Symposium SM05—Progress in Multimaterials and Multiphase-Based Multifunctional Materials

A simple and effective way to prepare multi walled carbon nanotubes (MWNT)/ /silica hybrid colloidosomes is presented. The colloidosomes have been generated by emulsion templating in a biphasic oil-in-water (o/w) system. Two trialkoxysilanes of complementary polarity, (3-aminopropyl)triethoxysilane and dodecyltriethoxysilane, were used to chemically immobilize the silica nanoparticles at the o/w interface and stabilize the as-generated PICKERING emulsions. The effects of varying the o/w ratio and the concentration of the added solids on the type of emulsion formed, the oil droplet size, as well as the emulsion stability have been investigated. The emulsion phase fraction was dependent on the silica content while the droplet size increased with increasing oil volume percentage. A solid shell emerged around the oil droplets from copolymerization between silane monomers. The thickness of the resulting shells was several hundreds of nm. Although MWNTs and silica nanoparticles both were co-assembled at the o/w interface, silica has shown to be the sole stabilizer, with APTES being crucial for the formation of the shell structure. Drop-casting of the emulsion and air-drying led to hierarchical open porous MWNT-silica nanocomposites. These new structures are promising as electrically conductive thin films for variety of applications, such as electro-optics, encapsulation, or chemical sensing. To the best of our knowledge, this is the first time that a CNT/silica colloidosome is prepared¹.
Reference
Grzegorzewski, F., Benhaim, A., Itzhaik Alkotzer, Y., Zelinger, E. and Mechrez, G., (2019). In situ fabrication of MWNT/silica hybrid colloidosomes by Pickering emulsion templating using trialkoxysilanes of opposite polarity, Polymers, 11(9): 1480.

The electrospinning (ES) technique is able to produce polymer fibres at micro- and nano-metric scale that find application in various technological and biomedical sectors. Although the technique is well established, it still has several limitations, such as the restricted variety of printable inks (due to nozzle clogging problems) and the low control of fiber deposition (due to bending phenomena). Indeed, for some applications, the orderly arrangement, and in general the control of the deposition of these fibers, is highly desirable and people try to achieve it typically by structuring the external electrodes or using very expensive masks. Here we propose an innovative approach, which turns out to be easy to apply and economical which we have called “pyro-electrospinning” (p-ES). This technology is able to print high viscosity inks by regulating the deposition of the fibers with true regularity at the microscale. The p-ES system is based on the pyroelectric effect of polar dielectric crystals such as lithium niobate (LN). The electric field generated by the pyroelectric effect acts electro-hydrodynamically on the liquid sample, allowing the ordered deposition of the fibers. Therefore, the use of syringes, electrodes, and nozzles generally used in standard technologies is avoided. The reliability of the technique has been demonstrated both in the production of ordered periodic array fibers mats of D, L-poly (lactic acid) (PDLLA) and in spiral-shaped polymethyl methacrylate (PMMA) fibers (up to 300 nm thick) directly on a support with a true regularity at the microscale. The technique proves valid also for the deposition of fibers of highly dense materials such as poly(lactic-co-glycolic acid) (PLGA) avoiding the limitations mentioned above. The results show that these structures are useful for cell patterning applications.

References
[1] Sun, D., Chang, C., Li, S., & Lin, L. 2006. Near-field electrospinning. Nano letters, 6(4), 839-842.
[2] Xue, J., Wu, T., Dai, Y., & Xia, Y. 2019. Electrospinning and electrospun nanofibers: methods, materials, and applications. Chemical reviews, 119(8), 5298-5415.
[3] Hohman, M. M., Shin, M., Rutledge, G., & Brenner, M. P. (2001). Electrospinning and electrically forced jets. I. Stability theory. Physics of fluids, 13(8), 2201-2220.
[4] Rega, R., Gennari, O., Mecozzi, L., Pagliarulo, V., Bramanti, A., Ferraro, P., Grilli, S. 2019. Maskless arrayed nanofiber mats by bipolar pyroelectrospinning. ACS applied materials & interfaces, 11(3), 3382-3387.
[5] Mecozzi, L., Gennari, O., Rega, R., Grilli, S., Bhowmick, S., Gioffrè, M. A., Grilli, S., Ferraro, P. 2016. Spiral formation at the microscale by μ-pyro-electrospinning. Soft matter, 12(25), 5542-5550.
[6] Mecozzi, L., Gennari, O., Coppola, S., Olivieri, F., Rega, R., Mandracchia, B., Grilli, S. 2018. Easy Printing of High Viscous Microdots by Spontaneous Breakup of Thin Fibers. ACS applied materials & interfaces, 10(2), 2122-2129.

A selective laser sintering (SLS) process has opened a novel patterning way for advanced electronic applications. The SLS process bases on the photothermal effect and features for high precision, fast processing, and room temperature accessibility without inert gas. Therefore, the effectiveness of the interaction between the nanomaterials and laser has examined the various conductive metal nanomaterials such as gold, silver, and copper. Although the laser sintering process has shown many achievements on metal nanomaterials, it has rarely studied for the interaction for the metal oxide nanomaterials. In this study, WOx thin film layer employs the SLS process for post-processing which enables patterning and annealing simultaneously with inducing photochemical reaction as well as photothermal effect. The SLS-processed WOx thin film has shown similar electrochemical performances for the electrochromic application to the thermal annealed WOx thin film. We have established facile and fast fabrication for electrochromic devices with the SLS-processed WOx thin film layer and demonstrated feasibility for the indoor temperature controllable feature.

In nature, the collective assembly is often observed which enrich the structural and functional diversities. For example, DNA for various creatures consist with double helix architecture via collective assembly of only 4 distinct types of building blocks (Adenine, Guanine, Cytosine, Tymine). The hierarchical structures via collective assembly can highly release the limitations on geometries and functionalities through a spatial arrangement of diversely designed 3D building blocks. In this presentation, geometrically tailorable 3D building blocks are introduced by controlling residual stress with rapid and reproducible fabrication without complicate and/or expensive equipment. Frontal photopolymerization (FPP) with variously designed photomask and different curing time are employed for spatiotemporal regulation of photopolymerization. The employed photocurable resin is composed of bio-compatible poly(ethylene glycol)diacrylate (PEGDA) matrix, photo-initiator and photo-absorber. The photo-absorber generates drastic gradient of light intensity during the photopolymerization, resulting in a residual stress via crosslinking density mismatch through the thickness. When the photopolymerization is terminated, a curvilinear 3D shape morphing occurs within 1 min as a result of shrinkage mismatch induced by immediate relaxation of the residual stress. The geometries of 3D building blocks are programmed by systematic change of spatiotemporal conditions of pre- and post-curing. The 3D morphed structures are hierarchically assembled to achieve self-similar scaled-up structures inspired by designs of famous landmark (e.g. the great pyramid in Giza). The regularly stacked geometry allows 3D assembled structure to withstand 150 times of its own weight by homogeneous distribution of normal stress. Furthermore, the electrically conductive property is rendered to 3D assembled structural by applying conductive silver pastes on the 3D layered structures. Hence, our design strategy of tailorable 3D building blocks for collective assembly can be a promising candidate for prototyping several platforms of electronics, optics, and metamaterials.

Stimuli-responsive unary materials and binary composites have employed for actuation of soft robots. However, collective motion of multiple soft robots is challenging when stimuli-responses are implemented without batteries and sensors. Herein, we present magnetic collective swimming of ternary polymeric nanocomposites capable of adaptably organizing. Core-shell design of nanoporous carbon nanotube yarn (CNTY) and magnetic particles is inspired by skeletal muscles surrounding spongy bone in musculoskeletal system. The magnetic particles are attached to the CNTY owing to sol-gel polymerized elastomers providing the function of connective tissue. The polymeric soft robots swim with multimodal motility of rectilinear translational motion and rotational motion under a rotating quadrupolar electromagnetic field. Multiple soft robots can be adaptably organized through magnetically interactive dynamic soft joints when varying the rotational frequency of the magnetic field. We will discuss collective swimming of modular soft robots that transport 850 microbeads above water and a semi-submerged milli-bead.

Covalent networks of semi-crystalline poly(ε-caprolactone) (PCL) are highly performant shape-memory materials (SMM) i.e. high fixity of the temporary shape and high recovery of the thermally triggered permanent shape. Being in addition biocompatible and degradable, applications in the biomedical field are foreseen. Advantageously, inserting reversible bonds in the network, adaptative materials are obtained which allows reconfiguration of the permanent shape while preserving the shape memory properties at the body temperature [1].
As an answer to the increasingly demanding biomedical field, we aim at providing to such covalent adaptative networks, an additional shape transition triggered by the presence of water at constant temperature. For this purpose, poly(ethylene oxide) has been selected as a hydrophilic component introduced in the PCL networks.

In the present work, a covalent adaptative PEO/PCL hybrid network is formed by Diels-Alder reaction between PCL and PEO stars purposely end-capped by maleimide and furan, respectively. After melt-mixing of these cross-reacting stars and a post-curing, the resulting covalent adaptable hybrid networks shows high crosslinking density, as demonstrated by swelling experiments while preserving enough crystallinity to exhibit high thermal triggered shape-memory performances that remain as good as the ones of PCL covalent networks. Thanks to the insertion of furane-maleimide Diels-Alder adduct in the covalent networks, this material can be recycled by solvent-free hot-melt reprocessing and the permanent shape of this SMM can be reconfigured, e.g. by using mold of a complex shape. In addition, water triggered shape transition was evidenced allowing to achieve medical devices of complex shapes exhibiting in vivo self-deploying properties.

[1] Defize, T.; Riva, R.; Jérôme, C.; Alexandre, M., Multifunctional Poly(ε-caprolactone)-Forming Networks by Diels–Alder Cycloaddition: Effect of the Adduct on the Shape-Memory Properties. Macromolecular Chemistry and Physics 2012, 213 (2), 187-197.

Hybrid nanomaterials combining semiconductor and metal nanostructures represent an efficient way to develop novel platforms for advanced applications, ranging from sensing to catalysis [1–3]. In particular, silicon nanowires (SiNWs) are a promising host matrix for the dispersion of metal nanoparticles (MeNPs). They exhibit excellent characteristics such as large surface area, relatively high mechanical stability and low cost [4]. SiNWs are prepared by a wet-etching technique, assisted by the deposition of an ultrathin metal film on (p-, n-doped or highly doped) Si single crystal. SiNWs with very high density and controllable aspect ratios can be obtained. In the last years, we have studied the decoration of the proposed SiNWs with different MeNPs, including gold, by pulsed laser deposition [2,3]. This technique allows for loading “naked” NPs on the NWs. As alternative approaches, wet-methods can be used to decorate the semiconductor nanostructures. In this communication, we report on the modification of SiNW platforms with chemically produced AuNPs by electrophoretic deposition (EPD). We exploit an innovative synthesis based on stainless steel as solid reductant for HAuCl₄ to prepare AuNPs [5,6]. This method is very easy, quick, cost-effective, and scalable, allowing the synthesis of highly stable NPs without additional capping agents [6]. Pros and cons of EPD of preformed NPs will be highlighted in comparison with direct reduction of gold precursor on SiNW surface. The role of silicon doping will be investigated in combination with the charge of AuNP surface to evaluate their influence on final material properties. To this aim, electrochemical, spectroscopic and morphological characterizations will be proposed.
1. D’Andrea, C.; Faro, M.J.L.; Bertino, G.; Ossi, P.M.; Neri, F.; Trusso, S.; Musumeci, P.; Galli, M.; Cioffi, N.; Irrera, A.; et al. Decoration of Silicon Nanowires with Silver Nanoparticles for Ultrasensitive Surface Enhanced Raman Scattering. Nanotechnology 2016, 27, 375603, doi:10.1088/0957-4484/27/37/375603.
2. Picca, R.A.; Calvano, C.D.; Faro, M.J.L.; Fazio, B.; Trusso, S.; Ossi, P.M.; Neri, F.; D’Andrea, C.; Irrera, A.; Cioffi, N. Functionalization of Silicon Nanowire Arrays by Silver Nanoparticles for the Laser Desorption Ionization Mass Spectrometry Analysis of Vegetable Oils. J. Mass Spectrom. 2016, 51, 849–856, doi:https://doi.org/10.1002/jms.3826.
3. Casiello, M.; Picca, R.A.; Fusco, C.; D’Accolti, L.; Leonardi, A.A.; Lo Faro, M.J.; Irrera, A.; Trusso, S.; Cotugno, P.; Sportelli, M.C.; et al. Catalytic Activity of Silicon Nanowires Decorated with Gold and Copper Nanoparticles Deposited by Pulsed Laser Ablation. Nanomaterials 2018, 8, 78, doi:10.3390/nano8020078.
4. Irrera, A.; Faro, M.J.L.; D’Andrea, C.; Leonardi, A.A.; Artoni, P.; Fazio, B.; Picca, R.A.; Cioffi, N.; Trusso, S.; Franzò, G.; et al. Light-Emitting Silicon Nanowires Obtained by Metal-Assisted Chemical Etching. Semicond. Sci. Technol. 2017, 32, 043004, doi:10.1088/1361-6641/aa60b8.
5. Izzi, M.; Sportelli, M.C.; Tursellino, L.; Palazzo, G.; Picca, R.A.; Cioffi, N.; López Lorente, Á.I. Gold Nanoparticles Synthesis Using Stainless Steel as Solid Reductant: A Critical Overview. Nanomaterials 2020, 10, 622, doi:10.3390/nano10040622.
6. López-Lorente, A.I.; Simonet, B.M.; Valcárcel, M.; Eppler, S.; Schindl, R.; Kranz, C.; Mizaikoff, B. Characterization of Stainless Steel Assisted Bare Gold Nanoparticles and Their Analytical Potential. Talanta 2014, 118, 321–327, doi:10.1016/j.talanta.2013.10.028.

Micro-energy storage devices are appealing, and highly demanded for diverse miniaturized electronic devices, ranging from microelectromechanical system, robotics, to sensing microsystems and wearable electronics.[1,2] However, making high-energy microcapacitors with currently available printing technologies remains challenging. Herein, we show the possibility to use latex polyvinylidene fluoride (PVDF) as aqueous ink for making dielectric capacitors on the microscale. The dielectric properties of printed microcapacitors can be optimized based on a novel approach, i.e., mixing PVDF latex with polyvinyl alcohol (PVA) to realize dielectric organic nanocomposites. The PVA prevents the coalescence of PVDF nanoparticles and serves as a continuous matrix phase with high dielectric breakdown strength. While the well-dispersed PVDF nanoparticles serve as highly polarizable and isolated domains, providing large electric displacement under high fields. Consequently, a high discharged energy density of 12 Jcm^-3 is achieved at 550 MVm^-1. [3] These printed microcapacitors demonstrate mechanical robustness and dielectric stability over time.
[1] Z. S. Wu, X. Feng, H. M. Cheng, Natl. Sci. Rev. 2014, 1, 277.
[2] M. Beidaghi, Y. Gogotsi, Energy Environ. Sci. 2014, 7, 867.
[3] F. Torres-Canas, J. Yuan, I. Ly, W. Neri, A. Colin, P. Poulin, Adv. Funct. Mater. 2019, 1901884.

