Symposium Organizers
Virginia L. Ferguson University of Colorado
John X.-J. Zhang The University of Texas-Austin
Conrad Stoldt University of Colorado
Carl P. Frick Abbott Vascular
OO1: Interface Science and Engineering I
Session Chairs
Karl Boehringer
John Zhang
Monday PM, November 26, 2007
Room 206 (Hynes)
9:00 AM - **OO1.1
Future Opportunities in Materials Design.
John Prater 1
1 Materials Science Division, US Army Research Office, Research Triangle Park, North Carolina, United States
Show Abstract9:30 AM - **OO1.2
Calcite Shape Modulation Through the Lattice Mismatch Between the Self-assembled Monolayer Template and the Nucleated Crystal Face.
Boaz Pokroy 1 , Joanna Aizenberg 1
1 School of Engineering and Applied Sciences , Harvard, Cambridge, Massachusetts, United States
Show AbstractThe nucleation and growth of crystals formed by organisms in the course of biomineralization are precisely controlled by the organism. This control is achieved by specific macromolecules, both in the form of templates and growth-modifying additives. The most abundant biogenic crystal is calcite – the most stable polymorph of calcium carbonate.Numerous studies have shown that the shape and morphology of synthetic calcite crystals can be modulated by the inorganic or organic solution additives. Hardly any studies have to date addressed the concept of controlling the shape of these crystals by organic interfaces. We show here that self-assembled monolayers (SAMs) that template calcite nucleation have two pronounced effects: in addition to inducing the highly oriented crystal growth (the phenomenon that we have extensively described in our previous studies), each SAM induces a clear modification of the calcite shape from its equilibrium rhombohedron. We show that this change in shape originates from the anisotropy of the lattice mismatch strains that develop between the nucleating crystal face and the organic SAM. We present a model that gives qualitative predictions for the shape of crystals grown on a variety of SAM substrates, as a function of the strain, and show that these shapes correlate extremely well with the experimental results. Our study provides a new, interesting concept – the influence of the mismatch strains at the organic/inorganic interfaces on the shape of the templated crystals. We believe that this mechanism might be utilized by organisms in the biomineralization process and that it can be further employed by man to finely tune the shapes of templated crystals by mismatch engineering at the organic/inorganic interface.
10:00 AM - OO1.3
Control of Calcite Crystallisation via Self-Assembled Monolayers.
Colin Freeman 1 , John Harding 1 , Dorothy Duffy 2
1 Engineering Materials, University of Sheffield, Sheffield United Kingdom, 2 Physics and Astronomy, University College London, London United Kingdom
Show AbstractMany organisms (including ourselves) grow minerals either internally (bones and teeth) or externally (shells). These organisms are able to exert high levels of control over crystal growth to produce high energy surfaces and complex shapes. This control is achieved by using large organic molecules, such as peptides and polysaccharides or arrays of molecules. Understanding and emulating these processes is a major challenge. Experimentally, selective surface growth is observed through using different organised molecular structures (e.g. self-assembled monolayers) that present a regular surface at which crystallisation can occur. By adjusting the packing density, ionisation, orientation and identity of the terminal functional groups in the self-assembled monolayers (SAMs) the expression of particular crystal faces can be controlled e.g [1].The mechanisms of selection are still not well understood and much debate remains over the contibutions of different factors [2-5]. Using theoretical models can provide us with the advantage of atomic scale visualisation and direct control over the environment. We have used potential based molecular dynamics to simulate a system that has been experimentally demonstrated to exert control over crystal growth [1,2]: the crystallisation of amorphous calcium carbonate on SAMs terminated with carboxylic acid groups. We have simulated the formation of a calcite nanoparticle at the SAM surface over the timescale of the simulations. Our calculations explore the effects of different monolayer properties: ionisation; head group orientation; charge density and epitaxy to the calcite crystal. The results demonstrate that ionisation of the monolayer is vital to stimulate crystallisation. However, we also report how the other factors contribute and can enhanceor inhibit the rate of crystallisation to differing degrees. When viewed together the results suggest that localised charge density effects may actually be hidden with epitaxial arguments and be the main control over the crystallisation of the calcite.[1] J. Aizenberg, A. J. Black, G. M. Whitesides, J. Am. Chem. Soc., 121, (1999), 4500[2] Y.-J. Han, J. Aizenberg, Angew. Chem. Int. Ed., 42, (2003, 3668[3] D. Volkmer, N. Mayr, M. Fricke, J. Chem. Soc., Dalton Trans., (2006), 4889[4] D. M. Duffy, J. H. Harding, Langmuir, 21, (2005), 3850[5] A. M. Travaille, L. Kaptijn, P. Verwer, B. Hulsken, J. A. A. W. Elemans, R. J. M. Nolte, H. van Kempen, J. Am. Chem. Soc, 125, (2003), 11571
10:15 AM - OO1.4
The Electrolytic Precipitation of Calcium Phosphate on Titanium Alloy.
Yen Pang Liu 1 , Fereshteh Ebrahimi 1
1 MSE, UF, Gainesville, Florida, United States
Show AbstractCalcium phosphate coatings are deposited on metallic medical implants for better bone fixation. Plasma-spraying is a commercially used technique for fabricating calcium phosphate coatings. However, thermally induced degradation of the substrate and thermal decomposition of the coating limit the application of this technique. Electrochemical technique has received much attention because it can be applied on irregular substrate shapes and under low temperatures. Calcium phosphate can be deposited in several crystal structures among which hydroxyapatite (HA) is the structure found in natural bones. The objective of this research was to establish electrodeposition parameters that result in formation of HA. We electrodeposited calcium phosphate on Ti6Al4V alloy substrate using different deposition parameters to investigate the precipitation process of calcium phosphate. The coatings were characterized for their crystal structure, composition, morphology, and crystal size. Consistent with previously reported results, increases in electrolyte temperature and current density promoted the formation of HA. Above 60oC the coating consisted of 100% HA and brushite was found at lower temperatures. Detailed analysis revealed the presence of a thin hydroxyapatite layer next to the substrate surface and under the brushite coating. Short time depositions confirmed that hydroxyapatite layer forms first before the nucleation of brushite can take place. In this presentation the mechanisms of crystallization of calcium phosphate using the electrodeposition technique will be discussed.
10:30 AM - **OO1.5
Neuroscience on a Chip.
Albert Folch 1
1 , University of Washington, Seattle, Washington, United States
Show AbstractCell culture methodology has remained basically unchanged for almost a century: it consists essentially of depositing a large population of cells on a homogeneous substrate and immersing the cells in a homogeneous fluid medium. This approach is becoming increasingly expensive to scale up and cannot mimic, neither in space nor in time, the rich biochemical and biophysical complexity of the cellular microenvironment, including the substrate, the surrounding cells, and the medium. In studies of nerve cells, the highly branched, multicellular tissue architecture makes it particularly challenging to mimic neuronal interactions in dissociated cell cultures.Microtechnology offers the attractive possibility of modulating the microenvironment of single cells and, for the same price, obtain data at high throughput for a small cost. Microfluidic devices and substrate micropatterning combined promise to play a key role for several reasons: 1) the dimensions of microchannels or patterns can be comparable to or smaller than a single cell; 2) the unique physicochemical behavior of liquids confined to microenvironments enables new strategies for delivering compounds to cells on a subcellular level; 3) the devices occupy a small footprint (thus more microscopy data can be acquired per image) and a small volume (thus they consume small quantities of precious/hazardous reagents, reducing the cost of operation/disposal); and 4) they can be mass-produced in low-cost, portable units. Not surprisingly, in recent years there has been an eruption of microfabricated implementations of a variety of traditional bioanalysis techniques. I will review the latest efforts of our laboratory in the development of cell-based microdevices for neurobiology studies, such as neuromuscular synaptogenesis, axon growth, and olfaction.
11:00 AM - OO1:Interfaces I
BREAK
11:30 AM - **OO1.6
Self-assembly from Nano to Milli Scales.
Karl Boehringer 1
1 Electrical Engineering, University of Washington, Seattle, Washington, United States
Show AbstractSelf-assembly is a well-established concept in physics, chemistry, and molecular biology. Only recently have researchers come to understand how self-assembly can be extended to engineered components, thus providing a promising alternative to conventional manufacturing. Instead of pick-and-place, positioning of components is accomplished by minimization of potential or interfacial energies. In this presentation, we discuss the principles and applications of engineered self-assembly, including 'programmable' self-assembly of silicon microcomponents and a 'protein laser printer.'
12:00 PM - OO1.7
Growth of Phospholipid Membrane Systems on Self-organized Semiconductor Templates.
Christian Teichert 1 , Gerald Trummer 1 , Daniel Pressl 1 , Gregor Hlawacek 1
1 Institute of Physics, University of Leoben, Austria, Leoben Austria
Show AbstractSpontaneous pattern formation during epitaxial growth or ion erosion of semiconductor wafers offers an elegant route towards large-area nanostructured surfaces. In the case of semiconductor heteroepitaxy strain relief leads to the formation of nanofaceted three-dimensional crystallites, which may self-organize into quasiperiodic arrays [1]. For low energy ion erosion of compound semiconductors, close-packed arrays of hemispherical dots with diameters between 30 nm - 50 nm are observed due to the interplay of sputtering and surface diffusion effects [2]. Since these self-organized nanostructure arrays cover the entire substrate, they can serve as large-area nanopatterned templates for subsequent deposition of all kinds of materials as was recently demonstrated for the deposition of magnetic thin films [3]. Here, we use atomic force microscopy (AFM) to study the formation of solid-supported lipid bilayers on a variety of nanofaceted self-organized SiGe films on Si(001) and ion eroded semiconductor surfaces in comparison to smooth Si(001) wafers. 1-Palmitoyl-2-Oleoyl-sn-Glycero-3-Phosphoethanolamine (POPE) and 1,2-Dipalmitoyl-sn-Glycero-3-Phosphocholine (DPPC) were used as model systems. The resulting film morphology and the change of surface roughness have been investigated as a function of initial roughness and morphology of the substrate. Phase imaging is used to distinguish between the soft lipid layers and the hard semiconductor substrate. On SiGe templates showing a dislocation network it was found that the ridge trench structures appearing at the surface guide the terrace edges of DPPC layers. When the lipid coverage is very low, 100 nm x 100 nm pits of {105} faceted SiGe film act as preferential deposition sites for lipid bilayers resulting in ordered arrays of small POPE islands. [1] C. Teichert, Phys. Rep. 365 (2002) 335.[2] S. Facsko, et. al., Science 285 (1999) 1551; T. Bobek, et al., Phys. Rev. B 68 (2003) 085324.[3] C. Teichert, Appl. Phys. A 76 (2003).
12:15 PM - OO1.8
Characterization of DNA Oligonucleotides Immobilized on Arsenic-terminated GaAs Surfaces (001).
Joon Hyuk Yang 1 , Lourdes Salamanca-Riba 1 , Mohamad Al-Sheikhly 1
1 Materials science and engineering, University of Maryland, College Park, Maryland, United States
Show AbstractImmobilization of DNA on a variety of substrates has recently become an important field because of its potential applications in molecular electronics, biosensors, and other diagnostic applications. We have successfully attached thiolated, single-stranded 8-bases, 28-base and 100-base DNA to As-terminated GaAs by means of covalent bonding between the sulfur and arsenic. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) with a fluid imaging cell were used to investigated the morphology of the oligos and their orientation with the surface of the GaAs as a function of length in the presence and absence of water and ionic strength of the solution. Some undesired bonding between N- and O- from the DNA and the As from the GaAs substrate also takes place even for the short ssDNA oligos. 6-mercapto-1-hexanol (MCH) was added enhance the brush-like structure of the probes via displacement reaction of the N-As and O-As bonding by the stronger/preferred S-As bonding. Our XPS results show that with increasing MCH concentration, the ratio of atomic concentration of S/As increases while the ratios of atomic concentration of N/As and O/As decrease. AFM results show a change in the surface morphology of the probes in the presence or absence of a good solvent such as water. In the absence of water the DNA oligos collapse forming relatively large size bundles of probes while in the presence of water the bundle size decreases and the oligos orient at a higher angle with the surface of the GaAs substrate. In addition, the effect of the ionic strength of the solution, which is controlled by [NaCl], to establish charge screening will be discussed. This work was supported by the Department of Energy-Innovations under the Nuclear Infrastructure and Education (INIE) program
12:30 PM - OO1.9
Dynamics of Chain Molecules Adsorbed on Lipid Bilayers.
