produces indiscriminate grafting reactions when irradiated by UV light, and the other group enables the polymer to be spin-coated into smooth, ultrathin films from polar solvents. Under specific exposure conditions, 10-30 nm thick crosslinked films possessing no soluble fraction can be obtained. We use this material to manufacture highly reactive surfaces to which hydrophobic materials can be deposited and immobilized. Our results show that even inert polymers such as poly(styrene) can be covalently affixed to these surfaces in short times and with microscopic spatial control, which bodes well for this material being potentially useful for attaching many other soft materials to surfaces in sensor, diagnostic, and antifouling applications.

Interest in soft and hard tissue adhesives as alternatives for conventional wound closing and bone fixation applications has increased in recent decades as a result of possible advantages such as better comfort and lower cost. Bioadhesives is a research topic of very high challenge in terms of materials science because they must be able to be spread on wound surfaces, which are wet with tissue fluids or blood, and also to provide adhesion in such tough conditions. Moreover, they should facilitate healing and maintain biocompatibility.
Novel tissue adhesives based on the natural polymers gelatin and alginate, and crosslinked by carbodiimide, were recently developed and studied by us. The combination of these three materials resulted in high strength, high biocompatibility and additional desired properties for various specific applications. Unique bioadhesives are achieved when loaded the basic formulations with functional additives, such as hemostatic agents, drug molecules and bioactive ceramics. These three types of composite functional bioadhesives will be described in terms of formulation-structure-property effects as well as in-vivo results.
We examined the effects of the bioadhesive component concentrations and their viscosities on the ability to bind hard and soft tissues. A qualitative model describing these effects in terms of adherence mechanisms was developed. Our results show that the adherence properties of our new bioadhesives are achieved by a combination of two main mechanisms: mechanical interlocking and chemical adsorption. The former mechanism is probably more dominant.
Specific formulations were loaded with hemostatic agents, such as kaolin, which improves adhesion and overall function in a hemorrhagic environment. Such formulations can be extremely beneficial for any application where it is necessary to reduce the liquids volume in order to get better sealing effects.
Delivering an antibiotic drug locally using our bioadhesive could decrease the risk of infections and increase the therapeutic effect of bioadhesive. Among the studied antibiotic-eluting formulations, clindamycin was selected as the preferred drug, since it is inert toward the cross-linking reaction.
In conclusion, bioadhesives, based on natural polymers and include functional fillers (hemostatic agents, drugs and ceramic fillers) are novel. They actually behave as composite bioadhesives, and thus present a new concept of adhesive biomaterials. The understanding of the relationships between formulation parameters, structure and the resulting relevant in-vitro properties and in-vivo functioning, are of great scientific and medical relevance. They are expected to provide new solutions to the basic needs in various medical.

Spatial organization as well as determination of mechanical behavior of the extracellular matrix (ECM) are ruled by specific non-covalent interactions of biomacromolecules. However, in biomaterial design, the use of covalent crosslinking strategies is predominant in order to stabilize hydrogels under physiological conditions. In the case of collagen, non-covalent strategies include e.g. stabilization of collagen by small diacids as well as coupling of collagen-related peptides through metal complexation or by π-π interactions.¹ Specificity and strength of the interaction is of primary importance on the way to more complex systems, e.g. when incorporating further components of the ECM, and therefore novel strategies for crosslinking and tailoring of mechanical properties are required. Decorin is a protein of the ECM that contributes to collagen fibrillinogenesis. We hypothesized that by elucidating the binding epitope of decorin to collagen, a rational design approach allows the identification of collagen binding peptides being applicable in biomaterial design. For this purpose, the horseshoe-like structure of decorin was divided into the distinct outer and inner surfaces. Consensus sequences of the highly repetitive sequence structures were proposed and corresponding peptides were synthesized on solid-phase.² In addition to the sequence of peptides, in circular dichroism studies it could be shown that the peptide sequences also adopt the secondary structures as in decorin, with peptides derived from the outer surface adopting α-helical conformation, while peptides derived from the inner surface displayed β-strand content. Peptides representative for the suggested consensus sequence of the inner surface of decorin showed binding to immobilized collagen up to dissociation constants of 100 nM in surface plasmon resonance. In contrast, peptides based on the outer surface did not show binding to collagen. Dimers of the peptide with the highest binding affinity increased the storage modulus G&’ of a collagen gel in a concentration-dependent manner by up to one order of magnitude. In addition, a decorin-derived peptide was covalently attached to hyaluronic acid, and the rheological behavior of such a system in the presence of collagen was investigated. In such protein-polysaccharide hybrid hydrogels based on components of the ECM, an increase of storage modulus by two orders of magnitude was achieved in comparison to a hydrogel consisting of hyaluronic acid and collagen. In summary, a strategy for identification of relevant binding motifs in protein-protein-interaction is presented, whose implementation could be successfully shown and which provided novel peptide sequences for biomaterial design and applications.
References
1: A. T. Neffe, C. Wischke, M. Racheva, A.Lendlein, Exp. Rev. Med. Devices2013, 10, 813-833.
2: S. Federico, B.F. Pierce, S. Piluso, C. Wischke, A. Lendlein, A.T. Neffe, Angew. Chem. Int. Ed.2015, DOI: 10.1002/anie.201505227.

Self-assembled supramolecular polymers are interesting materials in the field of nanoscience and for biomedical applications. One of the main challenges thereby is to control the polymerization of such a material to form well-defined and well-ordered nanostructures.^[1] A promising starting point are dendritic symmetric peptide-based amphiphiles. This β-sheet encoded monomers are known to build one-dimensional polymers in water.^[2,3]
In a first approach we synthesized a series of anionic dendritic peptide amphiphiles and by controlling the hydrophobicity in the sequence of the peptide backbone, we could tune the triggered polymers.^[4] The switch between the monomeric and the polymeric state of the peptide amphiphiles is induced by pH or ionic strength. Via the incorporation of fluorinated peptide side chains the pH-triggered monomer to polymer transition at physiological ionic strength is shifted form pH 5.0 to pH 7.4. We show that compensating attractive non-covalent interactions and hydrophobic effects with repulsive electrostatic forces is a sensitive tool to regulate one-dimensional supramolecular polymerisation processes in water.
In a second approach we manipulate the balance between the attractive supramolecular interactions and repulsive forces using steric constraints. Therefore we use a small library of charge neutral dendritic peptide amphiphiles. The branched monomeric hydrophobic based core is conjugated to hydrophilic dendrons of variable steric demand. Below a critical size of the dendron, the monomers assemble into well-defined rod-like polymers, whereas in larger dendritic side-chains, into isotropic particles is observed. The supramolecular morphologies are in agreement with the mechanistic insights obtained from fitting polymerisation profiles: non-cooperative growth leads to degrees of polymerisations that match the experimentally determined nanorod contour lengths distributions, based on monomers with nanomolar affinities.
The reported designs for the aqueous self-assembly into well-defined anisotropic particles has potential for biomedical applications and the development of functional multi-stimuli responsive supramolecular materials. Our goal is to explore new avenues for applications in imaging and therapy like targeted molecular imaging and diagnostics or responsive and switchable drug delivery vehicles.
References:
[1] T. Aida et al., Science, 2012, 335, 813.
[2] C. Schaefer et al.,ACS Macro Lett. 2012, 1, 830-833.
[3] M. v. Gröning et al.,M. J. Mater. Chem. B 2013, 1, 2008-2012.
[4] R. Appel et al., Org. Biomol. Chem.2015, 13, 1030-1039.

In this study, we present a new and simple way to generate polymer brushes with excellent restoring capabilities even under tribological stress and the potential biomedical applications. Hydrophilic polymer brushes grafted on surfaces are known to display effective lubricity in aqueous environment. Coefficients of friction lower than 0.001 have been reported based on repulsive interaction between opposing polymer brushes. However, such lubricating effect is warranted under mild contact pressure only, and the immobilized polymer chains suffer from rupture under harsher tribostress. Furthermore, “grafting-from” techniques often employed to functionalize surfaces with polymer brushes demand cumbersome multistep procedures. While “grafting-to” approach may provide simpler and long-term stability based on continuous formation of lubricating film under tribological stress, it requires excess polymers surrounding the contacting area to regenerate films, which limits the scope of applications. In the presently reported “inversed grafting-to” approach, a layer of poly(dimethyl siloxane-block-poly(acrylic acid)) (PDMS-b-PAA) is added on top of PDMS substrate and cured. Then, spontaneous segregation of PDMS-b-PAA in the matrix of PDMS network upon interfacing with water leads to the formation of PAA brush layers on PDMS surface. Thus, the surface lubricity becomes an integral part of the material properties and does not originate from post-modification of the surface. Sliding contacts against PDMS counter surface provided µ values down to 0.003 by pin-on-disk experiments under 10 N. This film can be applied to any materials on which PDMS film can be coated, such as elastomer, glass or metal surfaces. An outstanding merit of the presently demonstrated approach is long-term lubricity without replenishment from external sources, due to the persistent generation of polymer brushes as they segregate from the PDMS matrix. For example, µ < 0.008 was maintained from the film generated up to 100,000 laps at 50 mm/s (> 10 h). Lastly, the effective lubricity observed from the condition of neutral pH and 150 mM NaCl suggests potential application as coatings for biomedical devices such as endoscopes and catheters where slipperiness is highly demanded at physiological salinity. Furthermore, given that the segregating polymer brush is PAA, a well-known mucoadhesive polymer, this approach can be utilized to immobilize mucin molecules and/or mucus gels atop, leading to the formation of in-vitro mucosa membrane model. This can provide a template with which the lubricating efficacy of tissue-contacting devices can be tested prior to clinical applications.

Self-assembling peptides have recently attracted significant interest for the design of hydrogels for a wide range of applications: from tissue engineering to drug delivery. The main challenge is being able to rationally design these peptides so as to engineer their physical properties, in particular mechanical. This requires an in depth understanding of the self-assembling processes at all length scales as the properties of the final materials will not only depend on the intrinsic properties of the fibres themselves but also on how they assemble and ultimately on the properties of the network formed.
β-sheet forming peptides are very attractive for the design of biomaterials in particular hydrogels due to the “simplicity” of the structure formed at the molecular level, the relative robustness of the β-sheet assembly and the ease of functionalisation. We have investigate the self-assembly of a family of b-sheet forming octa-peptides based on the alternation of hydrophobic and hydrophilic residues (Saiani et al., Soft Matter, 5, 193, 2009). Using a range of techniques including FTIR, TEM, AFM, SAXS, SANS and rheometry we have investigate how the primary structure of the peptide affects the fibrillar assembly as well as the topology of the network formed and ultimately the mechanical properties of the resulting hydrogel. We have shown that the promotion of self-consistent heterogeneities within the fibrillar network by promoting the lateral aggregation of the fibres strongly affect the mechanical properties of the hydrogels. This was achieved by either controlling the properties of the surrounding media or by specifically designing the primary structure of the peptide so as to promote fibre aggregation (S Boothroyd et al., Faraday Discussions, 166, 195-207 2013).
The in-depth understanding of the factors affecting the mechanical properties of these materials has allowed us to design functional and non-functional hydrogels with tailored mechanical properties for a range of application including as 3D-scaffolds for cell culture (Acta Biomat., 9, 4609, 2013), injectables hydrogels for the delivery of cell and drugs (D Roberts at al. Langmuir, 28, 16196-16206 2012), as well as sprayable muco-adhesive hydrogels for topical drug delivery (C. Tang et al. Int. J. of Pharm., 465, 427, 2014)

Some amphiphilic block copolymers can form not only micelles, but also physical hydrogels in water. In the latest decade, our group has made investigation of a thermogel of polyester and polyether [1-10]. Especially, PLGA-PEG-PLGA block copolymers can, under appropriate block lengths, be dissolved in water at low temperature to form a sol, and the sol is spontaneously transformed into a physical gel upon heating. If the sol-gel transition temperature is below body temperature, the underlying system affords a unique injectable and biodegradable hydrogel, which can encapsulate drugs and cells very conveniently. My lecture will introduce the underling microstructure, corresponding sustained release carriers of drugs, and other potential in vivo applications.
(1) A subtle end-group effect on macroscopic physical gelation of triblock copolymer aqueous solutions
Lin Yu, Huan Zhang, Jiandong Ding*, Angew. Chem. Int. Edit., 45, 2232-2235 (2006)
(2) Temperature-induced spontaneous sol-gel transitions of Poly(D,L-lactic acid-co-glycolic acid)-b-Poly(ethyleneglycol)-b-Poly(D,L-lactic acid-co-glycolic acid) triblock copolymers and their end-capped derivatives in water
Lin Yu, Guangtao Chang, Huan Zhang, Jiandong Ding*, J. Polym. Sci. Polym. Chem., 45, 1122-1133 (2007)
(3) Injectable hydrogels as unique biomedical materials
Lin Yu, Jiandong Ding*, Chem. Soc. Rev., 37, 1473-1481 (2008)
(4) Injectable block copolymer hydrogels for sustained release of a PEGylated drug
Lin Yu, Guangtao Chang, Huan Zhang, Jiandong Ding*, Int. J. Pharm., 348 95-106 (2008)
(5) Roles of hydrophilic homopolymers on the hydrophobic-association-induced physical gelling of amphiphilic block copolymers in water
Huan Zhang, Lin Yu, Jiandong Ding*, Macromolecules, 41, 6493-6499 (2008)
(6) Enhancement of the fraction of the active form of an antitumor drug topotecan via an injectable hydrogel
Guangtao Chang, Tianyuan Ci, Lin Yu, Jiandong Ding*, J. Controlled Release, 156, 21-27 (2011)
(7) A long-acting formulation of a polypeptide drug exenatide in treatment of diabetes using an injectable block copolymer hydrogel
Kun Li#, Lin Yu#, Xiaojun Liu, Chang Chen, Qinghua Chen*, and Jiandong Ding*,Biomaterials, 34(11), 2834-2842 (2013)
(8) Tumor regression achieved by encapsulating a moderately soluble drug into a polymeric thermogel
Tianyuan Ci, Liang Chen, Lin Yu, and Jiandong Ding*, Sci. Rep., 4: 5473 | doi: 10.1038/srep05473 (2014)
(9) Effects of molecular weight distribution of amphiphilic block copolymers on their solubility, micellization and temperature-induced sol-gel transition in water
Liang Chen, Tianyuan Ci, Ting Li, Lin Yu, and Jiandong Ding*,Macromolecules, 47, 5895minus;5903 (2014)
(10) Effects of molecular weight and its distribution of PEG block on micellization and thermogellability of PLGAminus;PEGminus;PLGA copolymer aqueous solutions
Liang Chen, Tianyuan Ci, Lin Yu, Jiandong Ding*,Macromolecules, 48(11), 3662-3671 (2015)

An increasing number of interventional surgeries are being performed nowadays under magnetic resonance imaging (MRI) acquisition. Such procedures require the use of dedicated tools (biopsy needles, catheters, positioning inserts). Because images in MRI are generated by the excitation - and energy release - of hydrogen contained in water, lipids, and other small and mobile molecules, polymers and metals are not easily visualised in MRI-guided surgery. This lack of signal, often coupled with magnetic susceptibility artifacts, impede precise interventions (e.g. biopsies of millimetre-sized nodules). In this study, the development of a new generation of paramagnetic hydrogels is reported. Such hydrogels could be applied at the surface of various metal and polymer biomedical objects. For this, mesoporous silica nanoparticles (MSNs) of high pore volume and well-controlled size distribution (sim;140 nm diam.) were synthesized using a modified Stöber methodology.¹ The outer surface of particles were grafted with DTPA chelators, followed by labeling with paramagnetic Gd³⁺ ions (a contrast agent allowing efficient signal-enhancement in MRI). The relaxometric properties of the MSN:Gd³⁺ suspensions, i.e. the expected signal-enhancement "performance" of such contrast agents in MRI, were measured at 1.41 Tesla (clinical magnetic field strength; r₁ = 26 mM^-1s^-1; r_2/r₁ = 1.46). The longitudinal relaxivity (r₁) of MSN:Gd³⁺ was 6.5 times higher than that of Gd³⁺-DTPA, one of the most widely used contrast agents in the clinics. As signal enhancement in T₁-weighted MRI is optimal in a relatively narrow Gd³⁺ concentration range, and for coating thicknesses in the same order as MRI voxels (100 - 500 microns), the volume dilutions were precisely calculated prior to polymerization procedures. Then, MSN-Gd³⁺ were suspended in preparations of polyethylene glycol-acrylate . Carefully cleaned titanium needles (diam.: 1.05 mm) having received a functional phosphatization treatment (phosphate-acrylate; assessed by XPS and FTIR analyses) were dip-coated in the polymer-MSN:Gd³⁺ preparation, followed by UV-curing for polymerization. The as-prepared hydrogel coatings were thoroughly cleaned, kept in aqueous solutions, measured for thickness (in optical microscopy; 40 - 70 microns average hydrated hydrogel thickness), and imaged in T₁-weighted MRI (for "positive" contrast). Cross-sections and longitudinal acquisitions of the needles performed at different resolution parameters, showed a positive contrast at the surface of 1.05 mm-diam. paramagnetic hydrogel-coated titanium biopsy needles. Standard spin-echo acquisitions performed in less than one minute, suggest the possibility to proceed to fast MRI acquisitions (less than 10 s) using T₁-w. MRI. Optimal conditions for avoiding partial volume effects, will be presented and discussed.
1. Bouchoucha M., Gaudreault RC, Fortin MA, Kleitz F, (2014) Advanced Functional Materials, Volume 24, Issue 37, pages 5911-5923, October 8, 2014.

Collagen based hydrogels have similar properties to native cornea and play an important role in ocular drug delivery. Here we report the extraction of type 1 collagen from bovine hide split and the preparation of various quantum dot (ZnO, TiO₂, SiO₂) /collagen hydrogel systems by making use of the interactions of the polymer capping on the quantum dots (Qd&’s). The Qd&’s can be embedded in the collagen matrix by gelation caused by chemical cross-links, by forming either intra or inter molecular bonds between the amino acid groups of collagen, photochemical cross-linking with ultraviolet light or by physical cross-linking. The hydrogels were characterized by FTIR, DSC and electron microscopy. The mechanism by which gelation occurred was studied by in-situ beamline SAXS measurements and will be discussed. Also, the responses of retinal epithelial cells (ARPE-19) to the collagen ZnO/PVP hydrogels were examined by cell viability assays and exhibited minimal cytotoxicity. The results from these experiments indicate that quantum dot/hydrogels are promising candidates for corneal implant applications and, that the system in general is useful for creating permeable substrates for ophthalmic and other biomedical applications.

Polymer engineering, specifically tuning monomer chemistries, polymerization kinetics and thin film interfaces, seeks to address grand challenges in neuroscience, semiconductor processing, the internet of things and additive manufacturing.
We demonstrate peripheral and cortical neural stimulators and recording devices using engineered low cure stress softening polymer substrates. Polymers can be implanted at moduli of more than 1 GPa and soften toward the modulus of tissue. Encapsulation materials include combinations of zwitterions, hydrophobic thiol-based polymers, parylene-C, silicon nitride, and ultrananocrystalline diamond. Neural interfaces allow for delivery of a large amount of information transfer, but current microstimulators or microrecorders fail chronically or are poorly suited for interfacing with small biological structures. We demonstrate the effects of self-coiling vagus nerve stimulators and self-wrapping cochlear implants. We demonstrate spinal stimulators that reduce inflammation and tissue response and behave in a manner similar to ball electrodes for use in understanding long-term muscle plasticity. We demonstrate softening peripheral neural interfaces for modulating sensory and motor input toward closed-loop feedback for prosthetics.
We demonstrate large area flexible substrates compatible with full photolithographic process with 2 micron minimum features sizes at temperatures cycles up to 300°C. Substrates compatible with high mobility semiconductors such as indium-gallium zinc oxide are highlighted. Devices are thermally cycled through thermal transitions and compared to state-of-the-art flexible substrates including biaxially oriented poly (ethylene naphthalate), polydimethylsiloxane, polyimides and others. Furthermore, we use these processes to show a host of sensor and energy harvesting applications powering the emerging internet of things. Pressure sensors on one of the world&’s softest fully elastic materials are demonstrated with matrix-addressed pixel accuracy. Engineered temperature sensors show changes in electrical performance of more than 6 orders of magnitude over less than 5 °C. Antenna technologies are discussed that allow wireless powering of flexible devices. We explore failure limits in strain tolerant thin film conductors on flex.
We demonstrate methods to 3D print materials that are isotropic, namely deformation perpendicular to the print grain does not lead to poorer thermomechanical properties than deformation in the XY plane along the print grain. This is accomplished using thiol-click chemistries and recently developed stereolithography printing techniques including our patent pending Z-Cup® paradigm. Tough materials across modulus ranges are printed into complex shapes and compared to state-of-the-art 3D printed materials. We take advantage of partial polymerization of oxygen-insensitive resins that can subsequently chemically crosslink into successive layers leading to strong tough materials.

High-performance polymer applications such as medical devices, aerospace components and others have led to a demand for polymers with stable and robust properties at elevated temperatures. Traditional polymers used in these environments, such as polyimides, are often synthesized using prepolymers, requiring solvent based depositions and removal of side products. Inclusion of these volatile species presents a challenge for post-processing of bulk samples, where leachable or volatile molecules can exit the final network and react further with outside packaging. Thiol-ene polymers, a potential candidate for these applications, are often polymerized via radical or nucleophilic (Michael addition) means. However, both routes generally require catalytic stimulation to proceed in a timely fashion. Using a copolymer network composed of maleimides and multi-functional thiols, a softening, high glass transition (Tg) thiol-click network is described for use as a viable option for applications in high heat environments.
In this study, several comparable networks are formed to investigate the mechanical properties of final polymer networks—such as Tg, Young&’s modulus, thermal degradation temperatures, and other characteristics—to isolate the contribution made by the succinimide thioether linkage, specifically for the increased glass transition above 100°C for an amorphous polymer network. The terminal reactive groups in question (alkenes, epoxies, and maleimides) are copolymerized with multi-functional thiols, and the thermomechanical properties and Fourier Transform Infrared (FTIR) spectrograms are explored.
These polymers show promise as a possible softening thiol-click network for use in high temperature, small molecule sensitive environments such as high vacuum systems and the semiconductor industry.

Click chemistry is a collection of organic chemical reactions that are rapid, selective, and high yielding. One of the most versatile and facile click reactions is the thiol-ene reaction, the radical-mediated reaction between a thiol (an -SH group) and an ‘ene&’ (an electron rich vinyl group, C=C) in the presence of a photoinitiator and light. Much work has been done to explore the reaction kinetics and mechanical, thermal, and optical properties of polymer networks formed using multifunctional thiol and ene monomers;^1,2 however, the incorporation of charged allylic species, such as ionic liquids, with multifunctional thiol monomers to create ion conductive membranes is relatively unexplored.
The design of highly tunable ion conductive thiol-ene networks hinges on an understanding of how the presence of ionic species affects the thiol-ene reaction and, consequently, the fabricated network properties. Thus, the presented work will explore the effect of cationic monomers with allylic functionalities on the thiol-ene reaction and exploit this understanding to the design of ion conductive networks with tailored properties. In particular, the incorporation of a diallylic quaternary ammonium monomer within a thiol-ene network formulation results in an ion exchange membrane with tunable and reproducible properties acceptable for energy conversion applications.³ Subsequently, a route to the design of networks with controlled morphologies will be described via the synthesis of novel dienyl cationic monomers.
(1) Li, Q.; Zhou, H.; Hoyle, C. E. Polymer2009, 50, 2237.
(2) Hoyle, C. E.; Bowman, C. N. Angew. Chem. Int. Ed.2010, 49, 1540.
(3) Tibbits, A.; Mumper, L.; Kloxin, C.; Yan, Y. Submitted.

Asymmetric hybrid nanoparticles have many important applications in optics, catalysis, nanomotion, sensing, and diagnosis, however, ways to generate the asymmetric hybrid nanoparticles are quite limited and inefficient. We recently discovered two facile methods for bottom-up, bulk synthesis of asymmetric hybrid plasmonic nanoparticles which incorporate both Au metal and poly(di-vinyl benzene) (PDVB) cross-linked polymer. The composite particles are made by interfacial polymerization using novel methods for symmetry breaking. The first method uses Au nanoparticles (NPs) as seeds, which initially start with a uniform coating of PDVB and grow asymmetrically due to the non-linear swelling of the rubber-like polymer. More recently we also demonstrated a one-pot synthesis of Janus Au/PVDB NPs, where the symmetry breaking occurred at the interface of the monomer droplets and the asymmetry is maintained due to incomplete wetting and spatially separate reactions. Both methods allow tuning of the plasmonic properties by the absolute size of the Au and PDVB components, as well as the ratio of their relative sizes. The different mechanisms can lead to better understanding of non-biological morphogenesis, as well as novel types of material combinations for Janus particles. Hierarchical assembly needs asymmetric building blocks, and efficient synthetic methods, as the ones shown here, are expected to stimulate the creation of novel complex structures.

Antibody-antigen precipitation or immunoprecipitation (IP) experiments are routinely performed by biologists to isolate specific antigens and to identify their interactors from complex protein mixtures. Immobilization of biomolecules, such as antibodies and other functional proteins, is a key step to increase the efficiency of immunoprecipitation. The conventional approach involving agarose supports utilizes protein A/G which selectively binds to the heavy chain within the Fc region of most antibodies for good antibody-binding capability. Agarose-based immunoprecipitation, however, often suffers from high nonspecific binding and antibody contamination. To overcome these disadvantages, we prepared silica nanospheres with poly(pentafluorophenyl acrylate) (poly(PFPA)) brushes which, upon sequential functionalization with antibodies and polyethylene glycol (PEG), showed reduced nonspecific protein adsorption and complete elimination of antibody contamination. Poly(PFPA) brushes were grated onto silica beads via surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization. The beads covered with poly(PFPA) brushes were used to monitor the detection capability of target protein using immunoprecipitation after post-modification with antibodies followed by modification using amine-terminated PEG for the reduction of surface hydrophobicity and nonspecific interactions. The resulting antibody-attached silica nanospheres were characterized by TGA, DLS, and TEM. Considering their versatility and convenient features, we expect that poly(PFPA) platforms could be utilized as an alternative to traditional agarose-based platforms.

For adherent cells, cell adhesion and spreading are the primary steps for cell migration and proliferation. Besides the junctions among cells, cell and extracellular matrix (ECM) interaction also plays an important role in cell adhesion, spreading and migration. Here we present an approach to observing subcellular confinement by fibronectin patterns created by microcontact printing (mu;CP) technique. Different sizes of circular patterns (diameter 3mu;m and 6mu;m) with consistent fibronectin coverage (~40%) are created. Human Umbilical Vein Endothelial Cells (HUVECs), Vein Smooth Muscle Cells (VSMCs) and 3T3 were used in the experiments. We observed the spreading stages of HUVECs and found that fibronectin coverage exerts minimal influences on HUVECs spreading but the gaps between patterns influence the HUVECs spreading dramatically. Fibronectin displacement was also observed and quantified to illustrate the influences of cell forces to ECM protein. The fibronectin pattern displacement is commonly observed in VSMCs culture (about 60%) but rarely observed in HUVECs culture (less than 1%). Finally we give a quantitative relationship between the focal adhesion (FA) sizes and the confinement of FA shapes exerted by the ECM patterns. With the enlargement of FA sizes, the FAs on the circular patterns are more and more confined to circular shapes while FAs on a uniform substrate are getting elongated.

Synthetic microparticles are a major class of “designer” materials, with applications ranging from drug delivery and biomedical imaging to directed assembly of photonic crystals and other functional materials. Successful synthesis of well-defined colloidal materials for these applications requires tight control over not only their chemical properties, but also their physical attributes such as microparticle size and shape. Unfortunately, many facile and scalable emulsion-based preparation methods result in heterogeneous, polydisperse colloidal mixtures. Overcoming this limitation via downstream sorting would enable purified populations of microparticles with specific desired morphologies to be obtained. Some bulk physical methods such as centrifugation can be used to enrich particles based on volume and size; however, microparticles typically cannot be sorted based on more subtle differentiating features that are critical for their ultimate functionality, such as shape or surface morphology.
Here we describe the use of fluorescence-activated cell sorting (FACS), a powerful method from the field of molecular and cellular biology, as a general tool for high-throughput, label-free sorting of synthetic microparticles based on morphology. Specifically, we used FACS to optically interrogate mixtures of microparticles one-by-one, using light scattering behavior to characterize and sort them based on size and shape. In contrast to bulk separation techniques like centrifugation, our FACS-based method analyzes and sorts each particle individually at high throughput (>1,000 objects/second), providing high resolution for enrichment and purification of microparticles with the desired properties. Crucially, we use standard optical measurements available in commercial FACS systems, requiring no instrument modification and thus enabling a “plug-and-play” approach for colloid researchers.
Using FACS, we achieved morphology-based sorting and enrichment for two model systems of synthetic microparticles. First, as a proof of concept, we sorted heterogeneous mixtures of stretched polystyrene ellipsoids based on their aspect ratios. Specifically, we performed a single-step four-way sort and enrichment of a mixture of ellipsoids with aspect ratios ranging from 1 to 3.5, based solely on measurements of small-angle scattering (forward scattering, or FSC) and large-angle scattering (side scattering, or SSC). Second, we applied our FACS-enrichment method to a novel class of block copolymer microparticles with applications in stimuli-responsive optical materials. Using FSC and SSC measurements, we enriched subpopulations of these copolymer particles with specific narrow size ranges from a highly polydisperse mixture. As FACS instruments become increasingly ubiquitous, easy-to-use, and powerful, this method could become a general approach for the sorting and enrichment of functional designer microparticles, toward the development of well-defined colloidal materials.

Stabilization of oil/water dispersion by particles gives raise to Pickering emulsion. They are widely used for several applications such as pharmaceutical, industrial processes, food production etc. Soft gels, as stabilizing agents, have attracted high interest over conventional hard particles, as they offer the advantage of tuning the emulsion stability as a result of changes in environmental conditions like pH or temperature.
Here we report the design and synthesis of a novel nanogel system based on methacrylates. The nanogels were synthesized via high dilution radical polymerisation using 2-(di-ethylamino)ethyl methacrylate (DEAEMA) or 2-(tert-butylamino)ethyl methacrylate (tBAEMA) as functional monomer, ethylene glycol methyl methacrylate as co-monomer and N,N&’-methylenebisacrylamide as cross-linker. Variation in chemical composition of the polymerisation mixture allows tuning and optimisation of physical-chemical properties of the Nanoparticles (NPs) such as thermal or pH response, hydrophilicity/hydrophobicity ratio, flexibility and ability to form Pickering emulsion. NPs size ranges from 5 to 10 nm depending on polymer composition as confirmed by dynamic light scattering (DLS) and transmission electron microscopy (TEM).
Nanogels were tested as emulsion stabilizers using octanol as oil phase. DEAEMA based nanogels were proven to be thermo-responsive (with transition temperature close to human body therefore suitable for biological applications) however they were not able to create stable emulsions. Instead, tBAEMA NPs showed to form stable water-in-oil emulsions. Data indicates that nanogels are able to respond to pH as confirmed by DLS measurements.
These NPs represent an excellent platform for the manufacturing of multi-application formulations. This project is therefore setting the starting point for the development of novel stimuli-responsive emulsions.

The fabrication of complex tridimensional structures is a very demanding issue of material science and technology. The light induced mass migration phenomenon showed by azobenzene containing material opens to new fabrication approach based on superficial reshaping of pre-patterned structures. The cis-trans-cis photo-isomerization cycles of the azobenzene molecules produces a reorganization of the host material, often a polymer, in which are embedded with a resulting macroscopic material motion in a direction parallel to the illuminating light polarization. Because of this effect the material exhibits a directional fluidization under illumination that allows a high degree of control on the reshaped structure. Here we realize complex tridimensional architectures by reshaping pristine pre-patterned pillar posts under different illumination condition. The resulting structures produce a change in the wetting behavior of the patterned surface with a demonstrated controlled directional droplet spreading. This feature makes the method suitable for microfluidic and biological application.