Robots and intelligent systems will be the key factor of Industry 4.0 revolution for aiding at any stage engineering and manufacturing processes. One of the most challenging demanded issue is to make available appropriate tools for full control of liquids. In fact, the manipulation of the liquid matter is of strategic importance in many procedures and facilities involving many fields of applications i.e. biomedicine, biotechnologies, food, cosmetics, just to cite few. Liquids, polymers and more in general soft-matter requires even more accurate, precise and full controlled handling apparatuses. So far, several engineering methods have been proposed for furnishing intelligent responses to environmental changes in order to drive liquids by external magnetic, electric or optical fields. However, until now, very few and shy approaches for locomotion and remote control have been featured to manage liquid actuation. The design of innovative portable devices, working in non-contact mode, easy to use, totally safe for the medical staff and based on handling of small amount of reagent and liquid to be analysed, is certainly a strategic ambition for all the researchers, scientist and industries all over the world. Actually, most of the systems in use are made of rigid components, not friendly, unable to self-adapt to various configurations and most important require the manual intervention by the operators (i.e. classical manual pipetting) so exposed to cross-contamination problems. Here we introduce a new working principle for liquid manipulation and a complete exploration of the opportunities of a multipurpose platform guided by physical intelligence, enlarging the opportunity of liquid handling via pyro-electrohydrodynamics (EHD). The platform is able to handle liquid volumes by reacting to thermal external stimulus on a functionalized substrate (i.e. ferroelectric crystal). The innovation consists in creating a multiscale digital microfluidic system for handling small amount of liquids and multiphase samples with volumes in a wide range from microliter to milliliter, in air and in three-dimensions. In fact, the huge electric field generated via the pyroelectric effect allows to manage the on/off activation system of the pyro-Electro-Hydro-Dynamic driving force for commanding a fast response in a smart way and for easily moving units of liquid with different size and volumes. We prove remote locomotion of liquid volume as a sort of tweezers able to move liquids along desired paths. Beyond the guiding property, we proved also additional functionalities like merging, stretching, mixing and jumping of liquid volumes and millimeter objects using a working distance of millimeter, i.e. bigger than the conventional distances used for liquid handling in classical digital microfluidic.

1. Nasti, G., Coppola, S., Vespini, V., Grilli, S., Vettoliere, A., Granata, C., & Ferraro, P. (2020). Pyroelectric tweezers for handling liquid unit volumes. Advanced Intelligent Systems, https://doi.org/10.1002/aisy.202000044

Frontal polymerization (FP) has emerged as a promising technique for rapid, energy-efficient preparation of bulk polymeric materials in ambient conditions without solvents. In FP, the monomer is converted to a polymer within a localized reaction zone that propagates spatially as a consequence of heat transfer from the exothermic polymerization to unreacted monomer. FP requires a minimal amount of energy to initiate the process, after which the polymerization front continues to propagate without further energy input. In this talk, we report the rapid, solvent-free synthesis of poly(1,4-butadiene) by FROMP of neat 1,5-cyclooctadiene (COD). Moreover, we find that FROMP of comonomer mixtures of COD and dicyclopentadiene (DCPD) produces mechanically robust cross-linked polymeric materials having a wide range of properties, from soft elastomers to rigid thermosets, which are tuned simply by varying the comonomer ratio. We use the ability to spatially control copolymer composition to rapidly fabricate materials with spatially varying properties capable of multistage shape memory actuation. By triggering instabilities in the front propagation, we can also create materials with complex gradients in materials properties.

Nature is a magnificent source of inspiration to develop new technologies. The evolutionary development of plants leads to functional traits that can anchor, twine, vine, or search. An interesting representative in this context is Selenicereus setaceus, a cactus found in the Atlantic forest of Brazil capable of climbing¹. Such biological functional system can serve as a source for bio-inspired robots with the potential ability to anchor, attach, and climb ^{2, 3}. We questioned how the process of development could be a shortcut to different forms. Our approach is the evolutionary design of a multi-material system inspired by the cactus. Selenicereus setaceus demonstrates a unique structural configuration along the different stages of the growth: the stem is circular at the base while the younger parts are star-like in shape at the apex. The cactus consists of soft tissues surrounded by a thin skin layer. The capability of transformation in shape not only optimizes its flexural rigidity but also provides flexibility to allow the cactus to search for light in the challenging environment of the seasonally dry Atlantic forest.
In our design concept for this evolutionary cactus-inspired artificial system, we selected the unique geometry, a star-like shape, of the cactus at the apex. Such a unique shape is 3D printed using a soft elastomeric polymer. Another soft material, a water-swollen polymer, hydrogel, is synthesized on the 3D printed structure. Herein, we demonstrated two developments directly inspired by the functional traits of the cactus. In the first, we demonstrated a controlled movement similar to the searcher component of the natural cactus, when the humidity is changed the hydrogel-elastomer system could bend toward low humidity through anisotropic swelling and de-swelling of the hydrogel. In the second, we demonstrated the change in geometry from star-like to circular shape, as the natural cactus does in nature as it grows, partly by means of isotropic swelling and de-swelling of the hydrogel. These evolutions show the possibility that we can directly learn from the behavior and structural configurations of plants to develop functional artificial systems. We hope that this study stimulates the design of novel plant-inspired ecological robotic systems.

References
1. P. Soffiatti and N.P. Rowe: Mechanical innovations of a climbing cactus: functional insights for a new generation of growing robots. Frontiers in Robotics and AI 7 (2020).
2. B. Mazzolai, L. Beccai and V. Mattoli: Plants as model in biomimetics and biorobotics: new perspectives. Frontiers in bioengineering and biotechnology 2, 2 (2014).
3. B. Mazzolai, F. Tramacere, I. Fiorello and L. Margheri: The bio-engineering approach for plant investigations and growing robots. A mini-review. Frontiers in Robotics and AI 7, 130 (2020).

Multifunctional material systems are breaking the elusive boundaries between functions previously deemed independent, necessitating a composite approach but with inferior response. While research in multifunctional materials for magnetoelectric coupling is thriving, polymeric (or organic) multiferroics are lagging behind due to several processing, characterization, and performance challenges. Commonly trending organic multiferroics exhibit lower magnetoelectric properties than their composite oxide-based counterparts, but report a measureable coupling at room temperature, positioning them as a superior class of materials in comparison to intrinsic single phase multiferroic materials. The latter has a diminished response at room temperature, deeming them impractical for any translational applications. The magnetoelectric response of organic multiferroics, on the other hand, can be further enhanced through the addition of mechanical or photonic energies. However, organic multiferroics suffer from complex phasic structure consisting of multiscale crystalline phases surrounded by amorphous regions, which can be tuned based on fundamental understanding of the process-structure-property interrelations. Thus, the objective of this research is to characterize a blend organic framework with multiferroic properties to elucidate the interdependence of the properties on the processing approach. Here, regioregular poly(3-hexylthiophene) polymer (P3HT) is blended with organic compound phenyl-C₆₁-butyric acid methyl ester (PCBM) to synthesize an excitonic multiferroic polymer with tunable properties. The structure of P3HT consists of a crystalline phase surrounded by amorphous regions, while PCBM forms nanocrystalline aggregates. The interrelationship between primary processing parameters, including the concentration of P3HT and the ratio of P3HT to PCBM, are discussed as a function of triphasic structure. The ferromagnetic polymers were characterized for their photomagnetic, piezomagnetic, and mechanical properties using a modified vibrating sample magnetometer with illumination source matching the absorbance band of the blend polymer and a mechanical loading mechanism. Overall, this study reports the first process-structure-property map of the blend P3HT:PCBM organic framework for magnetoelectric coupling, which will accelerate translation applications in flexible and wearable electronics. Future research will focus on multiscale characterization of the interaction between the boundaries separating the amorphous and crystalline phases of P3HT and the interfaces between P3HT and PCBM.

We have developed a new approach to manufacturing thermoset materials with complex morphology and function using frontal ring-opening metathesis polymerization (FROMP). Propagation of uniform fronts enables rapid, efficient fabrication of neat polymers and composites. In this work, we explore the instabilities that arise during FROMP, which lead to non-uniform front propagation and complex patterns and property gradients within the material. We utilize the synthetic reaction-thermal diffusion system that arises from the FROMP of dicyclopentadiene (DCPD), 5-ethylidene-2-norbornene (ENB), and 1,5-cyclooctadiene (COD) to take advantage of the positive and negative feedback loops for patterning. Spontaneous pattern formation is achieved in an open mold geometry which causes non-uniform front propagation and gives rise to the competition between thermal transport and reaction rates. The effects of boundary conditions, co-monomers, chemical inhibitors, and energy inputs are investigated and monitored visually using an infrared camera. By tuning the reaction kinetics, ambient temperature, and thermal initiation conditions, we achieve a spin mode propagation, causing wavelike surface patterns to develop across the entire length of the material. The wavelength of the surface patterns is systematically varied by adjusting the parameters of the experimental system. By layering co-monomers based on density differences, we achieve materials with functionally graded properties. The thermophysical properties of these functional materials are tunable and highly reproduceable.

The incorporation of metal organic frameworks into advanced devices remains a desirable goal, but progress is hindered by difficulties in preparing high quality, multifunctional metal-organic framework (MOF) films with suitable electronic performance. We demonstrate the direct growth of large-area, high quality, and phase pure single MOF crystals through chemical vapor deposition of a dimolybdenum paddlewheel precursor, Mo₂(INA)₄. These exceptionally uniform crystals cover areas up to 8600 µm² and can be grown down to thicknesses of 30 nm. Scanning tunneling microscopy indicates that the Mo₂(INA)₄ clusters assemble into a two-dimensional, single-layer framework. Devices fabricated from single vapor-phase grown crystals exhibit reversible nearly 10-fold changes in conductivity upon illumination at modest powers. Moreover, we identify vapor-induced single crystal transitions that are reversible and responsible for 30-fold changes in conductivity of the MOF as monitored by in situ device measurements. Gas-phase methods, including chemical vapor deposition, show broader promise for the preparation of multifunctional molecular frameworks, and may enable the integration of these materials into devices, including detectors and actuators.

Additive manufacturing (AM) allows for rapid fabrication of complex structures with the advantage of multi-material composition and high structural complexity, or a unique combination of the two. Recently, there is an increasing interest in creating multi-material components which have optimal interfacial interactions between layers. However, the challenge lies with determining optimal compatibility between printed components, and how those influence bulk property of the multi-material structure. Previous investigation of direct-ink write (DIW) printed epoxy-silver composite structures did not produce conductive parts. Therefore, we study silver conductive ink material composition and compatibility with epoxy, including interfacial connections and layer-by-layer material adhesion. As a result, an optimal material for multi-functional composite parts was developed for a variety of thermal, mechanical and electrical applications. Electronics such as strain gauges and light sensors were DIW 3D printed. Additionally, we demonstrate a deicing unit for potential use on an aircraft, such as unmanned aerial vehicle (UAV) wings. Thus, utilizing material science, we solve material compatibility issues that frequently arise when 3D printing multi-material components, eliciting desired features within a printed part.

Bone is a multi-phase multifunctional material that can sense the mechanical loading and adjust itself by adding more minerals to the region of high stress and reducing them to the low stress region so that it can increase the efficiency and lifespan of the material. However, it has been a challenge to synthesize load-bearing materials with such capabilities. Inspired by bone mineralization mechanisms, we have investigated a multi-phase material system that self-senses mechanical loading and proportionally triggers mineral formation from media with mineral ions so that the material can mitigate damages and increase lifespan. The mineralization rate within the material system is autonomously modulated in response to changing loading conditions, resulting in a 30-180% increase in the modulus of the material upon 1 to 5 N cyclic loadings. Moreover, the multifunctional material adds more minerals to the region of high stress and vice versa for that of low stress so that the material can mitigate the damage and enhance its lifetime. We envision that our findings can open new strategies for making synthetic multifunctional materials with self-adaptable mechanical properties.

Acknowldegements: This work was supported by the Air Force Office of Scientific Research Young Investigator Program Award (Award number: FA9550-18-1-0073, Program manager: Dr. Byung-Lip (Les) Lee), Johns Hopkins University Whiting School of Engineering start-up fund, and Temple University Maurice Kornberg School of Dentistry start-up fund.

Reference: S. Orrego, Z. Chen, U. Krekora, D. Hou, S.-Y Jeon, M. Pittman, C. Montoya, Y. Chen, S. H. Kang, Advanced Materials, 1906970 (2020).

Digital light processing (DLP) based 3D printing is an additive manufacturing process which utilizes light patterns to photopolymerize a liquid resin into a solid. Due to the accuracy of modern digital micromirror devices (DMD) and a layer of thin resin being cured rapidly (1-5s), DLP has the advantage of high speed and high resolution. However, conventional DLP method is not suitable for multimaterial printing because it uses a single vat of resin. Recent advances in resin chemistry now make it possible to create functionally graded structures using different light intensity values, also known as grey-scale DLP (g-DLP). In this talk, we present some our recent efforts in using g-DLP to 3D/4D print multimaterial multifunctional composites, including creating functionally graded materials with modulus spanning three orders of magnitude, creating inflatable structures. As digitally graded light pattern can impose concentration gradients upon the different reacting chemical species, which in turn can cause diffusion of these components throughout both the liquid resin and the solidified regions. This effect can affect both spatial resolution as well as physical property resolution in g-DLP printing. In this talk, we will briefly present a reaction-diffusion model coupled with radiative transfer to analyse the effects of component diffusion and its impact upon the resulting mechanical property resolution on a sub-pixel and macro scale. Our aim is to accurately model the underlying physics along with additive manufacturing process to quantify these phenomena and use the information gained to optimize printing parameters such as light exposure time, grey-scale distributions, and resin composition.

Due to its high intrinsic mobility, germanium (Ge) is emerging as a likely alternative material to replace silicon in the next generation of high-mobility and high-frequency field effect transistors. However, unlike silicon dioxide, Ge oxide is neither stable nor of good quality. Thus, the preparation of an interfacial layer enabling to passivate and insulate Ge surface is still problematic. A promising approach consists in using self-assembled molecular monolayers (SAMs) [1] with high dielectric constant K. In this perspective, the aim of this work is to design new SAMs grafted on Ge exhibiting highly insulating and passivating properties as new high-K self-assembled nanodielectrics [2].
We have studied SAMs of model molecules such as alkylthiols and fluoro-alkylthiols, and of specially synthesized non-charged novel push-pull chromophores bearing electron donor and acceptor groups, separated by a pi-conjugated bithiophene bridge which promotes electron transfer and a subsequent dipole formation [3]. Indeed, due to the alignment of the oriented dipoles promoted by the SAM deposition strategy, such push-pull chromophores have been shown to form highly polarizable insulating films in the literature [2]. We have adapted and developed the original Ge deoxidation/grafting technique in hydro-alcoholic solution [4] and shown that, compared to the usual deoxidizing acid treatment, it gives smoother surfaces and well-organized SAMs, which is proven by ellipsometry, wettability measurements, and scanning probe microscopy analyses. The grafting of alkylthiols and fluoro-alkylthiols on Ge has been performed directly in a single step thanks to the affinity of sulfur with Ge, whereas for the push-pull chromophores designed with a carboxylic anchoring group, we have achieved a two-step grafting with amide bonding on pre-assembled amine-terminated sticking layers. Among the latter, we have demonstrated aminothiophenol SAMs exhibit a better arrangement than cysteamine, with a smooth monolayer film suitable for grafting ordered push-pull SAMs on top. UV-Visible absorption spectroscopy has been carried out to probe push-pull chromophores in solution to determine the concentration limit to avoid aggregation. X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR) analyses demonstrate the oxide removal from the Ge surface after the SAM formation process.
Statistical electrical analyses of the various SAMs on Ge have been carried out by using eutectic GaIn contacts. With such push-pull SAMs, we have been able to decrease the current by a factor of 10⁵ compared to Ge, and 10⁴ compared to dodecane SAMs of similar thickness. Results have been analyzed by transition voltage spectroscopy [5], and successfully correlated with spectroscopic analyses of molecular levels, using inverse photoemission spectroscopy and XPS valence band determination for probing the unoccupied and occupied molecular orbitals respectively, as well as with DFT calculations, thus allowing to identify the highest occupied molecular orbital as the level involved in the electronic transport through the push-pull SAM. Dipole formation has also been evidenced in the SAM. Further work will address multilayers of aligned organic push-pull chromophores to increase the overall dipole of the films for enhanced dielectric properties.