Shashishekar Adiga 1 , Tapan Desai 2
1 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Material Sciences Department, Idaho National Laboratory, Idaho Falls, Idaho, United States
Show AbstractThe problem of translational diffusion of adsorbed chain molecules on phospholipid bilayers is not only of fundamental interest in biology but also in applied areas such as drug delivery and smart nanostructures. Experimental investigation of diffusion of DNA molecules adsorbed (dilute coverage) on supported lipid bilayers has showed that the center of mass diffusion coefficient scales with the degree of polymerization as D ~ N-1 [1]. Recently, simulations of a single adsorbed polymer chain at a solid-liquid interface have revealed that D ~ N-x, with x = 3/4 and 1 for smooth and corrugated surfaces, respectively [2]. These simulations substantiate that the diffusion of polymer adsorbed on lipid bilayer is similar to the corrugated surface case where friction of the adsorbed molecule dominates and hydrodynamic coupling between the monomers becomes less important. Here, coarse grained molecular dynamics simulations are performed to investigate the dynamics of polymer chains adsorbed on lipid bilayers. In particular, we will discuss the dynamics of polymer chains at bilayer-water interface with respect to scaling of diffusion coefficient, radius of gyration and relaxation time with degree of polymerization. We will also discuss the effect of polymer adsorption on diffusion of lipid molecules and investigate the phenomenon of slaved diffusion as reported by recent experiments [3].References[1] B. Maier and J. O. Radler, Phys. Rev. Lett. 82,1911 (1999).[2] T. G. Desai, P. Keblinski, S. K. Kumar and S. Granick, Phys. Rev. Lett. 98, 218301 (2007).[3] L. Zhang and S. Granick, Proc. Nat. Acad. Sci. 102, 1918 (2005).
12:45 PM - OO1.10
Effect of Ligand Density Gradient on the Adhesion Kinetics of Biological Membranes.
Alireza Sarvestani 1 , Esmaiel Jabbari 1
1 Chemical Engineering, University of South Carolina, Columbia, South Carolina, United States
Show AbstractThe attachment of cells to substrates is mediated by the interactions between the transmembrane receptors and surface ligands. The kinetics of adhesion is controlled by mobility of the receptors along the membrane and the concentration of ligands on the substrate. A mathematical model is proposed to study the effect of ligand density gradient on the adhesion kinetics of a single giant vesicle with mobile transmembrane receptors. A numerical method has been used to solve the corresponding diffusion equation with varying boundary condition due to the gradient in ligand density. The extent of adhesion, the speed of expansion at the front edge of adhesion zone, and distribution of the binders along the membrane are evaluated as a function of time. For a surface with increasing ligand concentration at a certain direction, it is shown that at each time point, the rate of expansion of adhesion zone is lower and the vesicle-substrate contact area is smaller than the corresponding values in the case of adhesion on a surface with uniform ligand density. In addition, it is shown that the displacement of the front edge of adhesion zone does not scale with the square root of the elapsed time, as observed in adhesion on substrates with uniform ligand concentration.
OO2: Biological Adhesion and Cohesion
Session Chairs
Virginia L. Ferguson
Daniel Fletcher
Monday PM, November 26, 2007
Room 206 (Hynes)
2:30 PM - **OO2.1
Lotus Effect: Roughness-Induced Superhydrophobic Surfaces.
Bharat Bhushan 1
1 MEMS/NEMS (NLIM), Ohio State University, Columbus, Ohio, United States
Show AbstractOne of the requirements for materials in micro/nanoscale applications is to decrease wetting, for water repellency and to facilitate fluid flow. When two bodies are brought in contact, any liquid present at the interface forms menisci, which increases adhesion/friction and the magnitude is dependent upon the contact angle. For non-wetting liquids, the contact angle with a rough surface is greater than with a flat surface and may approach 180o, as reported for leaves of water-repellent plants, such as lotus. These leaves are superhydrophobic due to the presence of micro/nanobumps and a thin wax film on the surface of the leaf. For fluid flow applications, superhydrophobic surfaces should have high contact angle and low contact angle hysteresis. It is desirable that surfaces form a stable composite interface with air pockets between solid and liquid[1]. We have fully characterized various leaf surfaces on the micro- and nanoscale and have attempted to separate out the effects of the micro- and nanobumps and the wax on the hydrophobicity[2]. The next logical step in realizing superhydrophobic surfaces that can be produced in the lab is to learn from the hydrophobic leaves and design surfaces based on that learning. We have explored the effect of micro- and nanopatterning on hydrophobicity, adhesion and friction for two different polymers with three types of patterned asperities, low aspect ratio, high aspect ratio, and lotus replica[3,4]. Scale dependence on adhesion and friction was also studied using AFM tips of various radii. We have also explored wetting properties for silicon surfaces patterned with pillars of two different diameters and heights with varying pitch values deposited with a hydrophobic coating[5]. We showed how static contact angles, hysteresis angle, and tilt angle vary with different pitch values on the patterned silicon surfaces. We studied the effect of droplet size on contact angle by using evaporation studies. A transition criterion was developed to predict when air pockets cease to exist. We have used an environmental scanning electron microscopy (ESEM) to study the effect of droplet size of about 20 μm radius on the contact angle.[1]Nosonovsky, M. and Bhushan, B., “Roughness Optimization for Biomimetic Superhydrophobic Surfaces,” Microsyst. Technol. 11, 535-549 (2005)[2]Bhushan, B. and Jung, Y. C., “Micro- and Nanoscale Characterization of Hydrophobic and Hydrophilic Leaf Surfaces,” Nanotechnology 17, 2758-2772 (2006)[3]Burton, Z. and Bhushan, B., “Hydrophobicity, Adhesion and Friction Properties of Nanopatterened Polymers and Scale Dependence for MEMS/NEMS,” Nano Letters 5, 1607-1613 (2005)[4]Jung, Y. C. and Bhushan, B., “Contact Angle, Adhesion and Friction Properties of Micro- and Nanopatterned Polymers for Superhydrophobicity,” Nanotechnology 17, 4970-4980 (2006)[5]Bhushan, B., Nosonovsky, M., and Jung, Y. C., “Towards Optimization of Patterned Superhydrophobic Surfaces,” J. R. Soc. Interf. 4, 643-648 (2007).
3:00 PM - OO2.2
Adhesion and Friction Force Coupling of Gecko Setal Arrays: Implications for Patterned Adhesive Surfaces.
Boxin Zhao 1 , Noshir Pesika 1 , Kenny Rosenberg 1 , Hongbo Zeng 1 , Yu Tian 1 2 , Patricia McGuiggan 1 , Kellar Autumn 3 , Jacob Israelachvili 1
1 Chemical Engineering Deaprtment and Materials Reserach Laboratory, Univerity of california, Santa Barbara, Santa Barbara, California, United States, 2 State Key Lab of Tribology, Department of Precision Instruments, Tsinghua University, Beijing China, 3 Department of Biology, Lewis & Clark College, Portland, Oregon, United States
Show AbstractThe extraordinary climbing ability of geckos is partly attributed to the fine structure of their toe pads which contain arrays consisting of thousands of micron-sized stalks (setae) which are in turn terminated by millions of finger-like pads (spatulae) having nano-scale dimensions. Using a Surface Forces Apparatus (SFA) we have investigated the dynamic sliding characteristics of setal arrays subjected to various loading, unloading, and shearing conditions at different angles. Setal arrays were glued onto silica substrates and, once installed into the SFA, brought towards a polymeric substrate surface, then sheared. Lateral shearing of the arrays was initiated along both the ‘gripping’ and ‘releasing’ directions of the setae on the foot pads. We find that the anisotropic microstructure of the setal arrays gives rise to quite different adhesive and tribological properties when sliding along these two directions, depending also on the angle that the setae subtend to the surface. Thus, dragging the setal arrays along the gripping direction leads to strong adhesion and friction forces (as required during contact and attachment), whereas when shearing along the releasing direction, both forces fall to almost zero (as required during rapid detachment). The results and analysis provide new insights into the biomechanics of adhesion and friction forces in animals, the coupling between these two forces, and the specialized structures that allow them to optimize these forces along different directions during movement. Our results also have practical implications for designing reversible and responsive adhesives, and articulated robotic mechanisms.
3:15 PM - OO2.3
Mechanics of Single-Cell Adhesion Strength Investigated Using a Microfluidic Device.
Kevin Christ 1 , Kyle Williamson 2 , Kristyn Masters 2 , Kevin Turner 1
1 Mechanical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractThe strength of cell-substrate adhesion is essential in physiological and disease processes as well as the development of implantable biomaterials. Despite the importance of cell adhesion, there remains a lack of understanding of the fundamental factors that determine the adhesion strength. In this work the role of cell shape and area, focal adhesion arrangement, loading rate, and extracellular matrix (ECM) protein concentration on the dynamic adhesion strength is investigated at the single-cell scale using a microfluidic adhesion assay and computational modeling. NIH 3T3 fibroblasts were sparsely seeded and cultured on collagen coated glass surfaces in a 50 micron high microchannel. Adhesion strength was measured by applying a monotonically increasing shear-stress, via a controlled flow, and monitoring individual cell detachment events using optical microscopy. The small dimensions of the microchannel allow high shear stresses to be achieved under laminar flow conditions, thus permitting controlled measurements of well-spread and strongly adhered cells. As the technique measures the adhesion of individual cells, the heterogeneity of adhesion strength in a population can be captured using this assay. The strengths of NIH 3T3 fibroblasts on collagen coated surfaces of varying density were measured using the microfluidc assay and the strength values were correlated to measurements of cell shape, area, ECM protein concentration, and focal adhesion arrangement. Results show that cell geometry plays a key role in the stress required for cell detachment and that increased cell spreading results in higher adhesion strengths. Furthermore, several distinct failure modes were observed when cells detach from the surface, and adhesion strength was found to correlate strongly with these failure modes. To interpret the experimentally observed trends, computational fluid dynamics models were used to predict the stress distribution on the cell induced by the flow and were coupled to a finite element simulation to estimate the loads at the cell-substrate interface at failure. These experimental and modeling results will enhance the understanding of the underlying mechanics of cell-substrate adhesion strength.
3:30 PM - OO2.4
Computational Analysis of Adhesion Forces during Indentation of Cells Using Atomic Force Microscopy.