Fundamental aqueous lubrication studies have recently turned to a twinned, or "Gemini" hydrogel interface to explore the friction behavior between two soft, permeable materials. Tribological experiments performed over four orders of magnitude of sliding speeds revealed a speed-independent regime due to thermal fluctuations in the polymer network and a speed-dependent regime in which polymer relaxation mechanisms dominate and cause the friction coefficient to increase like a 1/2 power. A follow-up study showed that the transition between these two lubrication regimes could be controlled by modifying the mesh size, xi;, of the hydrogel network. The lubricity of a Gemini hydrogel interface could therefore be described with a simple scaling law: µ₀ ~ xi;^-1, where µ₀ is the average friction coefficient in the speed-independent regime. Interestingly, nearly all friction coefficients reported in this recent study fell below µ₀ < 0.01 and for some measurements, µ₀ ~ 0.005. This is remarkable considering that for the last two decades many of the lowest reported friction coefficients in the literature have been achieved only with rigid, crystalline surfaces under vanishingly small contact areas, high contact pressures, and in pristine sliding environments under vacuum. Motivated by this discovery, current efforts have focused on bringing to light the ability to achieve superlubricious friction coefficients with large (millimeter-sized) contact areas, low (milliNewtons) applied normal forces, in an aqueous sliding environment featuring a very poor lubricant, ultrapure water. Experiments have shown that friction coefficients of less than 0.005 are possible, but under very specific conditions.

Cells in their natural environment (extracellular matrix, ECM) respond in a complex manner to a variety of physical and chemical stimuli. Hence, there is a strong interest in understanding cell-material interactions and in combining different functions in a single material system. The challenge is to replicate such features in smart biointerfaces for in vitro and in vivo cell studies. Among others, introducing in the biointerface the capability to record electrical signals related to cell activity and to electrically stimulate cells is fundamental. In this regard the emergent area of organic bioelectronics employs organic semiconductors and conducting polymers (CPs) as soft, biocompatible, functional materials for the development of smart biointerfaces and bioelectronic devices.[1-2] On the other hand, the design of biomimetic scaffolds for cell culturing and guidance is focused on mimicking the hierarchical structural organization of ECM, thus providing topographical cues which are known to direct cell alignment and to promote their growth and differentiation.[3]
With the aim of combining the functionality and dynamic patterning capability of CPs (conductivity, surface switching for cell adhesion/repulsion, electrically triggered ion/drug release) with a tunable micro-nanostructured topography, we focused our attention on the use of surface wrinkling as a rapid and convenient self-assembly method for surface patterning of multifunctional biointerfaces. Thermally induced shrinking of thermo-retractable polystyrene (PS) creates surface wrinkling of a top thin layer of spin-coated PEDOT:PSS. By modifying the top layer composition and thickness we are able to tune the surface topography and its conductivity, depending on the specific application and cell type. A comprehensive characterization by means of SEM, AFM, profilometry, permitted to rationalize the surface wrinkling phenomenon according to available models in surface mechanics. Investigation of cell proliferation on different biointerfaces permitted to assess the optimal topography for cell culturing. Conducting polymer surfaces (heat-shrinkable PS + PEDOT:PSS) with aligned micro-nanowrinkles proved to be effective in promoting the alignment and enabling the electrical patterning of C2C12 mouse myoblasts and normal human dermal fibroblasts (nHDF).[4] Similar biointerfaces with uniaxial wrinkles periodicity in the range 0.2 - 3 mu;m and multiscale wrinkles amplitude (from tens of nanometers up to 1.5 - 2 mu;m) were also used for culturing neuron-like cells (human SH-SY5Y neuroblastoma), evaluating their effect on the process of neuritogenesis. Remarkable effectiveness in enhancing neurite length and in orientating their outgrowth is observed.
References
1. G. G. Malliaras, Biochim. Biophys. Acta (BBA) 1830, 4286 (2013).
2. M. Berggren, A. Richter-Dahlfors, Adv. Mater.19, 3201 (2007).
3. A. Marino et al., Acta Biomater. 10, 4304 (2014).
4. F. Greco et al., ACS Appl. Mater. Interf.5, 573 (2013).

Poly(N-isopropylacrylamide) (PNIPAM) has gained widespread interest due to its ability to switch between two extreme wetting states viz. superhydrophilic and superhydrophobic states. This wetting behavior of PNIPAM extends its applications to include responsive surfaces, self-cleaning surfaces, tunable optical lenses and lab-on-chip systems. In this study, we use electrospinning to produce PNIPAM fibers and investigate its wettability by measuring the contact angle made by a liquid droplet on the surface of the samples. Contact angle measurements were also compared with that of spin-coated PNIPAM thin films and the effect of electrospinning on wettability was determined. CA made by the liquid droplet on PNIPAM fibers at 50 °C temperature were seen to be 137° while the CA on spin-coated PNIPAM was determined to be 81°. 70 % improvement in the CA indicates that electrospinning improved the hydrophobicity of the fibers. The enhancement of the wettability property is attributed to increase in the surface area due to fiber formation.
CA measurements at ambient temperature (23°C) demonstrated that the PNIPAM fibers absorbed the droplets immediately while CA on spin-coated PNIPAM was determined to be 50°. These results demonstrate that electrospun fibers displays hydrophilicity at ambient temperature and hydrophobicity at 50 °C.
Our results show tremendous potential of using electrospun fibers as smart materials with special wettability. Current work is focused on characterizing the amount of water absorbed by the samples when placed in a controlled humidity chamber.

The fabrication of stimuli-responsive soft materials has opened new doors in drug delivery, synthetic extracellular matrices, autonomous sensors and injectable biomaterials. These materials can passively monitor biological environments and proceed through a substantial shift in mechanical, volumetric or optical properties when a targeted analyte or environment is present. However, invoking unique stimuli-responsive events such as the collapse and stiffening of a material is still a design challenge. We have developed a near-close packed nanoparticle-hydrogel composite which specifically responds to targeted enzymes through an unusual chemical-to-physical cross-link transition. The catalytic cleavage of the network structure of the hydrogel initiates the self-assembled formation of secondary physical cross-links between pendant chains of the hydrogel network and the surface of the nanoparticles. This secondary network formation results in a 1200% increase in storage modulus. Furthermore, the mechanism can be exploited to produce response photonic crystals with broad visible responses to targeted enzymes. The spectral response invoked by the targeted enzyme was ~240nm, which to our knowledge is the largest response to an enzyme reported for a photonic crystal. Moreover, the materials exhibited threshold responses, requiring a 70% of cross-links to be enzymatically cleaved before the response occurred. This provided the possibility to construct Boolean logic gates (OR and AND), which responded to specific assortments of enzymes. This unique mechanism provides new avenues in the design of stimuli-responsive soft materials, which can stiffen in response to degradation events.

Inspired by successful work with hydrogels¹, we recently demonstrated that it was possible to design a new type of elastomer, able to deform reversibly up to more than 100% strain with very little hysteresis, while being significantly tougher than conventional elastomers². These new materials are composed of two or more interpenetrated networks synthesized by sequences of swelling and polymerizations, creating therefore different populations of chains with a variable level of deformation, in an overall isotropic material. The monomers used are ethyl acrylate, methyl acrylate and butyl acrylate producing an elastomer at room temperature. A first network is polymerized with a variable amount of crosslinker by UV polymerization. This first network is dried and swollen again with monomer and a very small (0.01 mol%) amount of crosslinkler until equilibrium. Depending on the type of monomer used and degree of crosslinking, the equilibrium swelling Q/Q0 can vary from 3 to 5. At this stage the monomer in the swollen first network is polymerized by UV again, creating a double network. Step 2 can be repeated if higher degrees of swelling of the first network are desired.
Depending on the volume fraction of first network, various types of mechanical behavior are observed. For a high volume fraction of first network (> 25% in our system), the sample breaks before any significant strain stiffening is observed in uniaxial extension and the elastomers are brittle. For intermediate levels of volume fraction (7-25%), the materials are more extensible an remain reversibly elastic but their stress at break significantly increases. Finally for very small volume fractions of first network (below 5-6%), the first network breaks extensively before the sample fails and can even form a necking region. In this regime the fracture energy Gc is the highest. We will explore the regimes where these mechanisms are observed and the underlying molecular mechanisms controlling the macroscopic properties, leading to a knowledge-based optimization of the material properties.
(1) Gong, J. P. Soft Matter2010, 6, 2583.
(2) Ducrot, E.; Chen, Y.; Bulters, M.; Sijbesma, R. P.; Creton, C. Science2014, 344, 186.

Branched and hyperbranched macromolecules offer an exciting platform and tremendous opportunities in addressing challenges posed by the complexity of modern nanomedicine. For efficient therapeutic intervention, circulation, targeting, tracking the fate and final outcome are essential parameters that need to be controlled. Chemists have taken this enormous task to develop versatile tools which can allow the design of tailor made nanocarriers that can combine multiple complimentary functions into a single scaffold of a nanostructure. We have recently developed facile synthetic routes to branched (miktoarm stars) and hyperbranched (dendrimers) architectures in which i) pharmaceutical agents can be physically encapsulated or covalently conjugated or combinations thereof for efficient delivery; and ii) orthogonally functionalized building blocks can be utilized to assemble a multivalent structure with desired spatial distribution of therapeutic, imaging and targeting capabilities. In this presentation, we shall elaborate on this macromolecule based nanotechnology, and discuss its potential in smart and efficient drug therapy. We shall demonstrate how one can easily construct multivalent nanoconjugates which can perform multiple tasks and help visualize drug delivery.

Membranes are crucial tools for green, energy efficient separations. To be commercially viable, membranes need to exhibit high flux and fouling resistance, and be readily fabricated in large scale. Membranes that change their properties in response to external stimuli can exhibit additional functionality. We introduce zwitterion containing amphiphilic polymers as a promising family of materials for membranes that exhibit all these features. Zwitterionic groups strongly resist biomacromolecular fouling due to their high degree of hydration, which makes them promising materials for membrane applications. Zwitterions are also documented to self-assemble into channel-type clusters 0.6-2 nm in size. Zwitterionic polymers change their conformation and hydrophilicity in response to changes in the concentration of small ions such as salts. We have prepared high flux, fouling resistant, size-selective membranes whose selective layers are made of random and comb-shaped copolymers of zwitterionic and hydrophobic monomers. We have shown that within certain composition ranges, these copolymers self-assemble to form bicontinuous networks of nanochannels that allow water passage, and filter out solutes larger than the channel size. We have synthesized such copolymers and formed thin film composite membranes by coating them onto commercial ultrafiltration membrane supports. Membranes made using random copolymers exhibit fluxes as high as 21 L/m².h.bar, which can be further be improved by better coating methods. Based on the rejection of anionic and neutral dyes of varying sizes, they show size-based selectivity with a cut-off around 1 nm. This pore size closely matches the size of the zwitterionic nanochannels, measured to be ~1.3 nm in diameter by transmission electron microscopy (TEM). These membranes also exhibit exceptional fouling resistance, showing little flux decline and essentially complete flux recovery with a water rinse upon the filtration of foulants such as protein solutions and oil suspensions. Their performance is stable even at varying salt concentrations, but can be tuned by annealing in saline solutions. In contrast, membranes made from comb-shaped copolymers with a hydrophobic backbone and zwitterionic side-chains are responsive to ionic strength changes. Their permeability changes reversibly when feed salinity is varied. These are the first examples of membranes that gain their selectivity from the microphase separation of zwitterionic groups, in addition to exploiting this functionality for fouling resistance. The properties of these membranes can be further tuned by varying polymer architecture, zwitterion chemistry, copolymer composition, post-treatment methods such as annealing in water or salt solutions, and using additives during casting. We expect these membranes to be promising candidates for various applications including the purification of pharmaceuticals and antioxidants, and textile wastewater treatment.

This talk will describe several approaches to incorporating responsiveness to multiple stimuli into polyelectrolyte multilayer (PEM) films. The stratification of materials that is possible with many PEM film constructs enables compartmentalization of chemistries in space, allowing different external stimuli to have different, pre-programmed effects on the material behavior. By incorporating photocleavable groups that give charge-shifting behavior to polycations within PEM films, the ion pairing interactions that contribute to the enthalpic driving force for PEM stability are disrupted by light, leading to photoinduced film dissolution. We have demonstrated that compartmentalizing photocleavable groups with difference absorption profiles facilitates wavelength-selective release of trapped guests from PEM films. In addition, we can use differences in photocleavage efficiencies to dissolve multiple compartments within a PEM film with selectivity. Finally, this talk will describe triple-responsive PEM films that use compartmentalized photochemical charge shifting chemistry to yield free-standing PEM films that can respond to chemical reducing agents for cleaving disulfide bonds to release a small molecule selectively, and respond to changes in pH to disrupt ion pairing interactions and dissolve the entire free-standing film.

Utilization of biomolecular multifunctionality such as molecular recognition and catalysis capabilities attracts a great deal of attention in materials science and engineering. Recently developed bionanotechnologies revealed that short peptides (peptide aptamers), which were isolated from phage or cell-surface displayed peptide libraries through affinity-based selection processes, bound specifically to the surfaces of artificial materials. These peptides were successfully utilized to design and engineer heterogeneous interfaces. Our group is interested in peptides that precisely recognize the structural differences of synthetic polymers. In this lecture, our recent progress in the identification and functionalization of polymer-binding peptides is outlined as the first topic. We found that polymer nanostructures such as a primary sequence, stereoregularity, amphiphilicity, crystallinity, chirality, linear/branch structure, assembly structure, and porosity were able to fit to the three-dimensionally regular nanostructures of peptides. On the other hand, enzymatic reactions under aqueous mild conditions have the potentials for realizing sustainable and environmentally friendly synthesis of polymer-based functional materials. Our group is interested in crystalline cellulose oligomers (cellodextrins), which can be synthesized by phosphorolytic reactions of cellodextrin phosphorylase using α-D-glucose 1-phosphate monomers and D-glucose derivative primers. As the second topic, our recent progress in the synthesis and functionalization of multiphase cellulose oligomers is outlined. We found that reactive nanosheets or well developed nanoribbons composed of crystalline cellulose oligomers were obtained by the enzymatic reactions under adequate reaction conditions.

Biomimetic materials have facilitated studies which have uncovered a variety of biomechanical and biochemical cues that influence both stem cell lineage commitment and tissue morphogenesis. Precision control over these parameters through the utilization of biomaterials has advanced the fields of tissue engineering and regenerative medicine towards to cusp of translation to the clinic. In particular, matrix stiffness, a known regulator of stem cell lineage commitment as well as tissue morphogenesis, may be regulated with relative ease through hydrogel design. Hypoxia, defined as local oxygen tension below 5%, is another powerful regulator of stem cell commitment and regeneration, specifically during vascular lineage differentiation and angiogenesis. An understanding of the intricacies and interplay of these two potent regulators of cellular function is paramount to the development of novel therapies, which aim to rapidly regenerate functional, stable, and long-lasting tissues.
We have previously shown the ability to control oxygen tension within polymeric hydrogels, which has enabled the study of the effects of oxygen tension on cellular function in a highly biomimetic, 3D setting. In the current study, we advance the design of our hypoxia-inducible hydrogels to independently control the mechanical properties and the oxygen tension within the same hydrogel system. We designed, synthesized, and analyzed hybrid hydrogels comprised of two polymer backbones, gelatin and dextran, that allow for control of physiologically relevant ranges of mechanical properties and oxygen tension. Both polymers were crosslinked via a laccase-mediated, oxygen consuming reaction. By modifying the concentration of phenolic molecules available to react, we precisely controlled the time in which the hydrogel remained hypoxic (TH) (<5% oxygen). We were able to achieve a range of TH from the order of minutes to greater than 10 hours. By incorporating a secondary crosslinker, transglutaminase, mechanical properties were adjusted in a user-defined fashion, with elastic modulus (G&’) values ranging from <20 Pa to >1 kPa. Importantly, we show that oxygen levels and substrate mechanical properties can be individually tuned and decoupled in the hybrid hydrogels.
Current studies focus on determining the individual and synergistic effects of oxygen tension and matrix stiffness on cell and tissue behaviors in vitro and in vivo. By decoupling the precise control over oxygen tension and mechanical properties in the polymeric hydrogel system, we expect that research utilizing the new hybrid hydrogels will enhance our understanding of the complex 3D cellular processes mediated by each parameter. Optimiziation of tissue morphogenesis and regeneration facilitated by hybrid hydrogels may also hold significant clinical interest as implantable tissue constructs as well as injectable acellular therapies to enable accelerated regenerative processes.

Protein-engineered, elastin-like polypeptide (ELP) hydrogels, with easily and independently tailored mechanical and biochemical properties, have been used as biomimetic scaffolds for fundamental biological studies and for development of tissue regeneration therapies. However, ELP hydrogels are opaque at physiological temperature due to ELP&’s lower critical solution temperature of ~ 34 °C. This opacity restricts the direct observation of the morphology and behavior of the encapsulated cells within the 3D ELP hydrogels. In order to improve light transmittance through ELP hydrogels, we designed a hybrid ELP-polyethylene glycol (PEG) hydrogel system using tris(hydroxymethyl) phosphine (THP) as a crosslinking agent. Fast gelation occurred at physiological conditions. Coherent Anti-Stokes Raman Scattering (CARS) microscopy revealed that hydrophobic ELP aggregates at 37 °C were much smaller in the hybrid ELP-PEG hydrogels compared with those in the pure ELP hydrogels. Therefore, less light scattering and higher light transmittance was obtained in the hybrid ELP-PEG hydrogels, facilitating the imaging of cell behavior at greater depths into the 3D scaffold. It was also demonstrated that the matrix stiffness and cell-adhesion ligand (RGD) density of these ELP-PEG hydrogels could be independently tuned. High viability (> 98%) was observed for the encapsulated human fibroblasts after 7 days of culture. The encapsulated cells responded to the matrix mechanical and biochemical signals by adopting a more spread morphology in hydrogels with lower matrix stiffness and higher cell adhesive ligand concentration. The good imaging performance and excellent cytocompatibility of these new hybrid materials together with the independently tunable mechanical and biochemical properties make them an ideal system for cell-matrix interaction studies.

Polymer gels undergoing the oscillatory Belousov-Zhabotinsky (BZ) reaction are one of the few synthetic materials that exhibit biomimetic mechano-chemical transduction, converting mechanical input into and chemical energy. Here, we consider self-oscillating BZ gels that are subjected to periodic mechanical forcing, and model the entrainment of the oscillatory gel dynamics to this external stimulus. The gel size is assumed to be sufficiently small that the chemo-mechanical oscillations are spatially uniform. The behavior of the system is captured by equations describing the kinetics of the oscillatory BZ reaction in the gel coupled to equations for the variations in gel size due to the inherent reaction and imposed force. We employ the phase dynamics approach for analyzing the entrainment of the BZ gel to force- and strain- controlled compressive deformations. The phase response curves are obtained using Malkin&’s method, and time-averaging is applied to extract the slow phase dynamics caused by the periodic forcing. We demonstrate that the entrainment of the self-oscillating BZ gel is sensitive to the chemo-mechanical coupling in gel, the mode of deformation, and the level of static compression. Kuramoto&’s model of phase oscillators is shown to be applicable if the external forcing is purely harmonic.

Confined crystallization has been theoretically and experimentally investigated for the preparation of novel functional crystals. This development can benefit a wide range of materials from metal nanocrystals and organic drug molecules by overcoming their property limits. In this research, biodegradable soft 1D matrix having 100~200 nm diameter was developed and used for confined crystallization, which was based on the electro spun nano fibers of chitosan, a natural biocompatible polymer. For matrix stability in various solvents, the composition of electro spinning solution was carefully chosen, and a blend of 60 wt.% chitosan and 37 wt.% poly(ethylene glycol) diacrylate was found to be able to meet our requirements of stable electro spinning and reliable crosslinking. After electro spinning, two-step cross-linking, UV and ionic crosslinking, followed. The matrix stability was assessed by measuring the long term dissolution behavior of matrix in water. A simple procedure, dipping the matrix into a solution and subsequent crystallization, could produce confined crystallization conditions, which is applicable to various materials. For silver cases, dipping into a silver nitrate solution and subsequent reduction in ethylene glycol produced silver nanoparticles. Silver nanoparticles, spherical shape having 10~40 nm size, were firmed located on the surfaces of nanofibers and also inside nanofibers with unique composite morphology. The resulting composite fibers could serve as antifouling hydrophilic surfaces without the problem of significant leaching of silver or limited active surface area of silver. This new biodegradable 1D matrix could be useful for the functional crystallization of various nanomaterials for the future applications.

In this paper, a facile and novel method was developed to fabricate high toughness and stiffness double network hydrogels made of ionical-linked natural hydrogel and synthetic hydrogel. The synthetic hydrogel network is formed firstly, and then the gel is soaked in the ionic solution to build second network to form double network hydrogel with high toughness and stiffness. Two different natural polymers, alginate and chitosan, are employed to build rigid and brittle network and poly(acrylamide) is used as soft network in double network hydrogel. The compressive strength of Calcium alginate/poly(acrylamide) double network hydrogels is increased 1 time than that of poly(acrylamide) single network hydrogels, and the Ca²⁺ ionically cross-linked alginate is the key to improve the compressive property of double network hydrogels as a sacrificial bond. However, the chitosan/poly(acrylamide) double network hydrogels exhibit no enhancement of compressive strength comparing to poly(acrylamide) single network hydrogels.

Through characterization of the mechanical properties of polymers, more effectively designed biomaterials may be synthesized. Our group&’s interest lies in treating the wear-prone cartilage found within human joints affected by osteoarthritis. As articular cartilage is worn away, the joint often suffers a loss of lubricating biopolymers resulting in degradation of the surrounding soft tissue. By applying aqueous solutions containing novel, biocompatible polymer architectures to synovial joints of the human body experiencing high friction, we hypothesize that the coefficient of friction between the two articulating surfaces may be lowered and this supplementation will therefore aid in preventing further wear. The lubricant functions at a cartilage-cartilage interface to preserve the mechanical integrity of the interracial tissue. While many existing lubricants are designed with only one lubrication mode in mind, ours are multifunctional in that they function efficiently in both mixed and fluid film regimes.
Varying the concentrations of monomer and crosslinker in the polymer network structure can alter mechanical properties of the polymer solutions, such as elasticity, viscosity, and coefficient of friction. We have synthesized a suite of polymer network compositions, ranging in solution concentration from one to fifty w/v% monomer (2-methacryloyloxyethyl phosphorylcholine), and spanning crosslinking densities from one to five % mol/mol monomer using two different crosslinkers of differing hydrophilicity (ethylene glycol dimethacrylate and methylene bisacrylamide). Polymerization was carried out via persulfate initiation, and lubricant solutions were characterized by rheometry for assessment of viscoelastic properties, and by dynamic mechanical analysis for investigation of lubrication mechanism. There exist three modes of lubrication in which lubricant solutions may operate, namely, fluid film, boundary, and mixed modes. Understanding the operating regime of our lubricants is essential to optimizing a polymer structure that lubricates most effectively. Multiple Stribeck curves were developed for the varying concentrations of monomer and crosslinkers, through linear reciprocating testing using an Instron. From this testing, insight into the key chemical parameters affecting mode of lubrication was gained, providing basis for the rational design of next generation biomaterial lubricants. Future studies will examine which mode is beneficial for varying types of articulating surfaces, and functional performance (magnitude of wear prevention, wear particle composition) will be assessed.

1D nanofibers by linear π-conjugated chromophores have numerous applications in the field of organic electronics.¹ In this work, we report a strategic approach to generate 'charge transfer-assisted supramolecular 1-D nanofibers&’ using pyrenebutyric acid (donor) and 2, 4, 7-trinitro-9H-fluoren-9-one (acceptor) in presence of a cholesterol derivative. For the first time, a cholesterol based structure-directing agent is developed to direct donor-acceptor assembly, which is stabilized by H-bonding, van der Waals and Charge transfer interactions. Since cholesteric units are easily available and relatively less expensive, using them as structure directing agents for 1D nanostructures leads to cost effective fabrication of opto electronic devices. The mechanism of the gel formation is proposed based on the results from infrared spectroscopy, X-ray diffraction, and atomic force microscopic techniques. Upon applying an electric potential, the three component assembly displayed a conductivity of 1.94 × 10^-4 S Cm^-1 which is superior to the reported assemblies by napthalenediimide and polythiophene derivatives.^2,3
References
1. S. Diring, F. Camerel, B. Donnio, T. Dintzer, S. Toffanin, R. Capelli, M. Muccini and R. Ziessel, J. Am. Chem. Soc. 2009, 131, 18177- 18185.
2. B. W. Messmore, J. F. Hulvat, E. D. Sone and S. I. Stupp, J. Am. Chem. Soc. 2004, 126, 14452- 14458; D. A. Stone, A. S. Tayi, J. E. Goldberger, L. C. Palmer and S. I. Stupp, Chem. Commun.,2011, 47, 5702- 5704.
3. H. Kar, M. R. Molla and S. Ghosh, Chem. Commun., 2013, 49, 4220- 4222.
4. T. M. Babu, E. Prasad, Chemistry-A European Journal (Manuscript in press)

Due to the harsh chemical environments of underground oil reservoirs, the widely used oil displacement agent, partially hydrolyzed polyacrylamide (HPAM), has some deficiencies in practical applications, such as shear thinning, chemical degradation at high temperature and phase separation in high mineralization reservoirs. All these deficiencies can result in a sharp decrease in viscosity of HPAM aqueous solutions, leading to an obvious reduction in displacement efficiency; thus HPAM is not suitable for application in the oil reservoirs of high-temperature and high-salinity. Aimed at these shortcomings, a novel oil displacement agent of Branched Preformed Particle Gel (B-PPG) was synthesized, which not only has a crosslinked network but also linear branched chains. The special structure of B-PPG provides particular performances; i.e., the crosslinked network provides a gel with an excellent temperature tolerance mechanism, elastic deformation and anti-shearing properties, while the water soluble linear branched chains provide high viscosity and suspension properties. Thus, the B-PPG can be used as an oil displacement agent due to its excellent viscoelasticity and ductility.
Based on the results of experiments, a physical and a chemical anti-ageing mechanism of B-PPG is proposed. Initially, part of the crosslinked network ruptures into branch chains and the outermost branch chains are first released from the network. Due to the lack of restriction by the crosslinked network, the molecular crosslinked particles can expand and the hydrodynamic volume becomes larger, leading to an enhancement in viscosity. After long-time ageing, the crosslinked network of the B-PPG gradually ruptures further, finally into smaller particles and the viscosity decreases similar to that of HPAM. In a word, due to the particular partly crosslinked structure, the chain scission process of B-PPG is dramatically delayed compared with HPAM. This is the physical anti-ageing mechanism for B-PPG. The chemical anti-ageing mechanism of B-PPG is by introduction of a comonomer N,N dimethylacrylamide (DMAM). After ageing for 3 months, some DMAM still exists in the molecular structure of B-PPG. The accelerated hydrolysis of -CONH₂ can be inhibited effectively by DMAM and the amide groups are protected in varying degrees, leading to a relative stable structure of B-PPG and better anti-ageing properties.
Owing to the synergistic effects of the double-protection mechanisms, the ageing properties of B-PPG is effectively improved over that of HPAM.

In order to get a better effect in profiling control the heterogeneous reservoirs, we synthesized a novel oil displacement agent of partly crosslinked polyacrylamide (B-PPG), which not only has a crosslinked network but also linear branched chains. ^1-2 The crosslinked network provides an excellent temperature tolerance mechanism, elastic deformation and anti-shearing properties, while the water soluble linear branched chains provide high viscosity and suspension properties. Thus, the B-PPG can be used as an oil displacement agent due to its excellent viscoelasticity and ductility, which has been successfully used in two recent pilot tests in Shengli Oilfield in China. As a new type of oil displacement agent, the flow behavior of the B-PPG in porous media, the profile control mechanism, and the oil displacement behavior of B-PPG were experimentally studied in this article.
A parallel connection of two sandpacked cores with the permeability ratio of 5:1 was used to carry out B-PPG profile control experiments. The fractional flow curve of B-PPG suspension in porous media showed that, in the pre-saline solution flooding period the fractional flow of the lower permeable tube is about 20%, after turning to the B-PPG flooding period the fractional flow increases quickly and the maximum can reach 92%. The production fraction of the lower and the higher permeable sandpacked core reversely turns to about 90:10 when 1 PV B-PPG suspension has been injected, which is obvious “fluid diversion”. Even in the early period of the following saline solution flooding, the “fluid diversion” still exists and the production fraction of the lower and the higher permeable sandpacked core maintains 90:10 for 1.2 PV. Then the fractional flow of lower permeable tube gradually decreases to about 20%, leading to another “fluid diversion”. At last, the production fraction maintained to 80:20 for about 0.7 PV.
The mechanism of “fluid diversion” is because after injecting B-PPG suspension, the particles initially prefers to flow into the high permeable tube and then plugging occurs, which increases the drag force of filtering flow and the inlet pressure, changing the flow direction of subsequent fluid, and then the suspension flows into the low permeable tube and the fractional flow of the low permeable tube increases obviously. Although the suspension flowing into the low permeable tube also contains B-PPG, since the pore-throat size of the low permeable tube is pretty small which makes the bigger B-PPG particles unable to pass through, resulting no plugging.
Thus, B-PPG could generate “fluid diversion” quickly and enlarge the swept volume of the lower permeable core not only during the B-PPG injection period but also during the early period of following saline solution injection process, indicating the effective and sustainable profile control ability of B-PPG.
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Aromatic Polyimide fibers with good mechanical Strength were fabricated via wet spinning process of polyamic, which derived from 3,3&’,4,4&’-biphenyltetracarboxylic dianhydride(BPDA), 2-(4-aminophenyl)-5-amiobenzimidazole(BIA), and 2,2&’-dimethy-4,4&’-diaminophenyl(DMB).
To promote the performance of polyimide fibers, Grapheme oxide(GO) which was modified by 4, 4prime;-diaminodiphenyl ether(ODA) was added into the polymer in a way of in situ polymerization. FESEM results indicate that the fibers forming well and GO-ODA nanosheets are well dispersed in the polyimide matrix. These functionalized nanosheets provide great reinforcement to polyimide fibers. The tensile strength and tensile modulus of fibers containing 0.5wt% of GO-ODA is 1.3Gpa and 80Gpa respectively. The fibers display excellent thermo mechanical properties according to DMA result, and glass transition temperature of all fibers is over 400#8451;#12290;FTIR spectroscopy is employed to study the hydrogen bonds between molecular chains. The results indicate that more than 30% molecular chains can form hydrogen bonds, which promote the tensile strength and tensile modulus apparently. And the crystalline structure and micro-morphology of the prepared PI fibers are investigated by WAXD and SAXS.

Pressure-sensitive adhesives (PSAs) are being used for a wide range of self-adhesive materials represented by adhesive double-sided, one-sided or carrier-free tapes, adhesive labels, protective foils as technical products and medical pads, hydrogels and biomedical . Under diverse PSA based on suitable kinds of polymers, such as acrylic, rubber, silicones, polyurethanes, polyesters, polyether, and ethylene-vinyl acetate copolymers (EVA) even acrylic offer promising advantages in comparison to other groups of polymers. Acrylic types of pressure-sensitive adhesives (PSAs) can be prepared by copolymerizing acrylic monomers, such as 2-ethylhexyl acrylate, butyl acrylate, and isooctyl acrylate. The versatility of acrylic PSAs results from how they can be formulated to have various thermal and viscoelastic properties, even in the absence of tackifiers.
Crosslinking is a technique used very widely to alter polymer properties. Typical crosslinking methods are based on the chemical reaction that takes place at elevated temperatures, although room-temperature (RT) curing is also known. Recently, radiation curing employing electron beams or a UV sources has also been used. The UV-initiated crosslinking process is the fundamental of important in advanced technologies, since it is one of the most efficient methods capable to achieve fast and extensive crosslinking of multifunctional oligomers and monomers.
In this study, UV oligomers that can give the UV curable properties to the general acrylic ressure-sensitive adhesive were prepared by simply blending isophorone diisocyanate (IPDI), acrylic monomer containing active hydroxyl groups such as 2-hydroxyethyl methacrylate (2-HEMA), 2-Hydroxyethyl Acrylate (HEA) or 4-Hydroxybutyl Acrylate (4-HBA), polymerization-inhibitor and catalysts. UV curable pressure-sensitive adhesives were prepared by mixing UV oligomers, acrylic pressure-sensitive adhesives and photo Initiator. We monitored difference of NCO groups remaining in UV oligomers according to different types of acrylic monomers and Mixing methods by Fourier transform infrared (ATR-FTIR) spectroscopy and Nuclear magnetic resonance (NMR). Properties (180° peel strength, ball tack, holiding power and gel fraction) of UV curable pressure-sensitive adhesives were measured.