1. A. Ulman, An Introduction to Ultrathin Organic Films, Academic Press (Ed.), Boston (1991)
2. A. Facchetti, M.H. Yoon, T.J. Marks., Adv. Mater. 17, 1705 (2005) ; Y.G. Ha, A. Facchetti, T.J. Marks, Chem. Mater. 21, 1173 (2009)
3. V. Malytskyi, V. Gadenne, Y. Ksari, L. Patrone, J.M. Raimundo, Tetrahedron 73, 5738 (2017)
4. J.N. Hohman, M. Kim, H.R. Bednar, J.A. Lawrence, P.D. McClanahan, P.S. Weiss, Chem. Sci. 2, 1334 (2011)
5. X. Lefevre, F. Moggia, O. Segut, Y.-P. Lin, Y. Ksari, G. Delafosse, K. Smaali, D. Guérin,V. Derycke, D. Vuillaume, S. Lenfant, L. Patrone, B. Jousselme, J. Phys. Chem. C 119, 5703 (2015).

Shape-programmable soft materials that exhibit integrated multifunctional shape manipulations, including reprogrammable, untethered, fast,
and reversible shape transformation and locking, are highly desirable for a plethora of applications, including soft robotics, morphing structures, and biomedical devices. Despite recent progress, it remains challenging to achieve multiple shape manipulations in one material system. Here, a novel magnetic shape memory polymer composite is reported to achieve this. The composite consists of two types of magnetic particles in an amorphous shape memory polymer matrix. The matrix softens via magnetic inductive heating of low-coercivity particles, and high-remanence particles with reprogrammable magnetization profiles drive the rapid and reversible shape change under
actuation magnetic fields. Once cooled, the actuated shape can be locked. Additionally, varying the particle loadings for heating enables sequential actuation. The integrated multifunctional shape manipulations are further exploited for applications including soft magnetic grippers with large grabbing force, reconfigurable antennas, and sequential logic for computing.

Layered Transition Metal Dichalcogenides (LTMD, MX₂) exhibit metallic, semi-metallic, semiconducting, insulating, or superconducting character depending on chemical composition and structure. Recent high-yield, exfoliation methods (i.e. Redox Exfoliation), which are sonication and surfactant-free, are providing oxidatively-resistant and colloidally-stable dispersions of Group IV-VI TMDs (>14 compositions) at high volume fraction (>10% v/v) in a broad range of polar and anhydrous solvents (e.g. acetonitrile, acetone, alcohols). In addition to expanding the range of surface hybridization chemistries, these methods are transforming approaches to LTMD nanocomposite fabrication, ink formulation, and film processing. These opportunities will be highlighted by examples of multi-functional materials and hetero-structures with unique optical performance for optical filters, GRIN optics, and non-linear absorbers.

Bio-enabled nanocomposites represent a novel class of functional materials, which uses principles of bioinspiration to design hybrid materials and structures with co-assembled biological and synthetic components to bring best of two worlds: versatile functions with responses to mechanical, optical, chemical, and light stimuli and mechanical strength, flexibility, environmental robustness, and scalability (see general reviews [1, 2]). We discuss general principles of organization in most popular biological components frequently explored for bio-hybrid materials including proteins (silk fibroins), polysaccharides (nanocelluloses) and common synthetic components such as metal and semiconducting nanoparticles/nanowires and two-dimensional metal oxides, nanoclays and graphene derivatives. For specific illustrations, we select recent results from our research group on designing flexible and strong nanomaterials with electrical conductivity, actuation, bright emission, and controlled photonic properties. In particular, we demonstrated robust patterned metallized biographene papers from graphene oxide monolayers “glued” by silk fibroins with intriguing biosensing properties and corresponding Kirigami structures with large stretchability and ability to transform from planar to 3D structures. Among most recent results, we reported chiral emission in organized biopolymer photonic films with embedded carbon quantum dots mediated by polymer linkers [3], co-assembly of cellulose nanocrystals with amorphous polysaccharides resulted in the preservation of the original structural colors and intercalation into the interstitial defects of nematic monolayers [4], and stable and robust MXene-silk composites [5].

[1] R. Xiong, J. Luan, S. Kang, S. Singamaneni, V. V. Tsukruk, Natural Biopolymers for Organized Photonic Structures, Chem. Soc. Review, 2020, 49, 983.
[2] R. Xiong, A. M. Grant, R. Ma, S. Zhang, V. V. Tsukruk, Naturally-derived biopolymer nanocomposite: interfacial design, properties and emerging applications, Mat. Sci. & Eng. Reports, 2018, 125, 1.
[3] R. Xiong, X. Zhang, M. Krecker, S. Kang, M. J. Smith, V. V. Tsukruk, Large and Emissive Crystals from Carbon Quantum Dots onto Interfacial Organized Templates, Angew. Chem., 2020, 59, 2
[4] K. Adstedt, et al., Intercalation of amorphous polysaccharides into chiral cellulose nanocrystal organization for controlled iridescence and enhanced mechanics, Adv. Funct. Mater., 2020, 202003597
[5] M. C. Krecker, et al., Bio-encapsulated MXene Flakes for Enhanced Stability and Composite Precursors, Adv. Funct. Mater., 2020, 2004554

3D printing has been known as additive manufacturing, with advantages of flexible design and rapid prototyping over subtractive manufacturing. Current 3D printing on the market includes material extrusion, ink jetting, photopolymer curing, and powder fusion. However, these methods rely on simple blending or premixing to fabricate multiple materials or multiphase composites. As a result, the dispersion quality and interfacial interactions have been a bottleneck to overcome during the layer-by-layer manufacturing that leads to weak properties in 3D printed composites. Our study reports an in-house 3D printer based on multiphase printing that can selectively deposit polymers and nanoparticles within distinct phases. In this way, the particle dispersions and their interactions with neighbor polymer chains can be precisely manipulated. Therefore, the composites will demonstrate improved mechanical and functional properties. We will demonstrate the uses of polyvinyl alcohol (PVA) and polyacrylonitrile (PAN) in this unique multiphase 3D printing. Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) with simple sonication will serve as printing inks. The composite structures (e.g., hierarchies, architectures), thermal transitions (e.g., glass transition or melting), and mechanical properties (e.g., strength and stiffness), as well as the performance of printed systems, will be the focus of our research.

Liquid metals (LMs) based on gallium have been explored as prospective functional materials in soft electronics and wearable technology. LMs are useful in applications which require high electrical and thermal conductivity while remaining mechanically deformable. Their widespread use is hindered by its high surface tension, large density, high cost, and rapid surface oxidation in ambient conditions. Augmentation to its rheology through the addition of solid particles or air bubbles can enable LM to be patterned and dispensed onto different surfaces while reducing the overall LM used [1]. Previous studies have demonstrated the need for particle-induced stabilization of air bubbles for traditional metal foams while gallium foaming can occur through simple stirring in air [2-3]. Furthermore, the mechanism for gallium foam formation during shear mixing in air is currently not well understood. In this work, we elucidate the mechanisms for which this foaming process occurs for liquid gallium and the effects of air entrapment on its density, rheology, and thermal properties [4]. We systematically show the structure-property relationships of gallium foam during shear mixing in air and how the surface oxide contributes to the formation and stabilization of air bubbles. From this, it is revealed that a critical amount of surface oxide fragments is necessary to transition the gallium LM into a foam-like LM. These studies provide fundamental insights into the effects of LM-processing on its material properties and open a pathway for exploring other methods to engineer multifunctional LM soft composites.

References:
[1] W. Kong et al., Adv. Mater., 2019, 31, 1904309
[2] X. Wang et al., Adv. Funct. Mater., 2019, 1907063
[3] J. Banhart, Adv. Eng. Mater., 2006, 8, 781–794
[4] W. Kong and N. U. H. Shah et al., Soft Matter, 2019, 16, 5801-5805

Acoustic forces are an attractive pathway to achieve directed assembly for multi-phase materials via additive processes. Programmatic integration of microstructure and structural features during deposition offers opportunities for optimizing printed component performance. Here, we demonstrate that acoustic fields can effectively assemble conductive particles into networks within polymer matrices, whose configuration is modulated prior to curing, to produce 2-D conductive, 1-D conductive, or insulating materials on-demand, all using the same precursor ink. Furthermore, patterning efficient percolated networks in this manner increases conductivity an order of magnitude over conventional dispersed-fiber composites with an order of magnitude lower particle loading, improving printability and allowing versatile orthogonal control of other properties. Although the focus is on electrical conductivity, the approach described is extensible to other transport phenomena. As a relatively material agnostic technique for microstructural control, acoustic-focusing-assisted additive manufacturing offers an expanded library of printable multiphase inks. This technology demonstrates a novel approach to modulating material properties via microstructure control to pave the way for 3D printing components with embedded electrical circuits or other spatially modulated properties.

Fiber-reinforced thermoplastic composites are increasingly being used for industrial applications as they reduce the weight versus traditional materials such as metals and thermosets without compromising structural strength while also allowing better stiffness, recyclability and short processing times. Traditional methods of healing thermoplastics by heating or inducing local heat through embedding heat sources requires external intervention and energy. This strategy may not be suitable for many large-scale industrial applications. Microcapsule-based strategies present an attractive alternative as they are autonomous, scalable and can be incorporated into traditional composite systems. Capsule-based self-healing has been widely shown in bulk polymers, and to some extent in thermoset composites, but autonomous healing in fiber-reinforced thermoplastic composites remains a challenge. The healing strategy proposed in this work utilizes a robust dual microcapsule system containing monomeric healing compositions which will undergo complete polymerization upon release from ruptured microcapsules within a damage zone. Multi-shell walled microcapsules coated with polydopamine are used to encapsulate a methacrylate-alkylborane based chemistry. One part of the microcapsule system contains a trialkyl borane-amine complex and the other microcapsule contains an acrylic monomer with an anhydride-based decomplexer. The microcapsule size has been tuned to the order of a few microns to avoid agglomeration and aid survival during composite manufacturing. The core content of the microcapsules is confirmed and quantified using ¹H NMR and elemental analysis techniques. Thermogravimetric analysis of the microcapsule system reveals enhanced thermal stability at temperatures up to 200 ^oC, which is required to survive stringent composite manufacturing conditions. Subsequently, the microcapsules are incorporated into a model glass fiber-reinforced polyethylene composite to assess its ability to heal delamination and quantify its healing performance. In addition to autonomous healing, this healing strategy offers other advantages such applicability of the healing chemistry to a wide variety of inert low surface energy thermoplastics and healing at room temperature.

The prominence of interactions between multiphysical domains give rise to the need for multifunctional materials that satisfy the broad requirements for the emerging fields of soft robotics and biomedical devices. These fields require efficient coupling of electrical and magnetic energies for sensing, actuation, and communication, preferably done with the same components to reduce system complexity. Composite multiferroic materials offer tunable extrinsic magnetoelectric coupling by engineering the piezomagnetic and piezoelectric materials in different proportions, geometries, and configurations. A major limitation for nearly all multiferroic composites stems from their composition of brittle and stiff ceramic and metallic materials, highlighting a greater property mismatch between the constituents. Such mismatch is detrimental in straintronics, where the main mediator between electricity and magnetism is mechanical strain. On the other hand, organic multiferroic materials are attracting scientific and technological interest due to their tunable properties while reducing the mismatch challenges since the entire framework is made of compliant polymers. However, a shortcoming of organic multiferroics is the basis that the donor-acceptor paradigm is an inferior magnetoelectric coupling mechanism due to the limited excitonic interactions. Presented herein is a novel approach to enhance the magnetoelectric performance of organic multiferroics through the addition of lattice deformation and charge injection mechanisms. The novel organic ferromagnetic polymer blend, P3HT-PCBM is interfaced with a well-established electroactive polymer, PVDF-TrFE, for its piezoelectric properties. The application of an electric field across the PVDF-TrFE surfaces result in a mechanical strain that can transfer to the adjacent P3HT:PCBM framework, enhancing the spin-lattice interaction. The polarization of PVDF-TrFE is also dependent on the electric field resulting in an accumulation of charges on the surface, hence improving the spin-electron interactions of the blend polymer. Therefore, the addition of PVDF-TrFE strategically and dynamically tunes the magnetoelectric properties of the blend polymer on demand. Furthermore, monochromatic illumination of the newly created composite has shown to manipulate the magnetic behavior through photon-exciton-spin coupling. Future research will focus on gaining an insight into magnetoelastic and magnetocrystalline anisotropies of this novel class of material which is forecasted to be fundamentally different from traditional magnetic materials.

Barium titanate (BTO) is a ferroelectric perovskite material that is currently used in energy storage applications because of its high dielectric constant. Wada et al. reported that the size of BTO strongly affects its dielectric constant [2]. In the study, BTO powders with diameters larger than 300 nm were found to have a dielectric constant of 4000, while BTO nanoparticles with a diameter of 70 nm exhibited a dielectric constant of over 15,000. These results are highly contested, but their implications to energy storage have motivated us to investigate the dielectric constants of BTO nanoparticles of various sizes. Here we present the relationship between BTO diameter and BTO dielectric constant, which was obtained through (1) capacitance measurements of polymer-matrix nanocomposites containing BTO nanoparticles, (2) a novel method of processing transmission electron microscope (TEM) images of highly agglomerated nanocomposites, and (3) more accurate COMSOL models of the nanocomposites using data obtained from our image processing method. The positions, agglomeration, shapes, and diameters of BTO nanoparticles in a polymer matrix were determined through our image processing method that extracts this information directly from TEM images of nanocomposites. We then developed a COMSOL Multiphysics model that simulates BTO nanoparticles embedded in a polymer matrix. The COMSOL model takes the results of our image processing technique as inputs and computes the dielectric constants of nanocomposites. By comparing experimental composite dielectric constants to those obtained through COMSOL modeling, we explored the relationship between BTO nanoparticle diameter and dielectric constant.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Durable hydrophobic coatings have seen considerable interest in the last decade. Currently, the most popular strategy to achieve mechanical robustness is by combining perfluoro-compounds (PFCs) with ‘armor’ structures for coating protection. These protective structures are usually large (>10 μm in thickness). However, in many cases thin (<100 nm) hydrophobic coatings are desired. For example, in dropwise condensation, atmospheric water harvesting, anti-icing, and water desalination, the heat and mass transfer rate can be significantly enhanced using hydrophobic surfaces that are less than 100 nm in thickness. Here, we achieve stable hydrophobicity with high mechanical robustness using polydimethylsiloxane-based self-healing thin films that are 1-10 nm thick. We designed and synthesized the vitrimer with polydimethylsiloxane network strands and dynamic boronic ester crosslinks (dyn-PDMS) to take advantage of the inherent hydrophobic nature of silicones. The dynamic bonds provide a mechanism for self-healing and damage resistance. We show that even for films having nanoscale thickness (<10 nm), the transparent coating maintains exceptional hydrophobicity after scratching, cutting, indenting, and steam condensation. The dynamic coating can also be easily deposited through scalable techniques like dip-coating on a variety of substrates including silicon wafer, aluminum, copper, and glass. The developed dynamic polymer chemistry is fluorine-free for better environmental sustainability compared to commonly used PFC-based materials. The presented work develops a paradigm shift in achieving long-term durable hydrophobicity enabling the implementation of self-cleaning, anti-icing, heat transfer, and microfluidic applications.