Yong-Wei Zhang 1 , Chun-Yu Zhang 1
1 Materials Science and Engineering, National University of Singapore, Singapore Singapore
Show AbstractThe mechanical responses of a cell to external stimuli and the adhesion of a cell to another cell or to an extracellular matrix are of great importance in many biological processes and biotechnological applications. Indentation using atomic force microscopy (AFM) has been emerging as a powerful technique to study the biological and mechanical behavior of living cells due to its capability of characterizing both the mechanical response of cells and the cellular adhesion behavior as well. By pushing the AFM tip (or a microbead attached to the end of the cantilever) against the sample to a certain depth and then retracting it, a complete force-indentation curve can be collected. By using an appropriate indentation model, the mechanical properties of cells may be determined from the indentation loading curve and the adhesion behavior may be obtained from the unloading curveIn the present work, a kinetics model was developed to investigate the indentation of an Atomic Force Microscopic (AFM) tip on a cell with adhesion mediated by receptor-ligand binding. Parametric studies were conducted to investigate the effects of indentation rate, indentation depth, indenter size and the mechanical properties of cells on the adhesion force. It was found that the presence of the adhesion between the cell and AFM tip may affect both the loading curve and unloading curve, which may in turns change the extracted elastic modulus value using the conventional indentation models. It was found that an increase in the receptor-ligand reaction rate may lead to a transition from an exponential decay of the maximum adhesion force with the indentation rate to an exponential growth of the maximum adhesion force with the indentation rate. It was also shown that the maximum adhesion force was sensitive to the indenter size while its dependence on indentation depth was related to both the receptor-ligand reaction rate and the viscoelasticity of cells.
3:45 PM - OO2.5
Biofilm Cohesiveness Measurement Using a Novel Atomic ForceMicroscopy Methodology.
Greg Haugstad 1 , Francois Ahimou 2 3 , Michael Semmens 2 , Paige Novak 2
1 Institute of Technology Characterization Facility, University of Minnesota, Minneapolis, Minnesota, United States, 2 Department of Civil Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 3 , 3M Company, Maplewood, Minnesota, United States
Show AbstractBiofilms can be undesirable, as in those covering medical implants, and beneficial, such as when they are used for waste treatment. Because cohesive strength is a primary factor affecting the balance between growth and detachment, its quantification is essential in understanding, predicting, and modeling biofilm development. In this study, we developed a novel atomic force microscopy (AFM) method for reproducibly measuring, in situ, the cohesive energy levels of moist 1-day biofilms. The technique is performed with off-the-shelf instrumentation. The biofilm was grown from an undefined mixed culture taken from activated sludge. The volume of biofilm displaced and the corresponding frictional energy dissipated were determined as a function of biofilm depth, resulting in the calculation of the cohesive energy density. Our results showed that cohesive energy increased with biofilm depth, from 0.1 nJ/m3 to 2.0 nJ/m3. This observation was reproducible, with four different biofilms showing the same behavior. Cohesive energy also increased from when calcium (10 mM) was added to the reactor during biofilm cultivation. These results agree with previous reports on calcium increasing the cohesiveness of biofilms. In addition, the protein and polysaccharide concentrations within the biofilm depths, as well as the dissolved oxygen (DO) concentration profiles within the biofilms, were measured. It was found that biofilm cohesion, though increasing with depth, did not with age. Level of biofilm cohesive energy per unit volume was strongly correlated with biofilm polysaccharide concentration, which increased with depth in the membrane-aerated biofilm. In a 12-day-old biofilm, DO also increased with depth and may therefore be linked to polysaccharide production. In contrast, protein concentration was relatively constant within the biofilm and did not appear to influence cohesion.
4:00 PM - OO2: Adhesion
BREAK
OO3: Cells and Interfaces
Session Chairs
Conrad R. Stoldt
Joel Voldman
Monday PM, November 26, 2007
Room 206 (Hynes)
4:30 PM - **OO3.1
Microtechnological Approaches to Studying Embryonic Stem Cell Self-renewal.
Joel Voldman 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractEmbryonic stem cells are cells that have the unusual ability to self-renew for extended periods of time in culture yet are pluripotent in that they can differentiate into any cell type in the adult animal. The decision to self-renew, differentiate, or commit apoptosis is determined in large part by diffusible and contact-mediated signals that come from the microenvironment. We are developing microtechnology to manipulate these signals in order to study the factors involved in embryonic stem cell self-renewal. These tools include microfluidic perfusion, by which we can modulate diffusible signaling between cells, and matrix-independent cell patterning via bio-flipchips, which allows control over diffusible and juxtacrine cell-cell signaling. These tools provide new approaches for studying stem cell biology, and, more broadly, cell-cell signaling in multi-cellular systems.
5:00 PM - OO3.2
Buckling of Microtubules in Living Cells Modulated by Surrounding Cytoplasm and Filament Network.
Teng Li 1 2
1 Department of Mechanical Engineering, University of Maryland, College Park, Maryland, United States, 2 Maryland NanoCenter, University of Maryland, College Park, Maryland, United States
Show AbstractThe mechanics of living cells is largely determined by their cytoskeleton, a dynamic network of microtubules and protein filaments in the cytoplasm. The difference in the rigidity of various cytoskeletal components is huge. For example, the bending rigidity of microtubules is about 100 times that of actin filaments. As the stiffest cytoskeletal component, the microtubules mostly bear compressive load. Experiments show that stimulation of cell contraction causes the microtubules to buckle. Although the persistence length of the microtubules is tens of times larger than the typical size of a cell, the microtubules in vivo often severely buckle into short wavelength. By contrast, other in vitro experiments show that isolated microtubules exhibit a classic Euler buckling instability, resulting in the formation of a single long-wavelength arc. Here we describe a mechanics model to explain the above inconsistency and quantify the wavelength, growth rate and amplitude of the microtubule buckling.In living cells, the stiff microtubules are surrounded not only by the soft elastic filament network, but also by the viscous cytoplasm. The buckling of microtubules causes not only the elastic deformation of the filament network, but also the viscous flow of the cytoplasm. In turn, both these processes influence the buckling wavelength and amplitude of the microtubules. For example, buckling at long wavelength requires viscous mass transportation over long distance, which is unlikely to occur incipiently. We study the coupled effect of the viscous cytoplasm and the elastic filament network on the microtubule buckling. The critical wavelength and the growth rate of the microtubule buckling are studied by a linear perturbation analysis. Furthermore, the buckling of the microtubule reaches a kinetically constrained equilibrium state, from which the buckling amplitude of the microtubule can be determined. Our quantitative mechanics model sheds light on developing new and robust methods to measure various in vivo mechanical properties of subcellular structures, e.g., bending rigidity of microtubules, elastic modulus of filament network, and viscosity of cytoplasm. The model can also be readily generalized to study the deformation of hard engineering materials at soft bio-interfaces.
5:15 PM - OO3.3
Interaction Forces and Mechanics of Cellular Membranes using Novel Atomic Force Microscopy Probes.
Benjamin Almquist 1 , Nicholas Melosh 1
1 Materials Science & Engineering, Stanford University, Palo Alto, California, United States
Show AbstractThe cell membrane is one of the most vital components of a cell, the gatekeeper into and out of the cytoplasm; studies ranging from neural activity to drug discovery to fundamental cell physiology rely upon controlling electronic or chemical flow across this barrier. Integration of inorganic structures with the cell membrane is poorly understood, and current techniques involve creating holes in or puncturing cell membranes to control access into the cell. However, functionalized materials with nanoscale hybrophobic layers may be able to directly fuse the lipid membrane edge to an inorganic structure, enabling non-disruptive electrical and chemical access into the cell. We have tested whether nanoscale inorganic probes integrate into the hydrophobic core of a lipid bilayer using an AFM probe with hydrophobically functionalized bands 5-20 nm thick at the end of the tip. We quantitatively measure the adhesion strength between the probe and the lipid bilayer, and correlate this molecule-membrane force with the molecular structure. We find the thickness of the nanoscale band and the identity of the hydrophobic molecules alters the ability to fuse to the membrane.
5:30 PM - OO3.4
Influence of EGF on HaCaT (Human Epithelial) Cells by Simultaneous AFM and 3-D Optical Deconvolution.
Kate Bagnoli 1 , Ali Langston 1 , Brian Aneskievich 2 , Bryan Huey 1
1 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States, 2 Pharmaceutical Sciences, University of Connecticut, Storrs, Connecticut, United States
Show AbstractThe widely applied optical technique of 3-D fluorescence microscopy and deconvolution has been uniquely combined with the high force sensitivity and spatial resolution of atomic force microscopy (AFM). These complimentary methods allow novel simultaneous optical and mechanical measurements of biological cells, particularly the cell shape, volume, and membrane compliance. In this study, living HaCaT (human epithelial) cells are monitored in vitro at 37 C, both with and without exposure to epidermal growth factor (EGF). Finally, results applicable to more general cell-AFM studies include optically characterizing living cell dimensions during concurrent AFM measurements. This reveals extensive cell deformation before statistically significant forces are detected with the AFM, suggesting that 3-D optics provide a more accurate measure of cell height than AFM imaging.
5:45 PM - OO3.5
Sol-gel Encapsulated Gold-Silica Nanoshells for SERS Detection of Peptide – Gold Binding.
Sandra Bishnoi 1 , Yu-Jen Lin 1
1 BCPS, Illinois Institute of Technology, Chicago, Illinois, United States
Show AbstractThe study of the interfaces between biological molecules and nanomaterials has become increasingly important to improve drug delivery and biological sensing. Surface enhanced Raman scattering (SERS) is a powerful technique that could be used to investigate these interfaces, but suffers from reproducibility issues under in vitro conditions. In order to increase our understanding of the mechanism of interactions between gold nanoparticles and "gold binding peptides," we have created sol-gel substrates for surface enhanced Raman scattering studies. By taking advantage of the large enhancements obtained with gold-silica nanoshells (~1010 over normal Raman),1 robust, SERS substrates with high reproducibility have been obtained. Using a protocol commonly used to immobilize proteins,2 we have created “biologically friendly” SERS sensors for the study of the interactions between gold binding peptides and gold nanoparticles. Specifically, by combining tetraethyl orthosilicate (TEOS), methyltrimethoxysilicate (MTMS), phosphate buffer, and gold nanoparticles we have created sol-gels with minimal fluorescence and Raman backgrounds. Since organic solvents have been eliminated in the synthesis, these porous materials are ideal for studying the attachment of various biological molecules to gold surfaces.1 Jackson, J. B.; Halas, N. J. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 17930-17935.2 Soyoun Kim, Youngdeuk Kim, Philseok Kim, Jeongmin Ha, Kyunyoung Kim, Mijin Sohn, Jin-San Yoo, Jungeun Lee, Jung-ah Kwon, and Kap No Lee. Anal. Chem. 2006, 78(21), 7392 -7396.
Symposium Organizers
Virginia L. Ferguson University of Colorado
John X.-J. Zhang The University of Texas-Austin
Conrad Stoldt University of Colorado
Carl P. Frick Abbott Vascular
OO4: Interface Science and Engineering II
Session Chairs
Mehmet Sarikaya
Conrad R. Stoldt
Tuesday AM, November 27, 2007
Room 206 (Hynes)
9:30 AM - **OO4.1
Molecular Biomimetics – Genetically Linking Biology and Material Using Designed Peptides for Technology and Medicine.
Mehmet Sarikaya 1
1 Materials Science and Engineering, University of Washington, Seattle, Washington, United States
Show AbstractIn technology and medicine, biological entities, such as proteins, enzymes, DNA, cell etc., are interfaced with solids mostly either by synthetic linkers (e.g., thiols and silanes), often producing non-natural interfaces, or serendipitously via non-specific interactions, both of which pose eventual issues that limit their wide-spread and lasting implementations. In organisms, however, solids are interfaced with proteins and peptides that provide chemical and mechanical coupling, linking the biology of the organisms and the solid materials (e.g., mineral or metal) and provide an entity that functions as a hybrid (e.g., bone, shells and spicules). Using biocombinatorics, we have adapted molecular biology protocols to select short (7-12 aa) peptides that specifically bind to individual solids, e.g., metals, ceramics, semiconductors. Through molecular characterization, e.g., quantitative binding, experimental and computational peptide-structure determination coupled with bioinformatics, it is now possible to control peptide evolution through sequence similarity, multimerization and architectural control to design next and higher generation peptides for specific applications including directed enzyme or nanoparticles immobilization, developing biocompatible surfaces and interfaces, and biosynthesis/biofabrication. We plan to present a summary of molecular biomimetics activities from our Center and collaborative groups directed towards both nanotechnology and medicine. Supported by NSF-UW/MRSEC, AFOSR-Bioinspired Materials, NSF-BioMat, and NIH.