Solar cell is one of the most attractive technologies for energy generation because it can generate the energy without usage of fossil fuels and emission of carbon dioxide. However, all of these solar cells have a critical problem that the absorption band generally does not include the entire photo-band of sunlight, and the solution of the problem is required to high energy conversion efficiency. Spectral conversion from UV to visible light is one of the candidates to solve the problem. Our group developed a spectral conversion film based on a transparent and fluorescent polymer with high Stokes shifts, which can be characterized by composite materials of general-purpose polymers such as polystyrene, LDPE and PVB with as fluorescent supramolecular gel from the glutamide derivative [1].
In this meeting, we demonstrate about tunable Stokes shift in polymer blend systems using newly-synthesized anthracene-doped L-glutamide. At first, to investigate the temperature dependence of the anthracene derivatives in solutions (n-hexane/THF (50 : 1)), the UV-visible absorption spectroscopy and fluorescence spectroscopy were conducted with controlling the temperature. A slight blue shift of absorption peak around the wavelength of 370 nm appeared when the temperature was changed from 10 #730;C to 60 #730;C. In fluorescence spectroscopy, the emission at the wavelength of 420 nm was remarkable at 60 #730;C. However, when the temperature decreased from 60 degree to 10 #730;C, another strong emission was observed at the wavelength of 526 nm, while the prior emission was reduced. These phenomena can be explained by induction of the assembling structures from monomeric to excimeric states. In addition, the intensity of emission at the wavelength of 526 nm depended on the cooling rate.
Secondly, we investigated about the influence of the polymer matrix on fluorescence behaviors. The top peak of anthracene lipid incorporated into a PVB film was observed at the wavelength of 422 nm, compared to 537 nm for the one of a LDPE film. These results indicate that the fluorescence behaviors of the anthracene moiety can be controlled in a solution state as well as a solid film.
[1] Hirokuni Jintoku and Hirotaka Ihara, Chem. Commun., 2012, 48, 1144

The thermoresponsive sol-gel transition behavior of PLGA-PEG-PLGA, composed of a hydrophobic PLGA (poly (D,L-lactic acid-co-glycolic acid)) block and a hydrophilic PEG (poly ethylene glycol) block, has been intensely investigated for its future medical applications. To create a thermoresponsive hydrogel with a very low polymer content, we have recently developed a new type of PLGA-PEG-PLGA nanocomposite with laponite, the synthetic clay forming nano-disks. We reported that the aqueous solution of PLGA-PEG-PLGA with the block molecular weights of 0.8k-1.5k-0.8k and 1.8k-3.0k-1.8k and laponite immediately transferred from sol to gel by raising temperature from 100C to 370C at a very low polymer content of 3.0 wt% and the laponite concentration of 0.9 wt%.
In this work, for the comprehensive understanding of the aqueous laponite/PLGA-PEG-PLGA solution, we synthesized different PLGA-PEG-PLGA by changing the PLGA/PEG block ratios and the molecular weights of PEG, followed by the composite process with laponite. The PLGA/PEG block ratios were controlled at either 1.0 or 2.5, and the PEG molecular weights were 1.0k, 1.5k, 3.0k, and 6.0k. The thermoresponsive sol-gel transition behavior, the mechanical and the microstructural properties of both the aqueous PLGA-PEG-PLGA solutions and the aqueous laponite/PLGA-PEG-PLGA solutions were studied.
It was found that the thermoresponsive sol-gel transition of aqueous single PLGA-PEG-PLGA solution depended solely on the PLGA/PEG block ratio: thermoresponsive sol-gel transitions could only be observed for PLGA-PEG-PLGAs with the PLGA/PEG block ratio of 2.5, while no transitions were detected for those with the ratio of 1.0. In fact, the transition behavior was independent of the molecular weight of PEG.
Intriguingly, it was found that the thermoresponsive sol-gel transition of aqueous laponite/PLGA-PEG-PLGA nanocomposite solution was independent of the PLGA/PEG block ratio. In fact, all PLGA-PEG-PLGA nanocomposite solutions with the block ratio of 1.0 indicated sol-gel transitions in the presence of the laponite. Moreover, the PLGA-PEG-PLGA nanocomposite solutions with the block ratio of 2.5 ended up in aggregates or precipitation even before the temperature rise, which eventually did not exhibit any thermoresponsive sol-gel transitions.
The viscoelastic properties were also analyzed by the dynamic mechanical analysis (DMA). The rheology of the hydrogels depended largely on the molecular weight of PLGA-PEG-PLGA: PLGA_0.5k-PEG_1.0k-PLGA_0.5k nanocomposite hydrogel with laponite presented the highest storage modulus of 600 Pa, whereas PLGA_1.8k-PEG_3.0k-PLGA_1.8k nanocomposite hydrogel showed only 170 Pa. The cryo-transmission electron microscopy (cryo-TEM) and the small angle X-ray scattering (SAXS) were utilized for the microstructural analyses, revealing the influence of both the PLGA/PEG block ratio and the molecular weight of PLGA-PEG-PLGA on the sol-gel transition behavior of the aqueous laponite/PLGA-PEG-PLGA solution.

This study investigates the low and high frequency dispersions in perfluorosulfonate ionomer solutions and membranes by dielectric spectroscopy (DS) and small angle X-ray scattering (SAXS). The dielectric relaxations of Nafion membranes, in particular, the α (f ~ 10^#8209;1 Hz) and β (f ~ 10⁵ Hz), were previously attributed to segmental polymer relaxations, interfacial polarization, and electrode polarization; however, no consensus about the origin of Nafion dielectric dispersions has been reached yet. The understanding of the mechanism involved in the α and β is considered crucial for determining Nafion morphology#8209;electrical properties relations, and for the development of high performance ionomers for electromechanical applications. DS and SAXS measurements revealed that the dielectric relaxations observed at low (α#8209;relaxation) and high (β#8209;relaxation) frequencies display giant dielectric permittivity values as well as typical features of the longitudinal and radial polarization, respectively, of rodlike polymeric aggregates. Such relaxations were attributed to counterion fluctuations in the vicinity of sulfonic acid groups, in resemblance with polyelectrolytes.

Nano building blocks (NBBs) composed of nanoparticle (NP) cores with well-defined polymer tethers offer new possibilities to learn and understand the general principles of molecular interactions and organization behaviors at a larger scale, as well as to apply the well-studied molecular behaviors for the design of new functional materials. We present a facile strategy for preparing a new type of hybrids NBBs with silica-like heads decorated and well-defined polymer tethers via the self-collapse of polymer single chains. Using amphiphilic block copolymers (BCPs) of one inert block and one reactive block containing 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), the intramolecular hydrolysis and polycondensation of silane moieties led to the formation of highly uniform hybrid NBBs with silica-like heads and PEO tethers. In a mixed solvent of THF/water, amphiphilic NBBs could assemble into spherical micelles, vesicles, and large compound micelles, depending on the size of silica heads and the length of polymer tethers. Given highly complex macromolecular architectures, the single chain self-folding of BCPs offers a straightforward synthetic strategy to manipulate the shape/size of nanomers cores and the length/number/location of their polymer tethers. Our study may present a general method to prepare polymer tethered NBBs with controllable geometries and topologies.

Fluroropolymers provide distinct characteristics, including high thermal stability, excellent chemical and weather resistance, low surface energy and low friction coefficients. Due to low surface energy of fluoropolymer, the fluoropolymers can produce hydrophobic surfaces, or even superhydrophobic surfaces with contact angles larger than 150°. The durable superhydrophobic surface can be applied in self-cleaning, anti-sticking, breathability, energy conversion and protecting layers of electronic device. Functionalizing polymers with fluorinated groups primarily affect the surface properties of materials, thus the fluorine content in the bulk may be reduced. Endgroup functionalization introduces a good strategy to modify the bulk and surface properties of polymers. In this project, our goals are to optimize and introduce favorable characteristics of a well-defined polyethylene terephthalate derivative PETG using the feasibility of the endgroup functionalization, and determine structure/property relationships. Different types of diisocyanates were used as linkers between perfluorinated alcohols and the aromatic polyesters through urethane chemistry. The endgroup was synthesized prior to polymer functionalization. The functionalized PETGs were then fabricated through solvent casting and melt processing methods. NMR spectra suggested the successful attachment of perfluorinated endgroup. The result also showed that those films had lower glass transition temperatures and lower processing temperatures for functionalized polymers compared to the prepolymers. The surface characterization indicated that the perfluoro- end groups are segregated at the surface and thus increase hydrophobicity. The next steps of the project are to measure the mechanical properties changes of films and functionalize the PETGs with various molecular weights.

The sedimentation stability of a carbonyl iron (CI)-based magnetorheological (MR)
fluid was improved by wrapping CI particles with a polystyrene (PS) foam layer. The PS
layer on the CI particles was synthesized via conventional dispersion polymerization and was
subsequently foamed using a supercritical carbon dioxide fluid to produce core-shell
structured particles. The density of particles decreased after the PS-layer wrapping and
subsequent PS-layer foaming. The surface morphology was observed by scanning electron
microscope (SEM) and the specific surface areas were determined by Brunauer-Emmett-
Teller (BET) adsorption measurements. Both modifications (PS-layer wrapping and foaming)
increased the surface roughness of the particles, yet preserved particle&’s spherical shape. The
effect of the volume expansion after modification on the magnetorheological properties was
investigated by using a vibrating sample magnetometer and a rotational rheometer. All
suspensions tested presented similar MR behaviors with the only difference in their yield
stress strengths. Finally, the sedimentation properties of the synthesized particles was
examined using a Turbiscan apparatus. MR fluids containing the newly developed CI
particles wrapped with the foamed PS layer exhibited remarkably improved stability against
sedimentation due to the reduced mismatch in density between the particles and the carrier
medium.

The need for open frequencies and higher bandwidth has driven usage of the K_a band (26.5-40 GHz) for communicatoins. Devices in this band are also inherently smaller, providing an advantage for low size, weight and power (SWaP) systems. Microscale 3D printing of RF devices in this range enables the rapid fabrication of complex architectures. Here, we introduce printable dielectric materials with low loss at 34 GHz. Using these inks, solid materials and those with spanning features are fabricated with feature sizes ranging from 10 to 100&’s of µm. To demonstrate their utility as dielectric materials, a simple band-pass filter is printed that is optimized for transmission at 29-38 GHz.

Approach of green lithography using water-developable sugar-based negative resist materials has successfully achieved for the use of pure water in the developable process of electron beam (EB) lithography, instead of conventionally used tetramethylammonium hydroxide and organic solvents. The sugar-based negative resist materials was developed by replacing the hydroxyl groups in the alpha-linked disaccharides with EB sensitive 2-methacryloyloxyethyl groups. 100 nm line and space pattern with exposure dose of 18 mu;C/cm², spin-coating properties on 200 mm wafer, highly efficient crosslinking, and low film thickness shrinkage in EB irradiation were obtained for the water developable, non-chemically amplified, negative tone resist material.

Columnar microfibrous multifunctional metamaterials (mimumes) of Parylene-C polymer were fabricated by a modification of conventional chemical vapor deposition (CVD) and investigated for mechanical, dielectric, and wetting characteristics. For each columnar mimume, a vapor of reactive Parylene-C monomers was collimated and obliquely directed towards a planar wafer at an angle c_v with respect to the wafer plane in a low-pressure chamber. The columnar mimume developed as microfibers grew at an angle c with respect to the planar wafer. An ‘increasing and intermittently constant&’ kind of dependence of microfiber inclination angle c on the monomer deposition angle c_v was found. This dependence of c on c_v is classified into four regimes of two different types and is reminiscent of Geneva gear mechanism. The crystal structure file of Parylene-C polymer was constructed and X-ray diffraction (XRD) experiments in reflection mode revealed the presence of three crystal planes in columnar mimumes in addition to the single plane found in a (highly oriented) bulk Parylene-C film. Columnar mimumes were found to be less crystalline than bulk films, and the XRD intensities of the columnar mimumes were found to reflect the four regimes of the c vs c_v plot. Resonance frequencies in infrared absorbance spectra of the columnar mimumes were found to be identical indicating the similarity in atomic bonding for all monomer deposition angles. Analysis of water-wetting characteristics revealed that the columnar mimumes have higher contact-angle hysteresis than the bulk film. The morphologically significant plane (MSP) of a columnar mimume exhibits higher static hydrophobicity than the vertical plane orthogonal to the MSP, but an isotropic nature was observed for the upper and lower limits of static hydrophobicity. By an appropriate choice of the monomer deposition angle, both static hydrophobicity as well as water wettability can be maximized.

Recently developed high-performance organic and carbon-based materials have demonstrated charge carrier mobilities and conductivities greater than 10 cm² V^-1s^-1 and 10³-10⁴ S cm^-1, respectively. In order to fully exploit these outstanding properties, reliable and scalable fine-patterning technology should be also accompanied for the realization of high-density soft material-based multi-functional system. Here, we report a facile and general route to achieve scalable high-resolution (sub-micron) patterning of organic and carbon-based materials via photochemically induced selective molecular disordering. Following the spatial photochemical patterning, various organic and carbon-based thin-film-transistors (TFTs) exhibit the well-defined active material isolation (current on/off ratio: >10⁷) and minimized parasitic current (on the order of pA). In addition, monolithically integrated large-array of hybrid photosensor circuitry with the patterned photo-sensitive organic films was demonstrated for fidelity of the fine-patterning process, which enabled uniform and high photocurrent modulation (~10⁴) in imperceptible dense electronics application.
Typically, proper isolation and patterning of the functional organic-based materials is required to suppress parasitic and off current, leading to less cross-talk between neighboring devices and minimum power consumption in high-density integrated systems. Fluorinated photoresists using an orthogonal solvent, pre-patterned self-assembled monolayers, and various direct printing techniques have been used to pattern such soft materials; however, several drawbacks, such as the process complexity, limited choice of materials, low throughput, and the resolution limit, have hindered their widespread use in the industry. Room-temperature photochemical routes via deep-ultraviolet (DUV) irradiation have been known to be effective in cleaving specific chemical bonds, which inspired us to explore the possibility of the chemical-free fine-patterning of organic and carbon-based functional materials using high-energy photon irradiation.
For the fidelity of the fine-patterning process in large area and dense electronics, we demonstrate a scalable 10×10 array of hybrid photosensor circuitry by monolithic integration of metal-oxide and photochemically patterned organic TFTs. We constructed and simulated the hybrid polyvalent photo sensor circuits that have the discrete sensory and amplifying functions by virtue of organic and oxide TFTs performance. The low-temperature solution-processed indium gallium zinc oxide (IGZO) TFTs offer a potential to be monolithically integrated with the optically-sensitive organic TFTs for more complex system on a flexible substrate in which, for instance, the optical sensing signal can be amplified with IGZO TFTs. Also, organic materials are patterned by using DUV selective irradiation, it enables to increase photosensitivity.

Ice formation and accumulation on surfaces can result in severe problems for solar photovoltaics, offshore oil platforms, wind turbines, and aircraft. In addition, blockage of pipelines by formation and accumulation of clathrate hydrates of natural gases (also called gas hydrates) can compromise project safety and economics in oil and gas operations, particularly at high pressures and low temperatures such as those found in subsea or arctic environments. Practical adoption of icephobic/hydratephobic surfaces requires mechanical robustness and stability under the harsh real-world environments. Here, durable and mechanically-robust bilayer poly-divinyl benzene (pDVB)/poly(perfluorodecylacrylate) (pPFDA) coatings are developed using initiated chemical vapor deposition (iCVD) to reduce the adhesion strength of ice/hydrates to underlying substrates (silicon and steel). Utilizing a highly cross-linked polymer (pDVB) underneath a very thin fluorine-rich polymer (pPFDA) in designed inherently rough bilayer polymer films deposited on rough steel substrates results in surfaces which exhibit receding water contact angle (WCA) higher than 150° and WCA hysteresis as low as 4°. Optical profilometer measurements were performed on the films and root mean square (RMS) values of R_q=18.9±5.4 nm and R_q =105.3±15.3 nm obtained on silicon and steel substrates, respectively.
The strength of ice adhesion is reduced more than six-fold when the surfaces are coated with the iCVD bilayer polymer films. Both water miscible and water immiscible hydrates are studied. Tetrahydrofuran (THF) is used to study the formation and adhesion of the water miscible hydrates. The strength of THF hydrate adhesion experiences a ten-fold reduction when substrates are coated with these iCVD polymers: from 1050 ± 250 kPa on bare silicon to 128 ± 100 kPa on coated silicon and from 1130 ± 185 kPa on bare steel to 153 ± 86 kPa on coated steel. To study water immiscible hydrates, cyclopentane (CyC5) is used as the guest molecule. The adhesion strength of the CyC5 hydrate deposits is reduced from 220 ± 45 kPa on rough steel substrates to 20 ± 17 kPa on the polymer-coated steel substrates. The measured strength of ice/hydrate adhesion is found to correlate very well with the work of adhesion between the liquid droplets (water, THF-water mixture, CyC5-in-water emulsion) used to form the ice/hydrate and the underlying substrates.

There is an industrial push toward using composites that offer high specific strength, flexibility, and flaw tolerance. Discontinuous fiber composites (DFCs) are of specific interest due to their use in bulk manufacturing techniques such as injection molding and tape casting. However, DFC&’s show reduced strength as compared to traditional continuous fiber composites. This is due to regions of high stress and strain at the filler-fiber interface which leads to poor load transfer from the matrix to the reinforcement fiber contributing to lower strength for DFCs, among other issues. In this work we suggest building a strength gradient around the filler-fibers to provide a local reinforcement to the fibers, reduce stress concentrations at the edges, and improve the surface interaction of the filler-fiber and the matrix allowing for a tougher material.
The proposed strength gradient is created by building a hierarchical structure around the filler-fiber. Alumina micro-platelets with 8-15 µm diameter are chosen as the reinforcing fiber in a polypropylene (PP) matrix. Single-wall carbon nanotubes (SWNT) are subsequently uniformly attached to the surface of the platelets by Van der Waals forces to create the first level of hierarchy. Due to the ability of SWNT to nucleate polymer crystal growth, lamella of isotactic PP are then grown on the surface of the hybrid SWNT-alumina platelets using a solvent/non-solvent based process. The final colloidal solution is filtered, dried, and hot pressed to create a film for mechanical testing and further characterization.
Electron microscopy image analysis of the SWNT-alumina platelets show uniform coverage of homogeneous dispersed SWNT on the platelets. Thermal analysis of the control and composite films show an increase in the crystallization temperature with the addition of SWNT-alumina platelets. This validates that the addition of SWNT on the platelets does nucleate PP crystal growth. Electron microscopy analysis of SWNT-alumina platelets following the solution processes also shows lamellar crystal PP growth directly on the surface of the platelets. Mechanical testing of the composite films as compared to the control PP samples demonstrate that with loading of SWNT-alumina an increase in elastic modulus, strength, and preserved ductility is achieved. This study demonstrates that the use of colloidal assembly processing is important for achieving hierarchical filler-fiber structures toward improving stress transfer in a DFC material.

Segmented polyurethanes are highly versatile and unique elastomeric block copolymers with their soft rubbery segments providing flexibility and hard glassy or semicrystalline segments providing strength. Segmented polyurethanes are known to be biocompatible, with their physical properties largely determined by the domain structures, which can be controlled over a considerable range through the selection of raw materials, their relative proportions, and the processing conditions.
One pressing issue faced by the vast global polyurethane market (projected to be over 73 billion USD by 2020) is the environmental stewardship associated with the usage of predominantly petrochemical based raw materials. To mitigate the environmental impact, one of the current focusing areas of polyurethane research is to make use of low-cost renewable materials in the synthesis and production of polyurethanes.
We have synthesized a class of thermoplastic polyurethanes using isosorbide, a cyclic, rigid and renewable diol as chain extenders. In order to examine the effect of isosorbide on the material behaviors including their thermal, mechanical, and structural characteristics in detail, we systematically adjusted the hard segment compositions between diphenylmethane diisocyanate, butane diol, and isosorbide. Notably, we interrogated the controlled morphology of these polyurethane materials using optical microscopy, atomic force microscopy, and ultra-small angle X-ray scattering. We found the polyurethanes display different morphology depending upon the relative molar ratio of the hard and soft segments. With the soft segments at 70% (70% SSC), the hard segments form individual domains that are well dispersed in the matrix of the soft segments. When the soft segments at 50% (50% SSC), we observed a co-continuous network formed by the phase-separated soft and hard segments. Using a detailed SAXS analysis, we found that in polyurethanes with 70 % SSC, the hard domain size varied between 2.4 nm and 2.9 nm, and decreases with increasing isosorbide content. In polyurethanes with 70 % SSC, we found that the correlation length and average repeat distances trended smaller with increasing isosorbide content. We also estimated the thickness of the diffuse phase boundary for polyurethanes with 70 % SSC, and found that this thickness was asymp; 0.5 nm and decreases slightly with increasing isosorbide content.

Powder coatings are organic films with environmental appeal due to their absence of solvents. Low-reflectance coatings are traditionally formulated large pigment concentrations but this would render powder melts too viscous for even application on a substrate. The solution for low gloss in powder coatings was to lower pigment concentration in conjunction with phase separation from a blend of acrylic polyurethanes, which were generated from a polyisocyanate curative reacting with acrylic polyols. Each component in the blend is distinguished by the relative quantities of hydroxyl groups (OH) in each acrylic polyol reactant (termed low OH and high OH).
To simplify spectroscopic characterization, nonpigmented (clear) films of the blend and its single components were prepared. Raman spectra for the single component clears had easily discernible intensity differences, but these differences disappeared in the blend, which hindered phase identification. To observe phase separation in the cross-section, we embedded samples in a polyester resin and dry-polished with a specialized hand polisher. These cross-sections were uncontaminated from polishing media and thus suitable for Raman analysis. The ensuing spectra from the matrix and low OH resin had an additional peak that stemmed from the alkene moiety in styrene monomer. However, the spectra from the high OH resin and domains did not have this peak. This observation allowed us to conclude that domains consist of the high OH polyurethane, and that styrene could be a novel and useful staining agent for spectroscopic analysis of polymer blends with chemically similar components. Styrene vapor was also found to be a useful staining agent for surface domains and thus could be controlled for degree of infiltration.
For improved observation of domains, we applied transmission electron microscopy (TEM) on microtomed sections stained with U and Pb salt solutions for enhanced contrast between phases. The augmented contrast enabled us to perceive domains in pigmented coatings. The pigments had completely segregated into the domains and changed their geometry from spherical to amorphous. Several domains were flattened on the substrate-polymer interface that suggested adhesion to the substrate. This adhesion by domains was observed for pigmented and clear films cured directly on metal substrates; this was not observed for films cured on primer. The pigment segregation and the substrate adhesion may be explained by a greater number of polar groups in the high OH phase raising its surface energy for greater adhesion to hard surfaces. Insight into domain evolution with and without pigments may be yielded with TEM analysis of the clear and pigmented blends quenched at different times of the cure. Information about the pigment-polymer bonding mechanism could also be yielded from photoelectron spectroscopy being applied toward the individual pigments and the films in different states of pigmentation.

We report a simple technique to produce polydimethylsiloxane (PDMS) sponge which consists of microwave assisted localized heating of the solutions of PDMS and the cross-linking agent. Localized heating leads to bubble formation as well as cross-linking reaction eventually resulting into a hydrophobic sponge. These sponges are oleophilic showing excellent absorption capacity for hydrocarbon liquids and organic solvents, and can be potentially useful in oil spill treatments. In order to utilize them in fields, it is important to be able to control and correlate their microstructure and mechanical properties. Microstructure which governs the porosity is related with the oil uptake. Study of the mechanical behaviour is motivated by the fact that the absorbed oil and organic solvents can be readily extracted from these sponges by simply squeezing them, making them suitable for recycling. Microstructure and mechanical properties together will decide the kinetics of the swelling of these materials. We are able to control the microstructure of these sponges, characterized by SEM, and mechanical properties, characterized by the uniaxial compression test, by mixing appropriate amount of surfactants such as CTAB and SDS. Increasing the surfactants leads to formation of finer pores and larger porosity. An elution experiment of a diesel shows a larger permeability in those sponges prepared with higher concentration of surfactants. Compressive stress vs compressive strain data shows nonlinear power law behaviour and clearly manifests two scaling regimes in all samples with varying concentrations of surfactant. The low strain regime is softer as compared to the large strain regime. However, the scaling exponents of both the regimes ‘monotonically decrease with increasing the surfactant concentration. Thus surfactants assist in softening of these sponges. Further correlation of the scaling exponents with the microstructure by theoretical and analytical methods is under way.

A hollow microsphere fulfilled with fuels is a crucial part in inertial confinement fusion physical experiments. Usually, hollow microspheres are fabricated into three layers (polystyrene (PS)-poly(vinyl alcohol)(PVA)-glow discharge plasma polymer(GDP)) and PVA layer is the key factor to prevent fuel from leakage which mainly controlled by the crystalline property of PVA.
In this work, a series of PVA films with average thickness among 70 mu;m~75 mu;m were cast from a 4.0 wt% aqueous solution. Changing cooling rate after annealing and solidifying temperature, the crystalliability of PVA films was systematically studied by using X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The XRD results have shown that the crystallinity of annealed PVA films was higher than that of unannealed sample, and the crystallinity upgraded to almost 50% with slower cooling rate. Moreover, the crystal peak of 10#8153; (2theta;asymp;19.4°) moved to a higher Bragger angle with the reduction of cooling rate, which indicated a reduced crystalline dimension. Similar results were also obtained in DSC experiments. In addition, the argon barrier property of PS-PVA-GDP microspheres prepared under the exactly same thermal treatments as PVA films were studied by using X-ray fluorescence spectroscopy (XRF). The results indicated that a much longer argon retention period was observed for microspheres cooled at slow rate due to an increasing crystallinity of PVA layer. Surprsingly, as for microspheres that solidified at 45 °C and 23 °C, later ones had a better capability of retaining argon whereas no obvious improvement in the crystallinity of PVA films was found. This phenomenon could be ascribed to that a modified structure of short-range order in amorphous regions of PVA molecular chains had negative effects on the permeability of argon through PVA layers.

Spontaneous phase segregation of an immiscible polymer blend system has been a major area of research as these surfaces can be potentially leveraged in a wide variety of applications like in organic solar cells, as templates in tissue engineering, as templates for selective deposition, as multifunctional substrates for combinatorial studies and many more. Spin cast films of these blends show a variety of random structures depending on the composition of the two polymers, the film thickness as well as the nature of the substrate. In this work, poly(styrene) (PS)- poly(methylmethaacrylate) (PMMA) blend thin films of various concentrations and compositions were spin coated on flat as well as on different topographically patterned substrates and the phase segregated morphology all the cases are compared. Multiple parameters including the molecular weight of the polymers, the surface energy of flat and patterned substrates and nature of the topographic confinement were varied. It was found that for a particular topography and a specific blend composition, below a certain critical blend concentration (Cn*), the phase segregation remains no more random and a perfect ordering of the two phases is observed due to the effect of physical confinement. Further, reduction in molecular weight and surface energy of the substrate enhances the level of ordering of these two domains. These structures can also be produced with appropriate parameters in blends of functional materials like P3HT-PCBM can result in improved optical properties and help creating better OPV or PEC cells.

Polymers typically have low thermal conductivity values that are unfavorable for thermal management of microelectronics. However, precise control of the molecular weight, molecular structures and crystallinity can increase thermal transport. The goal of this study is to investigate thermal conductivity and thermal conductance of polymer systems with different molecular structures, molecular weights, and crystallinity. The amphiphile polymer, poly(vinyl acetate) (PVAc), was analyzed by Frequency Domain Thermoreflectance (FDTR) to determine its thermal conductivity and thermal conductance. For FDTR, Si/Au-PVAc-Au and Si-PVAc-Au configuration was used, where the polymer layer was deposited using the Langmuir-Blodgett (LB) technique. Depositions of the polymer were performed at various temperatures and different polymer phases to compare thermal transport between the resulting polymer samples. The polymer phases ranged from the liquid condensed (Lc) to the liquid expanded (Le) phase on the surface pressure - area isotherm curve. Experimental results obtained provide insights on factors determining heat conduction in polymeric materials and directions for developing high performance thermal interface materials.

As an effort to understand the microscopic nature of glass transition, we use single molecule fluorescence microscopy to investigate segmental motion in polymer thin films. By de-focus single molecule fluorescence microscopy, rotational motion of individual fluorescence molecules is visualized, which reflects the alpha-relaxation process of the system. The fluorescence molecules are either doped in the polymer matrix or chemical attached to polymer chain ends. Attention is paid to the effect of dimension of fluorophores undergoing rotational motion under different temperature.
Poly (vinyl acetate) (PVAc) is adopted as the model system and a series of pyrene-based fluorescent derivatives were chosen as the probes. By spin-casting, PVAc films with 100 nm thickness were prepared with fluorophores doped inside. Under single molecule de-focus microscopy, which exposes the phase information of the fluorescence emission, the pattern of fluorescence emission is clearly recorded, exhibiting the spatial orientation of the dipole moment of individual fluorophore. By image analysis, the temporal profile of rotational motion of individual fluorophores is determined, and attention is paid to the change of number of molecules undergoing rotational motion, as a function of temperature. It is discovered that the fraction of rotating molecules (f_r) - the ratio of rotating molecule number over the total number of molecules, experiences a sharp increase with the increase of temperature near the glass transition temperature (T_g): an increase from almost zero to unity. The most interesting feature is the value of the transition temperature increases with the increase of fluorophore&’s dimension. The comparison of the data with other types of T_g measurements, such as DSC and ellipsometry, shows that only the data of a fluorophore with the dimension of 1.9 nm match the data set of T_g determination, while the values of those of different dimension are either lower or higher than the value of T_g.
Such results of the dimension effect of probes provide supporting evidence of the dimension of cooperative relaxation region (CRR) at the occurrence of glass transition - only when the dimension of fluorophores is comparable to that of CRR, it starts to exhibit a dynamic homogeneity at the dimension of the probes&’ size.

We recently characterized the voltage-activated thinning and electrowetting of copolymer-stabilized bilayer interfaces (CSIs) formed between aqueous droplets submerged in oil. When placed in an oil mixture containing ABA-type tri-block copolymers (PEO-PDMS-PEO), the droplets become rapidly coated in a low-tension polymer monolayer due to the amphiphilic triblock structure. However, unlike droplet interfaces stabilized spontaneously by phospholipid bilayers (DIBs), we observed that a reversible connection between neighboring droplets is achieved by applying sufficient voltage to be applied between droplets. This finding suggests that the applied electrical field acts as a pressure on the interface to assist in the removal of excess oil that prevents spontaneous thinning. Above the critical voltage (>|100mV|), the thickness of the thinned region of the interface is constant but the area of the thinned interface increases significantly due to electrowetting. Unlike DIBs, the removal of voltage then results in a complete separation of the connected droplets and we have measured much larger changes in interfacial area due to electrowetting. These properties suggest that CSIs, possibly due to their low-tension state, may provide improved functionality for a variety of droplet-based electrowetting platforms. One of the important unknowns is the tension state of both the thinned polymer interface and the monolayer.
In this work we aim to measure the equilibrium tensions of CSI-stabilized droplets in three oils to evaluate the effect of the solvent on the electrowetting performance of polymer-coated droplets. Initial studies shows that the polymer-coated water droplets deform very easily under oils, suggesting that the surface tension of the monolayer is very low. Due to extremely low surface tension of CSIs&’ monolayers, a pendant droplet goniometer is unable to measure the equilibrium tension because the weight of the droplet prevents it from remaining attached to the dispensing needle. Instead, we will employ a multistep technique developed recently by our group for DIBs to measure the membrane specific capacitance and tensions of CSIs in three oils (pure hexadecane, 1:1 mixture of hexadecane and silicone oil (AR20), and pure silicone oil) that require different critical voltages for interface thinning. Preliminary results indicate that the specific capacitances for these interfaces are 0.19, 0.13 and 0.12mu;F/cm² (n=3), respectively. By knowing the specific capacitance, the tensions of the bilayer interface and the monolayer will be estimated by applying successive voltages across the membrane and measuring the resulting contact angle between two droplets during electrowetting. By knowing the tension state for this system, we can predict droplet shapes under the oil with and without the electrowetting effect.