A natural phase change material, lauric acid (LA), was encapsulated in polystyrene (PS) hollow fibers through three green approaches: 1) co-fabrication of the mixture solutions, 2) thermally triggered nanocapillary transportation and encapsulation, and 3) solvent-assisted nanochannel encapsulation. By simply tuning the encapsulation parameters such as the LA/PS weight ratio, temperature and concentration, the obtained LAPS composite fibers achieved an unprecedented thermal energy storage capacity up to 82.0% (147.8 J/g) of pristine LA (180.2 J/g) owing to the high LA loading and the lightweight and porous nature of the PS matrix. Simultaneous TGA-DSC, ATR, Raman, and SEM measurements confirmed the homogeneous distribution of LA inside the fibers across the whole membranes. Further, the LAPS composite fibers showed a long-lasting stability during cycling without storage capacity deterioration, as well as an exceptional structural stability without LA leaking and fiber rupture during 100 heating-cooling cycles. The energy-dense and form-stable LAPS composite fibers have a great potential for various thermal energy storage applications including solar energy storage, “temperature-smart” buildings, thermal regulating textiles, and thermal therapy devices.

While microbubbles (MBs) are currently mainly used as cardiac and perfusion imaging agents in the clinic, engineering MBs with bioresponsive properties would expand their use to detect pathophysiologic changes. This can be achieved by stiffening the MBs shell with a bioresponsive “cloak” to decrease their oscillations and silence their signal, and rescuing the MB elasticity when they are exposed to a biomarker of interest. This strategy would allow the switching between a stiff 'OFF' state and an elastic 'ON' state that would allow MBs to become detectable only when exposed to biomarkers of interest (e.g., pH, reactive oxygen species, hypoxia, or enzymes).
To validate our hypothesis, we used conjugated MBs with hyaluronic acid (HA) and crosslinked the resulting polymeric shell with pH-sensitive crosslinkers to obtain activatable pH-sensitive MBs (pH-MBs). We first validated the successful conjugation of HA to MBs and targeting of pH-MBs to CD44-positive cells. Using ultrasound imaging, we confirmed the harmonic signal loss that is associated with the stiffening of pH-MBs. We used a clinical ultrasound scanner equipped with Cadence contrast pulse sequencing to image pH-MBs before and after acidification and observed a fivefold increase in harmonic signal. Because the crosslinker cleavage is reversible, we were able to silence harmonic signal again by neutralizing the acidic suspension was neutralized, confirming that harmonic signal is dependent on the cross-linked HA. Interestingly, the rate of rise and the magnitude of harmonic signal increase could be manipulated by varying the phospholipid composition and the number of crosslinkers, indicating that the platform can be tuned to the desired response needed.

Jiancheng Luo, Sheng Zhao, and Pengfei Cao^*
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA

Thermoset elastomers with multifunctionality such as self-healable and recyclable capability, stretchability, and stimuli-responsive shape, are attractive to numerous applications. In this work, polyurethane (PU) vitrimers with well-defined network topology are design by connecting tetra-armed crosslinkers with PDMS chains bearing disulfide bonds. Compared with the random network, the well-defined network endows elastomeric vitrimers significant improvement on their mechanical performance. Through tuning PDMS chain length, the elastomers exhibit outstanding mechanical properties with ultimate tensile stress ranging from 1.5 MPa to 11.2 MPa, and elongation at break ranging from 290% to 884%. The elastomers also exhibit good solvent resistance and self-healability, and meanwhile show no obvious loss on mechanical performance after 5 reprocessing cycles. By embedding carbon nanotubes (CNT) into polymer network, the as-prepared conductive elastomers can be used to fabricate various soft electronics, i.e., strain and electrocardiogram sensors. The network design principle here provides a feasible approach to achieve recyclable thermoset elastomers with excellent mechanical performance.

For decades, bioadhesive materials have garnered great attention due to their potential to replace sutures and staples for sealing and repairing tissues during minimally invasive surgical procedures. However, the complexities of delivering bioadhesives through narrow spaces and achieving strong adhesion in fluid-rich physiological environments continue to present substantial limitations to the surgical translation of existing glues and sealants. We introduce a new strategy for minimally invasive tissue sealing and repair based on a multilayer bioadhesive patch, which is designed to repel body fluids, form fast, pressure-triggered adhesion with wet tissue surfaces, and resist biofouling and inflammation. The multifunctional patch is realized by a synergistic combination of three distinct functional layers: (i) a micro-textured bioadhesive layer, (ii) a dynamic, blood-repellent hydrophobic fluid layer, and (iii) an antifouling zwitterionic non-adhesive layer. The bioadhesive patch is capable of forming fast and robust adhesion to tissue surfaces in the presence of blood, and exhibits superior resistance to bacterial adhesion, fibrinogen adsorption, and in vivo fibrous capsule formation. By adopting origami-based fabrication strategies, we demonstrate that the multilayer bioadhesive patch can be readily integrated with a variety of minimally invasive end effectors to provide facile and effective tissue sealing in ex vivo porcine models, offering new opportunities for minimally invasive tissue sealing and repair in diverse clinical scenarios.

Dynamic covalent polymer networks will go through topological rearrangements under stimulations to relax internal stress and switch the features of materials. Via continuously exploring new internal force programming approaches, the structure of dynamic materials can be manipulated in a more and more controllable fashion. Here, besides the generally deformed by macroscopic stretching, bending or twisting, we present a microscopical way which is freezing, to impose internal force toward a dynamic hydrogel and establish a flexible micromanufacturing method. Specifically, the hydrogel is crosslinked by disulfide bonds and owns capability of photo-induced network rearangements. During freezing, microphase separation occurs, forming two phases: ice crystals and a squeezed polymer phase. After spatial UV exposure, polymer chains are relaxed due to the disulfide bond exchange and entropy of the network is increasing as well. Subsequent ice melting will lead to porous patterns with the feature size of 20 μm, and the obtained porous hydrogels can be directly utilized to spatially store functional inks for transfer printing. Additionally, the present ice-templating photo patterning method requires no solvent washing step, and uses mostly water (98%) with the remaining organic component easily recyclable, thus generating zero organic waste. Therefore, it can open up an avenue for sustainable and flexible micromanufacturing.

To overcome a limitation of typical immunoassays like an enzyme-linked immunosorbent assay (ELISA) in terms of multi-step procedure, one-pot immunoassays are in high demand for point-of-care (POC) testing that can be used by individuals at any time and anywhere.
In this study, we suggest a one-pot immunosensor composed of Cy5/capture antibody/gold nanorod conjugates and an Au/TiO₂ photocatalytic film. After injection of solution for an immunoassay, delayed production of H₂O₂ from the photocatalyst by ultraviolet illumination enabled a one-pot assay by quenching of Cy5 due to 4-chloro-1-naphthol precipitates that produced by the enzymes bound to the conjugates via interleukin 8 (IL-8) antigens. As a result, our one-pot immunosensors could detect IL-8 within the range of 1 pg mL^–1 – 1,000 pg mL^–1, which was as sensitive as the purchased ELISA kit for IL-8 detection. Therefore, this sensor platform could pave the way for highly sensitive, portable, easy-to-use POC biosensors for individuals.

Homogeneous single synthetic materials typically have limited functions as multifunction is always related to multimaterial systems. By mimicking the nature of biological species to introduce spatially heterogeneous distribution of active components in synthetic materials, the design space for advanced multifunction is widened. Here, we introduce the heterogeneity at the programming process after material synthesis/fabrication step by a digital photothermal effect. Our first work allows spatio-selective programming of crystallinity in a shape memory polymer (SMP). Consequently, a pre-stretched 2D film with spatial heterogeneity in shape recovery ratio can morph into designable 3D permanent shapes, achieving the 4D transformation. Following the first work, we design a supramolecular SMP with intrinsic time-temperature dependency. Spatial controlling of deformation temperature and time brings heterogeneity in shape recovery rate, thus leading to highly non-monotonic shape-shifting pathways and tunable evolution lifetime. The benefits of these unique features are demonstrated by multi-shape transformation, an “invisible” color based clock and a time-temperature indicator (TTI). Heterogeneous material in our work, as a novel kind of multimaterials, provides a versatile idea for manufacturing multifunctional devices.

Multifunctional nanocomposites which exhibit well-defined physical properties and encode spatio-temporally controlled responses (including changes of shape, microscopic morphology, mechanical strength and permeability) are emerging as components for advanced responsive systems. For instance in the case of biomedical applications magnetic nanocomposite materials have attracted significant attention due to their ability to respond to spatially and temporally varying magnetic fields changing their intrinsic structure, undergoing time-dependent deformations, or releasing cargo on demand.^1-3

The combination of MNPs and established 3D printable polymeric hydrogel formulations can provide multifunctional and stimuli-sensitive systems with spatial-, temporal- and dosage-controlled release properties. Here, our work towards bio-applications of magnetic hydrogels is described in two fabrication cases, (i) conventional manufacturing, where magnetic materials are utilized in conventional manufacturing processes during solidification/gelation, as well as (ii), magnetic structuring, where the presence of magnetic fields or 3D printing was used to spatially pattern materials with encoded magnetic responsiveness.

A combination of in-house built multi-head and commercial 3D printers was used to extrude selection of magnetic composite hydrogels. Magnetic nanoparticles were synthesised, stabilized and dispersed homogenously through the gels to optimise their hyperthermic responses. Oscillatory and rotational rheology measurements confirmed the viscoelastic properties providing ideal materials for 3D printing well-defined architectures with high fidelity for both magnetic and non-magnetic components of integrated multi-component builds. The hybrid inks showed complete shear- and temperature-recoverability/reversibility to their initial state, confirming that at particle concentrations that enable magnetic responses the necessary printability is not lost. Multiple complex structures were printed with high resolution (~150 mm) with independent magnetic and non-magnetic patterned components and these were shown to be reproducible and robust. Post-printing chemical crosslinking was used to retain long-term fidelity of the printed structures, whilst retaining magnetically responsive hyperthermic responses at low particle concentrations. Thermoresponsive contractile elements were also embedded from selection of polymers based on poly(N-isopropylmethacrylamide) with chemically programmed volume temperature transitions at physiologically relevant range of 32 to 45°C.

For AC-magnetic field responsiveness, high resolution IR thermography confirmed that incorporated magnetic nanoparticles retain sufficient magnetic response to provide spatial temperature gradients for cell stimulus and for stimulus-responsive timed delivery of biomolecules. The advantages of spatial patterning of thermally active components will be described in the context of kidney and cerebral organoids, as well as for stem cell differentiation. Applications of DC-magnetic fields to physical stimulation of patterned magnetic gels will also be presented.

1. Zhang, X. et al., The Pathway to Intelligence: Using Stimuli-Responsive Materials as Building Blocks for Constructing Smart and Functional Systems. Advanced Materials 2019, 0 (0), 1804540.
2. Lyons, S.; Mc Kiernan, E. P.; Dee, G.; Brougham, D. F.; Morrin, A., Electrostatically modulated magnetophoretic transport of functionalised iron-oxide nanoparticles through hydrated networks. Nanoscale 2020, 12 (19), 10550-
3. Stolarczyk, J. K. et al., Nanoparticle Clusters: Assembly and Control Over Internal Order, Current Capabilities, and Future Potential. Advanced Materials 2016, 28 (27), 5400-5424.

ACKNOWLEDGMENTS
The authors acknowledge support from Science Foundation Ireland (16/IA/4584 and 13/IA/1840).

Plants structures and their motions are a result of long-term interplay between evolution, failure, and adaptation to their local environments. Motions of plants are driven by their growth. Typical examples of the plant kingdom where the motion is relevant are searchers of liana or the tendrils of climbing plants. In both examples, the capability of coordinated actuation such as coiling upon response to specific external stimuli can be observed. To enable biomimetic innovations, special attention has been payed to understand the coiling of plant structures. [1, 2] A promising approach to mimic this behavior are multifunctional multimaterial systems, in which orchestrated interplay of functions could provide this coiling behavior. Here we report on development of a multimaterial fiber as an artificial tendril. The multimaterial fiber is composed of shape-memory polymer fiber core and an elastic outer matrix. As fiber core we selected a poly[ethylene-co-(vinyl acetate)] (PEVA) fiber (d ≈ 400 μm), whereas a silicone based soft elastomer was chosen as a matrix. The core fiber provides a temperature dependent actuation (expansion/contraction) that propagates coiling of the tendril due to the mismatch in the modulus of outer matrix and inner core. Therefore, we considered the mismatch in elastic modulus as a control parameter. The modulus of the matrix (E_matrix) was varied between 0.1 and 0.5 MPa to achieve various coiling behaviors of such multimaterial tendrils. The maximum number of coiling per unit centimeter (N = 0.35) was observed for the tendril with an intermediate E_matrix = 0.29 MPa. Our study stimulates the design for plant inspired multimaterial tendrils with tunable coiling and reversible motion responses.

References
Gerbode, S.J., et al., How the Cucumber Tendril Coils and Overwinds. Science, 2012. 337(6098): p. 1087-1091.
Xiao, Y.Y., et al., Biomimetic Locomotion of Electrically Powered "Janus" Soft Robots Using a Liquid Crystal Polymer. Advanced Materials, 2019. 31(36).

Direct crystallization is widely used in the production of multicrystalline silicon for solar energy and electronics. In the process of direct crystallization, the melt flow is controlled by the heat convection force resulting from a temperature gradient. This leads to the appearance of convective disturbances and melt turbulence. These effects have a negative impact on the quality of the obtained material.
The efficient way to control the melt mixing is to use both continuous and variable magnetic fields. Continuous magnetic fields smooth effectively convection flows in the melt, and variable magnetic fields influence substantively on the melt mixing.
This paper presents the results of mathematical modeling of electromagnetic stirring of silicon melt under various conditions. Mathematical modeling was carried out using COMSOL Multiphysics software. In the course of modeling, the distributions of the magnetic field induction, the densities of the Lorentz force, and the melt stirring rates were obtained. The distribution of the surface rate of melt movement was determined.
Experimental studies were carried out on a direct crystallization unit with the crucible size of 860x860x450 mm and the ingot weight of up to 500 kg. To create a running magnetic field, a current pulse generator was made. The current amplitude of an inductor was regulated in the range from 10 A to 700 A, the frequency of current pulses was from 20 Hz to 200 Hz, and the phase shift was from zero to 180 degrees.
The research results are as follows:
- a physical and mathematical model of electromagnetic stirring of silicon melt was developed, modeling of electromagnetic stirring was carried out;
- on the basis of the developed model, the configuration of the pilot unit was selected;
- a pilot unit was created and experimental studies on the influence of the magnetic field parameters on the melt surface rate were carried out;
- the optimal conditions for obtaining a stable, repeatable process of silicon melt stirring were established.
The obtained results were used for multicrystalline silicon production. Studies on the effect of the current shape in inductors were conducted.