10:00 AM - OO4.2
Guiding Neurons with Micropatterned Solid Substrates.
J. Nevill 1 , Luke Lee 1 , Mu-ming Poo 2 , Sarah Heilshorn 3
1 Bioengineering, University of California, Berkeley, California, United States, 2 Molecular and Cell Biology, University of California, Berkeley, California, United States, 3 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractDuring development, young neurons sprout several processes (called neurites) that probe their environmental niche. Based on a combination of intracellular signaling molecules and extracellular cues, one neurite develops into the axon (the portion of the neuron that can transmit electrical and chemical signals) while the remaining neurites become dendrites. While this developmental program is tightly regulated in vivo, currently there are no methods to control neuronal polarity in vitro. We have designed a protocol to pattern various guidance cues on surfaces to guide the development of rat hippocampal neurons. Soft lithography was used to create microfluidic devices that generate patterned regions of guidance cues physically adsorbed to the culture substrate within a polypeptide matrix. This protocol is compatible with both small-molecule guidance cues as well as protein guidance cues such as the neurotrophins semaphorin 3a and brain-derived neurotrophic factor. Our patterned surfaces are able to specify axon initiation as well as guide the path-finding of the developing axon. These patterns are currently being used to study the development of human embryonic stem cell derived neurons.Complex patterns of multiple bioactive molecules on a single solid substrate can also be created using these microfluidic techniques. As proof of principle, arrays of three bioactive molecules were patterned on glass substrates. Rat hippocampal neurons plated onto these substrates aligned into ordered arrays, initiated axons at a specified location, and sprouted neurites that followed predetermined paths. This is a first step towards guiding the formation of simple neuronal circuits in vitro. The ability to guide neuronal development on patterned substrates has potential application in bioMEMs devices, living neural networks, biosensors, and scaffolds for tissue engineering of nerve grafts.
10:15 AM - OO4.3
Neuronal Adhesion and Growth on Modified Diamond-Like-Carbon Substrates.
Frederik Claeyssens 1 , Ed Regan 2 , Eric Mayer 3 , James Uney 2 , Andrew Dick 3 , Joe McGeehan 4 , Stephen Kelly 2
1 School of Chemistry, University of Bristol, Bristol United Kingdom, 2 Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Bristol United Kingdom, 3 Bristol Eye Hospital, University of Bristol, Bristol United Kingdom, 4 Department of Electrical and Electronic Engineering, University of Bristol, Bristol United Kingdom
Show AbstractMaterials that produce minimal immunogenic and thrombogenic responses in vivo are potentially useful for the coating of many orthopaedic implants and implantable devices. The physical properties of the material also bear much importance on functional “life-expectancy” of implants, as wear debris can cause inflammatory responses and release of potentially cytotoxic substances such as metal ions. Diamond-Like-Carbon (DLC) is a hard, wear resistant and chemically inert material that can be deposited onto the surfaces of implants. DLC has been shown to support in vitro growth of multiple cell types including osteoblasts, monocytes, macrophages and neutrophils, without significant alteration in cellular metabolism.[1,2] In vivo tests have demonstrated the high level of biocompatibility of DLC: including year-long implantation of DLC-coated titanium into rabbit skeletal muscle without detectable damage to surrounding tissue.[3]DLC can be deposited via various methods including cathodic arc deposition,[4] Radio Frequent Sputtering [5] and Pulsed Laser Deposition (PLD).[6] Further surface modification of or the incorporation of dopant materials in the deposited films can be used to alter the physical characteristics and haemocompatibility of DLC. Phosphorous doping [7] and surface fluorination[8] have been shown to improve the antithrombogenic properties of DLC.In this study the adhesion, survival and morphology of neuroblastoma N2a cell lines and rat primary cortical neurons is described on DLC thin films on glass substrates deposited at room temperature by PLD. Three different types of DLC films were studied (i) nascent DLC films, (ii) surface oxidised DLC films and (iii) phosphorus doped DLC films. The interaction of cells with DLC substrates is assessed using an adhesion score method and measures of cell metabolic activity are determined using an MTT assay. Morphology of neurons was determined using scanning electron microscopy. These measures were compared to address the neuro-compatibility of the different DLC surfaces. This is correlated with the properties of these materials, assessed with Raman spectroscopy and contact angle measurements. Furthermore, the possibility of patterned growth of neurons on these substrates is explored. [1]W.J. Ma et al., Biomaterials 28 (2007) 1620-1628[2]A. Singh et al., Biomaterials 24 (2003) 5083-5089[3]M. Mohanty et al., Biomolecular Engineering 19 (2002) 125-128[4]B. Bhusban, Diamond and Related Materials 8 (1999) 1985-2015[5]S. Ulrich et al., Surface & Coatings Technology 97 (1997) 45-59[6]A.A. Voevodin et al., Surface & Coatings Technology 82 (1996) 199-213[7]S.C.H. Kwok et al., Diamond and Related Materials 14 (2005) 78-85 [8]T. Saito et al., Diamond and Related Materials 14 (2005) 1116-1119
10:30 AM - OO4.4
Carbon Micro-arrays as a Substrate for Patterned Cell Growth.
Genis Turon Teixidor 1 , Manish Kulkarni 2 , PremPrakash Tripathi 3 , Jamuna Subramaniam 3 , Ashutosh Sharma 2 , Marc Madou 1
1 Mechanical and Aerospace Engineering Department, University of California, Irvine, Irvine, California, United States, 2 Chemical Engineering , Indian Institute of Technology, Kanpur, Kanpur, Uttar Pradesh, India, 3 Biological Sciences and Bioengineering, Indian Institute of Technology, Kanpur, Kanpur, Uttar Pradesh, India
Show Abstract10:45 AM - OO4.5
Magnetically Patterned Co-Cultures for Probing Cell-Cell Interactions.
Edward Felton 1 , Daniel Reich 1 , Yoojin An 2 , Christopher Chen 2
1 Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland, United States, 2 Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractThe ability to selectively pattern cultures of biological cells has led to novel approaches to several areas of interest, from tissue engineering to the study of cell-cell interactions. We have introduced ferromagnetic nanowires as a tool for applying forces to cells; their high remanent magnetization allows cells bound to nanowires to be manipulated in low-strength magnetic fields. Interaction of these nanowires with patterned ferromagnetic microstructures allows cells bound to the nanowires to be guided precisely to predetermined positions on substrates. Surface functionalization techniques that control cell adhesion can then be used to retain the cells at these positions for periods of several days. We have exploited these techniques to organize cells into a variety of patterns with a single cell type, and have created arrays of cells in which heterotypic cell pairs are magnetically trapped at each array site. The cell pair yields obtained with this magnetic method are significantly higher than has been obtained by random seeding using non-magnetic techniques. This method of producing isolated heterotypic cell pairs is potentially useful in studies of cell-cell interactions between different cell types.
11:00 AM - OO4:Interfaces
BREAK
11:30 AM - OO4.6
Co-patterning Mobile and Immobilized Proteins on Surfaces to Model Cell-cell Interactions with Cell-surface Contacts.
Darrell Irvine 1 , Bonnie Huang 1
1 Mat. Sci. & Eng./Biological Eng., MIT, Cambridge, Massachusetts, United States
Show AbstractPatterned surfaces are powerful tools for the study of cell functions, and we have a long-standing interest in using patterned surfaces to study T cell biology. T cells are activated by forming a long-lasting cell-cell contact with an antigen presenting cell (APC), forming an immunological synapse at the cell-cell interface. We experimentally modeled T cell-APC interactions by studying the interaction of T cells with synthetic surfaces as artificial APCs. Glass substrates were photolithographically patterned with arrays of ‘activation sites’, 1-10 micron patches of arbitrary geometry displaying T cell receptor (TCR) ligands, surrounded by co-patterned adhesion proteins. A biotinylated polyelectrolyte photoresist previously developed in our laboratory was used, which allows for sequential deposition of proteins into two different regions of a patterned surface (foreground and background) under mild aqueous conditions. Each activation site models a discrete APC; T cells seeded on these surfaces adhere and migrate, and form synapses when they encounter activation sites. In prior work, we immobilized TCR ligands in the activation sites via short poly(ethylene glycol) tethers. However, the protein ligands displayed on the surfaces of APCs are mobile and diffuse in the 2D plane of the membrane; further it is known that T cells binding to ligands on the APC surface cluster these ligands using their cytoskeletons. To provide 2D mobility to ligands in activation sites, we developed a strategy to photolithographically pattern patches of supported lipid membranes as the activation sites, with immobilized adhesion proteins on the surrounding background. Liposomes were fused with photolithographically-pattered resist films, followed by a ‘lift-off’ step to remove lipid from the background regions of the pattern. T cell ligands were anchored to the membrane patches through biotinylated lipids incorporated in the deposited membranes. The mobility of lipids and membrane patch-tethered TCR ligands was characterized using fluorescence recovery after photobleaching techniques, and revealed fluidity comparable to typical supported lipid bilayers on glass. Microscopy studies of T cells seeded on these lipid membrane patch arrays showed that cells halted migration and elevated intracellular calcium on contact with lipid patches bearing TCR ligands, mimicking their response to live APCs. Within minutes of contact, T cells clustered their ligands when interacting with patterned lipid membrane patches. Ongoing studies are comparing the effect of these biophysical changes in ligand presentation (mobile vs. immobilized ligand) on endpoint functional T cell responses (proliferation, cytokine secretion). These surfaces, combining mobile ligands on activation sites with immobilized ligands on the ‘background’, may be of general utility for studying cell-cell interactions and the interface of synthetic materials with living systems.
11:45 AM - OO4.7
Role of Biopolymers on the Crystal Structure and Growth of Hydroxyapatite in Biopolymer/Hydroxyapatite Nanocomposite Bone Biomaterials.
Devendra Verma 1 , Patrick Dunlap 1 , Kalpana Katti 1 , Dinesh Katti 1
1 Civil Engineering, North Dakota State University, Fargo, North Dakota, United States
Show AbstractTuesday, Nov 26Transferred Poster OO6.2 to OO4.7 @ 10:45 AMRole of Biopolymers on the Crystal Structure and Growth of Hydroxyapatite in Biopolymer/Hydroxyapatite Nanocomposite Bone Biomaterials. Devendra Verma
12:00 PM - OO4.8
Controlling Hemostasis with Inorganic Surfaces.