The photocuring epoxy is fundamental to many applications such as 3D printing¹. The sensitivity of current initiators to UVA radiation in solar light makes photocured products unstable² and creates the need for initiators that can only be triggered during the printing process by wavelengths outside the spectrum of solar light. Using semiconducting nanoparticles as photo initiators may address this as their bandgaps can be engineered via different phenomena such as the quantized effect³. Semiconducting quantum dots can be synthesized using flame spray pyrolysis (FSP). Here, we study the effect of using such flame-made TiO₂ particles and the addition of silica on the photocuring of epoxy. Pure and silica-doped titania semiconducting nanoparticles made by FSP are investigated and compared to commercially available titania nanoparticles (Evonik P25) under a UVA lamp. Pure titania, with surface area of approximately 300 m²/g as measured by nitrogen adsorption, exhibits the highest photocatalytic activity, almost 5 times higher than P25. The high rate by which particles pass through the steep temperature gradient of the flame may have a quenching effect resulting in a monoclinic fraction in the crystal structure. This is confirmed by XRD, TEM, electron diffraction and Raman spectroscopy. Addition of silica stabilizes a bigger fraction of monoclinic crystal structure in the final powder in agreement with literature⁵. It also reduces the crystal size leading to a blue shift in its absorbance in accordance with the quantized effect³. This constitutes a significant milestone towards creating and using quantum dots that absorb exclusively outside the solar spectrum to rapidly make stable 3D printed parts.
Crivello JV. The Discovery and development of onium salt cationic photoinitiators. Journal of Polymer Science Part A: Polymer Chemistry. 1999;37:4241-4254.
Hare CH, The degredation of coatings by ultraviolet light and electromagnetic radiation. The Journal of Protective Coating & Linings. 1992; 5: 58-66.
Alivistatos AP. Semiconductor clusters, nanocrystals, and quantum dots. Science. 1996;271:933-937.
Mädler L, Stark W J, Pratsinis S E. Rapid Synthesis of Stable ZnO Quantum Dots. Journal of Applied Physics. 2002;92:6537-6540.
Kogure T, Umezawa T. Formation of TiO₂(B) nanocrystallites in sol-gel-Derived SiO₂-TiO₂ film. Journal of American Ceramics Society. 1999;82:3248-3250.

Hydrophilic polymer networks exhibiting shape-memory properties are potential candidate materials for applications, in which the diffusion of small molecules are important factors such as for biomedical applications.^[1] The thermally-induced shape-memory hydrogels (SMHs) reported thus far were non-porous and exhibited an almost constant material volume during the shape fixity and recovery process.^[2,3]
Here we explored, whether 3D structured SMHs can be designed by incorporating oligo(ε#8209;caprolactone) as switching segment into hydrogels. By utilizing different porogenes during thermal crosslinking 3D structured hydrogels having pore diameters between 30 and 390 µm and wall thicknesses ranging from 10 to 190 µm were synthesized. The swelling behavior, the thermal, and the thermo#8209;mechanical properties were investigated as function of the OCL content, which was varied between 20 and 40 wt%. The structured hydrogels exhibited good shape fixity and shape recovery ratios above 80% in compression experiments. In conclusion these 3D structured SMHs are interesting materials for specific applications in biomedicine with on demand directed movements.
[1] N. Annabi, J. W. Nichol, X. Zhong, C. Ji, S. Koshy, A. Khademhosseini, F. Dehghani, Tissue Eng. Part B Rev. 2010, 16, 371.
[2] Y. Osada, H. Okuzaki, H. Hori, Nature1992, 355, 242.
[3] M. Balk, M. Behl, U. Nöchel, A. Lendlein, Macromol. Mat. Eng.2012, 297, 1184.

We have sought to develop new approaches that yield soft, water-based shape memory polymers exhibiting local and macroscopic ordering. In this talk, we will present two distinct approaches toward achieving this goal, one involving local ordering by liquid crystallinity and the other involving macroscopic ordering through aligned fiber-reinforcement. For the liquid crystalline approach, we will introduce a simple synthetic approach to yield a new liquid crystalline network featuring elastomeric softness, water-swelling and shape memory characteristics. By comparing with a non-mesogenic network prepared using the same procedure, we will reveal structure-property relationships of the liquid crystalline and crystalline polymer networks. Wide angle and small angle x-ray scattering studies were used to examine the liquid crystalline ordering in both dry and hydrated states. Such ordering was found to be related to the observed shape memory and actuation (two-way shape memory) properties and these phenomena are highlighted with demonstrations of shape change in response to heat and water stimuli. For the fiber-reinforcement approach, an anisotropic hydrogel composite was developed by incorporating aligned thermoplastic fibers into an otherwise isotropic hydrogel. The resulting anisotropic composites exhibited shape memory characteristics that could be activated in response to hydration or dehydration, with a basis in anisotropic swelling. We observed that different helicoids or spirals could be formed in anisotropic hydrogel composites by varying the orientation of fiber angles and ply thickness. To further characterize these anisotropic hydrogels, the dependences of helicoids&’ pitch and radius of curvatures were studied as a function of fiber angle orientation and composite thickness. This study provides insight into the mechanisms affecting the shape evolution of water-activated anisotropic hydrogels and enables the future design of materials or devices for a variety of applications. By comparing the two approaches, we will reveal relative advantages and disadvantages for different applications, which will be attributed to both chemical composition and microstructure - a matter of scale.

The field of soft robotics encompasses actuators, sensors, devices, and machines that can deform, flex or conform in response to their environment, while performing their predesigned functions. A common approach for making polymers responsive to external stimuli is to incorporate functional nanoparticles. Moreover, different arrangements of nanoparticles within the polymer can be used to control the response of the nanocomposite. Embedding magnetic nanoparticles (MNPs) in polymers allows their actuation using magnetic fields, where the magnitude of the response is usually controlled by the particle size and concentration. When the dipoles of MNPs are aligned in an external field, they can assemble into chains along the field lines. Chaining of MNPs causes magnetic anisotropy, where the chains magnetize more easily along the chain direction. In applied magnetic fields, alignment of chains of MNPs parallel to the field is consequently favored. Actuation of polymer composites containing chained MNPs with magnetic fields allows for controlled bending, thus coupling the magnetic properties of the MNPs and the mechanical properties of the polymer.
We have demonstrated controlled and selective bending of arms of a cross-shaped elastomeric thermoplastic polyurethane film containing chained 30-nm Fe₃O₄ nanoparticles. The sample has been prepared with the chains aligned parallel to two arms (parallel arms) and perpendicular to the remaining two arms (perpendicular arms). When the sample is supported in the middle, gravity causes the arms to hang down. Application of the uniform horizontal magnetic field of an electromagnet parallel to the chains causes the parallel arms to lift and become nearly aligned with the field direction but does not lift the perpendicular arms. We have designed a simple model of the magnetic interactions (Zeeman energy and interparticle dipolar coupling) and gravity that provides an excellent match to experiment while neglecting effects of elasticity, magnetocrystalline anisotropy, and thermal energy. When rotating the sample in uniform magnetic fields, magnetic hysteresis causes mechanical hysteresis in the bending response, which is explained by the competition between the elastic energy of the polymer and the magnetostatic energy of the MNPs. When the cross-shaped sample is pinned in the center on a flat surface, the magnetic field gradient of a permanent magnet held above the sample generates a higher force on the parallel arms, causing selective lifting, while the perpendicular arms do not lift. These results highlight the potential for dipolar interactions among chained MNPs to impart controlled actuation to polymer nanocomposites, which will have applications in soft robotics, where the absence of any moving parts is desired.

Transfer printing encompasses a set of techniques for deterministic assembly of micro-and nano-objects, termed "inks," into spatially organized, functional arrangements with two and three-dimensional layouts. These processes offer a degree of flexibility in the creation of heterogeneously integrated functional systems that is unmatched by traditional microfabrication techniques, and have proven valuable in the fields of flexible electronics, curvilinear optoelectronics, and bio-integrated sensing and therapeutic devices. Printing typically involves either the transfer of a single pre-fabricated ink or pre-arranged layer of inks, with the ability to print an arbitrary pattern of inks in a scalable way yet to be demonstrated. Here, we demonstrate such a process, whereby an array of inks is printed to a receiving substrate in an arbitrary pattern using a carbon-doped, thermally-sensitive shape memory polymer (SMP) as the functional material. Pre-fabricated arrays of inks may be retrieved en masse through mechanical deformation of the SMP surface microstructure to maximize SMP-to-ink adhesion, and then selectively printed by utilizing localized heating of the SMP above its glass transition temperature to enable passive shape-reconstitution, thereby enabling release of these inks by minimizing the SMP's adhesion to them. Heat is delivered rapidly by the absorption of laser energy within the selectively carbon-doped SMP microstructure.

Amorphous polymers achieve shape memory behavior through the large change in the chain mobility above the glass transition. Above the glass transition temperature, the polymer chains are mobile and can recover quickly to equilibrium when unloaded. Below the glass transition, the chains slow to recover when unloaded. The temperature span of the glass transition has a direct effect on the shape memory behavior. Materials with broad glass transition region can store and recover multiple shapes and remember not just the deformation but also the programming temperature. Since the glass transition is the underlying mechanism of shape memory behavior in amorphous materials, shape recovery can be achieved by either increasing the temperature in the material above the glass transition temperature or by decreasing the glass transition temperature to below the temperature of the material. The latter can be achieved with the absorption of a small weight fraction of solvents. In this presentation, I will demonstrate the thermally activated temperature memory and multiple shape memory effect for both temperature and solvent driven shape recovery. Specifically, I will show the correspondence between solvent and temperature driven recovery phenomenon. For solvent-driven shape recovery, the programming temperature and solvent type both strongly influence on the shape recovery behavior. Thus, the temperature memory effect can be used to program multiple shapes for multi-staged recovery in solvent. Analogous to the temperature memory effect, different solvents can also induce different shape recovery and can also provide a mechanism for multi-staged and multiple shape memory recovery in solvent

Shape-memory polymer networks, which are capable of reversible shape changes upon heating and cooling, have been recently introduced as novel kind of thermo-sensitive actuators. [1-3] So far the reports about two-way shape-memory polymers (2W-SMP) concentrate on the characterization of macroscopic samples. One example for 2W-SMP are crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) consisting of crystallizable polyethylene (PE) domains with a broad melting transition. Here PE crystallites in the high melting temperature range act as shape determining skeleton domains, while lower melting PE crystals are responsible for the reversible temperature driven actuation. [1]
In this work, we explored whether microcubes can be prepared from cPEVA and equipped with a free standing, reversible bidirectional shape-memory effect (rbSME).
A template-based replication method was applied for preparation of cPEVA microcubes with an edge length of 10 or 25 µm from poly[ethylene-co-(vinyl acetate)] with a vinyl acetate (VA) content of 18 wt% (cPEVA18) or 40 wt% (cPEVA40) and dicumyl peroxide as crosslinking agent. For rbSME functionalization the microparticles were deformed by compression at 70 °C and 100 °C, respectively. The change in single particle height and area of the programmed microcubes during cyclic heating and cooling between 75 or 60 °C and 20 °C was monitored by optical microscopy (OM) and atomic force microscopy (AFM). A pronounced rbSME was achieved for both type of microcubes cPEVA18 and cPEVA40 with a reversible strain in the range of 5 to 7%, whereby higher compression ratios resulted improved reversible strains. The observed micro rb-SME performance is comparable to that reported for macroscopic cPEVA actuators [1].
The findings obtained for cubic model microparticles will be helpful for designing the next generation polymeric microactuators or micromanipulators.
References:
[1] Behl M, Kratz K, Noechel U, Sauter T, and Lendlein A. Proceedings of the National Academy of Sciences2013;110(31):12555-12559.
[2] Saatchi M, Behl M, Nöchel U, and Lendlein A. Macromolecular Rapid Communications2015;36(10):880-884.
[3] Gong, T., Zhao, K., Wang, W. X., Chen, H. M., Wang, L., Zhou, S. B., Thermally activated reversible shape switch of polymer particles, 2014, Journal of Materials Chemistry B, 2(39): 6855-6866

Most research on stimuli-responsive materials, in particular, shape memory polymers, has focused on the macroscopic deformation and bulk recovery mechanism. Recently, the stimuli-responsive properties of the micro- or nanostructured surfaces have garnered more attention. While studies of mechanically deformable surface pattern on polymers have been reported, there is a dearth of study on correlating geometrical designs of surface textures with pattern deformation in response to mechanical stretching. Herein, we fabricated grating and hole structures with a range of length scales, feature designs (protruding vs recessed) from shape memory thermoplastic elastomer polyurethane by nanoimprinting. The pattern deformation can be achieved through stretching the polymer film above the glass transition temperature (Tg) of the soft segments and locking the temporary shape upon cooling, followed by the removal of external stress. Upon reheating above the Tg, the deformed structure could be recovered. From the scanning electron microscopy and atomic force microscopy analysis, non-uniform deformation has been observed in all patterns investigated. Specifically, on protruding grating, there is a decreasing effective tensile stress (strain) from the base (bulk of the film) to the top part of the grating. Furthermore, variation in length scale (200nm vs 2µm line width, both at aspect ratio of 1:1 and duty cycle of 1:2) resulted in different degree of deformation, with nanoscale pattern exhibiting higher strain at the top part of the grating. The recessed hole structure was elongated along the stretching direction, with an increased anisotropy (i.e. circle to ellipse). In terms of vertical dimension, some axial pre-strain was rebounded upon the low temperature unloading process, which increased the heights of the lines. Recessed (hole) structures exhibited a more significant change in the hole depth, as compared with that in the heights of the protruding lines for grating. For micro- and nanopatterns, nearly complete shape recovery was retained even after 10 cycles. The deformed and recovered micro- and nanopatterns were investigated for the surface wettability properties. On original or recovered gratings, the water droplet displayed a Cassie-Baxter (C-B) wetting behavior. Increasing the line spacing as a result of tensile strain reduced the water contact angle (CA) on nanograting, suggesting that, in addition to the tip, the sidewall of the lines was partially wetted. In contrast, the CA on micrograting was increased at low elongation due to lower solid-air fractions (obeying C-B state), and began to decrease marginally at high elongation. The CA on the hole structure remained relatively unchanged with elongations. Our results suggest that the stimulus-responsive function in shape memory polyurethane may be tuned by varying the geometries of the micro- and nanoscale surface patterns.

Short bowel syndrome is a disorder caused by a lack of sufficient intestinal length that occurs in children at a rate of up to 25 per 100,000 births and affects near 15,000 adults in the U.S. Without sufficient digestive and absorptive capacity due to the resultant intestinal failure, patients are unable to maintain growth or weight via enteral nutrition and then must rely upon parenteral nutrition, which is associated with a 50% mortality rate and $2.3B in costs per year in the U.S. Distraction enterogenesis is an alternative treatment involving the application of mechanical force to the bowel in order to increase its length and surface area. A solvent-driven shape-memory polymer has been proposed as a material to achieve distraction enterogenesis by absorbing fluid to decrease the glass transition temperature (Tg) for activation in vivo. The objectives of this study were (1) design a solvent-driven shape-memory polymer system with tailorable recovery rates and (2) demonstrate in vitro biocompatibility and in vivo feasibility with a rat model. Isobornyl acrylate, 2-hydroxyethyl acrylate (HEA), and hexanediol diacrylate were mixed in five varying ratios and cured at 405nm with Irgacure 819 to produce polymer films. Each composition was analyzed by dynamic mechanical analysis to determine Tg. Dry Tg increased from 79.7°C to 97.1°C as isobornyl acrylate wt% increased. Water content increased from 1.8% to 5.4% as HEA wt% increased. Elastic modulus decreased from 225 MPa to 6 MPa over 7 days of immersion. Films were programmed at their respective Tg into a compact shape and recovered either in air at 37°C or in saline at 37°C without constraint. Recovery in air ranged from 6.8% to 96.9% and recovery in saline ranged from 13.5% to 100% over 7 days. Recovery amount increased as water content increased. Human intestinal fibroblasts were seeded onto discs. The cells showed continued viability throughout 14 days and showed proliferation via MTT assay, as well as, matrix deposition as demonstrated by collagen assay. The animal study was performed in accordance with the IACUC of Boston Children&’s Hospital. Young Sprague Dawley rats underwent a Roux-en-Y isolation of a small intestinal segment, which was wrapped around an extraluminal, radially expanding shape-memory polymer device. After 14 days, devices showed a 70% increase in circumference. Intestinal segments increased from 24±3mm to 50±15mm, while control segments increased from 35±9mm to 37±6mm. No difference in muscularis thickness was detected between groups, which suggests elongation is due to tissue growth, not stretching. This work demonstrates the feasibility of distraction enterogenesis with a tailorable, solvent-driven shape-memory polymer device, where high Tg polymers can be activated with saline uptake. Further studies will investigate upscaling the device size for larger animals and bowel function after distraction.

Despite their advantages, the inherent low strength and stiffness of shape-memory polymers (SMPs) can limit possible applications. A common method to improve polymer strength and stiffness is to increase the chemical crosslinking, or the addition of reinforcement such as glass/carbon fibers; however, both approaches severely limit ductility, effectively negating the purpose of an SMP. Aromatic polymers such as poly(phenylene sulfide) (PPS) and poly(ether etherketone) (PEEK) are a unique and advantageous class of polymers because they are stronger and stiffer than more common polymers and have large fracture strains relative to composites. The defining microstructural feature of these materials is the abundance of phenyl rings in the polymer backbone, which results in high strength, high stiffness, and stability at high temperatures. To date, aromatic polymers have been largely unexplored for use as SMPs.
The purpose of this study was to investigate the shape-memory behavior of poly(para-phenylene) (PPP) under varying programming temperatures, relaxation times, and recovery conditions. PPP is an inherently stiff and strong aromatic thermoplastic, not previously investigated for use as a shape-memory material. Initial characterization of PPP focused on the storage and relaxation moduli for PPP at various frequencies and temperatures, which were used to develop continuous master curves for PPP using time-temperature superposition (TTS). Shape-memory testing involved programming PPP samples to 50% tensile strain at temperatures ranging from 155°C to 205°C, with varying relaxation hold times before cooling and storage. Shape-recovery behavior ranged from nearly complete deformation recovery to poor recovery, depending heavily on the thermal and temporal conditions during programing. Straining for extended relaxation times and elevated temperatures significantly decreased the recoverable deformation in PPP during shape-memory recovery. However, PPP was shown to have nearly identical full recovery profiles when programmed with decreased and equivalent relaxation times, illustrating the application of TTS in programming of the shape-memory effect in PPP. The decreased shape recovery at extended relaxation times was attributed to time-dependent visco-plastic effects in the polymer becoming significant at longer time-scales associated with the melt/flow regime of the master curve. Under constrained-recovery, recoverable deformation in PPP was observed to have an exponentially decreasing relationship to the bias stress. This study demonstrated the effective use of PPP as a shape-memory polymer both in mechanical behavior as well as in application.

Smart shape memory polymers (SMPs) can memorize and recover their permanent shape in response to an external stimulus, such as heat, light, and solvent. They have been extensively exploited for a wide spectrum of applications ranging from biomedical devices to aerospace morphing structures. However, most of the existing SMPs are thermoresponsive and their performance is hindered by heat-demanding programming and recovery steps. Although pressure is an easily adjustable process variable like temperature, pressure-responsive SMPs are largely unexplored. By integrating scientific principles drawn from two disparate fields - the fast-growing photonic crystal and SMP technologies, here we present a new type of SMP that enables unusual "cold" programming and instantaneous shape recovery triggered by applying a contact pressure or exposing the sample to various vapors (e.g., acetone, ethanol, and toluene) at ambient conditions. This interdisciplinary integration simultaneously provides a simple and sensitive optical technique for investigating the intriguing shape memory effects at nanoscale. We have also demonstrated the reversible fabrication of reconfigurable nanooptical devices, such as photonic crystal filters and lasers, as well as tunable antireflection coatings, using these new stimuli-responsive SMPs. The striking chromogenic effects induced by the unusual shape memory behaviors of the smart polymers provide vast opportunities for a plethora of applications ranging from reconfigurable nanooptical devices to chromogenic pressure and chemical sensors to novel biometric and anti-counterfeiting materials.

Many marine organisms produce underwater adhesives via complex coacervation, the formation of a water insoluble fluid by combining oppositely charged polyelectrolytes. Translating nature's highly effective strategy to synthetic materials enables the construction of dynamic and robust hydrogels by simply mixing ABA triblock copolymers containing oppositely charged end-blocks [1]. This facile formation of non-covalent—yet strong—crosslinking points represents a promising avenue for the fabrication of materials which require mild processing conditions.
Using this versatile crosslinking platform, we prepare micron scale coacervate hydrogel particles as potential colloidal carriers for release applications. Microgels are obtained through coacervate formation from PEG-based anionic and cationic triblock copolymers in a microfluidic flow focusing device. This microfluidic approach not only offers control over particle size with narrow distribution but also enables incorporation of charged dyes as model cargos into the coacervate domains through electrostatic interaction with the charged polymer end-blocks. Release kinetics can be tuned through the 1) particle diameter, 2) functional group of the dye, and 3) ionic strength of the solvent. By leveraging the bio-inspired assembly of precise building blocks, these non-covalent microgels may serve as a model release system for future development in controlled delivery.
[1] Hunt, J. N.; Feldman, K. E.; Lynd, N. a; Deek, J.; Campos, L. M.; Spruell, J. M.; Hernandez, B. M.; Kramer, E. J.; Hawker, C. J. Tunable, High Modulus Hydrogels Driven by Ionic Coacervation. Adv. Mater.2011, 23, 2327-2331.

Polymeric microparticles that incorporate functional materials are widely used in diagnostics, tissue engineering, drug delivery system, microelectromechanical systems, and anti-counterfeiting. Despite recent advances in synthesis methods, large-scale particle manipulation still remains as major challenge. Approaches to position large numbers of microparticles in precise patterns are critical for increasing the throughput of multiplexed assay or generating the large encoding capacity in microenvironment fabrication and anti-counterfeiting applications. However, current methods either lack sorting capacity or are not suitable for large-scale, high throughput arrangement of particles. Therefore, a new technique is required to arrange functional microparticles at precise locations with high yield, low error rate, and high throughput.
Here, we present a porous microwell platform that is used to generate large-scale, geometry-selective, ordered microparticle arrays with high throughput. Microwells are molded into diverse 2D extruded structures on top of a porous membrane with the help of soft stamps. Microparticles are synthesized by stop flow lithography, and have well-defined 2D extruded geometries and mechanical properties. To generate the large-scale particle arrays, we steer the microparticles to the microwells via hydrodynamic forces associated with fluid flow through open pores inside the microwells. Guided microparticles are inserted into congruent microwells, whereas geometrically mismatched particles are removed in a subsequent washing step. Controllable driving force provides the appropriate magnitude for various microparticles (25-150 µm), and has the ideal direction of force field to guide the microparticles. By iterating assembly and washing steps, large-scale (10³-10⁴) particle assembly are generated, with high filling yield (94 %) and large yield of initial particles (88 %), in less than 100 seconds. Shape, size, and modulus sorting are achieved with high specificity (> 95 %). Because microparticles were assembled into specific microwells and maintained their positions during the iteration, complex microarrays can be fabricated. After fabrication, the particle assembly can be collection and transferred for further applications.
To demonstrate the unique capabilities of the new techniques, we rely on the large encoding capacity and low decoding error rate of microparticle arrays for an anti-counterfeiting application. Pre-synthesized upconversion nanoparticle (UCN)-laden microparticles are arranged into 2D coded patterns, which are covert and process-inert. This approach has the potential to achieve 10²⁰ encoding capacity, one order of magnitude larger than the total number of sand grains on Earth.

The past decade has seen micro- and nanogel particles receiving increased attention in theoretical and applied studies. These particles combine properties of typical colloids with soft character and responsiveness of gels, which makes them suitable materials for cosmetics, coatings, food, drug delivery, sensing, fabrication of photonic crystals and purification technologies. It was found recently that poly(N-isopropylacrylamide) (PNIPAM) based gel particles are able to adsorb at the fluid/fluid interface and lower the surface tension of water. This property is of big importance since fluid interfaces are ubiquitous in Nature and are central to a host of many applications. Despite the fact that stabilizing properties of micro- and nanogels have been well demonstrated the stabilization and destabilization mechanisms involved are still object of studies.
Here we report the use of Neutron Reflectometery (NR) and surface tension measurements to probe the interfacial properties of PNIPAM nanogels. We studied how the interfacial structure varies with the temperature at the air/water interface. Nanogel particles (protonated and deuterated) with varied amount of cross-linker (N,N&’-methylenebisacrylamide, MBA, 10-50%) were synthesized. They exhibit spherical shape (as tested by AFM and TEM) and size between 5 and 40 nm, depending on amount of MBA. They undergo transition from swollen to collapse state with increase of temperature. All of them lower surface tension of water however less cross-linked nanogels are more surface active than those with higher concentration of MBA. NR measurements revealed that nanogels deform strongly upon adsorption at the interface resulting in ‘fried egg-like&’ morphologies. Increase in cross-linker concentration decreases nanogel deformability. The layer of adsorbed particles can be divided into two regions. A polymer rich are facing the air in which polymer chains are collapsed, and water submerged one where polymer chains are fully solvated.
Nanogel behaviour at air/water interface as a function of temperature was evaluated. Increase in temperature led to higher adsorbed amounts and it is accompanied by changes in nanogels conformation. At 40°C, below the volume phase transition temperature of 47°C, the neutron data suggest strong GISANS scattering from an ordered structure. This is tentatively related to a possible association of nanogels below the interface, in order to minimize the free energy of the system. The data presented bring a new light into the understanding of interfacial behaviour of gel particles and may help to understand how those particles stabilise the interfaces.

The microfluidic production of droplets is a well controllable process, which allows templating small spherical containers that can subsequently be transferred into uniformly sized polymer microgel particles by a crosslinking reaction. Recently, the per-channel production rate of N-isopropylacrylamide (NIPAAm) droplets (w-phase) dispersed in a low-viscosity fluorocarbon oil could be increased by a delayed surfactant addition, while maintaining the advantageous dripping regime. Here it should be evaluated, if delayed surfactant addition can be applied to enhance droplet production also for high viscosity continuous phases (o-phase), which is associated with a change to a inviscid drop scenario compared to the previously used setting of viscous drops. It could be illustrated that the concept of delayed surfactant addition holds true also for viscous continuous phases and allows ~8 fold increased flow rates in the dripping regime. Surprisingly, the droplet size increased at higher total flow rate with constant flow rate ratios of w- and o-phases, which is discussed in this work.

The gene carriers should be developed with the specific or targeting recognition by endothelial cells (ECs) with aim to enhance transfection efficiency, proliferation and migration of ECs. Here, REDV and CAG-mediated polycationic gene carriers were prepared and used for pZNF580 (pNDA) delivery. These functional peptides were coupled with methoxy poly(ethylene glycol) ether-poly(L-lactide-co-ε-caprolactone)-PEI (1800Da) block copolymer, and the corresponding targeting nanoparticles (REDV or CAG-NP) were formed by self-assembling method. REDV or CAG-NP/pDNA complexes were prepared by mixing the nanoparticle suspension with pNDA plasmid solution at different N/P molar ratios. pDNA plasmid was efficiently and significantly expressed by these carriers, which may be attributed to the EC-specific peptides of REDV and CAG. The pZNF580 protein level expressed by these functional complexes in ECs was higher than that by PEI 25 kDa/pZNF580 complexes. Additionally, the introduction of CAG and REDV peptides onto the polycationic gene carriers can also promote the migration capability of ECs, which benefits for the revascularization. The targeting peptide modified gene carriers may be a promising platform for enhancing endothelialization.

Safe and effective delivery of genetic materials remains a challenge. Viral vectors are commonly used and can be highly efficient, but safety is a persistent problem. Polymers are promising non-viral vectors because of their safety and high chemical versatility, but they usually suffer from low efficiency. Here, I review our recent work on a family of biodegradable, multifunctional poly(amine-co-ester)s, including new materials that include orthoester groups in the main chain. The polymers were designed to provide multiple functions simultaneously: 1) biodegradability; 2) positive charge provided by tertiary amines in the main chain, which is used to bind with nucleic acids; 3) high hydrophobicity to assist in complex formation; 4) acid-sensitivity provided by the orthoester groups; 5) high tunability of the different functions, which enables the easy optimization of the polymer to accommodate different cargos. We have shown that hydrophobicity allows stable gene binding with a greatly lowered positive charge density on the polymer, making the polymer less toxic. These polymers have low toxicity and are highly efficient in delivery of both plasmid DNA and various RNA constructs.

Langer/Farokhzad group have elegantly demonstrated the benefits of using pre-functionalized biomaterials to generate drug-encapsulated surface active nanosystems over the post-functionalization of the NS. The degree of ligand substitution at the NS surface is critical for receptor mediated delivery and this can be optimized only with the flexibility in the polymer functionality, which the current approaches lack as bio-conjugation is often achieved at the terminal end groups of the polymers.
Very recently our lab made novel precision polymer (P2s) platform to overcome the limitation of conventional polyesters for ligand conjugation. These P2s are PLA-PEG based block co-polymers with periodically placed functional groups via linkers along the polymer backbone. A range of amphiphilic polymers was prepared by altering the ratios of lactide to ethylene glycol or PEG and varying the lengths of PEG chains in the co-polymers. P2s were tailored to obtain a range of molecular weights, hydrophobicity and the kind, number and density of functional groups to accommodate ligands of different functionalities and drugs of varying physico-chemistry. A variety of ligands with different functionalities i.e. carboxyl, hydroxyl and amine were conjugated to P2s. The P2s can hold approximately 10-fold higher ligand concentration compared to conventional polyesters like PLGA for the same amount of polymer. These P2s-ligands were processed to form nanosystems (P2Ns) encapsulating a range of drugs with distinct physicochemical attributes e.g. insulin, paclitaxel. The P2Ns outclassed PLGA-NS in caco-2 cell uptake studies treated with same polymer concentration accompanying different ligand densities. P2Ns present a tunable platform to deliver drugs to desired tissues with enhanced bioavailability as well as tailored release profile owing to varying amphiphilicity of the polymers.
These P2s offer novel platform peroral delivery technologies for life cycle management of existing drugs with potential to minimize attrition rates in the drug discovery program, as well as convert injectables to peroral route.

Hollow particles have been the focus of considerable attention in the literature because of their wide range of potential applications, which include pharmaceuticals, cosmetics, food, insulation and agriculture. Colloidosomes are micrometer-sized hollow particles that have shells consisting of coagulated or fused colloid particles. Here, a new family of pH-responsive microgel-colloidosomes was prepared using microgel particles as the building blocks. Microgels are crosslinked polymer particles that swell when the pH approaches the pK_a of the polymer. Uniquely, our method for colloidosome preparation uses only one type of (colloidal) building block for shell assembly, i.e., the pre-formed vinyl-functionalised microgel particle which acts as a macro-crosslinker. Our simple and versatile method used covalent inter-linking of vinyl-functionalised microgel particles adsorbed to oil droplets to form shells of doubly crosslinked microgels and was demonstrated using two different microgel types. The colloidosome surface morphology had a texture that originated from inter-linked microgel particles. The doubly crosslinked microgel colloidosomes were strongly pH-responsive and exhibited a major pH-triggered swelling response in the physiological pH region which supports the view that they have good potential for biomaterial applications. The success of doubly crosslinked microgel formation provided novel experimental support for the occurrence of microgel interpenetration at oil/water interfaces (which has been postulated by other groups) and enabled a new approach for preparing stimulus sensitive polymer capsules.