Long-range ordering of magnetic particles has been reported by generating magnetic dipole moments and dynamic swarming motion in aqueous medium under external magnetic field. However, the self-organization is not reversible and reliable because the position of magnetic particles is not stationary. Alternatively, we suggest periodic polymeric micropillar arrays with inclusion of magnetic particles for reversible and programmable magnetic self-organization in a stepwise manner. When magnetic field is applied, individual micropillars are magnetized and operate as micromagnets. The vicinal pair of pillar tops magnetically attract each other for magnetic self-organization while the pillar base is still fixed to the substrates. As the magnetic flux density increases, the paired micropillars undergo quad-body organization, and then the long-range connectivity of pillar tops is accomplished. We will discuss the influence of spacing and anisotropic cross-sections of the micropillars on the stepwise magnetic self-organization by investigating the geometry form factors such as rectangular, square and circular cross-section.

Microcapsules with a liquid core and solid shell have been used for storage and release of materials in various purposes. The shells that have regular size of continuous pores or microchannels provide molecular-size-selective permeation so that they allow transmembrane transport for smaller molecules than the pores while excluding or retaining larger molecules. The size-selective permeation is of great importance for protection of delicate large encapsulants while allowing transmembrane transport of small molecules, in particular for encapsulation of catalysts or enzymes and nanoparticle-based sensors. The shells with tunable cut-off threshold of size-selective permeation are promising for reversible encapsulation and release of encapsulants in a highly controlled and programmed manner. The molecules smaller than the cut-off threshold can be inserted into the core of the microcapsules by diffusion, which is encapsulated by lowering the cut-off below the size of the molecules. The encapsulants will be released into surrounding by increasing the cut-off, which can be done in single step or multiple steps.
Hydrogels are one of the promising shell materials to achieve the tunable cut-off threshold. Hydrogels have three-dimensional network of hydrophilic polymers. When the network is swollen by water, large free volume is formed in the mesh, through which small molecules can diffuse. More importantly, the use of stimuli-responsive polymers to form the mesh enables to control the degree of swelling. However, the precursors for hydrogels are usually hydrophilic and soluble in water, which makes it challenging to produce microcapsules with water core and hydrogel shell using conventional templates of water-in-oil-in-water (W/O/W) or oil-in-water-in-oil (O/W/O) double-emulsion drops.
In this work, we use a novel thermoresponsive hydrogel precursor to produce the semipermeable microcapsules with tunable cut-off threshold of permeation with a template of W/O/W double-emulsion drops. The precursor is poly(N, N-diethylacrylamide) (PDEAM) functionalized with benzophenone (BP). BP self-initiates the reaction under the irradiation of ultraviolet (UV) in the absence of photoinitiator, crosslinking PDEAM to form a mesh. PDEAM has the lower critical solution temperature (LCST) around 34°C with water. Due to the hydrophobic BP moiety, PDEAM-BP is highly soluble in organic solvent and weakly soluble in water even at room temperature. Using the solution of PDEAM-BP in chloroform as an oil phase, we produce W/O/W double-emulsion drops with ultra-thin oil shell with a glass capillary microfluidic device. The innermost water drops and continuous phase contain a high concentration of salt, which exerts a osmotic pressure and helps prevent the formation of tiny water droplets in the oil shell. The double-emulsion drops are incubated at 50°C for removal of chloroform, which makes the PDEAM-BP more hydrophobic and further suppresses the formation of water droplets in the oil shell. After complete consolidation, PDEAM-BP is crosslinked by UV irradiation and the resulting microcapsules are washed with distilled water at room temperature. The microcapsules show temperature-dependent changes of diameter and shell thickness. The cut-off threshold is estimated to be below 4kDa in size at 50°C, whereas that is between 4kDa and 10kDa at 25°C and 4°C. The temperature-dependent change of the cut-off threshold is highly reversible, which enables us to load and release molecules in a programmed manner. In addition, the release can be done in multiple steps by repeating heating and cooling. Moreover, the cut-off threshold of the microcapsules can be further controlled through the controlled irradiation of near infrared light by encapsulating photothermal agent of polydopamine (PDA) nanoparticles in the core. We believe our microcapsules with tunable cut-off threshold will provide new opportunities for microreactors and microsensors as well as drug carriers.

Construction of a 3D structure from 2D flat geometry has received great attention in the materials community. Although various methods are reported to achieve 2D to 3D shape-morphing, photothermal actuation has been emerged as a promising method for contactless shape-reconfiguration. The photothermal heating method often use black inks on the shape memory polymers to localize photothermal heating. However, this method could cause further undesirable actuation as the ink patterns remain even after creating the desirable 3D structures. In this study, adhesive tape patterns were employed instead of the ink patterns in order to achieve transparent 3D structures as well as prevent undesirable actuations. When black adhesive tapes were irradiated with NIR light, the patterned areas absorb photons and generate photothermal heating. When the temperature exceeds the polymer glass transition temperature, shrinkage of polymer occurs by recovery of random coil conformation from biaxially pre-strained coils. We discuss the effects of various radial and chiral tape patterns on curvature control for complex 3D structures. Furthermore, we will demonstrate sequential folding by temporal regulation of the NIR irradiation. We will also discuss shape-reconfiguration of heterogeneous materials with the addition of compliable papers and introduction of conductive functions on 3D morphed polymers.

While the predetermined mechanical properties of both conventional rigid electronics and emerging soft electronics allow them to perform target-specific functions, their fixed rigidity limits their extensive applications. Rigid electronics such as smartphones and laptops are easy to handle and can endure external stress owing to their robust structures. However, their high stiffness makes them incompatible with soft biological tissue, thus they are not suitable for use in wearables and implantable devices. While the compliant interface of soft electronics allows conformal contact with the curvilinear body, it does not provide sufficient load-bearing capability when operated in an off-body application. Stiffness tuning is one of the promising solutions in order to leverage the key features of both rigid and soft electronics. Recently, transformative electronic systems (TES) with reconfigurable shape and stiffness have been developed by using gallium as a thermally-tunable mechanical platform. However, the gallium platform experiences supercooling phenomenon during its liquid-to-solid phase transition which prevents soft-rigid TES mode conversion at its freezing temperature (29.76 °C) and makes the fast bi-directional soft-rigid conversion of TES a challenging task.
Here, we present an advanced architecture for gallium-based TES, which integrates graphene and a flexible thermoelectric device (f-TED) to enable a rapid bi-directional soft-rigid transformation mode. Graphene facilitates the mitigation of the degree of supercooling as a catalyst to accelerate the nucleation of gallium during the liquid-to-solid phase transition, while the f-TED offers active temperature control to accelerate the overall phase transition of the gallium platform. During the solidification process, the f-TED lowers the temperature which assists in overcoming the supercooling of gallium that leads to a reduction in the liquid-to-solid transition time. In a similar way, the f-TED can shorten the time required for the solid-to-liquid transition of gallium by actively heating the TES platform. By integrating the graphene-gallium interface platform and f-TED, we could significantly reduce the time for the melting and freezing, by 91% (from 255 to 23 s) and 55% (from 175 to 79 s), respectively, as compared to TES design built with pure gallium. Based on this design strategy, we could successfully demonstrate a TES that can facilitate rapid conversion between a rigid handheld display and a flexible wearable pulsimeter/display. The proof-of-principle demonstration of TES capable of rapid bi-directional transformation suggests broad utility of the proposed design, which may open new opportunities for electronics, robotics, and biomedical devices.

The tuning of both covalent bond formation as well as dissociation remains a grand challenge in the design of photodynamic systems. The light-responsive adaptation of polymer materials requires different wavelengths to induce reversible covalent bond formation and dissociation. Our efforts have been devoted to pioneer a toolbox of photocycloadditions that can be triggered by lower energy visible light, while their cycloreversion should function at the least energetic wavelength, too. The lecture will showcase the latest applications of reversible photochemistry for the generation of light adaptive micro-structured materials via 3D laser lithography.¹

Further, the lecture will explore visible light-triggered reversible triazolinedione (TAD) chemistry and its application in materials science. We have recently pioneered the photo-chemically driven reaction of TADs with naphthalene as a dynamic covalent cross-linking platform that enables green light-induced network formation (525 nm), while network degradation is triggered by merely switching off the light, thus introducing the new class of Light Stabilized Dynamic Materials (LSDMs).² These materials can undergo a repeatable change in morphology from a covalently cross-linked material into a liquid polymer formulation by switching the visible light source on-and-off without the need for any additional triggers. Furthermore, TADs exhibit a strong purple colour which fades upon reaction with suitable substrates, thus facilitating online monitoring of the material’s property transformation with the naked eye.

We subsequently expanded TAD photochemistry in the field of light-fuelled covalent non-equilibrium chemistry. Under green light, naphthalene-containing polymers can be folded into single chain nanoparticles (SCNPs) driven by [2+4] cycloadditions with a bivalent TAD crosslinker, whereas the SCNPs unfold into their linear parent polymers in the absence of light.³ Such photonic fuel driven dynamic SCNPs constitute the first example of a reversible light triggered folding of single polymer chains, mimicking their naturally observed spontaneous folding of proteins.

Moreover, we have established a new method for the photoinitiated, additive-free precipitation-driven synthesis of particles by crosslinking pre-synthesized low molecular weight polymers. Microspheres were produced by employing the nitrile-imine mediated tetrazole-ene cycloaddition reaction upon UV irradiation (λ = 300 nm), therefore forming intrinsically fluorescent particles.⁴ The reaction wavelength was subsequently red-shifted to 415 nm by exploiting o-quinodimethanes that undergo [2+4] cycloadditions with suitable dienophiles or [4+4] via self-dimerization.⁵ Critically, a variety of crosslinking molecules and dienophiles were investigated, imparting unique properties to the particles such as chemical degradability, chemiluminescence and acid triggered fluorescence switch-on. Finally, we combined our visible light driven particle design platform technology with the visible light-driven reversible [2+4] cycloaddition of TADs with naphthalene prepolymers, creating degradable microparticles that do not require any external degradation trigger other than darkness.<sup>6

1</sup> Gernhardt, M.; Frisch, H.; Welle, A.; Jones, R.; Wegener, M.; Blasco, E.; Barner-Kowollik, C. J. Mater. Chem. C 2020, 8, 10993-11000.
² Houck, H. A.; Blasco, E.; Du Prez, F. E.; Barner-Kowollik, C. J. Am. Chem. Soc. 2019, 141, 12329-12337
³ Kodura, D.; Houck, H. A.; Bloesser, F. R.; Goldmann, A. S.; Du Prez, F. E.; Frisch, H.; Barner-Kowollik, C. 2020, submitted.
⁴ Hooker, J.; Delafresnaye, L.; Barner, L.; Barner-Kowollik, C. Mater. Horiz. 2019, 6, 356-363.
⁵ Hooker, J.; Feist, F.; Delafresnaye, L.; Barner, L.; Barner-Kowollik, C. Adv. Funct. Mater. 2020, 30, 1905399
⁶ Schmitt, C. W.; Walden, S. L.; Delafresnaye, L.; Houck, H. A.; Barner, L.; Barner-Kowollik, C. 2020, submitted

Soft, elastically deformable composites can enable new generations of multifunctional materials for flexible devices and reconfigurable structures. An emerging material architecture is to create solid–liquid composites with liquid metal (LM) inclusions dispersed in elastomer matrices. These materials have shown exceptional combinations of soft mechanical response, tunable electrical properties, and high thermal conductivity. Such properties are strongly dependent on the material composition and microstructure. However, approaches to control the liquid metal microdroplet morphology to program mechanical and functional properties are lacking. Here, we overcome this limitation by thermo–mechanically shaping LM droplets in soft composites to create programmable microstructures. This enables LM loadings up to 70% by volume with prescribed particle aspect ratios and orientation, enabling control of microstructure throughout the bulk of the material in stress–free conditions. The influence of microstructure on the mechanical and functional response is theoretically and experimentally determined and a general framework is developed to design soft composites with desired functional characteristics. Through this microstructural control in soft composites, we simultaneously achieve a thermal conductivity as high as 13 W/mK (> 70 x increase over polymer matrix) with low elastic modulus (<1.0 MPa) and high stretchability (>750% strain), representing one of the highest thermal conductivities for soft, deformable materials. The exceptional thermo–mechanical properties of LM programmed composites enables thermal control in rigid and highly deformable systems. We demonstrate this capability with electronics integrated into 3D printed materials, soft heat sinks, and thermal shielding in artificial muscles for a prosthetic hand. We envision that the ability to program microstructure in solid–liquid composites will enable further advances in flexible electronics and robotics, medical devices, and shape morphing structures.

High temperature thermosets display exceptional thermomechanical behavior due to densely crosslinked networks and chemically resistant bonds. Traditionally, increases in polymer crosslink density present greater challenges for recyclability. Here we show incorporation of a selectively cleavable moiety at the crosslink junction allows for significant increases in crosslink density and glass transition temperature while maintaining a pathway for recyclability. Co-polymerization of multi-functional cyclic olefins featuring silyl ether moieties with dicyclopentadiene (DCPD) produces degradable poly(DCPD)-based thermosets with high glass transition temperatures (T_g). Crosslinking density and glass transition temperature are controlled by tuning structure and molar concentration of the degradable co-monomers. These robust thermosets are degraded via exposure to a triggering fluoride stimulus, and the resulting soluble products can be incorporated into new polymers networks. The effects of these multifunctional cyclic olefins on crosslink density, glass transition temperature, and the rate of structural degradation are studied, and the properties of the recycled materials are characterized. Incorporation of silyl ether crosslinking units leads to thermosetting materials with high T_g (>180 ^oC) and that are readily recyclable.

Soft, elastically deformable materials with high thermal conductivity are critical for numerous industries including healthcare, aerospace, automotive, and flexible electronics, where combinations of high mechanical compliance and high thermal conductivity are required. An emerging material architecture are elastomer composites that are composed of liquid-metal (LM) microdroplets embedded in hyperelastic polymers. These all soft-matter systems exhibit exceptional thermal properties, are electrical insulating even at high volume loadings, and remain soft and stretchable even at extremely low temperatures (-80 ^oC). Although these materials exhibit a unique combination of properties, the high density and high volume loading of the LM filler significantly increases the density of the composite, which is problematic for large-area thermal management and weight sensitive applications such as wearable electronics, aerospace thermal control, and clothing. Here, we introduce a new lightweight, LM inclusion that has a unique combination of properties including high thermal conductivity, low mass density, and high deformability when embedded into an elastomer matrix. Furthermore, the composition of the lightweight, LM inclusion can be tailored, enabling a large range in density with negligible changes to the thermal conductivity of the inclusion as the thermal conductivity is dominated by electrons. Experimental thermal conductivity results measured using the transient hot-wire method agree well with the Bruggeman and Cheng-Vachon models of effective medium theory. As with previously reported LM embedded elastomer composites, this composite shows increased thermal conductivity under strain and is able to achieve maximum strain above 400%. This work presents a new material architecture to enable independent control of the thermal conductivity and density of LM elastomer composites, offering new opportunities to tune functional properties of systems where weight is critical.