April Sawvel 1 , Sarah Baker 1 , Galen Stucky 1
1 Chemistry, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractThe ability to control bioprocesses via interface interactions with inorganic materials is evident in biomineralization1, supported enzyme activity2, 3, and protein folding or denaturation4. The development of advanced wound-dressing materials is an emerging field of materials chemistry that exploits the tunable surface properties of inorganic materials to modulate the intrinsic coagulation response5-8. Inorganic hemostatic agents are estimated to have saved hundreds of lives in the current military conflicts5 and are finding an increasing number of civilian applications9.Our work has resulted in the further development of rapid-acting hemostatic agents and in a better understanding of how to use inorganic surfaces to control coagulation. We have tested a variety of inorganic materials that vary with respect to their surface and materials properties, and have identified the key materials properties necessary to stimulate a pro- or anti-coagulant response. The materials studied were thoroughly characterized with respect to their physical properties and rheological studies were used to assess the blood clotting response in vitro. In addition to investigating the physical properties of these materials, we have also studied the dependence of intrinsic coagulation on particle size and morphology. As a consequence of systematic investigations into the coagulation response to various inorganic materials, we have been able to develop superior hemostatic agents and are working towards a more detailed understanding of the enzymatic and cellular response to inorganic surfaces.1. Zaremba, C. M.; Belcher, A. M.; Fritz, M.; Li, Y.; Mann, S.; Hansma, P. K.; Morse, D. E.; Speck, J. S.; Stucky, G. D. Chem. Mater. 1996, 8, 679.2. Han, Y.-J.; Watson, J. T.; Stucky, G. D.; Butler, A. J. Mol. Catal. B: Enzym. 2002, 17, 1.3. Carrado, K. A.; Macha, S. M.; Tiede, D. M. Chem. Mater. 2004, 16, 2559.4. Charache, P.; MacLeod, C. M.; White, P. Journal of General Physiology 1962, 45, 1117.5. Harris, E. Nature 2007, 446, 369.6. Ostomel, T. A.; Shi, Q.; Stucky, G. D. J. Am. Chem. Soc. 2006, 128, 8384.7. Ellis-Behnke, R. G.; Liang, Y.-X.; Tay, D. K. C.; Kau, P. W. F.; Schneider, G. E.; Zhang, S.; Wu, W.; So, K.-F. Nanomedicine: Nanotechnology, Biology and Medicine 2006.8. Fischer, T. H.; Thatte, H. S.; Nichols, T. C.; Bender-Neal, D. E.; Bellinger, D. A.; Vournakis, J. N. Biomaterials 2005, 26, 5433.9. Marshall, J. New Scientist 2006, 28.
12:15 PM - OO4.9
A Robust Coating for Nano Titanium Dioxide which Blocks Photocatalytic Activity.
Chien-Hsiu Lin 1 , Wilson Lee 1 , Nadine Pernodet 1 , Bingquan Li 2 , Eli Hatchwell 1 , Miriam Rafailovich 1
1 Material Science, SUNY-Stony Brook, Stony Brook, New York, United States, 2 Department of Earth & Environmental Engineering, Columbia University, New York, New York, United States
Show Abstract12:30 PM - **OO4.10
The Cellular Cytoskeleton as a Mechanically Adaptive Material.
Daniel Fletcher 1
1 Bioengineering & Biophysics, University of California-Berkeley, Berkeley, California, United States
Show AbstractThe ability of cells to generate forces and resist deformation is critical for organism development, maintenance, and repair. Within the cell, physical stresses are mediated by an interconnected and adaptive network of filaments known collectively as the cytoskeleton. Composed of actin filaments, intermediate filaments, and microtubules, the cytoskeleton provides an internal framework that organizes the cytoplasm, enables dynamic shape changes, and can mechanically link the cell to its external environment. Among the most dynamic structures within the cytoskeleton are actin filament networks, whose growth plays a critical role in cellular process ranging from crawling motility to endocytosis. Monomeric actin polymerizes into non-covalent polymer filaments that are organized by actin-binding proteins into branched and cross-linked actin filament networks. In dendritic actin networks that drive lamellipodial protrusions, new filaments are formed by the branching complex Arp2/3 at locations near the cell membrane, while old filaments are terminated by a capping protein present throughout the network. The repeated steps of branching and capping result in the formation of a highly oriented network that drives membrane deformations. Despite extensive biochemical knowledge of proteins necessary for actin network formation, little is known about how the cytoskeleton adapts to external forces. This talk will present recent work investigating adaptive properties of dendritic actin networks using a series of atomic force microscopy (AFM)-based experimental tools integrated with epi-fluorescence microscopy. In our experiments, actin networks are reconstituted in vitro and directly probed with AFM under controlled loading conditions to measure both static and dynamic properties. First, we find that these networks exhibit three regimes of elasticity under compression: linear, non-linear stress stiffening, and non-linear stress softening. The data is consistent with a network of filaments that experience buckling of individual elements under large stresses. Second, we find that growth of an actin network under load alters its growth velocity in a history-dependent manner, suggesting that network density is altered. These data challenge existing models of actin network assembly and offer insight into the design of adaptive materials.
OO5: Tissue Scaffolds and Implant Materials
Session Chairs
Tuesday PM, November 27, 2007
Room 206 (Hynes)
2:30 PM - **OO5.1
Designing Shape Memory Polymers Networks for Biomedical Applications.
Ken Gall 1 , Chris Yakacki 1 , Alicia Ortega 1 , Alan Greenberg 1
1 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractShape memory polymers have potential applications in minimally invasive surgery through the delivery of compacted devices that deploy into functional form once implanted. The objective of this talk is to overview the design of shape memory polymer networks for various biomedical applications. We will examine chemical and structural factors important to the thermo-mechanical behaviour of shape memory polymers during deformation, storage, and recovery. We will begin by discussing structure-property requirements for relatively compliant cardiovascular applications and relatively rigid orthopaedic applications. We will subsequently consider (1) the effect of temperature on deformability of the networks, (2) the effects of crosslinking density on recoverable strain limits, and (3) the effects of glass transition temperature and rubbery modulus on recovery time and stress. The talk will end with conclusions and avenues for future research.
3:00 PM - OO5.2
Microfabrication of Biomimetic Cardiac Tissue Engineering Scaffolds.
George Engelmayr 1 , Mingyu Cheng 1 , Christopher Bettinger 2 4 , Jeffrey Borenstein 4 , Robert Langer 1 3 , Lisa Freed 1
1 Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 MEMS Technology Group, Charles Stark Draper Laboratory, Cambridge, Massachusetts, United States, 3 Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractTissue engineered cardiac grafts (TECG) comprised of heart cells and scaffolds are conceptually appealing for use in the repair of congenital and acquired lesions of the heart. To date, however, scaffold materials applied to TECG have only been capable of promoting a limited subset of the anisotropic structural-mechanical properties of native myocardium. For example, collagen sponge, while sufficiently compliant to allow for contractility, fails to promote native-like cell alignment due to its isotropic microstructure, and generally exhibits insufficient strength to support high tensile loading. In contrast, nonwoven poly(glycolic acid) has a relatively high tensile strength and can induce some degree of cell elongation along fibers; however its high initial stiffness can impede robust contractility. Toward recapitulating biomimetic structural-mechanical properties in TECG, biologically-inspired scaffolds with controlled mechanical anisotropy and cell-orienting pore structures were microfabricated by excimer laser microablation of the bioresorbable elastomer poly(glycerol sebacate) (PGS). Patterns of square and/or rectangular holes were drilled through an ~250 µm thick PGS membrane to yield grid-like scaffold structures with 50 µm wide struts and geometrically well-defined open pores. PGS scaffolds with 1:1 aspect ratio (200 x 200 µm) square pores, 2:1 aspect ratio (400 x 200 µm) rectangular pores, and other novel anisotropic pore structures were fabricated and assessed for their utility in fabricating TECG. PGS scaffolds with 2:1 aspect ratio and other anisotropic pore structures were found to exhibit mechanical properties, including anisotropy, similar to native ventricular myocardium, as assessed by tensile testing of oriented scaffolds and native ventricles. Upon seeding with neonatal rat heart cells, all PGS scaffolds yielded spontaneously contractile TECG which could be paced by electrical field stimulation at frequencies of 1 to 4 Hz. On culture day 7, PGS scaffolds with 2:1 aspect ratio pores exhibited a significantly lower excitation voltage threshold when the electric field was applied parallel versus perpendicular to the preferred strut direction (0.75 ± 0.06 vs. 0.91 ± 0.01 volts; p < 0.05), and a significantly higher index of cellular orientation (scale 0-1) than scaffolds with 1:1 aspect ratio pores (0.48 ± 0.04 vs. 0.10 ± 0.03; p < 0.0001) as assessed by F-actin labeling and image analysis of confocal micrographs. Toward scaling-up to thicker TECG, a prototype bi-layered PGS scaffold (~400 µm thick) with a fully interconnected three-dimensional pore network was fabricated by a combination of excimer laser microablation and lamination, and was also demonstrated to yield a contractile TECG. In conclusion, PGS scaffolds microfabricated to include specific anisotropic pore structures can overcome the principal structural-mechanical limitations of previous scaffolds to promote the formation of more biomimetic cardiac grafts.
3:15 PM - OO5.3
Polyurethane-Hyaluronic Acid Copolymers as Hemocompatible, Bioactive Materials.
Fangmin Xu 1 , John Nacker 2 , Wendy Crone 1 2 3 , Kristyn Masters 1
1 Biomedical Engineering, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Engineering Mechanics Program, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Engineering Physics, University of Wisconsin - Madison, Madison, Wisconsin, United States
Show AbstractAfter several decades of research into hemocompatible biomaterials, there remain surprisingly few materials that can be used in blood-contacting applications. We have synthesized copolymers of polyurethane (PU) with hyaluronic acid (HA), a glycosaminoglycan that is naturally anti-thrombotic, with the goal of creating materials that incorporate an inherently non-thrombogenic, bioactive component into the bulk polymer structure. Low molecular weight HA was incorporated into the polymer backbone as a chain extender during PU synthesis, and both the physical and biological properties of the resulting copolymer were directly controlled by the HA content. Increases in HA content led to a linear increase in hydrophilicity and corresponding increase in surface energy and decrease in protein adsorption compared to polyurethane controls. Increasing HA content also led to significantly increased elastic modulus. Incorporation of even small amounts of HA resulted in negligible platelet adhesion to the PU-HA copolymers, representing a 20-fold decrease in platelet adhesion compared to PU controls. Red blood cell adhesion also significantly decreased with increasing HA content, a result that correlated well with theoretical trends predicted using work of adhesion calculations. Preliminary studies of endothelial cells seeded on the materials confirmed that the PU-HA materials were also highly cytocompatible and supported cell adhesion and viability. Thus, we have demonstrated the synthesis of a unique bioactive polymer whose physical and biological properties are easily tailored, and whose potent anti-thrombogenic properties demonstrate its great promise for use in vascular applications.
3:30 PM - OO5.4
Mechanical Properties of Nanoparticle Hydroxyapatite/gelatin Constructs.
Steven Fox 1 , Inessa Stanishevskaya 1 , Shafiul Chowdhury 1 , Andrei Stanishevsky 1
1 , University of Alabama at Birmingham, Birmingham, Alabama, United States
Show Abstract3:45 PM - OO5.5
Osteogenic Differentiation of Mesenchymal Stem Cells on Biomineralized Collagenenous Scaffolds for Bone Tissue Engineering.
Harold Castano 1 , Chuanbin Mao 1
1 Chemistry & Biochemistry, University of Oklahoma, Norman, Oklahoma, United States
Show AbstractIn this work we study the osteogenic differentiation of mesenchymal stem cells (MSCs) seeded on biomineralized small intestine submucosal (SIS) membranes and evaluate in vivo bone regeneration on MSC-seeded SIS mmebranes. SIS membrane is a naturally occurring 3D collagenous biomaterial derived from the submucosal layer of porcine small intestine. It is predominantly composed of type I collagen fibers and also rich in growth factors that can support the growth of different types of cells. Thus SIS membrane is a potential biomaterial for bone tissue regeneration. We first studied the biomineralization of the SIS membrane in order to integrate the bone mineral hydroxylapatite into the collagenous scaffold. We then evaluated the attachment, proliferation, and differentiation of rat MSCs toward the osteoblastic phenotype seeded on the biomineralized SIS membranes. Rat critical size cranial defect was used as an animal model to study the in vivo bone regeneration on MSC-seeded SIS membranes.