In this work, the coaxial electrospinning approach has been applied to fabricate smart core shell nanofiber for controlled release of anticorrosion material. Acetal-dextran was used as pH controlled shell [1] of the fibers and polyvinyl alcohol (PVA) as a hydrophilic core. Scanning Electron Eicroscope (SEM) analysis of the fiber morphology and spinnabilty (occurrence of beads-on-stirring) indicated that the solution concentration of the shell was the most important parameter for the fibers formation. Transmission electron microscopy (TEM) and confocal microscopy confirmed the core shell morphology. We also demonstrated the possibility to encapsulate two different dyes in each layer of the fiber, which was confirmed by confocal microscopy. Caffeine, as an anti-corrosion inhibitor [2] was encapsulated in the fiber core to test its potential application as anticorrosion coating. Almost negligible release was noticed at neutral pH. In acidic pH, the fibers quickly respond by releasing caffeine cargo. This smart system could be easily scaled up and used as a promising platform for stimuli responsive membranes that could be used in industrial anticorrosion coating applications.
1. Bachelder, E.M., et al., Acetal-derivatized dextran: an acid-responsive biodegradable material for therapeutic applications. Journal of the American Chemical Society, 2008. 130(32): p. 10494-10495.
2. Fu, J., et al., Acid and Alkaline Dual Stimuli-Responsive Mechanized Hollow Mesoporous Silica Nanoparticles as Smart Nanocontainers for Intelligent Anticorrosion Coatings. ACS nano, 2013. 7(12): p. 11397-11408.

Differential Scanning Calorimetry was performed on a series of aqueous solutions of PEO-PPO-PEO (L101, P104, P105, and F108) amphiphiles in the low concentration regime (0-2%) to resolve the critical micelle concentrations (cmc) of the neat polymers. Work was done from 2% wt/v to 10% wt/v (in 2% wt/v increments) amphiphilic copolymer concentrations and co-formulated with cisplatin concentrations (0% wt/v-0.1% wt/v in 0.02% wt/v increments) to resolve any deviation in the enthalpy of micelle formation. Enthalpy-entropy compensation plots for each neat copolymer and each amphiphile solution mixed with cisplatin were obtained. Two types of behaviors were observed; a drug influenced compensation temperature profile (P104), and a drug invariant behavior (L101, P05 and F108) where the change in compensation temperature was less than 1#8304;C. Only neat P104 was found to be profoundly influenced by the presence of cisplatin that must reorganize the interface between the hydrophobic and hydrophilic regions of the micelle. Adding cisplatin lowered T_compensation from 302.1 to 288.8 K.

Self-assemblies of nanoscale colloidal building blocks attract increasing attention for the creation of various superstructures such as clusters, superlattices, worms, ribbons, and chains. For example, directional attraction between colloidal building blocks with orthogonal repulsion to the attraction can produce a supracolloidal chain. The strategy of balancing attraction and repulsion to guide a linear superstructure was recently applied to nanorods and nanoparticles of gold and spherical micelles of triblock copolymers in order to produce their supracolloidal chains. Furthermore, chemical characteristics of colloidal building blocks can be preserved in supracolloidal chains so that properties of supracolloidal chains can be tuned by modifying colloidal building blocks and can be multiply functionalized by incorporating dissimilar colloidal building blocks into supracolloidal chains. Recently we demonstrated supracolloidal chains by linear self-assembly of diblock copolymer micelles. We cross-linked the polar core of diblock copolymer micelles and then made the solvent preferable to the core block but still compatible with the corona block. Thus, spherical micelles were converted to colloidal micelles with the corona reorganized into two non-polar patches and the central core that was directly exposed to the solvent. With these reorganized micelles, their linear superstructures were induced by increasing the polarity of the solvent. In this presentation, we applied the same protocol to functionalized diblock copolymer micelles, which were produced by incorporating fluorophores in the micellar cores. The colloidal building blocks of fluorophore-functionalized micelles were then self-assembled into supracolloidal chains. In addition, copolymer micelles functionalized with different fluorophores were combined to demonstrate multi-functionalized supracolloidal chains.

Research on semiconducting organic crystals has been actively investigated for achieving high performance organic thin-film transistors and applying to diverse electronic applications. Particularly, in order to control the position and orientation of organic single crystals with a well-ordered molecular structure, several techniques such as inkjet printing and sheared deposition using a self-assembled mono-layer pattern have been suggested. In this presentation, we used surface-mediated solvent vapor anneal (SMSVA) process of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic films, forming diverse patterns of their organic single crystals. Room-temperature photochemical patterning of polymer dielectric layer by using deep ultraviolet (DUV) enables the determined organization of C8-BTBBT single crystals with controlled-position and orientation. In SMSVA process, C8-BTBT small molecules become mobile on soluble polymer layer and re-assembled into micro rod-shaped single crystal only at pristine polymer dielectric region.
C8-BTBT single crystal arrays ware produced on the narrow trench of pristine polymer dielectric while their diverse patterns such as a simple line, zigzags and radial direction were readily possible as well. Based on these large arrays of C8-BTBT single crystals, we fabricated high performance of organic single crystal transistor on 3-um-thick flexible film in which the saturation mobility of devices exceeds ~ 3 cm²/Vs. It was also found that the high performance of single crystal transistor remained functional without noticeable degradation following the aggressive bending test. More details will be presented at the conference.

Double network hydrogels attract more and more attentions in materials science due to their extremely high mechanical performance which can be tailored to mimic a wide variety of load-bearing biological tissues, ranging from “soft” tissue such as muscle to firmer tissue such as bone. The enhanced mechanical strength exhibited by such hydrogels is likely attributed to the stress transfer between the two interpenetrating networks, instead of the stress being confined to the smallest crosslink of a single component gel. However, current double network hydrogels are mostly based on fully or partially chemically crosslinked networks which lack designable stimuli-responsiveness and dynamic controllability. Herein we present the first example of an entirely self-assembling and supramolecular double network hydrogel, which is formed from the combination of two distinctly different hydrogel systems: one through DNA hybridization, and the other by host-guest interactions of cucurbit[8]uril (CB[8]). Unlike the formation process of chemically crosslinked double network hydrogels via a two-step polymerization, our supramolecular system can be fabricated by a simple “one-pot” mixing method attributed to the highly precise and specific recognition motifs. Fluorescence labeling verified that the individual DNA and CB[8] networks were physically interpenetrating and bound within each other contributing to the increased mechanical properties and thermal stability. Furthermore, the interpenetrating behavior provides advantages for the double network hydrogel, i.e., excellent stretchability and ductility contributing resistance to fracture. Based on the dynamic and reversible supramolecular interactions, the double network hydrogel possesses shear-thinning and thixotropic properties, which show great potential as injectable soft materials for in vivo applications. Finally, on the account of the natural biodegradability of the DNA and cellulose backbones, the double network hydrogel is responsive to nuclease and cellulase as well as to small molecules. We believe that all of the advantages above make our supramolecular double network hydrogel an excellent new soft material scaffold that can be used in a wide variety of applications including dynamic surface coatings, controlled release and tissue engineering.
References
1. J. P. Gong, Y. Katsuyama, T. Kurokawa, Y. Osada, Adv. Mater. 2003, 15, 1155.
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3. J.-Y. Sun, X. Zhao, W. R. K. Illeperuma, O. Chaudhuri, K. H. Oh, D. J. Mooney, J. J. Vlassak, Z. Suo, Nature 2012, 489, 133.
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6. C. Li, M. J. Rowland, Y. Shao, T. Cao, C. Chen, H. Jia, X. Zhou, Z. Yang, O. A. Scherman, D. Liu, Adv. Mater.2015, 27, 3298.

Janus particles are special particles whose surfaces have two or at least two distinct properties and/or polarities. Due to their special characteristics, Janus particles offer tremendous potential for various applications. The past decades have developed synthetic strategies for the successful preparation of diverse well-designed and functionalized Janus particles, but most of them merely focus on one or one class of core substrates. General methods of surface modification and functionalization regardless of the natures of the core properties have seldom been reported. Herein, we reported the combination of the employment of liquid marbles as microreactors with the remarkable adhesive ability of polydopamine to develop a novel route to the synthesis of Janus particles from micron-sized particles. Since polydopamine has demonstrated strong adhesion to virtually all types of surfaces, these microreactors would be suitable for depositing polydopamine films to various particle shells, making it a common method to fabricate Janus particles generated from different materials. Similar to the Pickering emulsion, when particles adsorb to the air/liquid interface, the distance that particles penetrate into the liquid phase is mainly dealt with their surface energies. Thus, it is possible to control the position of the particles at the air/water interface through the addition of surfactants, salts and/or organic solvents to the liquid marbles, resulting in the change of Janus balance at the particle surface. Furthermore, owing to the many functional groups in polydopamine, versatile strategies could be introduced to use these Janus particles as platforms for secondary modification, including particle immobilization, metal ion chelating and reduction, and chemical reactions. Given the flexibility in the choice of cores and the secondary modification strategies, this developed two-step method is distinctive in its high universality, good controllability and great practicability. Moreover, with a proper design of the core/shell properties, tremendous applications could be achieved in physical, chemical, and biological fields.

Oligodepsipeptides (ODP), i.e. alternating oligomers of α-amino and α-hydroxy carboxylic acid, are of interest as biomaterials, as they do not show acidification upon hydrolysis, while the amino acid subunit allows the facile incorporation of diverse side chains.¹ The limited use of ODP is mainly associated with the challenging synthesis of morpholine-2,5-diones (MD) used as a monomer for ring opening polymerization (ROP), as well as the ROP itself. Amination reaction of bromoacetyl bromide with an amino acid followed by ring closure in presence of a base is one of the most utilized methods to prepare MD. The low yield of the ring closure step is considered to be the main barrier to prepare a sufficient amount of MD within reasonable time. Thus, the effect of different reaction conditions on the yield of ring closure reaction of pure N-(bromoacetyl)-L-amino acids was studied. In this way, the yield of the ring closure reaction could be increased, e.g. of β-O-benzyl-N-(bromoacetyl)-L-serine to about 53 mol% compared to previous reported yield of 20 mol%² by combination of temperature control, use of DMSO as solvent, slow addition of precursor solution, and activation of the ring closure by potassium iodide. The ROP of MD has been most extensively studied with tin(II) 2-ethylhexanoate, though other Lewis acids have been successfully employed in the ROP of e.g. dilactides. In the case of MDs, using other Lewis acids resulted ODP showing similar molar mass, polydispersity and thermal transitions compared to the one prepared by using tin(II) 2-ethylhexanoate. A ratio of about 5 mol% racemization was, however, observed for other Lewis acids which could be caused by the high temperature needed to initiate the oligomerization. The oligomers with a M_n of 5800 gmiddot;mol^-1 and a polydispersity of 1.1 were used to prepare submicron sized particles by nanoemulsion. The particle size (250-450 nm) was mainly influenced by the choice of the surfactant: surfactants with a HLB value of 18-19 giving smaller particles than surfactants with HLB value of 15.
References
1- Y. Feng, J. Lu, M. Behl, A. Lendlein, Macromol Biosci. 2010, 10, 1008-1021.
2- G. John, S. Tsuda, M. Morita, J. Polym. Sci. Part A Polym. Chem. 1997, 35, 1901-1907.

The structure of thermally expandable microcapsule (TEMs) is consisted of a thermoplastic shell which is filled with liquid hydrocarbon at core. The shell of TEMs becomes soft when the temperature is higher than boiling temperature of liquid hydrocarbon. The shell of TEMs is expanded under the high temperature because the inner pressure of TEMs is increased by vaporization of hydrocarbon core. Therefore, the TEMs are applicable for blowing agents and light weight fillers. Carbon nanotubes (CNT) are the well-known filler for increasing thermal, electrical conductivity and mechanical strength. However, dispersing CNT in polymer matrix is one of big challenge for using CNT. In this research, TEM was polymerized with acrylonitrile (AN) and methyl methacrylate (MMA) along with CNT in water. Since surface treated CNT has hydrophobic property, CNT was embedded into the TEM shell consisting AN-MMA co polymers. The TEM containing CNT at its shell was then mixed with epoxy resin and 2 mm sheet was fabricated by doctor blade. The sheet was then cured at 180 ^oC for 5 minutes. Electromagnetic shielding effectiveness (EMI SE) of sample was compared with virgin epoxy sheet and epoxy sheeting containing CNT. Epoxy sheet with TEM containing CNT at the shell showed better EMI SE property than the other two samples.

Polyurethane (PU) is an important class of polymers that have wide application in a number of different industrial sectors. The goal of this work was the synthesis of flame-retarded PU foam with expandable graphite (EG) or commercial graphene. Additionally, the sound behavior of PU foam composites has been investigated. The flame retardancy and thermal stability of the foams has been studied through cone calorimeter analysis, the limited oxygen index and thermal conductivity. The presence of expandable graphite brings an improvement in fire behavior. In particular, the limited oxygen index increases in a linear way and the highest limited oxygen index values are obtained for PU-EG composite foams. The results from the cone calorimeter are in agreement with those of oxygen index; EG filled foams show a considerable decrease of peak-heat release rate (peak-HRR) with respect to unfilled foams. The results of thermal conductivity show that an increase in expandable graphite amount in PU foams lead to an increased conductivity.

Biofouling is a key first step for the onset of foreign body response responsible for poor performance of implantable biosensors. The aim of this contribution is to explore the bias-dependent biofouling characteristics of thin hydrogel films. For this, gold-coated electrodes were self-assembled with thiol-based monolayers (SAM) that later reacted with poly (ethylene glycol) (PEG)-containing copolymers affording covalent grafting. Low molecular weight PEG chains (i.e. 6-8 glycol units) were shown to exacerbate biofouling as opposed to higher molecular weight branches. In this contribution we show that we were able to improve on the biofouling of the working electrodes by applying the proper bias with respect to a reference electrode. The biofouling of both positive- and negative-charged proteins were significantly decreased upon the application of proper bias. The effect of pH and ionic strength were also investigated in relation of the applied bias. This study offers an opportune venue for minimize biofouling in implantable electrochemical devices.

Colloid-polymer composite systems are of significant interest due to their unique and important properties. To date, most applications have focused on the mechanical properties of such systems, and the potential of such systems for creating materials with interesting electrical and electrochemical properties has been limited. For example, it remains quite challenging to create a colloid-polymer composite which can dynamically reconfigure to provide variable electrical and/or electrochemical properties. Previous theoretical work (Jadrich & Schweizer, PRL, 2014) has shown that an abrupt insulator-to-metal transition can occur with low packing fraction conductive colloids within a large mesh porous gel by tuning the polymer colloid interactions. This theory was based around a large mesh system with the rod (fiber) length, greater than the pore size, colloidal diameter, and rod (fiber) thickness. To realize this system experimentally, we electrospin synthetic polymeric fibers with long persistent lengths as well as large mesh sizes (several microns) and combine them with electrically conductive colloids. Specifically, 200-500nm diameter poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM) fibers are chosen for the network due to PNIPAM&’s temperature responsiveness and the relatively high mechanical strength of these specific copolymer fibers. Submicron conductive colloids consisting of tin-nanoparticles encapsulated in elastic hollow carbon nanospheres are synthesized and put into the fiber network. As the temperature is cycled around the lower solution critical temperature (LCST) of the polymer, the system can be triggered between insulating and conducting states through the reversibility of the colloid aggregation. As another proof-of-concept, we construct a redox-responsive system where 60, 90, and 750nm electrochemically active poly(vinylbenzyl-ethylviologen) (RAPs)-based colloids, are immersed within a porous rigid polymer network. This work could be potentially applied to building a novel class of flow batteries in the future.

Poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is one of the most promising conducting polymers with high conductivity because it enables cost-effective and flexible devices as well as roll-to-roll mass production. In addition, nanoparticles possessing electro conducting property are useful since they can be applied to electrical-magnetic shields, batteries and electrochemical display devices. However, previously reported methods for conductive nanoparticles require complex and energy consuming process, and resultant coating must be very weak under abrasion.
Herein, we propose a simple and one-pot method to synthesize cyanoacrylate/PEDOT:PSS composite nanoparticles. This method is designated as “supersaturated gas cored instant polymerization” (SGCIP). Mixing aqueous solution of PEDOT:PSS and acetone leads to the emission of supersaturated gas and cyanoacrylate instantly polymerizes around the gas to form polymer shells. The existence of PEDOT:PSS in polymer shell was observed by the detection of sulfur with EDX (Energy Dispersive X-ray spectrometry). The conductive nanoparticles coated onto glass showed the conductivity of 13.4 S/cm, measured by the four-probe method, and contact angle of 140°. Cyanoacrylate is known for “super glue” and strengthens the binding force between particles and substrates. Thus, cyanoacrylate/PEDOT:PSS composite nanoparticles have possible application for conducting hydrophobic surfaces with high mechanical durability on antenna or electrical-magnetic shields.

Ionic liquids have drawn significant research interests as gate dielectrics in electrochemical transistors because of their extremely large specific capacitance and wide electrochemical windows. For a practical standpoint, it is desirable to control the fluidity of ionic liquids to avoid leakage problems by constructing 3D polymer networks in ionic liquids. To this end, we have blended copolymer, poly(vinylidene fluoride-co-hexafluoropropylene), P(VDF-HFP) with different ionic liquids and formed solid polymer electrolytes, which are known as ion gels. The resulting stretchable ion gels based on P(VDF-HFP) and ionic liquids such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMI][TFSI], 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [BMI][TFSI], 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate, [BMPYR][FAP], 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMPYR][TFSI], 1-butyl-3-methylimidazolium hexhafluorophosphate, [BMI][PF₆], 1-butyl-3-methylimidazolium tetrafluoroborate, [BMI][BF₄], 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate, [EMI][FAP], 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMPYR][TFSI] show outstanding mechanical characteristics including strain at break values at ~300% and Young&’s modulus at ~1 MPa. As we increased the polymer content to 80 wt% in P(VDF-HFP) based [EMI][TFSI] gels, the gel showed increases in Young&’s modulus and crystallinity. By using these ion gels, we have fabricated thin-film transistors that operated at low voltages below 2 V and showed high ON/OFF current ratio of 10⁵. These results demonstrate an attractive route to prepare mechanically robust polymeric gel electrolytes for various applications.

UV nanoimprint lithography is a useful method to fabricate patterns with high fidelity. Especially, roll-to-roll UV nanoimprinting process shows a promise for continuous patterning of nanoscale structures in large scale at low cost and low temperature. These advantages of the roll based imprinting can be suited as a processing technology for flexible substrate but several issues still hamper its wider commercial applications. One of them is that the reactivity of oxygen in air eliminates radicals and terminates a photo-curing process, so-called oxygen inhibition problem, in a radical polymerization system. It hinders the process from achieving the high resolution in the imprinted patterns. In order to address this concern and to enhance release property in imprinting process, we have developed cationic UV nanoimprint resins that can transfer high fidelity patterns without anti-sticking layer coated on the surface. By adopting cationic polymerization system (1,4-butanediol divinyl ether and 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate) instead of radical polymerization, we have solved the problem of the oxygen inhibition. Also, we added a fluorinated monomer (3-perfluorooctyl-1,2-propenoxide) to render an intrinsic hydrophobicity without having to utilize the anti-sticking layer coating process.
The functional surfaces with nanoscale patterns have been demonstrated by using roll-to-plate UV nanoimprinting of the newly developed fluorinated cationic photo-curing resin. The amount of curing in the resin was analyzed by FT-IR spectroscopy. The imprinted patterns and surface morphology were characterized by field emission scanning electron microscopy (FE-SEM), and the inherent hydrophobicity of the resin was measured by contact angles using tensiometer. We confirm from the FT-IR results that the resin is cured well under the UV dose during the roll-to-plate nanoimprinting process. High fidelity of transferred patterns is demonstrated by checking the error-rate using FE-SEM images. Furthermore, the surface energy of the resin with fluorination agent is measured to be lower than that of the resin without the additive, which means enhanced releasing property.
This research was supported by the MSIP(Ministry of Science, ICT and Future Planning), Korea, under the “IT Consilience Creative Program” (IITP-2015-R0346-15-1008) supervised by the IITP(Institute for Information & Communications Technology Promotion).

Gas sensors are important in many areas, such as industrial production, medicine, food storage and environmental monitoring [1]. Sensors based on thin films can be obtained by the Layer-by-layer (LBL) method, which has many advantages over other traditional methods including simplicity, low-cost, low temperature of deposition, controllable thickness and no need of complex equipment. Furthermore, the addition of inorganic conducting nanoparticles incorporated between layers can improve sensor performance due to their electric properties [2]. Graphene oxide (GO) belongs to the carbon-based materials family with remarkable electrical, mechanical and thermal properties, moreover, GO presents a two-dimensional (2D) structure and large surface area [3], useful for sensing applications. In the present work, nanostructured films based on polyaniline (PANI), graphene and zinc oxide (ZnO) were obtained by LBL method aiming applications in chemical sensors. PANI was purchased from Sigma Aldrich, GO and ZnO were previously synthesized by the Hummers and hydrothermal methods, respectively. LBL films with 2, 3 and 4 tetralayers of PANI/GO/PANI/ZnO were deposited onto gold interdigitated electrodes. The samples were characterized by UV-vis absorption spectroscopy, micro-Raman mapping, scanning electron microscopy (SEM) and electrical impedance measurements. UV-vis spectroscopy and SEM confirmed the homogeneous adsorption of tetralayers of PANI/GO/PANI/ZnO onto the substrates. The GO and ZnO presence was confirmed by micro-Raman mapping. The impedance analyses were carried out to explore the electrical properties confirming the conductivity increase owing to the number of layers. After characterization, the modified electrodes were tested in air with different concentrations of ammonia. Upon exposure to ammonia gas, the impedance measurements revealed satisfactory sensor sensitivity from 50 up to 500 ppm of ammonia, confirmed by statiscal analysis, indicating the potential application of PANI/GO/PANI/ZnO film architecture for designing ammonia sensors.
Acknowledgments: This work was supported by CNPq, CAPES, FAPESP and Embrapa.
References:
1. Severini C., et al., Changes in the Aromatic Profile of Espresso Coffee as a Function of the Grinding Grade and Extraction Time: A Study by the Electronic Nose System. J. Agric. Food Chem. 2015, 63, 2321minus;2327.
2. Dhingra, M., et al., Polyaniline mediated enhancement in band gap emission of Zinc Oxide. Composites: Part B, v. 45 p. 1515-1520, 2013.
3. Jeon, J. W., et al. Polyaniline nanofiber/electrochemically reduced graphene oxide layer-by-layer electrodes for electrochemical energy storage. J. Mater. Chem. A, 2015, 3, 3757-3767.

3D architectured gelatin-based hydrogels (ArcGels) have been shown to be a suitable material for the successful biomaterial-driven induction of bone regeneration in critical size bone defects [1]. ArcGels are prepared by stabilizing gelatin through the reaction with lysine diisocyanate ethyl ester (LDI), in water, under stirring and in the presence of a surfactant. This leads in a one-step procedure integrating synthesis and processing to an open-porous structure (pore sizes 190-210 mu;m). The material consists only of amino acids, linked by amide or urea bonds. The 3D structure as well as the chemical topology of the network comprising protein chains, oligourea crosslinkers, as well as grafted oligoureas led to different mechanical behavior on different length scales. Local elasticities were determined by light microscopy guided AFM indentation experiments and show increased Young&’s moduli at lower LDI content (E = 40-1200kPa). This can be explained by the fact that local elasticities are ruled by the covalent network, while in ArcGels with higher LDI content a larger number of grafted chains is generated. The macroscopic compressive modulus did not depend on the LDI content. This can be rationalized by the increasing local moduli being levelled out by an increasing material density, as was observed for the gelatins with increasing LDI content. In macroscopic tensile tests, the Young&’s modulus increased with the LDI content. Here, the grafted oligourea chains play a role as physical crosslinkers and increase the stiffness of the material.
The structure and mechanical behavior of the ArcGels were furthermore followed during hydrolytic degradation. The pore sizes of the material increased during degradation, which is a unique behavior and closely related to the stretching of the polymer chains during the formation. During degradation, this leads to merging of pores. Interestingly, even though the degradation leads to the hydrolytic cleavage of bonds, ArcGels retain the mechanical integrity for a long time, likely due to the gradual self-organization of the gelatin chains into single and triple helices, which was confirmed by WAXS measurements. Depending on the ArcGel composition, starting triple helical content was between 1 and 2 % and after 4 weeks of degradation it increased to values between 4 and 6 %.
Human bone marrow derived mesenchymal stromal cells (hMSC) homogenously distributed along both surface and interior of the ArcGels as early as 3 h after cell seeding, with no difference in cell invasion or viability at early time points. Induction of osteogenic differentiation was however more prominent on materials with lower LDI content and higher local Young&’s modulus. This demonstrates the importance of the mechanical properties of the ArcGels for their biofunctionality

Polydimethylsiloxane (PDMS) has come to be the most widely used material for fabricating microfluidic devices for biological applications. Interestingly, PDMS can be easily modified with a wide range of functional molecules and proteins which can be further finely tuned to allow specific molecular interactions. In this work we study how the surface functionalization and physicochemical properties of PDMS affects the mechanisms of adhesion, growth and motility of Xylella fastidiosa, an important phytopathogenic bacterium.
The PDMS microfluidic devices with channel widths in the range 5-60 µm were developed using conventional photolithographic fabrication methods and subsequently functionalized to enable bacterial cell adhesion. We first optimized the surface hydroxylation process, which was a crucial step prior to the functionalization of different biomolecules. The microchannels were first activated by piranha solution followed by grafting of Amines using ethanol amine hydrochloride. Subsequently, polyethylene glycol (PEG) and carboxylmethyl cellulose (CMC) were attached onto the aminated surface. Furthermore, different cell adhesive promoters such as gelatin and the afimbrial protein XadA1 were functionalized over the CMC and PEG grafted surfaces respectively for comparison studies. The influence of different functional groups towards the adhesion of cells was studied in detail. The experiment was performed via a syringe pump to maintain a continuous flow of cells over the functionalized surfaces and monitored in-situ via a fluorescence microscope. We observed that, in the gelatin modified surface, the cell density was 40 times higher than that of pristine sample. In addition, the cell density increased by 70% when the channel width was varied from 5 to 30 µm channel. Furthermore, in gelatin modified channels, the cell movement is 5.5 time slower as compared to pristine channel (for a particular width); this behavior may be attributed to strong columbic interactions between bacterial cell and surface functional groups. Our results suggest that both microenvironment and surface functionalization have tremendous influence on the growth and motility of bacterial cells. This study also provides a potential approach to understand the early cell adhesion dynamics on PDMS-based microdevices, and thereby facilitate its potential use in on-chip bioanalysis studies.

Great scientific efforts have been done in order to provide better materials and technologies for energy issues, which endeavor is driven by the reduction of the total energy consumption by tailoring efficient devices and then overcome the global warming and energy demand dilemmas. In particular, smart windows (SWs) play a fundamental role on climate adaptive building shells by the regulation of the solar transmission, reducing air conditioning costs through sunlight blocking in summer or improving light harvesting in winter. One way to tune the transparency of SWs in response to weather conditions is using thermosensitive polymers, inasmuch as these materials are structure/color-sensitive to the temperature. Hence, the main goal of this study is to use the poly(N-vinylcaprolactam) (PNVCL) as an active material in smart windows based on its response to the temperature variation, induced by intense sunlight irradiation or induced heating (Joule effect). The PNVCL has an interesting feature of undergoing a coil-globule transition in aqueous solution at 34°C (lower critical solution temperature, LCST), as well as it is a non-toxic and renewable material, which makes the thermodynamic reversibility of this material an insight for SWs devices. To aim this purpose, the synthesis of PNVCL and the SWs were designed to lead to switchable devices. In the first instance, the PNVCL was synthesized by the radical polymerization of NVCL monomer with azobisisobutyronitrile as initiator at 70°C for 4h in dimethyl sulfoxide, posteriorly centrifuged and washed in hot deionized water. The SWs were built with two transparent conductive oxide (TCO) substrates as a heating element and dynamical control of the temperature by bias applied. Then, the gap between the TCO substrates was filled with an aqueous solution with 1 and 5% w/w of PNVCL. The efficiency of the produced device was analyzed by in situ UV-vis spectroscopy, which was possible to verify the PNVCL as a thermochromic material even in low loads, changing the transmittance of the SWs from transparent to totally opaque color during the LCST of PNVCL. In addition, the correlation between bias applied and temperature was determined to evaluate the kinetics and the critical point of transition phase of PNVCL. This analysis showed that the transition phase of SWs is a function of temperature (thermodynamic property) and depends on the hydrophilic/hydrophobic balance of polymer chains and the solvent. This means the PNVCL can be switchable without being degraded over cycles, as observed by UV-vis spectroscopy.

Among the different routes of drug administration, oral route is the most used in the therapy since it is a easy, noninvasive administration, allowing higher patient acceptance and dose changes. However, conventional oral dosage allows a quick drug release after administration, which might lead to dose fluctuation, increasing the risk of subtherapeutic or toxic levels compromising the therapeutic response. Therefore, the temporal and spatial control of drug delivery is of great interest in the research and development of new drug delivery systems, since it represents a valuable strategy to enhance the therapeutic response. Different approaches can be explored, concerning formulation and/or technologies, such as the controlled release systems that are designed to modulate the release rates over the gastrointestinal tract. Starch is of particular interest in the design of innovative drug delivery systems due to its wide availability, low cost and biodegradability, since it undergoes chemical degradation in vivo by enzymatic hydrolysis, resulting in non-toxic products. The ability of high amylose origin inclusion complexes with high enzymatic resistance was studied to obtain controlled drug delivery systems. Amylose complexes with praziquantel (PZQ) were successfully prepared by a simple and low cost method with high yield (>57%) and drug content (until 68.16%) achieved. The influence of the drug:polymer ratio, temperature and presence of palmitic acid on the complexes were evaluated. DSC, X-ray diffraction and NMR data evidenced the drug-polymer interaction and the formation of inclusion complexes with semi-crystalline structures related to type II complexes. The inclusion of drugs allowed the drug release control in both acid media (pH 1.2) and phosphate buffer (pH 6.9). The complexes were sensible to the presence of pancreatin, which promoted a significant increase in release rates of both drugs, evidencing the enzymatic degradability of these complexes. The release data correlated better with Weibull model in non-enzymatic medium, indicating that the release occurred by complex mechanisms involving diffusion, swelling and erosion. In pancreatin-containing medium, the best correlation was for 1st Order model, evidencing the acceleration of the release rates of drugs in early times due to enzymatic degradation and subsequent erosion of polymer.

Glycocalyx is a polysaccharide-rich layer that forms around and protects epithelial cells. Although it is known that the primary function of this glycocalyx layer is to act as a sieve for biological analytes approaching the cell surface, the functionality and specificity of this sieve is dependent on a number of biological and physiological factors, and the mechanism of sieving is not fully understood. The interaction of the glycocalyx with an approaching agent is a function of the size, charge, chemical composition and biophysical structure of the agent resulting in varied responses. In light of this, we are developing new hybrid surface structures that will serve as models for the glycocalyx layer of endothelial cells. Our goal is to prepare multi-component hybrid surface structure containing brush like glycocalyx-mimicking glycopolymer layers along with ligands, such as proteins, peptides or other biomolecules. This hybrid structure contains a base polymer layer, poly-p-xylylene with orthogonal pendent reactive groups (alkyne and bromoisobutyrate groups). This base polymer layer is prepared via chemical vapor deposition (CVD) co-polymerization. The resulting surface reactive sites on the polymer allows for surface-initiated atom transfer radical polymerization (SI-ATRP) and azide-alkyne Huisgen cycloaddition (or “click” reaction) to generate well-defined glycopolymer brushes along with ligands on the surface. The chemical composition of the base polymer layer prepared via CVD co-polymerization was validated via Fourier transformed infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). We also showed that the ratio between the two surface reactive sites can be finely tuned by controlling the feed ratio of the precursor materials during the CVD copolymerization process. This enables us to control the density of the glycopolymer brush and the ligand. As a proof of concept, glucose- and sorbitol-containing polymer brushes were successfully grafted from the base polymer layer via SI-ATRP, as confirmed via FTIR and XPS. Furthermore, fluorescence assays using azide-functionalized FITC indicated that the underlying alkyne groups on the base polymer layer (with 1:1 alkyne to bromoisobutyrate sites) were accessible and reactive after 7nm of glucose-polymer brushes are grafted on the base polymer layer, allowing for the attachment of ligands to create hybrid structure containing well-defined glycopolymer brushes and ligands to study the interactions between the glycocalyx-micmicking layers and biological analytes.