The demand for shape memory polymer (SMP) development has risen due to their multifunctional abilities and numerous applications in a variety of industries. This project explores a new approach to reconfigurable shape memory elastomeric composites (Re-SMEC) by altering the roles of the individual phases to create an inverted shape memory elastomeric composite (i-SMEC). In our previous work, we confirmed the feasibility of reconfiguration attributed to a dynamic covalent exchange between neighboring anhydride groups occurred, enabling the customization of the target geometry during shape memory activation. In the present work, we exploit these properties in the form of a new type of shape memory elastomeric composite that features a fibrous thermoplastic elastomer web combined with a reconfigurable elastomeric polyanhydride (PAH) matrix in a novel geometry controlled and manipulated thermomechanically. Contrary to traditional fiber-reinforced composites, where the fibrous phase temporarily fixes the geometry, this shape memory system utilizes the reconfigurable matrix for shape-fixing and elastic fibers as the memory retaining phase. We report the morphology, quantification of the mechanical properties, and the effect of fiber diameter on the shape memory abilities. Further, we introduce a new shape memory testing methodology of particular use for SMPs with fixing via matrix reconfiguration.

This talk will discuss new work in our group (and with collaborators) on soft composites that utilize liquid metals. Liquid metals composed of gallium are compelling materials for multifunctional materials because they can be incorporated, patterned, or mixed readily into elastomer. The addition of the metal alters the electrical and thermal properties, but without significantly stiffening the composite relative to the pure elastomer. In addition to imparting metallic thermal or electrical properties (the latter of which is useful for creating wires, antennas, and electrodes), it can also tune the effective dielectric properties of the material and also go through phase transitions to produce enormous changes in modulus. I will discuss several aspects and implementations of these multifunctional properties. First, characterizing the dielectric and electrical properties of such soft composites for pressure sensor applications. Second, utilizing such materials for conductors and electrodes that can undergo enormous changes in mechanical properties. Third, describing composites with electrical conductivity that increases with deformation, which is highly unusual. Fourth, printing of such composites by modifying the rheology to enable 3D printing. This work has implications for stretchable electronics, responsive materials, and soft robotics.

Liquid crystalline materials are pervasive in our homes, purses, and pockets. It has been long-known that liquid crystallinity in polymers enables exceptional characteristics in high performance applications such as transparent armor or bulletproof vests. This talk will generally focus on a class of polymeric liquid crystalline materials: liquid crystalline elastomers. These materials were predicted by de Gennes to have exceptional promise as artificial muscles, owing to the unique assimilation of anisotropy and elasticity. Subsequent experimental studies have confirmed the salient features of these materials, with respect to other forms of stimuli-responsive soft matter, are large stroke actuation up to 400% as well “soft elasticity” (stretch at minimal stress).

This presentation will survey our efforts in directing the self-assembly of these materials to realize distinctive functional behavior with implications to soft robotics, flexible electronics, and biology. Most notably, enabled by the chemistries and processing methods developed in my laboratories, we have prepared liquid crystal elastomers with distinctive actuation and mechanical properties realizing nearly 40 J/kg work capacities in homogenous material compositions.

Advanced, immersive systems for virtual and augmented reality (VR/AR) will transform the way that we interact with computer-generated environments and, by extension, with one another. Although audio-visual aspects of VR/AR hardware are increasingly well developed, a frontier, underexplored opportunity for engineering science is in the development of interfaces that add spatio-temporally controlled physical sensations to the VR/AR experience, with the skin as the input interface. This talk summarizes a collection of foundational ideas in materials science and electrical engineering that enable a unique class of technology for this purpose – thin, soft, lightweight sheets that embed wirelessly powered and programmed arrays of high-speed, millimeter-scale mechanical actuators, capable of gently laminating onto the skin at nearly any location on the body, including but not limited to the fingertips. These systems qualitatively expand the VR/AR interface through complex patterns of physical sensory inputs across substantial areas of the body, time-coordinated with visual and auditory cues. Three example applications – one in social media interactions, a second in feedback for the control of robotic prosthetics, and a third in video gaming – illustrate the operational possibilities.

Metamaterials are architected materials that possess unique properties not observed in nature, which makes them promising candidates for a broad range of applications. After fabrication, existing metamaterial systems can only tune their properties to a limited extent. The coupled multimaterial system and multiphysics control provide a new strategy to achieve active metamaterials with widely tunable physical properties. Fabricated by recently developed magnetic shape memory polymer, demonstrated metamaterials can soften upon heating, and the embedded high-remanence magnetic particles drive the rapid and reversible shape change under the application of magnetic field. Once cooled, the stiffness of the composite can increase by three orders of magnitude to lock the deformed shape. Furthermore, the coupled magneto-mechanical actuation at high temperature realizes various deformation modes, which lead to widely tunable physical properties including stiffness, Poisson’s ratio and elastic wave bandgaps. Additionally, the combination of magnetic shape memory polymers with magnetic soft materials, together with the cooperative stimuli of magnetic field, mechanical loading and temperature, enable dexterous manipulations of material systems with tunable physical properties and shiftable mechanical behaviors.

Thermoelectric generators (TEGs) can directly convert low-grade heat to electricity, and thus are very promising energy sources for wearable electronics and ‘Internet of Things’. However, conventional TEGs are rigid and brittle, and thus are not adaptable to the complex geometrical and compliant material properties of human body. Recently, developing flexible TEG systems has attracted a lot of attention, including using thermoelectric (TE) films, TE bulks, printable TE inks, TE fibers and organic TE materials. However, very few studies reported TEGs with good stretchability, which is critical to ensure conformal contact with complex geometries of human body for optimal thermoelectric performance. Inspired by the self-healing capability of human skin, self-healable electronics has also shown promising potential in wearable electronics for improved reliability and durability. However, this capability has not been achieved in TEG systems yet.
In this work, a high-performance wearable thermoelectric generator with superior stretching, self-healing, recycling, and Lego-like reconfiguration capabilities is reported. To achieve these properties, high-performance modular thermoelectric chips, dynamic covalent thermoset polyimine as substrate and encapsulation, and flowable liquid metal as electrical wiring are integrated through a novel mechanical architecture design of “soft motherboard-rigid plugin modules”. This TEG can self-heal when it’s damaged by mechanical cut. When not needed, this TEG can be fully recycled, and the recycled polymer solution, thermoelectric chips and liquid metal can all be used to fabricate a new generation of TEG device. The lego-like reconfiguration capability allows reconfiguring multiple TEGs into a single TEG with increased power output. This TEG can produce a record high open-circuit voltage density of 1 V/cm² at temperature difference 95 K, which is promising for harvesting low-grade heat to power ‘Internet of Things’ and wearable electronics. These features enable TEGs to be adaptable to the rapidly changing mechanical and thermal conditions, and user requirements. The reported TEG demonstrate superior mechanical compliance and deformability. It can be bent and stretched without sacrificing the thermoelectric performance. Cyclic bending test of the TEG for 1000 times led to no obvious degradation. When subjected to a tensile strain of 120%, the TEG still functioned well. Furthermore, a wavelength-selective metamaterial film is integrated at the cold side of the TEG to simultaneously maximize the radiative cooling and minimize the absorption of solar irradiation. Therefore the thermoelectric performance can be greatly enhanced under solar irradiation, which is critically important for wearable energy harvesting during outdoor activities. The design concepts, approaches and properties of the TEG system reported in this work can pave the way for delivering the next-generation high-performance, adaptable, customizable, durable, economical and eco-friendly energy harvesting devices with wide applications.

Hydrogels are hydrophilic polymer networks, which contain water and electrolytes. Double network hydrogels have enhanced mechanical properties relative to single networks [1]. The presence of a secondary network that consists of a bioderived material, alginate, can dissipate energy through sacrificial bonds that break during elongation, while the first polymer network remains intact. The double network hydrogel can be toughened further by ionic crosslinking between carboxylic groups in alginate and di- or trivalent metal ions. With this interaction, hydrogel stiffness can be tuned locally. Previously, ionoprinting with Cu²⁺ was employed to increase stiffness locally to actuate and modify the stiffness of hydrogels [2]. However, this method can increase stiffness only at the surface of the gel. Here, we used metal redox reactions between Bi particles and Ag⁺ to tune hydrogel stiffness locally. By controlling particle distribution and reaction time, we control the properties of the gel. The gel is multifunctional since it has both tunable mechanical and anti-bacterial properties arising from the ions.
We fabricated polyacrylamide/alginate double network hydrogels embedded with Bi particles. The hydrogels were dipped into AgNO₃ solution to initiate a reaction between Bi and Ag⁺. Bi particles are ionized into Bi³⁺, which crosslinks with carboxylic groups (COO^-) of the alginate. The crosslinking bonds stiffen the hydrogels, leading to an increase of the dynamic modulus by two-fold. The local strain level within the hydrogel was mapped using digital image correlation (DIC). By correlating the particle distribution with the local strain level, we confirmed Bi³⁺ produced on the Bi particle surfaces caused a heterogeneous local strain level in the gel. Tuning the dipping time in AgNO₃ solution leads to the gradient of modulus in the hydrogels. We mapped dynamic gradient modulus by cutting the hydrogels into different parts, which were measured separately. Modulus gradient hydrogels from the reactions can act as a bridge between soft and hard materials. This modulus gradient was similar to that of cartilage. With Bi particles settling in the pre-gel solution, the hydrogel was found to bend toward the side with high particle density due to the difference in modulus within the hydrogels. As an application, we confirmed Ag particles generated by the redox reaction could be used as antibacterial agents. Bacterial inhibition zone increased with increasing concentration of AgNO₃.

References
[1] Jeong-Yun Sun, Xuanhe Zhao, Widusha R. K. Illeperuma, Ovijit Chaudhuri, Kyu Hwan Oh, David J. Mooney, Joost J. Vlassak, and Zhigang Suo (2012). Highly Stretchable and Tough Hydrogels. Nature, 489: 133–136.
[2] Etienne Palleau, Daniel Morales, Michael D. Dickey, and Orlin D. Velev (2013). Reversible Patterning and Actuation of Hydrogels by Electrically Assisted Ionoprinting. Nat. Commun., 4: 2257.

The structural complexity and multifunctionality of composite biomaterials and biomineralized particles arises from the hierarchical ordering of inorganic building blocks over multiple scales. While empirical observations of complex nanoassemblies are abundant, physicochemical mechanisms leading to their geometrical complexity are still puzzling, especially for non-uniformly sized components. Here we report the assembly of hierarchically organized particles (HOPs) with twisted spikes and other morphologies from polydisperse Au-Cys nanoplatelets [1]. The complexity of Au-Cys HOPs is higher than biological counterparts or other complex particles as enumerated by graph theory (GT). Complexity Index (CI) and other GT parameters can be applied to a variety of different nanoscale materials to assess their structural organization. As the result of this analysis, we determined that intricate organization of HOPs emerges from competing chirality-dependent assembly restrictions that render assembly pathways primarily dependent on nanoparticle symmetry rather than size. These findings and HOPs phase diagrams open a pathway to a large family of colloids with complex architectures and unusual chiroptical and chemical properties. Developed GT methods and new index-property relations were also applied to design complex biomimetic composites for energy and robotics applications [2].

References
[1] W. Jiang, Z.-B. Qu, P. Kumar, D. Vecchio, Y. Wang, Y. Ma, J. H. Bahng, K.Bernardino, W. R. Gomes, F. M. Colombari, A. Lozada-Blanco, M. Veksler, E. Marino, A. Simon, C. Murray, S. Ricardo Muniz, A. F. de Moura, N. A. Kotov, Emergence of Complexity in Hierarchically Organized Chiral Particles, Science, 2020, 368, 6491, 642-648.
[2] Wang, M.; Vecchio, D.; Wang, C.; Emre, A.; Xiao, X.; Jiang, Z.; Bogdan, P.; Huang, Y.; Kotov, N. A. Biomorphic Structural Batteries for Robotics. Sci. Robot. 2020, 5 (45), eaba1912. https://doi.org/10.1126/scirobotics.aba1912.
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As warm-blooded mammals, the human body is constantly maintaining its core temperature against ambient fluctuation. For extreme temperatures or suboptimal physiological conditions, it may result in serious health issues. For example, at low ambient temperature, blood pressure and viscosity may increase, which are strongly correlated with cardiovascular diseases. This is the reason why cardiovascular diseases often have seasonal dependence. On the other hand, at high ambient temperature, excessive sweating can cause electrolyte imbalance or even heat stroke. Commercial body heating/cooling devices, such as Joule heating or Peltier cooling, are prohibitively energy-intensive or bulky for continuous use. In this talk, I will demonstrate our recent research progress in energy-efficient adaptive textiles that can adjust the heat balance via controlling the heat transfer coefficients rather than actively supplying power. First, I will introduce the wearable varied emittance (WeaVE) device that modulates the human body radiative heat transfer to accomplish thermoregulation with ultralow energy consumption. The electrochemically-operated WeaVE can switch the mid-IR emissivity by more than 40% within less than one minute. Kirigami design enables superior stretchability and conformality when applying to the human body. By communicating with ambient temperature and humidity sensors, the WeaVE can autonomously stabilize the body heat loss to accomplish thermal comfort in a natural and continuous manner. Second, I will demonstrate the multimodal moisture-responsive wearable device that modulates both radiative and convective heat transfer to accomplish large tunability. In both projects, I will explain how the judicious choice of materials and design, based on fundamental physical principles, can directly result in high performances in multiple aspects.

With a fast-growing interest in flexible and stretchable soft electronic devices (e.g. electronic skin, soft robotics, implantable devices, tactile sensors, wearable electronics, smart textiles, etc.), there has been an increasing demand for similar sustainable power sources. Commonly used power sources such as batteries are rigid and require frequent recharging. Rigidity inhibits the stretchability/wearability, limiting the usage of the device, and frequent recharging limits the operating range of the device. Moreover, implantable devices that utilize batteries exhibit a limited life-time and require additional surgeries to replace the battery thereby presenting a huge risk to the users. To address these limitations, efforts have been made to develop soft energy harvesters that can convert human motion/ambient mechanical energy to electrical energy. Energy harvesting can eliminate the need for frequent recharging, which allows the device to operate in a tether-free manner. Furthermore, users can generate mechanical energy at their will, which enables the harvesters to power the devices in remote settings. Triboelectric and piezoelectric generators are prominently used harvesters for converting mechanical energy to electrical energy. Triboelectric harvesters have gained great popularity due to their relatively straightforward fabrication. They induce electrical current based on contact electrification (rubbing two surfaces) and electrostatic induction (oscillating the distance between charged surfaces). Triboelectric harvesters generate high voltages and low currents. They require moisture-free environments and rubbing components to enable contact electrification. Piezoelectric generators, in contrast, generate electricity due to inherent polarization when subjected to mechanical deformation. However, they require extensive fabrication techniques and suffer loss in energy conversion when converted to flexible/stretchable devices, as their fundamental materials are intrinsically hard and brittle. We report a new approach to energy harvesting that utilizes liquid metals. These devices generate about 0.2 mW m^-2 by harnessing energy from mechanical motion. We have characterized the behavior of these devices as a function of a variety of parameters including material properties (chemical composition), design parameters (organization and volume of each component), and physical deformation (amplitude and frequency of the mechanical energy input). We have developed a physics-based model to predict device performance. The devices behave as expected and the response of the devices to deformation matches the model. The liquid metal-based soft device is stretchable and can generate an electrical signal when deformed, which may be useful for energy harvesting as well as wearable self-powered sensors. These devices can be used to monitor human activities thereby find many applications in wearable electronics, dynamic tactile surfaces, healthcare systems like rehabilitation and prosthetics.

Stimuli-responsive materials have proliferated in recent years due to their potential for a broad range of applications including switching, actuating, sensing, energy harvesting, and soft biorobotics and wearable devices. Herein we describe a bilayer system that can generate programmable deformation reversibly in response to photothermal stimuli (e.g. low-energy near infrared-induced photothermal heating) or heating a few degrees above room temperature.