4:00 PM - OO5:Scaffold/Imp
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4:30 PM - OO5.6
Hydrogel Nanoparticle Aggregates at the Wound-Dressing Interface.
John St. John 1 , Lynda Waller 1 , Daniel Moro 1 , Daniel Hatef 2 , Spencer Brown 2
1 Research, ULURU Inc., Addison, Texas, United States, 2 Plastic Surgery, University of Texas Southwestern Medical School, Dallas, Texas, United States
Show AbstractA full thickness dermal wound represents a dynamic tissue environment where normal cellular function has been dramatically challenged to force repair of a compromised surface. We report on the development of a new class of advanced wound dressings composed of dehydrated hydrogel nanoparticles. The hydrogel nanoparticle powder when applied to a wound surface adsorbs exudate and the dehydrated nanoparticles hydrate and irreversibly aggregate forming a film with intimate contact to the moist granulating wound bed.The nanoparticles were formed from poly-2-hydroxyethyl methacrylate and poly-2-hydroxypropl methacrylate with uniform particle sizes. The nanoparticles were subjected to rigorous purification, lyophilization and sterilized with gamma radiation. Application of the powder to a moist wound surface resulted in the immediate formation of a solid hydrogel film that covered and sealed the wound. The hydrogel nanoparticle wound dressing allowed high volume transpiration of wound exudate and did not require a secondary occlusive dressing for the duration of application to 30 days. Data for gross wound healing and appearance for the dressings applied to full and partial thickness surgically induced porcine wounds shown excellent results. Wound healing data were also shown for application of the powder to surgically debrided chemical burns.Histolological observations for biopsies taken at the wound/dressing interface over time showed changes both in tissue morphology and the interaction between new tissue and the nanoparticle wound dressings. Differences between the hydrogel nanoparticle dressing and control dressings with traditional moist wound healing protocols were observed for both wound healing and for the granulating tissue. Data for the local acute immune response were shown with TNFα levels obtained by microdialysis near the wound site, and the nanoparticle dressing showed no elevation over controls. Of more critical importance to advanced wound healing is the possible introduction of growth factors or other bioactive agents from the nanoparticle dressing at the wound surface.. Growth factors were added to nanoparticle formulations and resulatant morphologic changes in the healing wound were observed relative to the respectice growth factor. Data for gross wound healing were correlated with histological and immunohistochemistry staining to show the influence of different growth factor release profiles from the solid material on the subsequent phases of wound healing. Therefore, these data showed that bioactive agents were delivered to the wound healing surface from a solid material in a bioactive form that retained biological activity.The hydrogel nanoparticle wound dressing is currently under commercial production. Advanced hydrogel nanoparticle wound dressings containing growth factors are under preclinical development.
4:45 PM - OO5.7
On the Release of Nickel from Dynamically Loaded Orthodontic Wires.
Thorsten Peitsch 1 , Arndt Klocke 2 , Oleg Prymak 1 , Matthias Epple 1
1 Inorganic Chemistry Department, University of Duisburg-Essen, Essen, North Rhine-Westphalia, Germany, 2 Department of Orthodontics, University Hospital Hamburg-Eppendorf, Hamburg Germany
Show AbstractIn orthodontics, different types of wires are used for the alignment of teeth with fixed appliances. NiTi-based shape-memory-alloys are routinely employed because of their special mechanical properties, i.e. the superelasticity caused by the stress-induced formation of martensite. A medical cause of concern for the orthodontic application of such superelastic NiTi alloys is their high nickel content (50 mol% in NiTi). Exposure to nickel is the most common cause of allergic reactions in patients. Therefore, we conducted in vitro studies on the release of nickel from NiTi wires simulating an intraoral environment with dynamic mechanical loading. The mechanical stress was applied according to the principle of single-armed-bending. This is similar to the motion of a single tooth relative to its neighbors and thus to a bending of the wire by the brackets fixed to the teeth. To study the release of nickel, a new testing apparatus was constructed from nickel-free components. With sample attachments made of plastic and trays made of PTFE, potential nickel contaminations were minimized. Surface-nitridated and uncoated NiTi wires were examined in water and in aqueous NaCl solution. Mechanical loading resulted in increased levels of nickel release and was ascribed to a continuous damage of the passivation TiO2 surface layer of the wire.Notably, the nitridation did not result in a significantly lower release of nickel. The release of nickel was significantly higher in NaCl solution compared to pure water. The absolute amount of released nickel of 790 ng after 36 days is relatively low, but could explain the adverse allergic reactions occasionally observed in clinical orthodontic practice.
5:00 PM - OO5.8
Drug Delivery Systems Based on Hydroxyapaptite-coated Poly(lactide-co-glycolide) Microparticles.
Qingguo Xu 1 , Jan Czernuszka 1
1 Department of Materials, University of Oxford, Oxford United Kingdom
Show AbstractCalcium phosphates, especially hydroxyapatite (HA), are very useful in bone replacement and reconstruction because of their osteoconductivity. However, its mechanical weakness limits the biomedical applications. Coating HA on a substrate is one of the most attractive alternatives. Here we utilize a constant composition precipitation method to coat HA on negatively-charged PLGA microparticles which have been drug loaded. This method has been used successfully coat HA on liposomes (1). Negatively charged PLGA microparticles were prepared by s/o/w solvent evaporation method using the anionic surfactant sodium dodecyl sulfate (SDS). 200mg PLGA in 2 ml dichloromethane is mixed with 50mg model drug amoxicillin (AMX) to form a primary emulsion by ultrasonication, and this was drop-wisely added into 100 ml of 1% SDS aqueous solution and stirred for 3 hours at 600 rpm. The PLGA microparticles were collected by centrifugation. The dual constant composition precipitation experiment was performed. A stable supersaturated solution with respect to HA was prepared by mixing CaCl2 and KH2PO4 at the molar ratio of 1.67, and the aqueous suspension of PLGA microparticles was added. The drop in pH and pCa of the reaction solution triggered the simultaneous addition of titrants from separate autoburettes containing CaCl2, KH2PO4. Then the HA-coated PLGA microparticles were freeze-dried overnight. Many HA crystals are formed on PLGA microparticles after 1 hour, and a complete HA coating can be achieved after 3 hours. A FIB image is shown in Fig 1 of a cross-section of HA coated PLGA microparticles (HPLG) after only 6 hours preparation. PLGA microparticles held a zeta-potential of -79.1mv and changed into -3.8mv after HA coating. The negative charge of PLGA microparticles perhaps was shielded by a layer of HA around the microparticles. FTIR spectra and XRD patterns were uaded to confirm the presence of HA. Compared to biomimetic method (2), constant composition method is much faster to achieve a complete and thick coating of HA. There is a continuous addition of calcium and phosphate when these ions were consumed, so that a very high degree of supersatuation can always be maintained resulting in fast HA growth rate. There is a layer of polar sulfate ions remaining on the PLGA surface which can directly act as nucleation and growth sites for HA. Thus no pre-treatment is needed and any change in properties of PLGA during coating can be avoided. A sustained release profile for HA coated and uncoated PLGA microparticles for at least one month has been seen, which is a typical tri-phase drug release (Fig 2). No obvious difference occurred in drug release profiles of AMX between PLGA and HPLG microparticles, and the burst release at first 12 hours is less than 10%. HPLG has great potential application in curing bone disorders to deliver therapeutic agents because it has both advantages of osteoconductivity from HA coating and controlled release from PLGA.
5:15 PM - OO5.9
Photoinitiated Chemical Vapor Deposition: A Dry Method for the Synthesis of Biocompatible Hydrogel Films.
Salmaan Baxamusa 1 , Karen Gleason 1
1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractPolymers are widely used to create biocompatible surfaces on biomedical devices. For devices such as biosensors where communication with the surrounding chemical environment is required, it is desirable to use surface modifications that allow the passage for water and small molecules between the device and its environment. Polymer brushes are an example of such a modification, but many biosensing devices cannot be chemically linked to long polymer brushes without degrading their functionality. In such situations, a physical modification such as a thin hydrogel can be used.Poly(hydroxyethylmethacrylate) (pHEMA) is a hydrogel widely used in biomaterials applications, most commonly as a copolymer in contact lenses. This work will describe the use of photoinitiated chemical vapor deposition (piCVD) to synthesize thin polymer hydrogels. piCVD is an all-dry process in which initiator and monomer vapors simultaneously flow into a vacuum; ultraviolet decomposition of the initiator results in free-radical polymerization of the monomer on a low-temperature substrate (<45 oC). The use of piCVD to synthesize crosslinked pHEMA homopolymer and pHEMA copolymers with perfluorodecylacrylate (PFDA) or poly(ethylene glycol) ethyl ether methacrylate (PEGMA) will be described.Because the piCVD produces conformal films in a solvent-free and low-temperature environment, it is suitable for the surface modification of delicate substrates such as biological devices. The process can be used to deposit thin films (10-1000 nm) on virtually any surface without damaging or chemically modifying the underlying substrate. Furthermore, the systematic addition of comonomer to the feed gas enables the compositional control of the film its properties; for example, the systematic addition of PFDA increases the ultimate receding contact angle from 20o to 45o and decreases the swollen water content from 30% to 5%. Spectroscopic ellipsometry has been used to measure the swelling behavior of the films, which will be shown to be both stable and reversible. The swelling behavior also elucidates the mesh-like structure of the polymer matrix. The mesh-size of the films is approximately 3 nm, which is large enough to allow for the passage of small analytes while blocking the transport of large macromolecules such as proteins. A sensor coated using the piCVD process will be shown to retain its ability to detect changes in ionic concentration. Contact angle and ellipsometric characterization have also been used to characterize the adsorption behavior of model proteins on these films. Ellipsometry allows for quantitative real-time measurements of protein adsorption, elucidating the degree, rate, and reversibility of biofouling by proteins. Strategies to prevent fouling will be discussed.
5:30 PM - OO5.10
Interaction of Silica Particles with Human Cells: Direct Studies and Applications.
Swaminathan Iyer 3 , Craig Woodworth 2 , Ravi Gaikwad 1 , Igor Sokolov 1
3 Chemistry , The University of Western Australia, Potsdam, Western Australia, Australia, 2 Biology, Clarkson University, Potsdam, New York, United States, 1 Physics, Chemistry, Clarkson University, Potsdam, New York, United States
Show AbstractInteraction of ceramics with biointerface at nanoscale is of both fundamental and applied interest. In this presentation we will show a small piece of that emerging research. We will describe direct measurements of interaction between silica particles and viable human cells with the help of atomic force microscopy (AFM). Silica particles of micron size can be attached to the AFM cantilever, which is used to “touch” the cells. Deflection of the cantilever, force response is recorded. Using this approach we can learn how silica particles interact with, say cancer and normal, even aging old cells. For example, we will show that AFM data can be use to derive effective number of molecules on the cell surface, which turned out to be different for normal and cancer cells. On the application side, this knowledge can be used for detection of cancer cells and cancer treatment. In this talk, we will demonstrate how cancer detection can be done for an example of cervical cancer cells. To do that, we use specially synthesized silica particles. Such particles, being silica from outside, have complex internal nanostructure, nanochannels. Fluorescent dyes put inside make those particles the brightest fluorescent tags ever synthesized. Using those particles, we suggest two methods of “labeling” cancer cells. This method can result in developing a method for fast screening of cancerous (and even precancerous!) epithelial tissue without biopsy.
5:45 PM - OO5.11
Polysilicon Thin Film Based Implants for Single Neuronal Recording/stimulation.