As electronics components become smaller and have more functions, the issues of cross-talk and interference between microprocessors become of paramount importance. Especially in the case of multi-chip modules, adhesives must have multifunctional purpose. Such polymers are used to attach bare dies to form high density packages. One main aspect to consider is having low dielectric properties while maintaining high adhesion. In the current work, we will demonstrate how some block-copolymers can be utilized to obtain ultra-low dielectric properties. More specifically, we will show how micro-phase separation, in addition to interpenetrated polymer networks (IPN), can be used to obtain ultra low dielectric materials with dielectric constant of below 2 and very low dissipation factor.

Bacterial colonization and subsequent biofilm formation on polymer surfaces is a pressing challenge. For example, annually in the United States, biofilms formed on intravascular catheters are linked to 250,000 blood stream infections with an associated mortality rate between 12 and 25%. Previously, it has been reported that bacteria have the ability to sense and differentiate between surfaces. This suggests that understanding how bacteria move over well-characterized polymer surfaces, like hydrogels, could potentially lead to better designed medical devices that prevent bacteria colonization. In this work, the interaction between bacterial species and well-characterized poly(ethylene glycol) (PEG) hydrogels was assessed in a defined flow environment. PEG hydrogels were synthesized as a function of crosslink density to obtain soft (310 kPa) and stiff (6,500 kPa) hydrogels, which had an associated theoretical mesh size of 27.2 Å and 10.0 Å, respectively. To decouple stiffness and mesh size, an additional soft PEG hydrogel (215 kPa) was synthesized with a reduced crosslink density, thus statistically increasing its mesh size to ~40.7 Å. Bacterial adhesion from flow was measured while the three PEG hydrogel surfaces were oriented vertically, which eliminated gravitational forces between the bacteria and the hydrogels. Experiments were conducted using two distinct model microbes, (i) highly motile Gram-negative Escherichia coli K12 MG1655 and (ii) non-motile Gram-positive Staphylococcus aureus MW2. For both S. aureus and E. coli, the frequency and duration of rolling encounters was greater on the stiff PEG hydrogel. However, only E. coli rolled significantly longer distances per encounter on the soft PEG hydrogels with the larger mesh size, which likely was due to microbe&’s extracellular filamentous protein appendages (10-20 Å in diameter). Bacterial “stick-and-roll” behavior is a physiological advantage of bacteria that leads to enhanced surface colonization by bacteria on non-adhesive antifouling surfaces. Understanding what materials properties can be synergistically used with anti-adhesive coatings to prevent bacterial settling will significantly aid in the future design of functional biomaterials and medical devices.

Macroscopic rotating engines powered by electricity or fuel are very common devices that are generally used to produce mechanical energy. However, it is very difficult, if not impossible, to integrate them into microdevices. Making high-speed and strong miniaturized torsional actuators with simplicity, robustness and low cost is always very challenging. Up to now, the strongest torsional actuators ever reported are based on the concept of twisted fibers. [1] The concept of twisted fiber can actually be used to develop torsional actuators by involving several mechanisms, such as thermal expansion [1], entropic elasticity of polymer chains, [2] solvent swelling in CNT or graphense yarns[3,4]. Here, we study the shape memory effect by twisting polymer fibers and explore their application for strong torsional actuators.
To make strong torsional actuator, it is necessary to reinforce the shear modulus of polymer fibers by inclusion of nanoparitcles. We prepared carbon nanotube (CNT)- or graphene oxide (GO)-doped Polyvinyl alcohol (PVA) fibers by using a wet-spinning method. As compared to pure PVA fiber, CNT and GO nanosheets have nearly the same reinforcement efficiency on the tensile properties. However, GO nanosheets have more significant effect on the improvement of shear modulus and torsion constant because of its unique two-dimension nanostructure. We used such strong GO fiber to prepare torsional actuators. By measuring the recovered angle against an applied constant torque, we achieved a maximum generated energy density as high as 2800 J/kg. To our knowledge, this is actually the first report of the use of graphene to reinforce torsional properties of polymer composites and the greatest energy density observed in torsional actuators.
[1] Haines CS, Lima MD, Li N, Spinks GM, Foroughi J, Madden JDW, et al. Artificial Muscles from Fishing Line and Sewing Thread. Science. 2014;343(6173):868-72.
[2] Yuan J, Poulin P. Fibers Do the Twist. Science. 2014;343(6173):845-6.
[3] Lima MD, Li N, de Andrade MJ, Fang S, Oh J, Spinks GM, et al. Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles. Science. 2012;338(6109):928-32.
[4] Cheng H, Hu Y, Zhao F, Dong Z, Wang Y, Chen N, et al. Moisture-Activated Torsional Graphene-Fiber Motor. Advanced Materials. 2014;26(18):2909-13.

The use of inorganic fillers as reinforcements in polymeric matrices has become a common practice over the last decades. In the present work, a hybrid filler consisting of both glass fibres (GF) (at 10 and 20 wt.%) and graphite nanoplatelets (GNP) (at 10 and 20 wt.%) was incorporated in an isotactic polypropylene matrix and a thorough evaluation of the physicochemical properties, was performed. Three sets of samples were prepared; one consisting of GF, one consisting of GNP and one consisting of both GF and GNP (hybrid filler), in order to comparatively observe the contributions from each filler in every set of samples. Melt-mixing with a twin-screw extruder was selected as a preparation technique, as it combines speed, low cost and it is the method most usually followed by industry. Glass fibres were selected since they are known to exhibit high specific stiffness and strength, they are lightweight and possess outstanding fatigue performance. Furthermore, GNP were also inserted in the composite material due to the fact that graphite is very stiff, with excellent thermal and electrical conductivity, while it is significantly cheaper than carbon nanotubes.
X-ray diffraction was initially employed in order to calculate the crystallinities of the matrix and the composite samples and the crystallinity percentage was found to be higher in the case of the composite samples. Tensile testing was afterwards performed and it was found that the two fillers act synergistically towards the improvement of the modulus of elasticity for the composite with the hybrid filler. Each filler was found to double the modulus of the matrix, at the higher loading, while the modulus of the hybrid composite with the higher loadings of GF (20 wt.%) and GNP (20 wt.%) was found to be three times higher than the modulus of the pure PP matrix. Raman spectroscopy was also applied in order to monitor the interfacial stress transfer and the reinforcement of the nanocomposite materials. The shifts of the Raman D band at ~1335 cm^-1 were recorded as a function of stress, which was employed through a four-point bending procedure.
Several temperature-dependent properties of the nanocomposites were also evaluated. Dynamic mechanical thermal analysis showed that the storage modulus was considerably higher in the case of the composite materials, while the glass transition temperature increased in the composites. Thermogravimetric analysis showed that the presence of GNP improved greatly the thermal stability of the matrix with or without GF, while the high loading of GF slightly reduced the thermal stability of the matrix due to the high number of aggregates that were formed. The same picture was formed in the crystallization study by differential scanning calorimetry; GF reduced the crystallization rates, while when GNP were present in the composites, the rates were significantly enhanced due to the superior nucleation activity of the nanoplatelets.

Environmental pollution with aromatic hydrocarbons is a ubiquitous and deleterious consequence of extensive fossil fuel use that poses significant human health concerns. However, naturally-occurring bacteria can metabolize aromatic hydrocarbons, which can be cheaper and more efficient than conventional methods. Bioencapsulation (physical confinement of cells in a 3D matrix) has been investigated as a method for deploying bacteria to remove hydrocarbons from contaminated water. While some cytoplasmic enzymes can catalyze reactions independent of cell viability (e.g. hydrolase enzymes), aerobic biodegradation of hydrocarbons employs intricately-linked systems of enzymes and redox cofactors within the cells. These requirements restrict our design to using cytocompatible gels for maintaining bacteria in a viable and metabolically active state. Silica gel encapsulation is an ideal candidate for this purpose, because silica is inert, cytocompatible, and inexpensive. Design of an encapsulation-based aromatic hydrocarbon biodegradation platform that will operate at an industrial scale must address stability, longevity, and efficiency issues, which are dictated by the mechanical properties, cytocompatibility, and the diffusion limitations of the gel.
In this study, porous silica gels were engineered for Pseudomonas sp. NCIB 9816-4, a bacterium that degrades more than 100 aromatic hydrocarbons. The design process focused on three aspects: 1) mechanical property enhancement, 2) gel cytocompatibility, and 3) reduction of the diffusion barrier in the gel. The mechanical testing results indicated that the compressive strength at failure (σ_f) and elastic modulus (E) changed linearly with the amount of silicon alkoxide used in the gel composition. Maximum values for σ_f and E reached 1,399.1 ± 192.0 kPa and 31.9 ± 2.8 MPa, respectively. Measurement of naphthalene biodegradation by encapsulated cells indicated that the gel maintained cytocompatibility at lower levels of alkoxide. However, significant loss in activity was observed due to methanol formation during hydrolysis at high alkoxide concentrations, as measured by FTIR spectroscopy. The encapsulation matrix with the highest amount of alkoxide (without toxicity from methanol) had a biodegradation rate of 3,077 ± 452 nmol/min/g-cell, σ_f = 652 ± 88 kPa, and E = 15.8 ± 2.0 MPa. Biodegradation activity was sustained for one month before it dropped below 20% of the initial rate. In order to improve the diffusion through the gel, polyvinyl alcohol (PVA) was used as a porogen. Addition of PVA resulted in a 48 ± 19% enhancement in biodegradation, but it impacted the mechanical properties negatively. The encapsulation platform developed here will enable further study of Pseudomonas sp. NCIB 9816-4, a model organism for biodegradation of aromatic hydrocarbon pollutants. This important result expands the engineering applications of this organism and will enable long-term use in flow-through bioreactors.

A multifunctional material would provide superior protection from biological, chemical, and physical threats. Proteins and peptides offer much promise for decontamination due to their specificity and ability to regenerate; however there is a challenge in maintaining their biological activity in a non-native environment. Polymeric encapsulation is an option for protecting and controlling the release of these molecules. Bacteriocins are antimicrobial peptides produced by bacteria to destroy competing organisms. These target bacteria and perturb the cell membrane thus killing the bacterium. Bacteriocins have the potential to be used as a defense against specific bacterial agents. The goal of the work described here is to develop a method for bacteriocin encapsulation (using commercially available nisin as a model) that will protect it from degradation and prolong its release. This is done via polyelectrolyte complexation with polyacrylic acid (PAA) followed by crosslinking with methylenebisacrylamide (BIS).
Polyelectrolyte complexes (PECs) are formed by electrostatic interactions between oppositely charged polymers. The charge ratio of the two polymers affects the size, stability, and surface charge of the PECs formed. When the ratio of one polymer to the other is great enough, full encapsulation is achieved. Nisin maintains a net positive charge and PAA maintains a net negative charge at pH 5. Thus, to form the PECs, each polyelectrolyte is dissolved in buffer at pH 5. The two solutions are combined in different ratios and the resulting particles are characterized via SEM, dynamic light scattering, and electrophoretic mobility. The particles are then crosslinked using BIS and evaluated for release kinetics. Finally, particles are aged and cultured with Staphylococcus aureus to test bactericidal activity and to assess degradation prevention. This work lays a foundation to develop these techniques for other bacteriocins and for the future design of multifunctional textiles that incorporate targeted protection and provide greater overall defense against the elements.

Poly (glycerol-adipate) (PGA) offers great opportunities as a new biocompatible and biodegradable platform in polymer-drug based technologies. Its highly tunable branched matrix with a pendant hydroxyl group for each repetitive unit can be used to engineer solid dispersions or micro- nanoparticles for healthcare applications. PGA is typically produced from divinyl adipate and unprotected glycerol by an enzymatic route. Polymers with an average molecular weight of 10 kDa, can be synthesized routinely without any post-polymerization deprotection reactions in a one step reaction under mild conditions. Materials with a low degree of branching (less than 10%mol/mol) are normally produced due to suppression of cross-linking thanks to the steric hindrance at the catalytic site of Novozym 435.
Interestingly, it is possible to change the average molecular weight of PGA in situ by changing the polymerization temperature and time. The resulting PGA is completely amorphous and is able to swell in water, thanks to the free hydroxyl groups, but is insoluble in water indicating viscoelastic properties for this polymer.
To modulate polymer properties a plethora of variants were prepared by functionalizing the pendant hydroxyl groups with different substituents yielding comb-like polymers. Various biologically compatible molecules such as fatty acids of different chain lengths, amino acids, cholesteryl moieties and antioxidants, antimicrobial and anticancer agents, were coupled pendant to the polymer backbone. The terminal groups were also coupled to PEG. This novel class of biocompatible polymers has been characterized through various techniques such as FT-IR, ¹H and ¹³C NMR, GPC, DLS, surface and thermal analysis.
PGA has thus been modified exploiting simple and common synthetic pathways achieving functionalization degrees ranging from 5 up to 95% mol/mol with esterification conversion over 70% regardless of the moieties used. The length of the fatty ester side-chains, the presence of aromatic rings, the number of condensed cycles, the nature of side functional groups and the degree of substitution considerably affect surface and bulk polymer physico-chemical properties in terms of their ability to form nanoparticles and to interact with drug molecules. In fact PGA modified with Stearic acid showed a remarkably high contact angle (up to a value of 121° compared with 59° for unmodified PGA) and different crystalline microstructures, in spite the amorphicity of the unmodified PGA. On the other hand a material soluble in water was obtained by Tyrosine modification above 50% mol/mol.
These results illustrate the possibilities of easily tailoring PGA through simple chemistry to expand its potential in the pharmaceutical and medical fields enormously e.g. in solid dispersions and drug encapsulation. This large set of modifications can offer materials with a greater range of molecular complexity compared to usual polymers without functional groups and active moieties.

The field of nanoscience and nanotechnology has offered numerous solutions in the areas of medicine, food industry and cosmetics, but also escalated risks of exposure to living animals and environment through uncontrolled disposal methods. Considering the toxic effects of nanomaterials and also heavy metal ions, it is important to develop new methodologies for the removal of nanoparticles from the contaminated environment. Here we discuss our recent efforts to develop new amino polymer based adsorbents for extracting nanopollutants from water. During the presentation, we will discuss synthesis and characterisation of a series of amphiphilic block copolyamines using RAFT polymerization and their application towards removal of silver (Ag) and gold (Au) nanoparticles, heavy metal ions such as Pb(II) and Cr(VI) ions from water. All amine-functionalized block copolymers showed maximum adsorption capacities (Qe) towards Au NPs (11 - 25 mg g^-1) and for Ag NPs (20 - 34 mg g^-1). Such materials could be used for developing new water purification technologies.
Acknowledgement: The authors thank the Environment and Water Industry Programme Office (EWI) under the National Research Foundation of Singapore (PUBPP 21100/36/2, NUS WBS no. R-706-002-013-290, R-143-000-458-750, R-143-000-458-731) for the financial support of the work.
Recent papers from our work: Valiyaveettil et al., RSC Advances 2015, 5, 32862-32871, ACS Sustainable Chemistry & Engineering 2014, 2, (4), 1014-1021, Journal of Applied Polymer Science 2014, 131, (20), 40943, Nanoscale 2013, 5, (8), 3395-3399, Nanoscale 2011, 3, (11), 4625-4631.

Although the artificial blood vessels have been developed and used in clinical for many years, the lack of a living functional layer of human umbilical vein endothelial cells (HUVECs) remains a significant challenge, especially for small diameter artificial blood vessels. Thus rapid endothelialization is a prerequisite for artificial vascular vessels. HUVECs can be adhered specifically by REDV peptide modified artificial blood vessels, so targeting peptide modified gene carriers could promote the proliferation and migration of ECs and inhibit that of human umbilical artery smooth muscle cells (SMCs), but it is still unexplored. It is of great interest to investigate whether it is possible to develop the novel targeting biodegradable nanoparticles to condense with genes in order to realize the specific adhesion and proliferation of HUVECs. The gene carriers should be developed with the specific or targeting recognition by endothelial cells (ECs) with aim to enhance transfection efficiency, proliferation and migration of ECs.
We reported a strategy for proliferation and migration of HUVECs based on targeting NPs/pDNA complexes, which exhibited outstanding endothelial cell targeting performance and low cytotoxicity. The excellent endothelial cell selective performance enabled the rapid proliferation and migration of HUVECs in the co-culture system by targeting transfection with these complexes. The targeting NP/pDNA complexes were adhered selectively by ECs, and then transfected into these cells in the co-culture system. After release from the complexes, ZNF580 gene was expressed, which is the main reason for the proliferation of ECs. Meanwhile, these NP/pDNA complexes had the targeting selective ability of ECs, namely, they could be recognized specifically and adhered efficiently by the α4β1 integrin receptor which only located on the membrane surface of ECs. Therefore, the probability of these NP/pDNA complexes entering into the SMCs reduced greatly.

Enhancing Warfighter survivability against chemical and biological threats can be achieved via improved protection on the uniform. A uniform comprised of a single multifunctional layer would be optimal because it could perform multiple functions without increasing the burden of the Soldier. Two critical functions to add to a Soldier&’s uniform would be water repellency and decontamination. Enzymes have been shown to be effective and selective decontamination agents. A multifunctional coating that is predominantly hydrophobic would repel water, keep the wearer dry and comfortable but also provide passive protection by allowing aqueous liquids to roll-off. However, enzymes and peptides require aqueous environments for proper activity. This situation presents an interesting problem; how can we achieve the highest decontamination activity without negatively affecting the water repellent properties and vice versa? In nature, the skin of the Stenocara desert beetle effectively balances orthogonal hydrophobic and hydrophilic surface properties. No catalytic activity occurs on the beetle&’s skin, but it does have hydrophilic patches that collect moisture and hydrophobic channels for liquid transport to its mouth for drinking.
In order to create a multifunctional surface for decontamination and water repellency, I have taken a cue from the beetle skin and made an amphiphilic surface from a diblock copolymer of polystyrene (hydrophobic block) and poly(acrylic acid), (hydrophilic block). Copolymer vesicles are formed in solution then cast onto a surface creating hydrophilic “islands” in a hydrophobic “sea”. The smaller poly(acrylic acid) vesicles have a carboxylic acid group to covalently attach enzymes. In this study I will report on the density of hydrophilic attachment areas and demonstrate how the hydrophobicity of the surface and enzyme activity changes with increasing area of the hydrophilic vesicles. The decontamination enzymes will be localized to the hydrophilic regions in the future, so systematically varying the amphiphilic ratio will allow me to achieve the highest decontamination activity while retaining maximum water repellency.

Nature has long inspired researchers to come up with new design principles for novel synthetic materials. Some key features of these biomimetic materials are self-healing, self-sorting and stimuli-responsive properties. Metal-ligand (M-L) coordination crosslinked material system have provided a unique platform to explore these “living” functions since they reversibly adjust their properties in response to a broad spectrum of physical and chemical stimuli.^[1-5] To elucidate mechanisms of these smart responses, we are particularly interested in luminescent metal-coordination polymers that allow us to gain better insight into the coupling between stimuli-response dynamics and the M-L interaction mechanics. We will present a versatile route to optically responsive luminescent metallogels.
[1] M. Burnworth, L. M. Tang, J. R. Kumpfer, A. J. Duncan, F. L. Beyer, G. L. Fiore, S. J. Rowan, C. Weder, Nature2011, 472, 334.
[2] N. Holten-Andersen, M. J. Harrington, H. Birkedal, B. P. Lee, P. B. Messersmith, K. Y. C. Lee, J. Herbert Waite, PNAS2011, 108, 2651.
[3] D. W. R. Balkenende, S. Coulibaly, S. Balog, Y. C. Simon, G. L. Fiore, C. Weder, J. Am. Chem. Soc. 2014, 136, 10493.
[4] D. Mozhdehi, S. Ayala, O. R. Cromwell, Z. Guan, J. Am. Chem. Soc. 2014, 136, 16128.
[5] A. J. McConnell, C. S. Wood, P. P. Neelakandan, J. R. Nitschke, Chem. Rev. 2015, 115, in press. DOI:10.1021/cr500632f.

The development of synthetic probes for the detection of various chemically and biologically species are attracted interests over the past few years. In particular, the detection of metal cations have been considerable interest because of their important role on biological systems. For example, Fe³⁺ is a vital nutrient for almost of living cells. Many organisms have developed specialized metabolisms to acquire and transport Fe³⁺. The sequestration of Fe³⁺ is important because Fe³⁺ can catalyze chemical reactions leading to the production of reactive oxygen species via the Haber-Weiss cycle. Although various design strategies of the fluorescent sensors have been reported to detect Fe³⁺, most of them are based on fluorescence quenching mechanisms due to the paramagnetic nature of Fe³⁺. In addition, most turn-on fluorescent sensors are detecting Fe³⁺ on solution state. The detection on solution state have a restricted application for devices. Therefore, the development of a chemosensor for Fe³⁺ is an important task.
The conjugated polymer based fluorescent sensors (CP-sensors) have received considerable attention as the active materials in chemosensors. Because the CP-sensors have advantages to modify easily many applications such as nanoparticle, film, fiber, fabric, etc. And the CP-sensors have higher sensitivity than small molecules of prove via FRET (Föster resonance energy transfer) between fluorescent prove and conjugated polymer. We designed fluorescent conjugated polymer attaching rhodamine 6G derivative for using a CP-sensor.
Rhodamine derivatives are used as a fluorescent reagent due to strong fluorescence and long wavelength emission. Among the rhodamine derivatives, the rhodamine 6G derivative with spirolactam form are colorless and non-fluorescent. Whereas the ring-opened amide form shows a pink color and strong fluorescence. Rhodamine 6G derivative with spirolactam form is generally changed to amide form in acidic condition by activating a carbonyl group on spirolactam moiety. Similarly, Fe³⁺ can induce color and fluorescent change by ligand interaction. So the rhodamine 6G derivative is working as a turn-on type fluorescent probe for detection of Fe³⁺.
Herein, we prepared monomer attaching rhodamine 6G derivative by EDC-NHS reaction. We synthesized the fluorescent conjugated polymer by Suzuki-coupling reaction. The fluorescent conjugated polymer had rhodamine 6G derivative as a side chain. And we made a conjugated polymer-based film sensor by spin-casting method. After the film sensor was immersed in Fe³⁺ solution, rhodamine 6G derivative in polymer is changed to amide form by ligand interaction with Fe³⁺. The emission of polymer film was decreased and the emission of rhodamine 6G was increased via FRET. But the film sensor was not responsive to other metal ions. Because the rhodamine 6G derivative couldn&’t have ligand interactions with the other metal ions. Our film sensor could be used for detection of Fe3+ selectively via FRET.

Improving toughness of glassy thermoplastics such as poly(methyl methacrylate) (PMMA) without sacrificing modulus and thermomechanical stability is a valuable but challenging objective. Rigid particulate fillers have been found to improve toughness of some polymers with complex dependence on matrix ductility, particle size, and particle-matrix interfacial adhesion. We tested the effects of both strong and weak interfacial adhesion on deformation and fracture of a model system comprising PMMA filled with monodisperse 1 µm diameter silica spheres. Fracture energy G_IC of PMMA was found to increase by over 50% when filled with 1 vol% of weakly bonded particles, while the force due to melt compounding increased by less than 15% and Young&’s modulus increased systematically with filler loading. However, G_IC decreased with filler loading above 1 vol%. This behavior is consistent with a modified Kinloch-type model considering localized shear banding and plastic void growth around debonded particles at the crack tip. We have extended this model to account for interruption of the crazing process at the crack tip in PMMA, which reduces the intrinsic toughness and toughenability of the matrix. Particles with strong interfacial adhesion provided a subtle toughening effect consistent with a partial crack pinning mechanism at low loadings, but otherwise reduced toughness of PMMA. The ability of the matrix to deform via shear yielding and plastic void growth was confirmed by digital image correlation measurement of volumetric strain in uniaxial tension. The experimental and modeling results suggest weakly bonded particles with size on the order of the craze width may provide optimum toughening of PMMA

Polymer-based matrices are good candidates as drug carrier system for hydrophilic and hydrophobic drugs. We work on developing a polymer system that is in the liquid phase at room temperature (so that it can be injected subcutaneously), whereas at physiological temperature it forms a gel that works as a matrix where one can encase nano- or micro-particles loaded with the drug. The particles can then secure a depot effect and reduce the burst effect of the drug. We employ several methods, among these small angle neutron scattering (SANS) to explore different polymer systems and in particular gel networks that could be candidates for such drug delivery systems. We here present the results for a triblock copolymer P(CL-co-LA)-b-PEG-b-P(CL-co-LA) with hydrophobic blocks at the ends and a hydrophilic part (poly(ethylene glycol)) in the middle. This is a thermo-responsive polymer that undergoes a sol-gel-sol transition with increasing temperature. Two analogs of the polymer have been employed, with varying length of the PEG-block. It will be shown that the length of the PEG-block drastically affects features such as the gel point, viscoelasticity, and structure of the network. SANS and rheological studies reveal interesting changes of the properties in connection with the sol-gel-sol transitions. We will discuss in detail the structural implications of a series of SANS and rheological data on this system.

A remarkable feature of certain biological species is their ability to dramatically alter their shape in response to environmental cues. We focus on thermo-responsive polymer gels that contain elastic fibers. The fibers are functionalized with spirobenzopyran (SP) chromophores. The SP moieties are hydrophilic in the dark in acidic aqueous solutions, but become hydrophobic under illumination with blue light. Hence, with the incorporation of these chromophores into gels, light can be harnessed to control the gel's swelling or shrinking and, thereby, dynamically alter the gel's shape. The introduction of fibers within the gel matrix plays a crucial role in improving the mechanical properties of the matrix, while chemical modification of these fibers can yield a route to tailoring the functionality of the material, as well as the optical and electrical properties of the composite. We isolate the effects of external stimuli (temperature and light) on the gel-fiber interactions and show that variations in the placement of the fibers leads to dramatic changes in the resulting 3D shapes. These composites can be patterned remotely and reversibly by illuminating the samples through photo-masks, and thus, be molded into a variety of shapes. Furthermore, we show that when the tips of the fibers extend relatively far from the surface of the gel, the motion of the tips effectively amplifies small changes in the gel-fiber interactions that are driven by the external stimuli. Our results point to a robust method for controllably reconfiguring the morphology of soft materials and amplifying the effects of external environmental changes (light or temperature) on these systems. Our findings also indicate routes for driving the self-organization of multiple reconfigurable pieces into complex architectures, which can be utilized to perform a range of vital biomimetic functions.

Within the material formulation, polymer nanoparticles (PNPs) and nanocapsules (PNCs) can improve functionality, reliability and duration of products, enhancing the customer-perceived quality and value as well. Here we present the synthesis and characterization of multiphasic PNPs with synergic properties to be applied in the fields of self-healing additives, latent thermal energy storage materials (LTES) and functional liquid-core nanocontainers. All the PNPs were prepared via miniemulsion polymerization, easy to scale-up and performed with eco-friendly solvents (i.e. water). Firstly, Poly(n-Butyl Acrylate)/Polystyrene (PBA/PS) PNPs were prepared with an original semicontinuous MiEP protocol. PBA/PS PNPs, combining the adhesive properties of PBA with the structural stability and low cost per unit weight of PS, behave as a potential capsule-based self-healing nano-additive. Composition and local mobility of the system are probed with solid state NMR (¹H-TD-NMR and ¹³C-NMR). All the data fit a morphological core-shell sharp interface model, demonstrating the sequestration of the PBA core into the PS shell and stressing that the peculiar mobility of each phase is preserved without any observable intermixing. Single PNP nanomechanics is performed with AFM force spectroscopy so that AFM images monitor the mechanism of the PNP breakdown and force spectroscopy allows the simultaneous estimation of the forces involved. Indeed a controlled increase in the external force acting on the PNP triggers the plastic deformation of PS shell and a further increment leads to the ultimate PNP baroplastic collapse. This is, to our knowledge, the first example of baroplasticity imaging at the nanoscale.
Then, promising n-hexadecane/polymethylmethacrylate (HD/PMMA) PNCs have been synthesized as LTES. HD can act as a temperature-responsive phase change material (PCM) with large heat of transition, as we demonstrated by DSC and ¹H-TD-NMR. Encapsulating HD into separate PNCs can solve most of the issues related with PCM contamination and PCM packaging, since the LTES can be delivered as a functional aqueous ink. HD/PMMA PNCs can also act as hybrid nanocontainers loaded with TiO₂ anatase nanocrystals. TGA and TEM were used to quantify the percentages of TiO₂ nanocrystals that can be dispersed inside the PNCs without any aggregation. Both DSC and ¹H-TD-NMR rigid fraction show that HD crystallization takes place only in unloaded PNCs; in TiO₂-loaded PNCs HD crystallization is inhibited due to confinement phenomena. Only with TEM is possible to collect the damage image related to the presence of HD. Lastly, TiO₂-loaded PNCs were used as additives for the formulation of a tunable refractive index bulk material. PNPs and PNCs prepared with aquoeus MiEP could shed new light on the production of smart eco-friendly functional aqueous inks in terms of sustainability and hazardous substances handling and transport.

Thanks to their biocompatibility and degradability properties, polyphosphates are appealing polymers for biomedical applications. In contrast to aliphatic polyesters, such as poly(e-caprolactone) and poly(lactide), the pentavalency of the phosphorus atom allows the easy modification of the polyphosphate properties by simply adjusting the nature, the length and the functionality of the polyphosphate pendant groups.
Macromolecular engineering of polyphosphoesters was applied to design well-defined architectures and functionalities adapted to drug nanocarriers.
In a first approach¹, amphiphilic block copolymers are synthesized by organo-catalyzed ring-opening polymerization process for the synthesis of a range of PEO-b-polyphosphate bearing various pendant groups. Post-polymerization thiol-ene click reactions preformed on PEO-b-polyphosphate copolymers was also investigated to improve the hydrophobicity of the polyphosphate. The self-assembly of these PEO-b-polyphosphate copolymers into micelles was investigated, particularly, the effect of the nature of the polyphosphate pendant groups (i) on the micelles characteristics, (ii) on the encapsulation of a poorly soluble drug and (iii) on the drug release profile. The toxicity of the different amphiphilic block copolymers was also evaluated by live/dead cell viability assays.
In a second approach², double hydrophilic copolymers based on polyphosphoesters have been used as templating agent for the synthesis of calcium carbonate particles. Indeed, the use of such microparticles is becoming more and more attractive in many fields especially for biomedical applications for which fine tuning of size, morphology and crystalline form of CaCO₃ particles is crucial. Although some structuring compounds, like hyaluronic acid, give satisfying results, the control of the particle structure still has to be improved. To this end, we evaluated the CaCO₃ structuring capacity of the well-defined double hydrophilic block copolymers composed of poly(ethylene oxide) and of a polyphosphoester segment with affinity for calcium like poly(phosphotriester)s bearing pendant carboxylic acids or poly(phosphodiester)s with a negatively charged oxygen atom on each repeating monomer unit.
¹RSC Advances, 2015, 5, 35, 27330-27337
²Journal of Materials Chemistry B, 2015, 3, 7227 - 7236

Rationally designed antimicrobial materials that effectively inhibit propagation of pathogenic microbes and prevent bacterial accumulation on surfaces have attracted a great deal of interest for applications such as medical devices/implants, food packaging, as well as air and water purification. To this end, we have designed and developed a series of antimicrobial polymers grafted on silica particle surface via different attachment modes. These polymer-coated silica particles aimed at offering effective antibacterial capabilities, while avoiding the limitation of time-dependent bactericidal properties and the use of biocidal agents that pose potential risks of residual toxicity, environmental contamination, and development of bacterial resistance. In one study, polyurethanes with and without free isocyanate end groups were synthesized by metal-free organocatalytic polymerization of isophorone diisocyanate and N-methyldiethanolamine, and were grafted onto various surface-functionalized silica particles, resulting in various structures of the polymer-grafted surface. The free tertiary amine groups in the polymer coatings were quaternized to impart antibacterial function. In another study, guanidinium and thiouronium-functionalized polycarbonates were synthesized via organocatalytic ring-opening polymerization of functional cyclic carbonate monomers, and were grafted onto surface-functionalized silica particles. The polymer-coated particles were characterized by X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA), which provide useful information on the surface quaternary ammonium groups and the amount of polymer coating, and how they relate to their antibacterial properties. The antibacterial efficacies and killing kinetics of the polymer-coated silica particles were investigated by microbial growth inhibition assays against Gram-positive S. aureus, and Gram-negative E. coli and P. aeruginosa. Overall, the polymer-coated silica particles exhibited excellent broad-spectrum antibacterial potency and rapid killing kinetics against the bacteria at a low particle concentration. Through field emission scanning electron microscopy (FE-SEM), physical lysis of microbial cell membranes occurred, which strongly suggests the antimicrobial action of these surface-grafted polymers via contact killing. It was also observed that the surface-grafted polymer was stable and the antibacterial effectiveness was maintained, and the same batch of particles could be used in repeated applications. Overall, these polymer-coated silica particles have good potential for practical antibacterial applications such as water and air purification.