The bilayer film consists of a polyarylamide layer containing a small amount of crosslinking dibenzocycloocta-1,5-diene (DBCOD) and is covalently bonded to a sheet of aligned carbon nanotubes (CNTs). Our design takes advantage of self-assembly of DBCOD units along the CNT longitudinal direction to generate directional thermal contraction upon the DBCOD conformational change. The coefficient of thermal expansion of CNTs is near zero while the polymer layer exhibits a large negative thermal expansion. This mismatch results in substantial thermal stress and thus large deflection of the bilayer with small changes in temperature. We have demonstrated a deflection of 6.5 mm per cm by heating from 20 to 60 °C. This deformation can be pre-programmed with the selection of CNT/cut pattern. Additionally, the bilayer inherits excellent cycle stability, moving as a single unit without separation due to the covalent bonds between polymer and CNT layers. This actuator offers thermal to mechanical energy conversion at an efficiency at least on par with state of the art of mechanoresponsive polymer systems. Finally, we have also demonstrated that electricity can be generated by photo- or thermal fluctuations by coupling the actuation to piezoelectric effects in a trilayer device.

Such a low-energy stimulus induced high-efficiency system paves pathways to develop remotely controlled actuators, low-energy driven artificial fingers as well as thermal-to-electric energy harvesting.

Compliant mechanisms have attracted tremendous interest for application in fields such as consumer products, soft robotics, and even animatronics. The fundamental design principle is the non-linear bending behavior of beams, which for non-trivial geometry and large deformations cannot be solved for analytically by using classical Euler-Bernoulli and Timoshenko-based equations. Therefore models are demanded that can predict said behavior through numerical solvers, or even analytically. The improvement of computing performance and more sophisticated software enabled such models which have incidentally become an integral part in the design process.

Examples are the Pseudo-Rigid-Body (PRB)(1) model and the Beam Constraint Model (BCM)(2). Here the Chained Beam Constraint Model (CBCM)(3), a development on the BCM, was applied, which to a high degree of accuracy can predict the complex bending behaviour of thin beams. This model is applied to a selection of beam shapes and were further developed as 3D-structures. These were manufactured using a shape-memory polymer (SMP) which when programmed through a counter-mold could add additional functionalities such as the switching of bi-stability of a given design or the amplification of deformation. We explored a design and fabrication scheme from conception of compliant mechanisms through the application of the CBCM, the design of molds to create demonstrators out of SMP and later the evaluation of functionalities through mechanical testing.

The modelling was realized through Python programming and implementing its non-linear solvers from the SciPy package to solve the governing equations of the CBCM. 3D-printed master molds were created to cast the polydimethylsiloxane (PDMS) molds. Consequently, demonstrators were created by casting poly[ethylene-co(vinyl acetate)] (PEVA) as a SMP in the PDMS molds.
This study demonstrates how one can conceptualize design and forecast complex bending behaviours using computational tools, and in turn apply SMPs such as PEVA to further amplify or modulate functionalities. This study could be seen as a step to create novel manufacturing schemes for the use in growing fields such as soft robotics.

1. H. Larry L., in 21st Century Kinematics, J. M. McCarthy, Ed. (Springer, 2013), chap. Chapter 7 - Compliant Mechanisms.
2. S. Awtar, S. Sen, A generalized constraint model for two-dimensional beam flexures: nonlinear load-displacement formulation. Journal of Mechanical Design 132, (2010).
3. G. Chen, F. Ma, G. Hao, W. Zhu, Modeling Large Deflections of Initially Curved Beams in Compliant Mechanisms Using Chained Beam Constraint Model. Journal of Mechanisms and Robotics 11, (2019).

We generated electroactive hydrogel light-guiding structures and demonstrated that their orientation, motion and - thereby the direction of their light output - can be precisely and remotely controlled through external electrical fields. This was achieved with a range of architectures including planar slab waveguides, individual and small arrays of cylindrical waveguides as well as long-range waveguide lattices (> 10 000 cm^-2). Waveguides were induced in electroactive photopolymerizable hydrogels by self-trapped visible beams from light-emitting diodes (LEDs). These nonlinear waves are elicited when photo-induced refractive index changes counter the natural divergence of light beams launched into the hydrogels. Because the refractive index changes are irreversible, self-trapped beams permanently inscribe cylindrical waveguides along their paths. Such structures would be impossible to fabricate through conventional photolithographic methods. Because they are electroactive, we could apply and vary external electric fields to dynamically control the bending, angular orientation, and rotation (up to 360°) of these pliant light-guiding structures.

The development of a practical gas sensor is of great interest for monitoring toxic
and non-toxic gases that might endanger our safety and wellbeing in different
settings. Hereby we present a practical gas sensor based on hydrogenated
graphene for CO₂ monitoring. Hydrogenated graphene was synthesized by a
single-step method directly onto an Au-pattern insulating substrate. Hydrogenated
graphene was then characterized using RAMAN spectroscopy, X-ray photoelectron
spectroscopy (XPS), and X-ray Diffraction (XRD). The materials interaction with CO₂ was systematically study at different PPM to determine our sensor’s detection limits. Some preliminary research reveals that the hydrogenated graphene-based sensor is capable of sensing CO₂ at the mid-ppm-level.

Hydrogenated graphene has been of great interest for the scientific community due to properties like ferromagnetism that are not usually present in graphene; requiring subsequent functionalization after synthesis to obtain them. Hereby, we present a novel method for synthesizing hydrogenated graphene via a single-step process. Hydrogenated graphene was characterized primarily by Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction spectroscopy (XRD) and Physical Properties measurement system (PPMS). Our Raman spectra confirms the presence of the 2930 cm-1peak associated with hydrogen functionalization, while the PPMS reveals the strongest ferromagnetism at room-temperature of a carbon-based material with a curie temperature higher than 350 K. These results are strong evidence of hydrogenated graphene’s capabilities for its implementation to spintronics & memory applications.

We have generated slim (2 mm to 3 mm thick), soft polymer films inscribed with Waveguide Encoded Lattices which - like arthropodal compound eyes - have enhanced panoramic field of view (FOV) and multiple optical functionalities. [1-3] These include an exceptionally high density of light harvesting waveguide units (>15,000 cm^-2), excellent imaging resolution, infinite depth of field and operability at all visible wavelengths including broad incandescent spectra (like sunlight) and discrete spectral ranges of lasers and LEDs. WELs transmit, focus and invert images without need for bulky optics and conversely, control the shape and trajectory of light beams. Different from the curved architectures of compound eyes, WELs are plane-faced, optically flat, slim films, which due to their translational symmetry could be extended over large areas (e.g. through roll-to-roll manufacturing) and due to their flexibility, integrated with ease into technologies such as LCDs, solar cells, cameras and smart phones.

1. Hosein, I. D.; Lin, H.; Ponte, M. R.; Basker, D. K.; Brook, M. A.; Saravanamuttu, K. Adv. Funct. Mater. 2017, 27, 1–11.
2. Lin, H.; Hosein, I. D.; Benincasa, K. A.; Saravanamuttu, K. Adv. Opt. Mater. 2019, 7, 1801091 (1-9).
3. Lin, H., Benincasa, K., Fradin, C., Saravanamuttu, K. Adv. Opt. Mater. 2019, 7, 1801487 (1-9).

The development of polymeric electronic skins (e-skins) enables applications such as telehealthcare, human-machine interfaces, prosthesis, and robotic perceptions.^1,2 The reliable sensing and monitoring require e-skin sensors to respond to mechanical stimuli sensitively and accurately with minimal data variation between contact cycles. However, hysteresis is always a trade-off with sensitivity in polymer-based sensors to limit their reliability. We propose a soft indentation process to generate annular metallic cracks on three-dimensional (3D) micro-elastomers.³ The cracking mechanism is explored via theoretical analysis and numerical simulations. Good control of crack morphology on elastomers enables a piezoresistive e-skin sensor (TRACE) with high tactile sensitivity yet a large reduction of hysteresis (2.99 ± 1.37 %). The assembled TRACE sensors array achieves precise monitoring of pulse waveforms and continuous track of pulse wave velocity (PWV). It also enables robotic perceptions on surface textures with improved reliability compared to large-hysteresis e-skin sensors.



References:
1. Ray, T. R. et al. Bio-integrated wearable systems: A comprehensive review. Chem. Rev. 119, 5461–5533 (2019).
2. Yang, W., Hon, M., Yao, H. & Tee, B. C. K. An Atlas for Large-Area Electronic Skins. 3840, (Cambridge University Press, 2020).
3. Yao, H. et al. Near–hysteresis-free soft tactile electronic skins for wearables and reliable machine learning. Proc. Natl. Acad. Sci. 117, 25352–25359 (2020).

Nuclear shape irregularities, especially subnuclear features like invagination and folds on the nuclear envelope, are commonly found in metastatic cancer cells. Assessment of nuclear irregularities, i.e. nuclear grading, has long been used to diagnose and grade cancer in clinical practice. However, the current evaluation of cancer nuclear morphology is mainly through human-based inspection of microscopy images, and largely relies on the experience and judgment of individual pathologist. Inevitably, it suffers from low consistency and reproducibility. Though the reproducibility and precision can be enhanced with the aid of artificial intelligence, the most available algorithm for automatic assessment only uses the whole-nucleus morphological parameters for grading. The subnuclear and nanoscale features are often overlooked due to the randomness of their distribution and thus difficult to locate and segment for quantitative analysis. In this work, we introduced vertically aligned nanopillar arrays with defined geometry and pattern to enable effective guidance on subnuclear abnormal features in cancer cells. Taking breast cancer cells as a model, we found that the low malignant MCF7 cells generated isotropic subnuclear deformation feature on nanopillars, while the high malignant MDA-MB-231 cells exhibited anisotropic patterns with the subnuclear features aligned with nanopillar arrays. By quantitative assessment of the isotropy of subnuclear features guided on nanopillars, differentiation of cancer cells in high and low malignancies was successfully achieved. We further demonstrated that the heterogeneity in a population of cancer cells can be quantitatively mapped. In addition, the therapeutic potential of drugs specifically targeting metastatic cells was also evaluated effectively using nanopillar arrays. We envision that the nanopillar-based nuclear grading will provide a new tool to improve both cancer diagnosis and anti-cancer drug screening.

Soft magnetic materials have shown promise in diverse applications due to their fast response, remote actuation, and large penetration range for various conditions. Those are usually composed of hard magnetic particles or discrete magnets incorporated in a base material, and the actuation of these materials arises from spatiotemporal interactions between the applied magnetic field, environment, and programmed magnetization. However, a limitation arises because actuation is constrained by the programmed magnetization profile because magnetic fillers are usually physically confined in the soft matrix after fabrication is completed. Here, we propose a new soft material composite, the ferromagnetic domain pattern of which can be reprogrammed without changing intrinsic magnetic properties of embedded magnetic particles or the molecular properties of the base material.

Our reprogrammable magnetic composite is composed of spatially separated magnetic microspheres embedded in the elastomeric matrix (Ecoflex 00-30). Each magnetic microsphere consists of neodymium-iron-boron (NdFeB) microparticles, with an average size of 5 μm, encapsulated in oligomeric polyethylene glycol (PEG). The magnetization profile of our composite can be easily reprogrammed using the phase transition of oligomeric polyethylene glycol which is encapsulating the magnetic microparticles.

If the encapsulating polymer changes from solid to liquid, the magnetic particles can freely move or rotate in the microspheres along the external magnetic field. As the material cools, the encapsulating polymer solidifies and it fixes the reprogrammed magnetic particle alignment. To verify the re-programmability of the magnetic composite, we measure the magnetic moment density in samples at various angles relative to the external magnetic field applied by the vibrating sample magnetometer.

As an illustrative example to demonstrate the ability to reprogram the magnetization pattern of our composite, we demonstrate several reconfigurable soft magnetic actuators. The actuators can be classified into three types; (1) complex transformations of a continuous magnetic membrane are realized as a fully functional origami. (2) various transformations of a magnetic origami sheet with discrete magnetic layers on a flexible substrate layer are demonstrated by utilizing our magnetic composite as a functional layer. (3) in situ reprogramming scenario is proposed by adding a conductive heating layer to the reprogrammable magnetic layer.

We expect that this soft magnetic composite with a reprogrammable magnetization pattern could be used to make reconfigurable soft material systems for a wide range of applications including biomedical engineering, flexible electronics, and soft robotics.

From so-called “smartwatches” to implantable pacemakers, wearable/implantable mechanosensors have been regarded as essentials and promising potentials for biomedical applications and even for raising the quality of daily life. Crack based mechanosensors have risen promising potentials for communicating with the human, so that they have been developed in the aspect of sensitivity, stretchability, durability, visualizing, and multi-functionality for few years. While valuable mechanical physiology is composed of complex stimuli such as strain, pressure, and torsion, however, due to the geometrical and mechanical properties of the cracks, the sensitivity of the crack based sensors is limited to the strain stimulus. Here, we describe the modified inner structures for transforming pressure to the plane strain, enabling the highly sensitive ability to the pressure. As a given pressure, the strain can be amplified over 3 times, which is a big advantage for the strain-sensitive mechanosensors. Attributed to the structure, the crack based sensor can detect the pressure up to 10 MPa with a 3x10^6/Pa sensitivity, which is more than 100 times sensitive than the normal crack based sensors. We found the advantages of the biomedical application which has complex strain and pressure, and especially, the jaw rehabilitation devices for the neck and head cancer patients. Despite the 3D printed supporters of the device, the sensor array can successfully discriminate each position and each pressure of the rehabilitating bite trials. The structures can be huge potentials for the biomedical physiology detection for the electronics.

Internal friction is essential for nearly all solids to dissipate kinetic energy through internal mechanisms. The pioneering analyses by Zener (Phys. Rev. 60 (1941) 906-908) and Kê (Phys. Rev. 71 (1947) 533-546) demonstrated the existence of a single friction peak in the loss modulus spectrum of polycrystalline solids, which is attributed to viscous sliding in grain boundaries. In this study, we establish a continuum model coupled elastic deformation, viscous creep and diffusion in grain boundaries and reveal the existence of a second loss modulus peak resulted from viscous deformation within grain boundaries [1]. The corresponding two frequencies, when internal dissipation reaches its local maximum, depend on grain size d: the lower frequency one is proportional to d^-3, and the higher frequency one is proportional to d^-1. The underlying deformation mechanisms accounting for the two peaks and the scaling laws are identified. The inherent scaling laws are related to the combination and architecture of the dissipative soft grain boundary layers and hard grains in polycrystalline solids. The effects of local elasticity and diffusion in grain boundaries on the loss modulus spectrum are examined. The findings can be applied to granular and porous materials, and complex rheology in geosciences, where internal dissipation is momentous for waves and seismic activities. The unifying picture revealed based on the combination of hard grains and soft grain boundary layers could be employed to many heterogeneous systems for their design for high damping performance.

Reference
[1] C Duan, Y Wei, Acta Materialia, 201(2020), 350-363. https://doi.org/10.1016/j.actamat.2020.10.004.

Accurate prediction of alkane phase transitions involving solids are needed to prevent catastrophic pipeline blockages, improve lubrication formulations, smart insulation and energy storage, and bring fundamental understanding to processes such as artificial morphogenesis. Solid-solid phase transitions are rarely modeled due to difficulties in long timescales for nucleation and dynamics, as well as lack or order descriptors. We report on the applicability, accuracy and computational performance of seven representative molecular dynamics models (TraPPE, PYS, CHARMM36, L-OPLS, COMPASS, Williams, and the newly optimized Williams 7B).