Rajarshi Saha 1 , Jit Muthuswamy 1
1 Harrington Dept. of Bioengineering, arizona state university, Tempe, Arizona, United States
Show AbstractWe had earlier determined the optimal doping density and processing conditions for electrical impedance and charge storage capacity of polysilicon thin films for neuronal recording/ stimulation [1]. Polysilicon films could be deposited and doped during gate fabrication in current CMOS processing thus making them compatible with VLSI design. The machinability of polysilicon further allows for the exciting possibility of integrating complex mechanical structures with the bio-interface. In this study, we successfully fabricate and package microelectrode arrays of polysilicon thin films using conventional photolithography techniques. Rodent cortical neurons were cultured on these arrays and spontaneous action potentials were successfully recorded after two weeks. Optimized processing conditions in high doped polysilicon (10^21/cm^3 annealed at 1100C for 1 hr) led to peak-to-peak amplitudes in the range of 100-200 µV. In order to estimate the effect of processing conditions on the impedance of the recording interface and on the recorded potentials themselves, we compare the SNR obtained under different annealing/doping conditions. The charge storage capacity of low-doped polysilicon films [1] in phosphate buffered saline was approx. 111μC/cm^2. Further, the effect of (a) shape and (b) perimeter of stimulation sites on the charge storage capacity of low doped polysilicon (10^15/cm^3 annealed at 1000C for 30 mins) was analyzed in different media conditions and in vitro neuronal cultures using conventional cyclic voltammetry (CV) studies. A 2D finite element analysis was carried out using FEMLAB to evaluate the electric fields around sharp edges of microelectrode arrays and the effect of media properties on electric field intensities were assessed. We conclude that polysilicon, with its added advantages of machinability and compatibility with CMOS processes over conventional metal interfaces, provides a viable material for fabricating 2-way communication interfaces with neurons. (1) Rajarshi Saha and Jit Muthuswamy, Structure-property relationships in the optimization of polysilicon thin films for electrical recording/stimulation of single neurons. Biomedical Microdevices, 9:3, 2007, pp. 345-360.
OO6: Poster Session I
Session Chairs
Virginia L. Ferguson
Carl Frick
Conrad R. Stoldt
John Zhang
Wednesday AM, November 28, 2007
Exhibition Hall D (Hynes)
9:00 PM - OO6.1
Functionalized Porous Silicon in a Simulated Gastrointestinal Tract: Modeling the Biocompatibility of a Monolayer Protected Nanostructured Material.
Lon Porter 1
1 Chemistry, Wabash College, Crawfordsville, Indiana, United States
Show AbstractOwing to its photoluminescent properties and high surface area, porous silicon (por-Si) has shown great potential toward a myriad of applications including optoelectronics, chemical sensors, biocomposite materials, and biomedical implants. However, the native hydride-termination is only metastable with respect to surface oxidation under ambient conditions. Por-Si samples oxidize and degrade even more quickly when exposed to saline aqueous environments. Borrowing from solution phase synthetic methods, a selection of hydrosilylation reactions has been recently reported for functionalizing organic groups onto oxide-free, hydride-terminated porous silicon surfaces. Monolayers, bound through direct silicon-carbon bonds are produced via thermal, microwave, carbocation, and Lewis acid mediated pathways. All of these wet, benchtop methods result in the formation of stable monolayers which protect the underlying silicon surface from ambient oxidation and chemical attack. However, no direct comparison of monolayer stability resulting from these diverse mechanisms has been reported. A variety of alkyl monolayers were prepared on porous silicon using the diverse hydrosilylation routes describe above and then immersed into a sequence of simulated gastric and intestinal fluids to replicate the conditions of potential por-Si biosensors or medicinal delivery systems in the human gastrointestinal tract. Degradation of the organic monolayers and oxidation of the underlying por-Si surfaces were monitored using both qualitative and semiquantitative transmission mode Fourier transform infrared spectroscopy (FTIR). Our initial results indicate that methods employing chemical catalysts incorporate these species within the monolayer as defects, producing less robust surfaces compared to catalyst-free reactions. Regardless, monolayer protected por-Si samples demonstrated superior durability as opposed to the unfunctionalized controls.
9:00 PM - OO6.10
Analysis of Silver Implanted GPC for Medical Applications.
Robert Zimmerman 1 , Claudiu Muntele 1 , Lynn Bowman 1 , Daryush Ila 1
1 Center for Irradiation of Materials , Alabama A&M University, Normal, Alabama, United States
Show Abstract9:00 PM - OO6.11
Diamond-like Carbon Film Coating for Artificial Blood vessels.
Yasuharu Ohgoe 1 , Yousuke Izumo 1 , Kazuya Kanasugi 1 , Akihiko Homma 2 , Kenji Hirakuri 3 , Akio Funakubo 1 , Yoshiyuki Taenaka 2 , Eisuke Tatsumi 2 , Yasuhiro Fukui 1
1 , Tokyo Denki University, Saitama Japan, 2 , National Cardiovascular Center, Osaka Japan, 3 , Tokyo Denki University, Tokyo Japan
Show AbstractDiamond-like carbon films have been interesting in biocompatible coating suitable for improving both short and long term stability in implantable medical devise. Additionally, radio frequency (r.f.) plasma chemical vapor deposition (CVD) technique is very useful for DLC films deposition on most substrates at low temperatures. Recent trials on DLC film coatings have indicated promise for applying to polymeric biomaterials. Polymeric biomaterials, for example polyester and polytetrafluoroethylene, have been applied as artificial blood vessels. However, thrombus formation on the vessel walls could pose a problem in blood compatibility and the long-term use of these materials. In our previous work, we found that DLC film has anti-thrombosis and good cytocompatibility. In order to improve thrombosis on the surface of the vessel’s inner-wall, we utilized DLC film coating on inner-wall of an expanded polytetrafluoroethylene (e-PTFE) artificial vessel, which was a cylindrical textile material. In this study, we focused on structural and compositional effects of DLC films on cell culture and protein adsorption as an investigation of biological response. In order to deposit DLC film uniformly on inner-wall of an e-PTFE vessel, we used r.f .plasma CVD technique with cylindrical electrode. The surface composition, roughness, potential, structures, and wettability of the DLC film was estimated using X-ray photoelectron spectrometer (XPS), Atomic force microscopy (AFM), Ar-laser Raman spectrophotometer (Raman), and contact angle measurement. And then, mouse fibroblasts (NIH 3T3) was grown on the DLC film for periods of up to 4 days. Moreover, protein adsorption experiment was carried out using albumin fibrinogen. The DLC films were deposited uniformly on the e-PTFE vessel inner-wall surface, and the surface results indicated the non-toxic nature of the surfaces on the cells. Additionally, according to the DLC film surface analysis, cell culture, and protein adsorption, it was observed that the cells spread and protein adsorption ratio depended on the surface conditions. This means that the deposition condition of the DLC film is possible to control cell spread and protein adsorption by changing the surface conditions. In recent studies, it has been reported that endothelial cell growth form is the most important factor of anti-thrombosis. This study indicates that the DLC film coating has an effect of endothelial cell growth for anti-thrombosis on the e-PTFE artificial vessel.
9:00 PM - OO6.12
Selected Cell Growth on the Patterned Nanostructured Surfaces.
Jau-Ye Shiu 1 , Chiung Wen Kuo 1 , Peilin Chen 1
1 Research Center for Applied Sciences, Academia Sinica, Taipei Taiwan
Show AbstractThe understandings of the cell-substrate interactions are important in many aspects including biocompatibility, cell culture, cell spreading and tissue engineering. It is recognized that the adhesion of cells on materials depends on surface characteristics such as hydrophobicity, surface charge, surface chemistry and roughness. In this study, pattered nanostructure fluoropolymer surface were use to study of the cell adhesion. By a combine of photolithography and oxygen plasma treatment, pattern fluoropolymer surfaces with various RMS roughnesses ranging from 1 to 35 nm have been obtain. The water contact angles measured on the surface were range from 120o to 168o. When these patterned surfaces were used to culture HeLa and 3T3 cells. It was found that both cell did not adhesion on the flat fluoropolymer surface. However, the adhesion of 3T3 cell on the patterned area increased with the surface roughness. Such nanostructure material could be used the new materials for tissue enginnering.
9:00 PM - OO6.13
Investigation of Astrocytes Growing on Tissue Scaffolds by Scanning Probe Recognition Microscopy.
Qian Chen 1 , Y. Fan 1 , L. Udpa 1 , V. Ayres 1 , I. Ahmed 2 , S. Meiners 2 , R. Delgado-Rivera 2 , S. Harris 2 , A. Rice 3
1 , Michigan State University, East Lansing, Michigan, United States, 2 , UMDNJ-Robert Wood Johnson Medical School, Piscataway, New Jersey, United States, 3 , Veeco Metrology Group, Santa Barbara, California, United States
Show AbstractElectrospun nanofibers in tissue scaffolds structurally mimic the extracellular matrix on which cells grow in vivo. These structures have demonstrated strong potential for use in injuries healing [1][2]. However, much fundamental understanding is needed to design scaffolds with the most appropriate nanobiomechanical properties for particular cells or cell classes. To evaluate the biocompatibility of nanofibers and their potential as a regenerative matrix, the mechanical, topographical and chemical properties of candidate nanofibers need to be analyzed accurately and efficiently. Surface roughness, elasticity, curvature, porosity and mesh density are all important properties of nanofibers which will trigger cell motility towards and adhesion to tissue scaffolds. Our group is using a new technique designed and developed by our group, Scanning Probe Recognition Microscopy, to explore these properties. Scanning Probe Recognition Microscopy allows us to adaptive follow along individual nanofibers within a tissue scaffold. Statistically significant and reliable data for multiple properties can be collected by scanning only over region of individual nanofibers. Surface roughness is investigated using a mapping technique developed by our group, in which the roughness is calculated within a user-defined local neighborhood region of each current pixel, entirely within the nanofiber boundaries [3]. Tissue scaffold elasticity is investigated by collecting force curves on the region of nanofiber where reliability of data is best guaranteed. Curvature is investigated through measurements with slope-based automated tracking optimization, augmented by deconvolution, to include tip-shape broadening and angle-dependence. Porosity and mesh density are investigated by calculating skeletons of nanofibers and fleshing these skeletons with their true diameters recovered from deconvolution.The results of our recent investigations of astrocyte attachment to electrospun nanofiber tissue scaffolds will be presented. In these studies, tissue scaffolds with properties that mimic the basal lamina which forms part of the blood brain barrier are investigated. The results of combined Scanning Probe Recognition Microscopy and Immunohistochemistry investigations are correlated and presented. [1] S. Meiners, I. Ahmed, A.S. Ponery, N. Amor, V.M. Ayres, Y. Fan and N.B. Ashwin, “Engineering Electrospun Nanofibrillar Surfaces for Spinal Cord Repair: A Discussion”, in press, Polymer International (2007)[2] J.C. Hu and K.A. Athanasiou, “A Self-assembling Process in Articular Cartilage Tissue Engineering”. Tissue Eng, Vol. 12, pp. 969-79 (2006)[3] Y. Fan, Q. Chen, V.M. Ayres, A.D. Baczewski, L. Udpa and S. Kumar, “Scanning Probe Recognition Microscopy Investigation of Tissue Scaffold Properties”, in press, Int. J. Nanomedicine (2007)Acknowledgements: The support of National Science Foundation DMI-0400298 is gratefully acknowledged.
9:00 PM - OO6.3
Engineering the Interface of Nanoparticle Molecular Magnetic Imaging Agents for Tailored Proton Relaxivity.
Conrad Stoldt 1 , Brian Larsen 1 , Michael Haag 1
1 Mechanical Engineering, University of Colorado, Boulder, Colorado, United States
Show Abstract9:00 PM - OO6.5
The Bactericidal Effect of Silver Nanoparticles and Nanowires.