Vesicles are microscopic volumes compartmentalized by a self-assembled molecular membrane. Due to their ability to retain various substances, much attention has been attracted to their potential application for drug delivery systems, nano-/micro-reactors, or artificial organelles. In some aspects, however, restricted membrane permeability at the hydrophobic layer hampers their use as functional reservoirs with in- and outflow of molecules. Thus, it remains challenging to develop vesicular nano-reactors with suitable permeability and sufficient stability under harsh in vivo environments, such as in bloodstreams. Recently, we have developed novel polyion complex (PIC) polymersomes (PICsomes), which can be formed through electrostatic interaction between oppositely charged pairs of block-ionomers with polyethylene glycol (PEG) and homo-ionomers in aqueous media. Notably, the PICsome membrane, consisting of a PIC unilamella sandwiched by PEG layers, shows semipermeability for water-soluble molecules. Moreover, PICsomes can be endowed with a long blood-circulating property by cross-linking of the PIC membrane with its biocompatibility retained. With such unique properties, PICsomes are promising as a versatile platform for drug delivery carriers. In this study, focusing on their applicability for enzymatic nano-reactors in bloodstreams, we constructed L-asparaginase (L-ASP)-loaded PICsomes (L-ASP@PICsomes). L-ASP is an enzyme remedy which performs an antiproliferative effect against asparagine-demanding cancer cells, by hydrolyzing and exhausting L-asparagine into L-aspartic acid in blood circulation. Although it is on clinical use, its short half-life in blood and immunogenicity can pose therapeutic hardships and serious side effects for patients. Herein, by examining physical properties of L-ASP@PICsomes and their functions in vitro and in vivo, we proved their utility as in vivo nano-reactors. L-ASP@PICsomes showed narrow size distribution of ~100 nm and vesicular morphology. Through in vitro evaluation, activity of the loaded enzyme was found to be retained, and kept almost constant for ~24 h under a pseudo-physiological condition in the presence of 10% fetal bovine serum. Moreover, L-ASP@PICsomes exhibited a significantly prolonged blood-circulating property than naked L-ASP. To evaluate their function in in vivo blood circulation, L-ASP@PICsomes were intravenously injected into mice and concentration of plasma components fluctuating via the enzyme-mediated reactions was analysed. 24 h after injection, concentration of the reaction products increased in mice administered with L-ASP@PICsomes, while those with naked L-ASP showed no significant increase. This is consistent with prolonged enzymatic reactions induced by L-ASP@PICsomes. Thus, we developed novel PIC nano-reactors with sustainable functionalities in blood circulation, which is promising for versatile carriers of therapeutic enzymes in intravital fluidic environments.

A dynamic network gel based on reversible imine bond exchange has been prepared by reacting poly(ethylene glycol) bis(3-aminopropyl) with benzene-1,3,5-tricarboxaldehyde in an equal functionality ratio in organic solvent ranging from non-polar to polar and also bulk polymer. Several tests such as rheology and dynamic mechanical analysis (DMA) demonstrated that the malleability of the gel is solvent dependent. Polar solvents have higher malleability than non-polar solvents. Rheology of sol-gel in three different solvents (acetonitrile, DMF, and toluene) clearly show the gel point is faster in toluene than DMF and acetonitrile. This is due to the polar solvent promoting the imine-amine bond exchange which slows down the gelation point. Strain creep revealed that the strain of gels undergo partially to fully irreversible deformation under constant stress. Stress relaxation shows stress decreased under constant strain due to dynamic bond exchange within the network. The bond exchange was also demonstrated at the molecular level by experimentally monitoring imine bond exchange in NMR studies. Primary amine and water were both taken into consideration for the bond exchange in the NMR study by adding certain amount of primary amine or water respectively. Primary amine was determined to be the major source for the imine bond exchange compared to water. There is significant correlation between bond exchange at the molecular level and rate of gel deformation at the macroscopic level. This unique property was applied as a self-healing capability and was demonstrated by bending two reattached dyed gels. The gels displayed little damage at the interface after leaving the sample overnight. This fundamental study can apply to various adhesives applications.

Copolymer-based particles are comprehensively explored for pharmaceutical applications such as targeted administration of therapeutics, including anti-cancer drugs and next-generation vaccines, or long term drug releasing systems.^[1] In addition, biomaterial development can be accelerated by integrated processes, in which e.g. polymer synthesis and processing (here particle formation) are performed simultaneously.^[2] Even for well-known processes such as emulsion polymerization of only two comonomers, the properties of the prepared particles (e.g. molecular weight, zeta potential) depend on several reaction parameters (e.g. concentration of comonomers in the feed and the emulsion, initiator concentration), which need to be adjusted carefully according to the demands of the products. A systematic study to determine process parameter/property relationship based on conventional synthesis, would require numerous and would thus a huge effort.
We explored, whether the parameters of such an integrated process can be determined in a combinatorial approach. A 48-membered library of particles based on poly[(methyl methacrylate)-co-styrene] was synthesized by soap-free emulsion polymerization via single parallel synthesis employing a robotic synthesizer. The particles of the combinatorial library were prepared und variation of comonomer ratio (five different molar ratios in the feed) and of comonomer concentration (up to five different concentrations in the reaction mixture). The particle library was characterized via highthroughput gel permeation chromatography and Fourier-transformation infrared spectroscopy^[3] as well as dynamic light scattering and surface scanning microscopy. The correlation of the properties with process parameters was elucidated via a principle component analysis (PCA). A strong correlation between the monomer concentration in the starting material mixture and the resulting zeta potential of the particles and between the molecular weight of the prepared polymers and their particle size were found. In this way we could show that roboter assisted synthesis is a powerful tool for the creation of well-defined particle libraries, which can be further evaluated for biomedical application e.g. in cell uptake studies.
References
[1] L. E. van Vlerken, M. M. Amiji, Expert Opin. Drug Deliv.2006, 3, 205 - 216.
[2] A. T. Neffe, B. F. Pierce, G. Tronci, N. Ma, E. Pittermann, T. Gebauer, O. Frank, M. Schossig, X. Xu, B. M. Willie, M. Forner, A. Ellinghaus, J. Lienau, G.N. Duda, A. Lendlein, Adv. Mater.2015, 27, 1738-1744.
[3] S. Baudis, A. Lendlein, M. Behl Macromol. Mater. Eng. 2014, 299, 1292-1297.

Organized supramolecular strands of hydrophobic dipeptide molecules can be woven together to form a hydrogel. This behavior is triggered via a change in the pH, salt concentration etc. and has been explored in bulk in some detail. Recently, we demonstrated that dipeptide molecules can be induced to self-assemble into thin films at the airminus;water interface via drop-casting [1]. Atomic force microscopy reveals that the strands are sim;40 nm wide and sim;20 nm high and are woven together to form layers that can be up to sim;800 nm thick. The use of Thioflavin T fluorescence suggests that the dipeptides are ordered in a β-sheet configuration. The entanglement between protonated strands results in the formation of an elastic sheet.
Building on this initial result, we have gone on to create macroscopic foams with long-term stability [2]. Here, we use metal ions to promote supramolecular self-assembly; the network of strands forms both at air-water interfaces and in the continuous phase. The former creates an interfacial film stabilizing the air bubbles while the latter forms a bulk gel, which prevents bubble movement and retards ripening. In the absence of bubbles, phase separation is observed between a hydrogel and a water-rich phase; in the foam this can be suppressed provided that the concentration of dipeptides and metal ions are sufficiently high. We speculate that the resistance of the bubble arrangement to compaction and hence further drainage arrests the process of phase separation leading to a symbiotic relationship on a hierarchy of scales. This foam system has the advantages of long stability, low cost, as well as easy preparation; therefore, it has potential applications in food manufacturing, drug delivery and personal care industries.
References:
[1] Tao Li, M. Kalloudis, A. Z. Cardoso, D. J. Adams, and P. S. Clegg, Langmuir, 30, 13854 (2014).
[2] Tao Li, F. Nudelman, H. Vass, D. J. Adams, A. Lips, and P. S. Clegg, submitted.

Freshwater resources are continuously being polluted by industrial waste, agricultural chemicals, etc. Many of these pollutants can be biodegraded by naturally occurring bacteria, a low-energy, green, and sustainable solution to this problem. Thus, interest in engineered biodegradation and biotransformation systems has intensified in recent years. A powerful method to utilize bacteria is bioencapsulation (i.e. physical entrapment of bacteria in a porous host structure), which provides a mechanical scaffold and protection to otherwise small and fragile cells, making the technology suitable for a range of applications in biomedicine and biotechnology. Silica is chemically inert, porous, resistant to microbial attack, mechanically robust and thermally stable, which makes it an ideal material for this purpose.
In this study, a cytocompatible method was developed for encapsulation of bacteria in silica gels formed by silica nanoparticles (SNP) and a silicon alkoxide crosslinker. Formulation of the gel was optimized by changing the SNP size, SNP to crosslinker ratio and crosslinker functionality. Hydrolysis and condensation reactions of silicon alkoxide were controlled by water to alkoxide ratio and pH of the solution. FTIR analysis verified that a reactive and temporally stable silicon alkoxide crosslinker was obtained. pH of the SNP sol was adjusted to neutral pH before adding bacteria, to minimize the pH stress on the bacteria. When bacteria suspension in SNP sol was mixed with the crosslinker, higher pH of the SNP sol promoted condensation reactions and a reactive silica-bacteria gel was obtained. Synthesized gels were evaluated based on their gelation time, biodegradation activity, diffusivity and mechanical strength.
As a case study, we investigated bioremediation of polycyclic aromatic hydrocarbons (PAHs) by encapsulation of Pseudomonas sp. NCIB 9816-4 (P9816), an organism which has been shown to degrade >100 aromatic hydrocarbons. PAHs are an important subset of environmental pollutants due to their carcinogenicity. Using the developed encapsulation method, we have shown that biodegradation activity of silica gel encapsulated P9816 was sustained for over a month. It was also observed that the degradation rates were oxygen limited, due to high oxygen requirement of aerobic degradation reactions. Aeration in large-scale bioremediation systems can be costly, thus we addressed this problem by co-encapsulating P9816 with oxygen producing Synechococcus elongatus PCC7942 (cyanobacteria). For this purpose, we improved the optical transmittance of the gels from 40% to 70% (at 680 nm, photosystem II absorbance peak), by reducing the SNP size and SNP to crosslinker ratio. Initial results showed that in an oxygen limited environment, cyanobacteria was able to provide sufficient oxygen when co-encapsulated with P9816 and complete PAH degradation was achieved. P9816 without co-encapsulated cyanobacteria failed to achieve complete degradation.

Polymer vesicles, or polymersomes, are being widely explored as synthetic analogs of lipid vesicles based on their stability, robustness, barrier properties, chemical versatility and tunable physical characteristics. Preparation of these vesicles, however, is both time and labor intensive, yielding low numbers of intact polymersomes. Here, we present for the first time, the rapid and high-yielding formation of giant (>4 mu;m) unilamellar polymer vesicles (pGUVs) using gel-assisted rehydration, and describe a mechanism of how formation and size distribution of pGUVs may be achieved. Using this method, pGUVs were formed from an array of polymer compositions and rehydration solutions, including cell culture media, rendering the technique broadly applicable for targeted and controlled release of therapeutic agents using pGUVs. pGUV size was tunable by altering temperature during rehydration or adding fluidizers to the polymer membrane, generating "leviathan"-sized pGUVs (>100 mu;m). The correlation between size and membrane fluidization suggests a unique mechanism from that proposed for lipid GUV formation in which both polymer diffusivity and osmotic potential drive the formation and size distribution of the pGUVs. This technique is capable of reliably producing pGUVs from different polymer compositions and charges with far better yields and much less difficulty than traditional methods. Furthermore, vesicles formed in biological buffers and media make them readily useful for biomimicry studies.
Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy&’s National Nuclear Security Administration under contract DE-AC04-94AL85000

While sulfonated polymers are commonly used in membranes for fuel cells and water filtration applications, challenges of controlling ionic aggregation and understanding morphology effects on conductivity and transport still remain. In this work, we investigate the aggregation of copolymer-grafted nanoparticles that are designed to form conductive structures with low sulfonation amounts of chains. We demonstrate that long grafts of polystyrene chains with sulfonated end groups form side-by-side aggregated strings and retain their structures in ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluormethylsulfonyl)imide [HMIM][TFSI]. Transmission electron tomography results revealed that these aggregates are monolayers of particles at low sulfonations and planar-like networks at 3 mol % sulfonation in the ionic liquid. Organization of magnetic nanoparticles with the polymer grafting approach is shown, for the first time, to enhance conductivity upon incorporation of an ionic liquid.

Fibres are fine substances with a high ratio of length to thickness, which have wide applications including apparel, industry and home uses because they possess extra-ordinary combined properties including light weight, large strength, high surface areas and flexibility. Fibers made of polymers can be fixed and recovered from a temporary macroscopic deformation upon exposure to certain external stimuli caused by an entropic elasticity of polymeric network as a driving force, which are called shape memory fibers (SMFs). Even though a number of polymer systems have been developed, SMFs are mainly made with segmented polyurethane which are composed of thermodynamically immiscible fixed (hard) and reversible alternative (soft) phases and can be spun via melt, wet, reaction, dry, and electro spinning methods with tunable functionality for respective applications. Generally fibers of cylindrical, hollow, Nano, and electro active composite can be produced with variable diameters/linear densities with functional properties. The fibre structure, polymer phase separation, thermal and mechanical properties of SMFs are greatly influenced by hard to soft segment ratio, method of spinning, drawing conditions and thermal setting processes.
It has been discovered that SMFs are not only used where shape changing property is a pre-requisite but also have the potential to serve applications where the stimulus-induced stress is needed with different programming conditions by a phenomenon namely, “Stress Memory”. More research also reveals that SMFs are not only able to memorize shapes, but also temperature, electricity and chemical signature as well as stress. Thus, they could be termed as ‘memory fibers in general&’. For stress memory, a distinct switch-spring-frame model is presented. The Fibres made of memory polymer has revealed its potentiality in an authentic development of smart compression stockings for chronic venous disorders, where programmable stress is essential. Memory fibres can widen its applications including massage devices, medical textiles, smart textiles and apparel, high-performance sensors, sportswear, artificial muscles, biomedical materials with tunable functionality and adaptability. In general MFs could be used for functional and protective textiles, healthcare products, self-fitting garments, smart filtration, wound dressing, biodegradable sutures and scaffolds for tissue engineering, orthodontics and vibration damping structures. Our paper will introduce the above contents with a focus on our recent discovery of stress memory of fibers and their applications.

In temperature-memory polymers, the switching temperature, where a thermally-induced change in shape occurs, can be adjusted by variation of the deformation temperature during programming.[1,2] The temperature-memory effect (TME) of multiblock copolyesterurethanes named PDLCL, consisting of crystallizable oligo(ε-caprolactone) (OCL) switching segments and crystallizable oligo(omega;-pentadecalactone) (OPDL) hard segments, is related to partially overlapping melting transitions of crystalline OCL and OPDL domains, whereby the hard segments support the TME at temperatures above 50 °C.[2]
In this study, we explored whether the deformation of PDLCL at temperatures below or above 50 °C results in different crystalline nano-structures. In this way the contribution of crystalline OCL and OPDL domains to the TME at different temperatures shall be investigated. The nano-structural changes of OCL and OPDL domains in solution casted PDLCL deformed at 20, 40, and 60 °C were investigated by differential scanning calorimetry (DSC), in-situ wide-angle and small-angle X-ray scattering experiments (WAXS, SAXS) and atomic force microscopy investigations (AFM).
The results indicated that different structures were generated after programming at different temperatures. With increasing deformation temperature the degree of crystallinity of OCL domains in programmed PDLCL was found to decrease, while at the same time the degree of crystallinity of OPDL domains increased. When deformed at 20 °C both amorphous domains of OCL and OPDL were highly oriented along the stretching direction, while OCL and OPDL crystals were fragmented and oriented perpendicular to the stretching direction. Deformation at 40 °C resulted in a lower degree of orientation in both amorphous and crystalline OCL and OPDL represented by a moderate lateral crystal size and long period. The lowest degree of orientation in amorphous and crystalline was observed in samples deformed at 60 °C, where OCL is in a completely amorphous state during stretching.
The present work provided new insights regarding the nanostructural differences of temperature-memory polymers comprising two crystallizable segments with overlapping melting temperature ranges deformed at different temperatures, which might be helpful for further understanding of the TME mechanism.
References:
[1] K. Kratz, S.A. Madbouly, W. Wagermaier, A. Lendlein, Adv. Mater. 2011, 23, 4058-4062.
[2] K. Kratz, U. Voigt, A. Lendlein, Adv. Funct. Mater. 2012, 22, 3057-3065

Materials exhibiting several functions are highly desired for combined sensing and actuation or replacement of whole devices. The smart materials community, however, is facing a challenge: It is difficult to design multiple functions in one material, without the optimization of one property interfering with the performance of another. New synthetic methodologies are needed. Block copolymers are one way to achievemolecular functionality variation with nanoscale structuring, yet this approach does not have a widespread application due to the synthetic complexity of making block copolymers with specific functionality. A simpler approach to similar spatial organization is an interpenetrating polymer network (IPN), a thermodynamically stable arrangement of multicomponent crosslinked polymeric materials. The IPN approach has been widely used for creating materials with novel static properties, and tougher materials since crack propagation is inhibited at the phase boundaries. More recently this strategy has been used to synthesize a monofunctional material (provide ionic conductivity) in addition to structural (elastic) properties. We expand this strategy, using simultaneous or sequential synthetic approaches, to design physically separate, nanostructured, continuous phases each with already optimized distinct smart material properties. Conceptually separating the optimization of a single material response function from the design of a multifunctional smart material allows for a mix-and-match combinatorial approach.

Temperature-memory polymers are capable to memorize the temperature, where they were deformed during the programming procedure. In this way various switching temperatures (T_sws) can be realized with one polymeric material. Crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units have been reported as excellent temperature-memory material, where nanostructural changes in crystalline PE domains control the temperature-memory effect (TME). [1, 2]
In this work, we explored the TME of single micron-scaled cylindrical pillars on structured cPEVA substrates with a vinyl acetate content of 18 wt%. The micro structured materials were programmed by compression to a temporary flat topography at different deformation temperatures (T_deforms) ranging from 40 to 100 0C. Atomic force microscopy (AFM) images of the as programmed samples revealed that only the compression at high temperatures of 80 °C and 100 °C resulted in a completely flat surface, while a certain reduced microstructure was present when lower T_deforms were applied. The height and diameter change of the cylindrical pillars during the recovery process were studied by AFM, while stepwise heating the test specimen from 20 °C to 100 °C. Here a pronounced TME could be observed for cPEVA micropillars, where T_sw could be tailored from 47±1 °C to 78±1 °C by adjusting T_deform. Independent from the chosen deformation temperature an almost complete recovery of the micropillars was achieved. Such microstructured cPEVA surfaces could be applied as intelligent substrates for the realization of functionalized 3D structured surfaces, where biomolecules or proteins are printed onto the temporary flat substrate and the desired 3D structure is achieved after activation of the TME.
References:
[1] K. Kratz, S.A. Madbouly, W. Wagermaier, A. Lendlein, Advanced Materials 2011, 23, 4058-4062.
[2] U. Noechel, C. S. Reddy, K. Wang, J. Cui, I. Zizak, M. Behl, K. Kratz, A. Lendlein, Journal of Materials Chemistry A 2015, 3, 8284-8293

Liquid crystalline elastomers are loosely crosslinked, anisotropic materials. Their salient features, with respect to other forms of stimuli-responsive soft matter, are exceptional actuation cycles of up to 400% as well “soft elasticity” (e.g. stretch at minimal stress). In this presentation, we summarize our recent efforts in developing materials chemistry amenable to arbitrary local control of the director profile within these materials. Enabled by this paradigm shift in materials preparation, we have demonstrated that complex actuators and mechanical elements can be prepared by tailoring the local director profile including flexible devices in which soft and comparatively hard elastic segments can isolate sensitive electronic components.

Multiblock copolymers PCL-PIBMD consisting of crystallizable poly(ε-caprolactone) (PCL) segments and crystallizable poly[oligo(3S-iso-butylmorpholine-2,5-dione)] (PIBMD) segments coupled by trimethyl hexamethylene diisocyanate (TMDI) provide a versatile molecular architecture for achieving shape-memory effects (SMEs) in polymers.^[1-3] The mechanical properties and the SME performance of PCL-PIBMD can be tailored either by the variation of the chemical composition (i.e. PCL to PIBMD ratio) or the physical manipulation like the application of different strains during the deformation or programming.^{[3, 4]}
In this study, we explored the influence of different strain rates applied during programming on the nanostructural changes of PCL-PIBMD. Solution casted films prepared from PCL-PIBMD with identical weight amounts of PCL and PIBMD were programmed at 50 °C to a strain of 50% with variable strain rates of 1, 10 and 50 mmmiddot;min^-1. The nanostructural changes during programming were investigated by in-situ wide and small angle X-ray scattering experiments (WAXS, SAXS), while the shape recovery processes under constant strain conditions were examined by in-situ atomic force microscopy (AFM) measurements.
During the uniaxial deformation, the oriented PCL and PIBMD amorphous phases enlarged the gap between two neighboring PIBMD crystalline lamellae. Simultaneously, the strain-induced crystallization of stretched polymer chains and fragmentation of previously existed PIBMD crystals occurred. At a low strain rate of 1 mmmiddot;min^-1, the relaxation of orientated polymer chains is predominant, resulting in a low remaining degree of orientation when deformed to 50%. With increasing the strain rate to 50 mmmiddot;min^-1, a higher orientation degree was observed in the amorphous domains and a high level of lamellar fragmentation occurred. Therefore, the differences in shape fixation and recovery of samples deformed with various strain rates can be attributed to their different nanostructures. The presented approach for analyzing the nanostructural variations in semi-crystalline multiblock copolymers can be helpful to further understand the influence of programming conditions on the shape-memory performance.
References
1. Feng Y, Lu J, Behl M and Lendlein A. The International journal of artificial organs, 2011; 34(2): 103-109.
2. Yan W, Fang L, Noechel U, Kratz K and Lendlein A. Express Polymer Letters, 2015; 9(7).
3. Yan W, Fang L, Heuchel M, Kratz K, and Lendlein A. Clinical hemorheology and microcirculation, 2015 Mar.; DOI: 10.3233/CH-151940.
4. Momtaz M, Razavi-Nouri M, and Barikani M. Journal of Materials Science, 2014; 49(21): 7575-7584.

The emergence of responsive polymers is of fundamental interest, and their ability to reversibly reply to a given stimulus, such as heat, electric voltage, or light, has practical applications in several fields, including soft robotics, active sensing, and actuation [1]. In this framework, the cooperation between the electrical conductivity and the hygroscopic nature of conductive polymers such as PPy and PEDOT:PSS has recently led to the development of a new class of CP actuators working in ambient air [2]. The actuation principle lies in the reversible contraction of the films upon the application of a current, ascribed to the desorption of water vapor as a result of Joule heating.
Here we present a class of double-layered, anisotropic humidity-driven actuators based on a passive layer of a soft silicone elastomer (PDMS) and an ultrathin active layer of PEDOT:PSS, with intrinsic sensing capability [3, 4]. These smart active materials possess electric- and humidity-driven active/passive actuation capabilities along with touch- and humidity-sensing properties. The adopted processing strategy, which consists of a few steps of spin coating, direct laser cutting and patterning, has the great advantages of a reduced complexity and high tailorability, allowing the rapid and simple fabrication of actuators with different designs. Several examples are reported, including site specific actuation (hand with individually addressable fingers), plants inspired structures (leaves, flowers), touch sensitive structure inspired by Mimosa pudica, and others.
A comprehensive evaluation of the electro-mechanical and hygromorphic properties is reported which permitted to assess the high reproducibility and reliability of the actuators. Millimeter-scale beam-shaped actuators showed a large bending displacement (maximum curvature radius asymp;0.3 mm^-1) with a rapid actuation time (response time< 1 s, full actuation time asymp; 8 s) at relatively low actuation power (full actuation power asymp; 250 mW). Operating frequency was up to 5 Hz while long-term reliability was verified up to 1000 cycles. The maximum blocking force detected (0.32 mN) was 12 times of the actuator weight.
In addition to bending movement, more complex behavior such as twisting can be imparted to the bilayer by an appropriate asymmetric pattern design on the active surface. This work envisions a series of interesting applications of these structures as active bioinspired elements with intrinsic sensing and actuation capabilities, for example as soft grippers, manipulators, or as active elements in millimeter-scale walking robots.
[1] M. A. Cohen Stuart, et al., Nat. Mater. 2010, 9, 101.
[2] H. Okuzaki, et al., Adv. Funct. Mater. 2013, 23, 4400.
[3] S. Taccola, et al., ACS Appl. Mater. Interfaces 2013 , 5 , 6324.
[4] S. Taccola, et al., Adv. Mater. 2015, 27, 1668.

Giant torsional actuation from highly twisted fibres and yarns has been recently discovered [1-6] with potential applications in microfluidic mixing [1] and digital displays [3]. Rotations per actuator length of such twisted structures were 1000 times larger than previously reported systems [7, 8]. Additionally, it was discovered that when the torsionally-actuating fibres and yarns are converted to coils, the fibre untwist translates to expansion or contraction along the coil axis. Tensile strokes as high as 49% were reported for twisted and coiled nylon-6,6 fibres delivering 2.48 kJ.kg^-1 contractile work capacity [6] and greatly exceeding that generated by natural skeletal muscle (39 J.kg^-1) [9].
Methods to accurately measure torsional actuation in oriented polymer fibres are described in this presentation. In addition, the effect of twist insertion and scaling effects are experimentally evaluated and modelled theoretically.
References
[1] J. Foroughi, G.M. Spinks, G.G. Wallace, J. Oh, M.E. Kozlov, S. Fang, T. Mirfakhrai, J.D.W. Madden, M.K. Shin, S.J. Kim, R.H. Baughman, Torsional Carbon Nanotube Artificial Muscles, Science, 334 (2011) 494-497.
[2] M.D. Lima, N. Li, M. Jung de Andrade, S. Fang, J. Oh, G.M. Spinks, M.E. Kozlov, C.S. Haines, D. Suh, J. Foroughi, S.J. Kim, Y. Chen, T. Ware, M.K. Shin, L.D. Machado, A.F. Fonseca, J.D.W. Madden, W.E. Voit, D.S. Galvatilde;o, R.H. Baughman, Electrically, Chemically, and Photonically Powered Torsional and Tensile Actuation of Hybrid Carbon Nanotube Yarn Muscles, Science, 338 (2012) 928-932.
[3] K.-Y. Chun, S. Hyeong Kim, M. Kyoon Shin, C. Hoon Kwon, J. Park, Y. Tae Kim, G.M. Spinks, M.D. Lima, C.S. Haines, R.H. Baughman, S. Jeong Kim, Hybrid carbon nanotube yarn artificial muscle inspired by spider dragline silk, Nat Commun, 5 (2014).
[4] S.M. Mirvakili, A. Pazukha, W. Sikkema, C.W. Sinclair, G.M. Spinks, R.H. Baughman, J.D.W. Madden, Niobium Nanowire Yarns and their Application as Artificial Muscles, Advanced Functional Materials, 23 (2013) 4311-4316.
[5] W. Guo, C. Liu, F. Zhao, X. Sun, Z. Yang, T. Chen, X. Chen, L. Qiu, X. Hu, H. Peng, A Novel Electromechanical Actuation Mechanism of a Carbon Nanotube Fiber, Advanced Materials, 24 (2012) 5379-5384.
[6] C.S. Haines, M.D. Lima, N. Li, G.M. Spinks, J. Foroughi, J.D.W. Madden, S.H. Kim, S. Fang, M. Jung de Andrade, F. Göktepe, Ö. Göktepe, S.M. Mirvakili, S. Naficy, X. Leproacute;, J. Oh, M.E. Kozlov, S.J. Kim, X. Xu, B.J. Swedlove, G.G. Wallace, R.H. Baughman, Artificial Muscles from Fishing Line and Sewing Thread, Science, 343 (2014) 868-872.
[7] C.K. Andrew, P.C. Gregory, Thermo-mechanical characterization of shape memory alloy torque tube actuators, Smart Materials and Structures, 9 (2000) 665.
[8] K. Jaehwan, K. Byungwoo, Performance test and improvement of piezoelectric torsional actuators, Smart Materials and Structures, 10 (2001) 750.
[9] R.K. Josephson, Contraction Dynamics and Power Output of Skeletal Muscle, Annual Review of Physiology, 55 (1993) 527-546.

Self-assembly of homopolymers has attracted much attention in recent years due to their facile synthesis compared to block copolymers. However, considering the little knowledge currently available about their self-assembly, it is necessary to investigate the mechanism of homopolymer self-assembly. Presented here are the self-assembling mechanism, structural analysis and photoinduced deformation behavior of a series of photoresponsive homopolymers. These epoxy-based azo homopolymers were synthesized by step-polymerization between 1,4-cyclohexanedimethanol diglycidyl ether and aniline, and post-polymerization azo-coupling reactions with several diazonium salts to introduce azo chromophores bearing different electron-withdrawing groups. Upon adjusting the conditions for the self-assembly, different kinds of self-assembled structures were obtained, which includes colloidal spheres and hollow microspheres with uniform shape and size. The self-assembling process of these homopolymers was investigated by laser light scattering and TEM. Photoinduced colloid deformation and surface modulation were investigated by laser irradiation. Rates of both colloid deformation and surface modulation showed a close correlation with the electron-withdrawing groups on the p-positions of the azobenzene moieties. The azo polymer bearing the carboxyl group as the electron-withdrawing substituent showed much faster rates for both the colloid deformation and surface modulation compared with the others in the series.

The processing of nanocarbons in polymer fibers form provides a route towards a variety of electro-active materials potentially useful in energy production and conversion. In particular, we show recent progresses related to the development of new shape memory torsional actuators and highly efficient biofuel cell microelectrodes. Graphene reinforced polymer fibers exhibit significant improvements of their shear modulus. As a result, such fibers can absorb a high amount mechanical energy when twisted at high temperature. This energy can be stored by quenching the materials to low temperature. It can be further restored by heating the material above its glass transition temperature. The fiber untwists and acts as a torsional actuator capable of generating an exceptionally high torque associated to a giant energy density. In addition, the temperature at which the maximum of energy is released can be tuned by changing the programming conditions. Graphene or CNT based fibers also exhibit electrical conductivity and can serve as efficient microelectrodes in bio-electrochemical applications. In particular, we present a new fiber spinning methodology that allows the one-step production of fibers made of CNTs and imbricated enzymes which act as catalysts for the reduction of O₂. The enzymes are distributed from the core to the surface of the fibers. As a result the present fibers exhibit enhanced activity compared to conventional microfibers which are surface coated. Lastly, scale-up efforts of the present technologies will be discussed.