Liquid-liquid phase separation (LLPS) of proteinaceous materials and crowding agents is emerging as a significant model facilitating the understanding of protein functions and malfunctions, which can find healthcare-related applications in the understanding, diagnosis, and treatment of diseases. In this presentation, we will report the construction, characterisation, and application of multiphase-based all-aqueous materials generated from the concept and mechanism of LLPS of extracellular proteins and crowding agents using microfluidic devices. Smart multiphase-based protein microgels, dynamic phase-separated protein microgels, and spatially inhomogeneous one-phase protein microgels will be demonstrated. The demixed states of proteins in crowding agents highlight the LLPS of the all-aqueous material systems. We will report the LLPS findings and explanations in micron-scaled compartments containing multiphase-based materials, and the LLPS of extracellular proteins and their surrounding environments at a larger scale. As a control study, spatially inhomogeneous one-phase protein microgels will be displayed. The possible mechanisms, fabrication techniques, applications, as well as the opportunities and challenges of the multiphase-based material systems will be presented. Microfluidic platforms can open up new routes for the advanced processing and precise controlling of biocompatible and bioactive materials at the microscale, in a fashion where conventional manufacturing was thought to be impossible. The microgels are promising models for temperature sensing, soft robots, as well as cell-culture scaffolds, which can promote the development of bioengineering and biophysics.

References:
Xu Y, et al. doi.org/10.1101/2020.12.08.416867, 2020. Submitted.
Xu Y, et al. arXiv preprint arXiv:2009.13413, 2020. Submitted.
Xu Y, et al. Small 16 (32), 2000432, 2020.

In the past few years, there has been a tremendous amount of scientific activity in the field of controlled release of volatile antimicrobial agents such as Thymol and Carvacrol, which have shown high antimicrobial activity and suitability for food and agriculture applications from the regulatory point of view. However, the ability to develop efficient and cost-effective controlled release formulations for essential oils is still highly challenging. This research presents the development of an active polymeric sheet for plant protection. Thymol is a natural monoterpenoid phenol, which is isomeric with Carvacrol found in thyme oil and has beneficial properties. Thymol will be dissolved and encapsulated in the minor phase of toluene-in-water Pickering emulsion or in the major phase of an inverse emulsion. Polycaprolactone or polydimethylsiloxane will be dissolved in the toluene phase. The studied emulsions with the encapsulated Thymol will be impregnated in a non-woven polypropylene sheet. After evaporation of the water and toluene, polymeric structures with Thymol in their matrix will be formed inside the non-woven sheet. The activity of the resulting sheets along with their release properties will be compressively investigated for protecting these plants; rosemary, mint, and thyme through bioassay infectivity analysis. The system, which will be developed in this proposed research, is expected to exhibit high tunability in terms of the release rates and clear ability to encapsulate known amounts of Thymol in the resulting capsule. In addition, this Pickering emulsion-based formulation has shown clear feasibility to be impregnated in polypropylene non-woven sheet, which results in the formation of active silica/polyacrylate microspheres on the filaments of the sheet.

Molecular dynamics simulations are employed to study an unentangled poly(ethylene glycol) (PEG) - silica nanocomposite melt with emphasis on the structure of the adsorbed layer around the nanoparticle and the dynamics of adsorbed and free chains in the melt. The simulations reveal significant differences depending on the type of PEG terminal group assumed (hydroxyl versus methoxy) arising from the different ways that polymer chains adsorb on the silica surface in the two cases: hydroxyl-terminated PEG chains are adsorbed by their ends giving rise to a brush-like structure, whereas methoxy-terminated ones are adsorbed equally probably along their entire contour which results in better local packing of adsorbed segments. In both cases, the dominant mechanism for the strong adsorption of PEG chains onto silica is the development of hydrogen bonds. Hydroxyl-terminated chains, in particular, prefer to develop hydrogen bonds through their terminal OH groups implying the development of graft-like conformations. Additional information about the structure of the adsorbed layer on silica is provided through a detailed analysis of adsorbed chain conformations in terms of trains, loops and tails, revealing appreciable differences in the statistical properties (population per adsorbed chain and length) between the two nanocomposites examined. How the dense interfacial layer that develops in both cases affects the dynamic behavior of free chains, especially in the nanocomposite where PEG chains are terminated with hydroxyl groups, is also discussed. MD simulation results for the relative population of tails, trains and loops are used to parameterize a theoretical model based on the Rouse model¹ on the assumption of a set of mixing (additive) rules. Overall, the proposed analytical model seems to provide a very satisfactory description (qualitative and quantitative) of the simulation findings, which in turn are found to practically match experimentally measured data for the dynamic structure factor already reported in the literature^2,3 for the two types of nanocomposites addressed in our work under exactly the same conditions.

References

1) Rouse, P. Jr, J. Chem. Phys 21, 1272, 1953.
2) Glomann, T.; Hamm, A.; Allgaier, J.; Hübner, E. G.; Radulescu, A.; Farago, B.; Schneider, G. J., Soft Matter 9, 10559, 2013.
3) Glomann, T.; Schneider, G. J.; Allgaier, J.; Radulescu, A.; Lohstroh, W.; Farago, B.; Richter, D., Phys. Rev. Lett. 110, 178001, 2013.

This study presents highly stable oil-in-water Pickering emulsions with tunable droplet size, suitable for individual encapsulation of fungal spores. The emulsions were stabilized by amine-functionalized TiO₂ (titania) nanoparticles (NPs). These emulsions were utilized for the development of a novel formulation for biological pest control with significant UV protection capability. The droplet size, stability, and structure of the emulsions were investigated at different titania contents and oil/water phase ratios. Most of the emulsions remained stable for 6 months. The Pickering emulsions' structural properties have been characterized by confocal microscopy and high-resolution cryogenic scanning electron microscopy (cryo-HRSEM). The presence of the titania particles at the interface was confirmed by both confocal microscopy and cryo-HRSEM. Metarhizium brunneum Ma7 conidia were incorporated into the emulsions. The successful encapsulation of individual conidia in the oil droplets was confirmed by confocal microscopy. The individual encapsulation of the conidia in the emulsions was significantly improved by dispersing the conidia in a 0.02% Triton X-100 solution prior to emulsification. Individually encapsulated conidia in a titania-based o/w Pickering emulsion have exhibited high UV protection levels, demonstrating the feasibility of the developed formulation to exhibit significant protection against UV for biopesticides.

Our combinatorial multi-functional materials have demonstrated self-sensing, movement, and programmability. Recent advances have allowed us to grow shapes from the bottom up. Now we are advancing to the ability to start growing autonomous material robots bottom-up from single molecules. In this invited talk reporting results of large collaborations, we highlight tools we have developed, including molecular dynamics simulations, to predict liquid-solid and solid-solid phase transitions. These enable the growth of functional swimming robots that are powered by environmental fluctuations and manufacturing processes by artificial morphogenesis.

We have investigated the effects of different surfactants and their concentrations in the microencapsulation of TiO₂ of phase change thermochromic materials procured commercially. These off-the-shelf phase change materials involve Leuco dye particles that has demonstrated color change (black to white) behavior at the low transition temperatures of about 36 ^oC. The role of TiO₂ encapsulation is to protect these thermochromic particles from the degradation due to solar radiation. Various surfactants such as CTAB, SDBS, Hexadecanol and Tetradecanol at different concentrations have been used to synthesize the TiO₂ microencapsulated phase change thermochromic particles. A number of physico-chemical characterizations such as XRD, SEM, EDS, FTIR and TGA/DSC have been carried out to understand the surface morphology, composition and thermal behavior of TiO₂ microencapsulated phase change thermochromic materials for thermal storage applications.

Fiber-reinforced composites containing epoxy-matrix are one of the key structural materials used in designing high-performance aircraft, automobiles, and athletic equipment. Several properties, including the deformation characteristics, thermal stability, fluid sensitivity, and interfacial properties, of these composite materials are dependent on the polymer matrix. Thus, understanding the matrix chemistry would allow us to improve their performance by tailoring the chemical structure. For example, using multifunctional epoxides has shown to augment the thermophysical and mechanical properties of such composite materials. Using computational techniques, we can enumerate large combinations of epoxides and amines and evaluate their properties. To efficiently model such polymer systems, we have built robust workflows using both quantum mechanics (QM) and molecular dynamics (MD). The workflows employ automated QM tools to identify key reaction steps and their kinetics involved in polymer synthesis and matrix-crosslinking. In this work, we have screened the key reaction barriers of amine/epoxy/accelerant combinations yielding 252 reactive barriers. The kinetics information for a subset of these epoxy-amine systems was then cast into our crosslinking workflows to obtain realistic in-silico systems. Subsequently, we computed the structural, thermophysical, mechanical, and water uptake properties of these systems. We demonstrate that by combining our QM tools with our accurate forcefield and GPU accelerated MD code, we can generate physically meaningful morphologies and efficiently study the properties of crosslinked polymer systems.

Alternating layers originated from natural systems can display high-performance mechanical, thermal, electrical, optical, and other functional properties. We have developed new manufacturing that can blend polymers and nanoparticles from different channels and selectively place them in alternating layers. These layers contain nanoparticles confined within a phase and bond each of these phases via polymer phases. This structure is similar to the brick-and-mortar structure in nacre, namely, the stiff and rigid calcium carbonate and soft polymer materials. The interface formation is critical in forming superior properties. We studied the fabricated filaments, thin films, and laminates, thus confirming the layered structures' scalability. Our results also validated the high reinforcement efficiency of carbon nanotubes and nanofibers. We will also study how the particle loading, particle morphology, and interfacial interactions influence their electrical and other properties.

A sealant is required for the Solid Oxide Fuel Cell (SOFC) to maintain hermeticity at high operating temperatures, keep fuel and oxidant from mixing, and avoid shorting of the cell stack. Glass and Glass-Ceramic materials are widely used as a sealant since their properties can be tailored to meet the stringent requirements of SOFC stack. This study used a self-repairable glass for crack healing kinetics and independent measurement of glass viscosity. The cracks on the glass surface are created using a Vickers’s indenter to achieve a well-defined crack geometry, and then the glass is exposed to elevated temperatures for different length of time to study the crack-healing kinetics. The crack-healing kinetics is compared with the predictions of our theoretical model and found to be in good agreement. In addition, glass viscosity is extracted from the healing kinetics and compared with the independent measurement of viscosity from dilatometric and sintering data to further validate the crack-healing theoretical model. These results will be presented and discussed.

Development of biological sensors that track basal and during-duty changes in biomarker levels can provide vital information for monitoring personnel workload and implementing remediation strategies. While biological systems (i.e. bacteria or yeast) have been proven to be robust systems for engineering sensing pathways to produce modular, tunable, and dynamic responses, the discovery or engineering of novel biorecognition elements (BREs) is a time consuming and tedious challenge. Aptamers, on the other hand, provide necessary selectivity and sensitivity. However, they do not provide easy means to capture a measurable signal. Therefore, we introduce a platform that combines Biomarker-Responsive 3D Aptamer-based Structures with Biological Cell-based Reporters to develop multiplexed sensing platform for rapid tracking of multiple stress- and fatigue-related biomarkers. The platform’s design combines DNA-based microcapsules with a well-established cell-based biological reporter, S. cerevisiae. The activation of the biosensor platform is based on a step-wise mechanism involving release of encapsulated chemical cargo upon ligand binding to an aptamer-based structure, followed by the activation of a yeast-based biosensor by released cargo. The large dynamic range exhibited by both sensing units makes them ideal for use in pseudo two-component systems, where diverse DNA aptamers can be reliably linked to a common whole-cell biosensor output without need for additional reengineering of the sensor with each novel analyte and/or reporter. Moreover, this design can include the activation of different genetic pathways to provide different type of readout outputs, including optical or electrochemical sensing. Alternatively, the genetic output can be linked to synthesizing active compounds for remediation purposes. Hence, by combining the best features of the biological systems and DNA structures, we aim to create a suitable multiplexed platform for monitoring of different analytes of interest and mitigation of performance degrading effects.

With the exponential advance of industries in the world comes the great concern with the possible contaminants generated in industrial processes and the health of the population. Clean and contaminant-free air is essential for the well-being of the population and environmental preservation. In this sense, the need to detect toxic and harmful volatile organic compounds (VOCs) generated in industrial processes and environments is essential, requiring a system or a device for this task, with precision and low detection limits [1–4].
In addition to the harmful problems on human health caused by toxic VOCs, recent analyses of exhaled air have demonstrated the association of diseases and VOCs [5–9]. Some compounds have proven to be efficient disease biomarkers, such as diabetes [10] and lung cancer [11].
Developing a device or material to detect volatile organic compounds (VOC) is no longer a challenge, despite its great interest. The difficulty is linked to developing a material that does not suffer from interferences, such as from humidity, other gases, or volatiles present in the analyzes. In this sense, we present a new way to modify zinc oxide (ZnO) hollow spheres with nickel (II) sulfide (NiS) nanosheets, a barely studied material in the literature, to increase the butanone selectivity and to reduce the negative effect of humidity in the final response of the sensor.
Under dry conditions, pure ZnO hollow sphere presents the best sensing response of 705.3 to 100 ppm of butanone followed by the 5%-NiS-ZnO heterostructure with a response of 123.8. However, the selectivity of 5%-NiS-ZnO improves and reaches a value of 12.92, which is more than four times higher than the selectivity of pure ZnO (3.12). Furthermore, the performance under humidity atmospheres shows that NiS heterostructures suffer less effect of the humidity. The responses to 100 ppm of butanone under 55% of relative humidity were 40.2 and 23.7 for 5%-NiS-ZnO and pure ZnO, respectively. Therefore, the developed butanone sensor demonstrated excellent response, selectivity, and a promising possibility for its practical use in sensing devices under real conditions of humidity.

Acknowledgments
This research was funded by São Paulo Research Foundation (FAPESP; grants 2018/00033-0, 2016/25267-8, 2017/01267-1).

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The scientific analysis of 2600-year-old archaeological and ethnographic materials has led to new perspectives on societies of past and present. Tangible cultural heritage objects are quite unlike materials prepared in known laboratory conditions because they were produced using traditional technologies in highly variable conditions. Particularly, In the Mediterranean region and Western Asia, the earliest man-made glasses in the Iron age were made from melting mixtures of natron (soda) and sand containing shell fragments (silica and lime), or ash derived from halophytic plants (soda and lime) and calcium-free sand or crushed quartzite (silica). Often knowledge about the source materials and technologies are lost, and they can only be reconstructed with careful scientific and forensic analyses. The present study focuses on two black glass beads decorated with either yellow or blue trails from 8^th to 7^th century BCE Sardis, glass beads that are exceptionally uncommon for this period, and on this site. A surface chemical analysis of the glass beads was made using high-resolution Imaging X-ray photoelectron spectroscopy (XPS) to understand the spatial relationships and historical evolution of chemical states inherent. We identified that the yellow glass is produced using lead stannate in which Tin in the glass is an opacifier. In the case of blue glass, copper and cobalt were the colorants. Exact chemical species identification of minerals and surface oxidation states of colorant metallic materials helps discriminate among source materials and thermodynamic processes, thereby permitting the reconstruction of technologies, provenance determination, and ancient trade routes. Funding is acknowledged NSF MRI: ECCS:1726636.