Responsive polymers have been investigated for a number of applications such as sensors and actuators. The two most widely studied systems are chromatic and deformable polymers. However, there remain several critical challenges including low sensitivity and reversibility and limited environmental stimuli in the further development. Herein, we have incorporated carbon nanotubes (CNTs) that are aligned to produce high-performance polymer composite materials that exhibit new sensitivities that have not been previously observed or predicted by the current rule. For instance, aligned CNT/polyacetylene composite films and fibers show rapid and reversible transitions in both color appearance and fluorescent intensity for more than a thousand cycles upon the pass of electric currents. Similar to pH test papers, we have firstly realized novel electric current test papers based on the electrochromatic composite material. The aligned CNTs are also utilized to induce the orientation of polyacetylene conjugated backbones to show controlled deformation. The composite film shows a reversible deformation by exposure to and evaporation of solvent, with the direction always perpendicular to the CNT length direction. Due to the combined excellent property including high thermal stability, sensitivity and electrical conductivity, the composite materials are promising for various applications.
References
(1) Sun, X.*; Zhang, J.; Lu, X.; Fang, X.; Peng, H.* Angew. Chem. Int. Ed. 2015, 54, 3630-3634.
(2) Sun, X.*; Lu, X.; Qiu, L.; Peng, H.* J. Mater. Chem. C 2015, 3, 2642-2649.
(3) Lu, X.; Zhang, Z.; Li, H.; Sun, X.*; Peng, H.* J. Mater. Chem. A 2014, 2, 17272-17280.
(4) Sun, X.; Zhang, Z.; Lu, X.; Guan, G.; Li, H.; Peng, H.* Angew. Chem. Int. Ed. 2013, 52, 7776-7780.
(5) Sun, X.; Sun, H.; Li, H.; Peng, H.* Adv. Mater. 2013, 25, 5153-5176.
(6) Sun, X.; Chen, T.; Yang, Z.; Peng, H.* Acc. Chem. Res. 2013, 46, 539-549.
(7) Sun, X.; Wang, W.; Qiu, L.; Guo, W.; Yu, Y.; Peng, H.* Angew. Chem. Int. Ed. 2012, 51, 8520-8524.
(8) Sun, X.; Qiu, L.; Cai, Z.; Meng, Z.; Chen, T.; Lu, Y.; Peng, H.* Adv. Mater. 2012, 24, 2906-2910.
(9) Wang, W.;dagger; Sun, X.;dagger; Wu, W.; Peng, H.;* Yu, Y.* Angew. Chem. Int. Ed. 2012, 51, 4644-4647.
(10) Sun, X.; Zhang, Z.; Guan, G.; Peng, H.* J. Mater. Chem. A 2013, 1, 4693-4698.
(11) Sun, X.; Chen, T.; Huang, S.; Li, L.; Peng, H.* Chem. Soc. Rev. 2010, 39, 4244-4257.

Due to its highly specific and thermally reversible nature of binding, DNA has been utilized as an intelligent glue to assemble nano- or micron-sized building blocks for designing complex superstructures with novel properties. However, the DNA attached to hard colloids is immobile and acts as a molecular Velcro, hindering the system from annealing into equilibrium structures [1,2]. Introduction of mobile DNA linkers by grafting DNA to lipid layers on hard spheres, vesicles and oil droplets has helped enable annealing of DNA linked superstructures [3-5]. However the preparations involving biotinylated lipids are long, cumbersome and expensive. We propose a new one step system involving only sodium dodecylsulfate (SDS) stabilized oil droplets that are coated with polylysin-polyethyleneglycol-biotin (PLL-g-PEG-biotin) as an equivalent of the biotinylated lipid stabilized droplets. After attaching streptavidin to these biotinylated PEG chains, DNA is then grafted to the oil droplets. These mobile DNA linkers alongside with variation in the grafting density of PLL-g-PEG-biotin on the surface of oil droplets and the excess concentration of SDS in bulk present a unique opportunity for studying a rich phase diagram involving transition from a fluid like behaviour to compact packing of hard spheres at the interface. We propose that the depletion interactions induced by SDS micelles in bulk result in softening of the otherwise repulsive colloid-colloid interactions at the ‘soft&’ interface and hence giving rise to an ordered assembly [6]. Further, single particle tracking and DDM studies on the colloids grafted to the interface show reduction in the diffusivities of the colloids by two orders of magnitude compared to those free in bulk. This significant reduction in diffusivity is thought to be due to increased drag from PLL-g-PEG chains tethered to the surface. Various control experiments show that the colloids are grafting to the interface strictly via the DNA mediated interactions, thermally reversible in nature. This controlled and reversible assembly of Polystyrene colloids at the oil/water interface could pave way for “Smart Emulsions” with tunable properties and better drug delivery systems.
[1] L D Michele and E Eiser, Phys. Chem. Chem. Phys., 2013,15, 3115-3129(2013)
[2] F Varrato, L D Michele, M Belushkin, N Dorsaz, S H Nathan, E Eiser, G Foffi, PNAS, 109 ,47,19155-19160, (2012)
[3] L. Feng, L.-L. Pontani, R. Dreyfus, P. Chaikin, J. Brujic, Soft Matter, 9, 9816 (2013).
[4] S A J van der Meulen, M E Leunissen, JACS, 135, 15129 (2013).
[5] P A Beales, J Nam, T K Vanderlick, Soft Matter, 7, 1747 (2011).
[6] L D Michele, T Yanagishima, A R. Brewer, J Kotar, E Eiser, and S Fraden, Phys. Rev. Lett. 107, 136101 (2011)

One of the most extensively investigated bio-based polymer, polylactide (PLA) stands out with its rather high mechanical, thermal and thermo-mechanical properties. Additional properties such as conductivity might as well be needed in the urge of several industrial applications. With that incentive, silver nanowires (Ag NWs) are utilized as conductive fillers, due to their high intrinsic electrical conductivity and relatively good oxygen stability among other metallic nanowires. Critical filler content, known as percolation threshold, was investigated resulting in a 3 dimensional connectivity within the polymer matrix providing electrical conductivity. Investigation of the percolative behavior eliminated excess Ag NW usage, since excessive amount of Ag NWs not only decreased mechanical performance but also increased viscosity and reduced manufacturability of the composites. In this work different amounts of Ag NWs were mixed with PLA via solution mixing method and 20 micrometer thick nanocomposite films were produced by doctor blading. Thermal gravimetric analysis in conjunction with conductivity measurements was used to determine the Ag NW content, while differential scanning calorimetry was used to investigate crystallization kinetics of the nanocomposites. Percolation threshold and maximum conductivity of the nanocomposites were obtained as 0.13 vol% and 13.34 S/m, respectively.

Graphene oxide (GO) functionalized by 4-4' oxydianiline (ODA) and GO as produced by Tours method are incorporated at 0.01 to 0.10 weight percent into a polyimide and their performance properties are compared. Uniformly, the ODA-GO functionalized films displayed significantly greater improvement in performance properties than unfunctionalized GO polyimide films. The results for functionalized GO are comparable to previous results citing GO weight percents 10 times higher than our loadings. The polyimide was made from 3,3'-benzophenonetetracarboxylic dianahydride (BTDA) and 4-4' oxydianiline (ODA) via in-situ polymerization to make GO-polyimide (PI) films. The 0.01% by weight ODA-GO polyimide film demonstrated the largest 8-fold decrease in water vapor transmission. In addition to water vapor transmission measurements to quantify gas barrier properties, the GO polyimide films at loadings of 0.01-0.1% by weight of both ODA functionalized GO and as produced GO were characterized by water gain analysis measurements to quantify solvent resistance, by thermogravimetric analysis to determine thermal stability and by mechanical testing. The 0.10% by weight ODA-GO film displayed the maximum increase of 82% in the modulus. The 0.06% functionalized ODA-GO PI film showed the maximum 27% decrease in water absorption. All ODA-GO PI films showed little change in polyimide&’s high level of thermal stability to over 400 0C. These are large improvements in key performance properties relative to other publications using higher GO concentrations. They are attributed to functionalizing GO with ODA to increase intermolecular interaction with the polyimide matrix and due to GO&’s highly asymmetric nano planar sheet structure, the hydrophobic nature of thermally reduced GO during polymerization and GO&’s high modulus.

The right combination of materials with distinct functionalities in a certain architecture is the basis of any working device. Energy conversion and storage devices, such as batteries, are made up of at least three components; two electrodes and the electrolyte. Since their invention over a century ago, these devices have been traditionally assembled in a simple macroscopic layered or stacked architecture. When porosity is introduced to the solid electrodes, the rate capability of batteries can be enhanced at the expense of active material and with the addition of dead mass due to void filling electrolyte. Incorporating the electrolyte layer and the second electrode into the void volume of the first electrode makes for the most efficient architecture. This 3D structure can increase areal energy density without sacrificing rate capabilities due to the significantly shortened ion diffusion length compared to the simple layered architectures. The fabrication of these so-called 3D batteries, however, has been proven most difficult and a working device with nanoscale dimensions of the components has not been demonstrated to date. Continuous ordered nanostructures based on block copolymer self-assembly offer a scalable platform for the fabrication and synthesis of ordered multi-functional hybrid architectures on the nanoscale, such as 3D-batteries. Here we present an approach based on block copolymer structure direction for the synthesis of free-standing three-dimensionally ordered carbon anode material with homogeneous, ultra-large mesopores. We demonstrate the conformal deposition of an ultra-thin polymer electrolyte on the carbon, electronically insulating but ionically connecting this negative electrode to the outside. The electrochemical functionality of the ordered nanoporous carbon-insulator hybrid as a working lithium-ion battery anode is demonstrated. The final multifunctional nanoarchitecture is completed by back-filling of the remaining nanoporosity of the anode-electrolyte assembly with the RedOx-active cathode material and a cathode-current collector. In the here reported all-solid-state polymer based multifunctional composite, all components are separated by only tens of nanometers, but integrated into an overall macroscopic device structure. The functionality of the polymer based backfilled cathode-current collector composite in nano-confinement is independently demonstrated in an insulating nanoporous framework with the same geometry as the anode-electrolyte hybrid. The performance of the completed 3D-battery architecture is evaluated. Our approach with solution processable polymer based components offers a scalable and low-cost path towards rationally designed three-dimensional nanoarchitectures for next-generation energy storage.

Macroscopically aligned electrospun nanofibers of biodegradable and biocompatible poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBHx) with profound piezoelectric properties were fabricated by collecting the fibers on the sharp edge of a rotary disk at a high angular speed. Morphological and structural characterizations, including wide angle X-ray diffraction (WAXD) and transmission Fourier transform infrared spectroscopy (FTIR) on fiber bundles, as well as selected area electron diffraction (SAED) and AFM-IR on single fibers, revealed the existence of a new strain-induced metastable β-crystalline form in the macroscopically aligned PHBHx nanofibers, with the polymer chains extended and adopting a planar zig-zag conformation. Piezoresponse force microscopy (PFM) was used to measure the piezoelectric properties of electrospun PHBHx nanofibers at the single fiber scale and the results show that the d₃₃ value of a single fiber varied from 2.4 pm/V to 17.8 pm/V with an average of 10.44 pm/V depending on the fiber diameter. In addition, the piezoelectric response of the nanofibers can be controlled by adjusting the rotating speed of the rotary disk, which changes the content of the beta-form crystals. Later, a thin flat sheet of well-aligned piezoelectric PHBHx nanofibers were interfaced with a flexible TOPAS plastic substrate to create a platform for voltage response characterization after small force cantilever deformation. The voltage generated has an average of ~150mV at a 10Hz strain rate of the cantilever, compared to ~12mV of the annealed rotary disk aligned PHBHx nanofibers which only contain alpha-form structure. These flexible and self-powered piezoelectric electrospun PHBHx nanofibers are very promising in applications such as energy harvesting, cellular-powered nanodevices and lab-on-a-chip medical diagnostics.

As a renewable and abundant natural resource, soy protein has been intensely studied for sustainable material systems and non-food applications in recent years. In particular, the potential of soy protein as adhesives and biopolymer to replace traditional petro-polymers has been widely investigated.
The proteins are well known by their complex structures, as a result of diverse inter/intra-molecular interactions, such as electrostatic interactions, hydrogen bonds, hydrophobic interactions , disulfide bonds, etc. Various protein structures could be produced via altering these interactions by proper chemical modifications, pH and temperature controls, etc., leading to protein materials with different properties and functions.
This uniqueness in protein materials suggests their great potential as new functional materials to modify different types of polymer materials. In this exploratory work, various protein denaturation methods were applied to obtain protein materials with different structures, morphologies and properties, as evidenced by structural and thermal analysis. The denatured soy proteins were then used to modify poly(vinylidene fluoride) (PVDF) membranes. Energy storage capability of resulting polymer membranes were studied by ferroelectric hysteresis analysis. The results show that, with proper denaturation, a certain amount of soy proteins can enhance the polarization and energy storage capabilities of PVDF membranes. Both denaturation conditions and concentrations of soy proteins showed remarkable effects on the energy storage performances. Furthermore, the energy loss of the resulting soy protein/ PVDF membranes was also discussed. This study suggests the promising future of this group of protein/polymer hybrid membranes for high performance energy storage applications, and is believed to lead to another successful non-food application of soy protein.

Mixtures of polymers and colloidal nanocrystals provide an attractive approach for fabricating electrochemical devices that combine the functional properties of both components. We are studying one interesting embodiment of this idea by dispersing colloidal tin-doped indium oxide (ITO) nanocrystals in a polymer electrolyte matrix. These nanocomposites combine the electrical conductivity and plasmonic electrochromic properties of ITO nanocrystals^1,2 with the lithium ion conductivity of polymers like poly(ethylene oxide) (PEO).
ITO nanocrystals were prepared by colloidal synthetic methods and the nanocrystal surface chemistry was modified to achieve favorable nanocrystal-polymer interactions. Homogeneous solutions containing polymer, nanocrystals, and lithium salt were then co-processed into nanocomposite films. The ITO nanocrystals form a complete, electronically connected electrode within the polymer electrolyte matrix, and the morphology of the ITO phase was manipulated using controlled partial phase separation, characterized by electron microscopy and small-angle x-ray scattering.
The nanocomposites display mixed ionic and electronic conduction through the polymer phase and nanocrystal phase, respectively. The coupled ionic and electronic conductivities can be controlled by changing the nanocrystal loading and morphology. Furthermore, the ITO phase is optically active, and exhibits electrochromic properties based on electrochemical modulation of the nanocrystals&’ localized surface plasmon resonance frequency. ITO-polymer nanocomposites were therefore used as building blocks for solid-state nanocrystal-based electrochromic devices fabricated by room temperature solution processing.
¹ G. Garcia, R. Buonsanti, E. L. Runnerstrom, R. J. Mendelsberg, A. Llordés, A. Anders, T. J. Richardson, and D. J. Milliron, Nano Lett., 2011, 11, 4415-4420.
² G. Garcia, R. Buonsanti, A. Llordés, E. L. Runnerstrom, A. Bergerud, and D. J. Milliron, Adv. Opt. Mater., 2013, 1, 215-220.

In an effort to speed up the layer-by-layer (LbL) deposition technique, electrophoretic deposition (EPD) is employed with weak polyelectrolytes and clay nanoplatelets. Applying an electric field during the LbL assembly results in nearly an order of magnitude increase in thickness relative to conventional LbL deposition for a given number of deposited layers. At an optimal electric field of 0.8 V, a 1µm thick 40-layer EPD-LbL polymer nanocomposite is produced (containing 74 wt% clay). This is nearly six times thicker than traditional LbL (150 nm in thickness and only 65 wt% clay for 40 layers). A well-aligned nanobrick wall structure forms with both LbL and EPD-LbL, but the greater clay concentration with EPD-LbL improves the elastic modulus and ultimate tensile strength of these films. An 20-quadlayer assembly, consisting of repeating QL of linear polyethyleneimine (LPEI)/poly(acrylic acid) (PAA)/LPEI/clay, has an elastic modulus of 45 GPa, tensile strength of 70 MPa, and thickness of 4.4 µm. Traditional LbL requires 40 QL to achieve the same thickness, with lower modulus and strength. This straightforward combination of electric field and layer-by-layer assembly allows for simple and fast film growth, yielding thick and strong films with fewer deposition cycles than LbL alone. Fewer layers required to achieve improved properties will open up many new opportunities for this multifunctional thin film deposition technique. It is likely that this approach could be used with other charged nanoparticles (e.g., graphene oxide) to yield additional property improvements.
* Submitted to Symposium H: Multifunctionality in Polymer—Based Materials, Gel and Interfaces

Hydrogen peroxide (H₂O₂) is an environmentally friendly oxidant whose current applications are limited due to its instability. Silica hydrogels obtained by sol-gel process has the potential of increasing its stability due to strong hydrogen bonding between the H₂O₂ molecules and the silanol groups (Si-OH) at the silica surface. In the present study, two different types of aqueous silicates, calcium and sodium, were used as starting precursors to form silica hydrogels. These hydrogels were evaluated to determine which matrix is more effective to stabilize H₂O₂. The pH of the sol determines the structure of the hydrogel and in the previous studies to date; it is controlled by adding an acidic or alkaline solution. In the present study, the pH of the sol is controlled by varying the sodium and calcium content of the silicates used. The effects of sodium and calcium ions on the kinetics of sol-gel formation and the structure of the resulting hydrogel and xerogels are studied. The surface area of the hydrogel/xerogel determines the availability of sites for H₂O₂ bonding in the presence of sodium and calcium ions. Therefore, the decomposition rate of H₂O₂ is studied at different sodium and calcium concentrations to understand the controlled release mechanism at room temperature. Samples are characterized by measuring the surface area, pore volume and average pore size using Brauner-Emmet-Teller (BET) analysis and scanning electron microscopy (SEM).

Herein, we first report an extremely versatile strategy to significantly improve gas transport properties of PEO-containing cross-linked membranes based on their specific swelling properties. Low-molecular-weight poly (ethylene glycol) (PEG) was deliberately incorporated into synthesized swellable pure PEO cross-linked membrane via immersing PEO membrane into PEG-water solution and membranes with various PEG loadings are obtained. The imbedded PEG molecules can be located between polymer chains to improve chain mobility and increase chain distance, resulting in the increase of fractional free volume (FFV), which is in favor of gas diffusion. On the other hand, the increment of CO₂-philic building units resulting from the imbedded PEG molecules leads to higher CO₂ solubility. Finally, the simple treated membranes exhibit significant increments in both CO₂ permeability (up to 762%) and CO₂/H₂ selectivity (up to 86%). The separation performance was correlated nicely with the microstructure of the membranes. This study may provide useful insights about the formation and mass transport behaviour of highly-efficient polymeric membrane applicable to clean energy purification and CO₂ capture, and possibly bridge the material-induced technology gap between academia and industry. Most importantly, our discovered strategy has great potential for treating composite membranes and regenerating “aged” membranes to realize clean energy purification and CO₂ capture by membrane technology.

We report a new type of block copolymer, poly(styrene-b-(4-vinyl)pyridine-b-propylene sulfide), which is successfully processed into a pH dependent asymmetric ultrafiltration membrane with isoporous selective separation layer. The short poly(propylene sulfide) block provides thiol functional groups covering the pore walls and membrane surfaces offering covalent attachment sites for desirable receptors/surface modifiers.
Our study shows that the membrane retains the traditional pH responsive behavior observed for conventional poly(styrene-b-(4-vinyl)pyridine) membranes, and has a narrow pore size distribution confirmed by protein rejection tests. Furthermore, the thiol functional groups are confirmed by NMR and redox reactions show that the thiol groups are active. By immersing the membrane into a maleimide-functionalized dye solution, permanent dye attachment via thiol-ene click chemistry is observed. Thiol-ene click chemistry and the successful post-membrane-fabrication attachment provide useful tools for modification and/or functionalization.
The thiol group on the membrane enables covalent attachment of desired molecules ranging from enzymes, proteins, to responsive homopolymers, or small molecules. Together with its pH responsiveness and ultrafiltration behavior we are expecting this functionalized membrane to be useful in numerous multifunctional applications.

Stimuli responsive materials is greatly being spotlighted as a technology to apply smart materials, such as a self-healing material, a smart adhesive and an actuator, the reversibility of which can be controlled by light, pH, and temperature. Among the above, Diels-Alder (DA) cycloaddition between furan and maleimide functional groups is a representative dynamic bond to form a covalently thermo-reversible cyclic coupling which can be restored to their original forms by controlling temperature. Futhermore, DA cycloadditions have been reported to have high and feasible reversible efficiencies. Hence, we tried to apply the thermo-reversible bonding to a water treatment membrane material for regeneration of a surface anti-biofouling property. In conventional anti-biofouling membranes, the anti-biofouling performance gradually deteriorated by accumulation of contaminants on membrane surfaces and in membrane pores. In order to solve this limitation, we introduced the furan-maleimide dynamic bond between a membrane surface and a hydrophilic polymer for regeneration of anti-biofouling property through a reversible “peel-and-stick” process of a hydrophilic layer.
Briefly, the regenerable anti-biofouling active membrane was prepared by attachment of a maleimide modified poly(ethylene glycol) (PEG) to a furan-modified poly(tetrafluoroethylene) (PTFE) membrane using reversible Diels-Alder (DA) cycloaddition reaction. The combined results of attenuated total reflection Fourier-transform infrared (ATR FT-IR), X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FE-SEM) measurements clearly reveal that the maleimide end-modified PEG is successfully coupled with the furan-modified PTFE membrane surface by DA reaction. In addition, the hydrophilic PEG layer is readily and repeatedly reformed on the membrane surface by a thermally driven dynamic peel-and-stick process. The PEG-coupled PTFE membrane shows effective anti-biofouling performance against highly concentrated protein suspended solution as as biofoulants. In particular, the anti-biofouling property is remarkably recovered after regeneration of the hydrophilic layer through the peel-and-stick process. Our approach opens up the possibility of creating a novel platformable separating system for dynamic membranes and multi-functional membranes because desired functionalities can reversibly be assembled and combined on the membrane surface.

In this study, a facile method to fabricate hybrid membranes with tunable water permeability is introduced. The membranes are fabricated by depositing thin polymer layers on anodic aluminum oxide (AAO) templates using initiated chemical vapor deposition (iCVD). Glassy p(methyl methacrylate) and rubbery p(butyl acrylate) polymers are used to fabricate the hybrid membranes with different mechanical properties. Furthermore, conformal and non-conformal depositions of the polymer layers resulted in hybrid membranes with different dominant permeation mechanisms. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) techniques are utilized to quantify the degree of conformality of the polymer deposition on the templates with high aspect ratio surface features. Elastic moduli of the glassy and rubbery thin films are obtained by atomic force microscopy (AFM). High pressure permeation experiments using DI water are performed to study the effects of mechanical properties of the polymer layer and the degree of conformality on the performance of the hybrid membranes.

There is long-standing interest in developing membranes possessing uniform pores with dimensions in the range of 1 nm and physical continuity in the macroscopic transport direction to meet the needs of challenging small molecule and ionic separations. However the current state of the art departs considerably from this ideal and is beset by intrinsic tradeoffs between permeability and selectivity. We successfully develop two effective and scalable methods to fabricate membranes with ideal morphologies with physically continuous and vertically aligned 1 nm pores. Our methods are based on directed self-assembly and subsequent cross-linking of a liquid crystalline mesophase with 1 nm ionic nanochannels formed by a wedge-shaped amphiphilic species. Our first strategy is to leverage the magnetic anisotropy of the amphiphile to control the alignment of these pores with a magnetic field. Characterizations by X-ray scattering and microscopy as well as transport studies show that magnetic field alignment can effectively produce polymer membranes possessing vertical 1 nm ionic nanochannels. The second approach is based on soft confinement to control the alignment of the mesophase. We demonstrate that sub-micron thickness polymer films with physically continuous and vertically aligned 1 nm pores can be simply achieved by soft confinement using an elastomeric pad of poly(dimethylsiloxane) or PDMS. The scalability, exceptional ease of fabrication, and potential to break the long-standing selectivity-permeability tradeoff of current water filtration membranes stand out as compelling aspects.

The lifetime and efficacy of implanted glucose biosensors are limited by membrane biofouling. When cycled above and below its volume phase transition temperature (VPTT, ~33 °C), poly(N-isopropylacrylamide) (PNIPAAm) hydrogels undergo deswelling and reswelling, respectively. This process effectively removes adhered proteins and cultured cells in vitro. We propose that a PNIPAAm-based hydrogel membrane could control biofouling in vivo via a “self-cleaning” mechanism induced by transdermal thermal cycling. This approach is feasible if the membrane can be designed with rapid deswelling/swelling kinetics for efficient cell release, ultra-strength and also sufficient glucose diffusion. In this work, several parameters were explored to achieve these properties including, incorporation of polysiloxane nanoparticles, a double network hydrogel matrix design and incorporation of an electrostatic comonomer. The impact of these design variables on key membrane properties were assessed, including: deswelling/reswelling behavior (gravimetric and differential scanning calorimetry - DSC), morphology (SEM) and modulus & strength (compression tests). Thermally-driven in vitro cell release and in vivo studies with a rat model demonstrated encouraging results in terms of membrane self-cleaning behavior.

Mussels can affix themselves to a variety of wet surfaces under harsh marine conditions by secreting liquid mussel foot proteins (mfps) as superglues. Inside the mussel, the superglues are fluid-like and are kept at low pH, i.e. pH 3. Upon secretion into seawater at pH 8, the superglues are cured efficiently through crosslinking of the catecholic amino acid 3, 4-dihydroxyphenylalanine (DOPA). In this work, we mimic the curing process of mfps by using synthetic catechol-functionalized polymers. The polymers are pH-responsive, i.e. water soluble at acidic pH, and insoluble at basic pH where crosslinking reactions of the catechols are triggered.
We synthesized copolymers containing 8 mol% catechol-functionalized monomers by free radical polymerization of dopamine acrylamide (DAA) and N-(2-aminoethyl) methacrylamide hydrochloride (AEMA). The polymers were characterized by GPC, ¹H NMR and UV-vis and the monomer reactivity ratio was determined by in-situ ¹H NMR. At low pH, i.e. pH 3, the catechols are stable, and the polymers were water soluble. At high pH (pH > 11), the catechols are readily oxidized to o-quinones¹. The highly unstable quinones were shown to further react with either catechols or amines in AEMA to form a crosslinked structure, yielding a water-insoluble polymer. Polymer films were prepared on glass substrates by a casting method under different conditions. We found that, polymer films prepared at low pH showed high water swelling behavior indicating a low crosslinking density. At high pH (pH > 11), the polymer film showed good water resistance indicating a high crosslink density. The property profile of this polymer is interesting for waterborne coating applications.
1. J. Yang, M. A. Cohen Stuart and M. Kamperman, Chemical Society Reviews, 2014, 43, 8271-8298.

Recently, herarchical organic/inorganic composites have been extensively studied, and considerable efforts have been focused on the synthesis of metal nanoparticles (NPs) coating on polymer templates. Here, i, a ternary hierarchical nanostructure was successfully fabricated by assembling Au NPs on polystyrene (PS)/polypyrrole (PPy) hybrid nanospheres and their structural evolutions have been investigated in detail. The ultrathin PPy coatings were firstly polymerized in PS emulsion by chemical oxidative polymerization of pyrrole using ammonium persulphate as an oxidant. The isolated products demonstrated a well-defined core/shell nanostructure without sacrificing the the spherical PS morphology. Theamino groups from PPy were beneficial for the Au NPs assembling on the polymer spheres by means of electrostatic interactions. The introduction of mercapto acetic acid was found to facilitate more Au NPs anchored on PS/PPy microspheres. Furthermore, this kind of ternary structures could serve as seeds for the growth of large and dense Au NPs with polygonal shape by in-situ reduction of HAuCl₄. Field emission scanning electron microscope, transmission electronic microscopy and atomic force microscope verified these hierarchical structures with the PPy ultrathin film connecting between the innermost PS layer and the outmost Au NPs coatings. X-ray diffraction and X-ray photoelectron spectroscopy confirmed the existence of PPy and Au coatings on the surface of the composite particles. This facile process for preparation of metal-coated polymer spheres supplies potential applications in biosensors, electronics and medical diagnosis.

In soft material systems, mechanical properties are generally governed by transient, dynamic interactions of various types over many hierarchal length- and time-scales. However, explicit control over these dynamics is typically not possible, leaving open questions into how transient interactions can be exploited to design soft materials with unique properties. Inspired by the adhesive chemistry and tough mechanics of mussel byssal threads, we present several studies on various soft polymer material model systems to show the diverse array of properties that can be engineered using bio-inspired metal-coordination. For example, we have begun to understand how to control the explicit effects of hierarchical metal-coordination dynamics on bulk material mechanics. This and other lessons from our attempts to expand the toolset of soft material design will be presented.

Biological materials, such as spider silk, the squid beak, and the muscle protein titin, illustrate the power of non-covalent interactions and hierarchical organization to mediate assembly phenomena, responsiveness, and mechanical enhancement. One nature-inspired approach is the design of supramolecular elastomers and interpenetrating network systems that probe the interplay of non-covalent and covalent interactions in structural organization and mechanical response. We have explored the role of interfacial control of self-assembly, composition, and dynamics as it relates to mechanical behavior. Another bio-inspired pathway toward responsive mechanics is the incorporation of supramolecular reinforcing, elements in polymeric composites. We have designed low molecular weight gelators that self-assemble into one-dimensional fibers to reinforce an elastomeric matrix. Highlighted in this design strategy is the ability to induce inherent dispersion via molecular-level control of filler assembly and to manufacture these composites via a facile process. Bio-inspired composites (ion- or water-responsive) were also derived from hierarchical electrospun nanofiber fillers that exhibit interfacially-controlled, mechanical switchability and tunable transport behavior.

While studying telechelic polymers with end-groups that associate by hydrogen bonding, we discovered that isophthalic acid-ended telechelic poly(1,5-cyclooctadiene)s (A-PCODs) demonstrate a highly temperature and chain-length dependent sol-gel transition in non-polar solvents at low concentrations (< 2wt%). Similar to other associative telechelic polymers in aqueous or organic solvents (e.g. HEURs and telechelic ionomers), A-PCODs form “flower-like” micelles at low concentrations and gels at high concentrations through bridging. However, unlike the widely studied hydrophobically end-capped PEOs, A-PCODs show clear thermo-responsive sol-gel transition in viscosity and dynamic modulus due to the presence of hydrogen-bonding end groups. In addition, literature on associative polymers containing hydrogen-bonding groups only focus on randomly functionalized polymers with hydrogen-bonding groups grafted along the backbone or tri-block copolymers with multiple hydrogen-bonding groups attached to the end blocks. Little is known about the topological behavior of telechelic polymers with single well-depicted associative group at each end. Our sol-gel transition and the underlying topological changes were observed for A-PCODs (M_w:10-50 kg/mol) near the overlap concentration of their corresponding non-associative backbones. To explain this phenomenon, we propose a molecular mechanism related to the aggregation number (the number of end groups within a micelle).
With increasing temperature the behavior of the A-PCOD gels qualitatively change from being similar to HEURs (plateau modulus is independent of temperature, only the relaxation time changes) to progressively changing topology, evident in both viscoelastic properties and neutron scattering patterns. We hypothesize that a decrease in aggregation number with increasing temperature results in the observed topological changes.
With various chain lengths, another qualitative change is observed: A-PCODs with short backbones (ca. 10 kg/mol) exhibit sol-gel coexistence at ambient temperature, A-PCODs with longer backbones (ca. 50 kg/mol) eliminate this phase behavior. The driving force for phase separation has been attributed to the aggregation number dependent entropic interaction between micelles in theory. We hypothesize that A-PCODs with shorter backbones exhibit higher aggregation numbers than longer ones, which leads to stronger micelle-micelle interactions and phase separation.