Domingo Ferrer 1 , Patrick Chen 1 , Miguel Jose-Yacaman 1
1 Chemical Engineering Department, The University of Texas at Austin, Austin, Texas, United States
Show Abstract9:00 PM - OO6.6
Micropatterned Polymer Substrates That Efficiently Orient Myotubes in Monolayers Cultures.
Jacinthe Gingras 1 , Robert Rioux 2 , Damien Cuvelier 3 , L. Mahadevan 3 , George Whitesides 2 , Jeff Lichtman 1 , Josh Sanes 1
1 Cellular and Molecular Biology, Harvard University, Cambridge, Massachusetts, United States, 2 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States, 3 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractThe regeneration and functional recovery of skeletal muscles following damage, from either endogenous or implanted stem cells, requires that the newly-formed myotubes align with each other in the proper orientation. In order to assess methods for promoting appropriate orientation, we have used C2C12 myoblasts, which typically grow and fuse in vitro, but lack alignment and orientation. Myoblasts were grown on poly (dimethylsiloxane) (PDMS) micropatterned surfaces fabricated by soft-lithography. We tested cubic, staggered-cubic, and hexagonal arrays of micron tall line, square, circle or diamond posts. Myoblasts fused into myotubes on all of them, but aligned on only a subset of them suggesting that myoblasts are sensitive to shape, height and symmetry of the patterned surfaces. Cubic patterns bearing square posts and diamonds both allowed for alignment of myotubes. On these surfaces, myotubes aligned at a ~25o angle across the posts or followed the diamond features along their lengths. This second pattern was reminiscent of the behavior of C2C12 cells on parallel lines, where alignment was successful (as expected) and parallel to the features. Circular posts or staggered-post patterns with cubic symmetry did not show any sign of alignment. All features were 20 μm wide and separated by 20 μm, and diamonds were 40 to 60 μm in length. A series of feature heights were also analyzed, and features of 3.5 μm height had the best alignment profile. This was also true for linear features, but shorter patterns (0.6 μm high lines) revealed an interesting feature where myotubes ran at a ~10o angle across the lines. We investigated cell motility to understand differences in alignment as a function of substrate patterning with live-imaging of myoblasts during their independent growth and fusion phases. Cellular alignment radiated from a focal point of dense myoblasts and spread to vicinal cells regulating their orientation and division properties.We also examined the molecular architecture of the myotube surface, using antibodies to label focal adhesion sites (anti-talin), the actin cytoskeleton (phalloidin), and the postsynaptic membrane (acetylcholine receptors). We found that topography of the substrate influences the location and the structure of all of these specialized domains. We have demonstrated that micropatterned PDMS substrates provide long-range cues that organize assembly of myoblasts into large (cm2) sheets of oriented myotubes, as well as short-range cues that organize adhesive and synaptic structures on individual myotubes. These results suggest a new approach for skeletal muscle tissue engineering.
9:00 PM - OO6.7
Ellipsometric Characterization of E. coli and C. xerosis Bacteria Films on Nanocomposite Carbon Surfaces.
Javier Avalos 1 , T. Merced 2 , K. Uppireddi 1 , B. Weiner 3 , G. Morell 1
1 Department of Physics, Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States, 2 Department of Science and Technolgy, Universidad Metropolitana, San Juan, Puerto Rico, United States, 3 Department of Chemistry, Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Rico, United States
Show AbstractWe have studied the optical properties of E. coli and C. xerosis bacteria films on nanocomposite carbon surfaces. There is strong interest in understanding the growth behavior of bacteria on various nanostructure media, such as nanoporous silicon, nano cobalt ferrite, and nano zinc oxide. Previous studies have focused on the bacterial attachment to surfaces, since this strongly influences many industrial and natural processes. Ellipsometric measurements of the refraction index, absorption and extinction coefficients were done during the logarithmic stage of bacterial growth. An increment in refraction index was observed that corresponds to a decrease in bacterial film thickness. The effective refraction index was measured to be 1.39 and 1.80 for E. coli and C. xerosis, respectively. The interaction between bacteria and the nanocomposite carbon surface is discussed.
9:00 PM - OO6.8
Structural Orientation Control of Hadroxyapatite Thin Films for Optimization of Surface Adsorption Property.
Takao Kobayashi 1 , Wakana Hara 1 , Yusaburo Ono 1 , Mamoru Yoshimoto 1
1 Department of innovative and enginnered material, Tokyo institute of technology, Yokohama Japan
Show AbstractHydroxyapatite (HAp; Ca10(PO4)6(OH) 2) is widely used as the artificial bone and dental. Moreover, it has the other functions such as ion adsorption etc. based on the particular surface structure of HAp. And it has the excellent property that is adsorbed protein, amino acid and various bacteria. The protein adsorption characteristics of HAp are affected by the atomic arrangement of Ca2+ and PO43- in the topmost adsorption surface site. Acid protein is preferentially adsorbed on the a-plane where Ca2+ exists mostly, and basic protein is adsorbed on the c-plane where PO43- exists mostly. Thus, it is important from the point of technology applications to control orientation of the topmost surface structure of HAp thin films. In this study, we aim achievement of c-axis preferential orientation of HAp thin films that is expected to make an improvement of surface adsorption property. In experiment, the deposition of thin films was conducted by pulsed laser deposition (PLD) method. We used the atomically flat ultra-smooth sapphire (0001) substrates (α-Al2O3), which have atomic steps of 0.2 nm in height and atomically flat terraces of 50-100 nm in width [1]. HAp has good lattice matching with sapphire substrates. KrF excimer laser beam (wavelength of 248 nm) was irradiated onto the sintered HAp target. We examined the influence of physical or chemical surface treatment of the substrate on crystal orientation of HAp thin films. Sapphire substrates were treated by sodium carbonate solution. As the result, nano-level surface morphology of the substrates didn’t change after the treatment but the surface hydrophilic property increased drastically. HAp films were deposited on the treated substrate and annealed at 500oC. Compared with the non-treatment substrates, enhanced c-axis orientation due to the chemical surface treatment was clearly observed by XRD analysis. In addition, it was observed by AFM that there was significant difference in the initial growth process of HAp films. [1] M. Yoshimoto et al., Appl. Phys. Lett. 67 (1995) 2615
9:00 PM - OO6.9
3-Mercaptopropionic Acid modified Porous Silicon Substrate used in Hyperammonemia.
Dong-hwa Yun 1 , Suk-In Hong 1 , Woojin Lee 1 , Jun-Hyoung Chang 1
1 Chemical & Biological Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractUrea is a biomolecule that is known to play a variety of roles for the welfare of mankind. The well-known role of urea is as a fertilizer, which satisfies the nitrogen requirement of the plant. However, in the human body it is a waste product. The urea sensors become indispensable in diabetics monitoring, in order to predict the nature and cause of diabetes and also as a direct indication for the onset of kidney failure or malfunctioning of the liver. With this sole motivation of monitoring urea levels in blood for an early diagnosis of organ dysfunction, an attempt has been made for the fabrication of urea sensor based on the membrane immobilization technology. Even though the various technologies such as UV-visible spectroscopy, potentiometry, ammonium ion-selective field effect transistor, coulometry and amperometry are applied for the monitoring of the urease-catalyzed reactions, the amperometric method gives the best result to diagnose hyperammonemia. However, because sensitivity in low concentration decreases remarkably, despite amperometric urea sensor has been studied for a long time it has not been applied for clinical diagnosis. In this paper, a new structure for an amperometric urea sensor was fabricated by MEMS, electrochemical etching, and electrostatic covalent binding techniques. Until now most amperometric urea sensors have had a membrane fixed on top of the transducer. That method often leads to malfunction of the sensor, arising from problems such as inadequate membrane adhesion, insufficient mechanical stability, and low sensitivity. To solve these kinds of problems, urease (Urs) was immobilized by electrostatic covalent binding method on the porous silicon substrate coated self-assembled monolayer (SAM). Electrostatic covalent binding method was used to keep anisotropic orientation of urease on SAM.
Symposium Organizers
Virginia L. Ferguson University of Colorado
John X.-J. Zhang The University of Texas-Austin
Conrad Stoldt University of Colorado
Carl P. Frick Abbott Vascular
OO7: Tissue Mechanics and Interfaces
Session Chairs
Reinhold Dauskardt
Virginia L. Ferguson
Carl Frick
Wednesday AM, November 28, 2007
Room 206 (Hynes)
9:00 AM - **OO7.1
Micro-mechanical Investigation of Fluid Interaction in Mineralised Tissues.
Andy Bushby 1 , Amanpreet Bembey 1 , Michelle Oyen 2
1 Centre for Materials Research, Queen Mary, University of London, London United Kingdom, 2 Engineering, University of Cambridge, Cambridge United Kingdom
Show AbstractMineralised tissues are composed of three main phases: mineral (carbonated apatites), protein matrix (mainly collagen) and water. The role of water in interacting with collagen and mineral to determine the mechanical properties at the ultra-structure scale is not clear. However, changes in mechanical behaviour in response to dehydration are important to the understanding of bone fracture and the influence of surgical or therapeutic procedures. Several studies have shown that these materials increase in stiffness on dehydration and that water acts as a plasticizer in collagen. Replacing the water with solvents of different polarity and molecular weight can change the stiffness and viscoelastic response by a factor of two. Here we use a nanoindentation creep methodology to explore the viscoelastic response of bone in a wide range of solvents. Ramp-and-hold loading using a spherical indenter geometry has been shown to be a promising method for determining the viscoelastic response of polymers. An analysis of the deformation under constant load using the elastic-viscoelastic correspondence principle was used to determine the time-zero shear modulus and infinite time shear modulus; the ratio of these two parameters giving a measure of extent of viscoelasticity. Bone samples were immersed in a series of solvents with different concentration and polarity. The experimentally-determined mechanical responses were considered within the context of solution physical chemistry. Although the stiffness of the tissue increased with the dielectric constant of the solvent, so did the relative viscoelastic response. The experimental data are also consistent with a poroelastic model, in which fluid is squeezed through a porous elastic network. Such experiments provide new ways to examine the ultrastructural configuration of biological composites and gain insights into the origins of their mechanical behaviour.
9:30 AM - OO7.2
Electromechanical Imaging of Biological Systems.
Alexey Vertegel 1 , Gary Thompson 1 , Brian Rodrigues 2 , Katyayani Seal 2 , Stephen Jesse 2 , Irene Revenko 3 , Sophia Hohlbauch 3 , Roger Proksch 3 , Sergei Kalinin 2
1 Bioengineering, Clemson University, Clemson, South Carolina, United States, 2 , Oak Ridge national laboratory, Oak Rodge, Tennessee, United States, 3 , Asulym Research, Santa Barbara, California, United States
Show AbstractThe coupling between mechanical and electrical phenomena is quintessential to the functionality of all biological systems, including cellular and tissue-level processes in the heart; subcellular voltage channel activity; and molecular-shape transformations during electrochemical and proton-transfer reactions on the molecular level. Although electromechanical properties of various cell types have been extensively studied, little is known about origins of biological electromechanical phenomena at the cellular and subcellular scale. Understanding the underlying molecular mechanisms will have a tremendous impact on general understanding of biological processes and specific biomedical applications. Electromechanical stimulation of cells at the nanoscale is one of the key challenges in understanding biological systems. Insufficient information about electromechanical phenomena in biological systems is a result of the lack of characterization techniques 1) capable of providing such information on the submicron to nanometer scale, and 2) capable of operation in a liquid environment. Recently, high-resolution piezoresponse imaging of model ferroelectric lead zirconate-titanate ceramics in aqueous solutions has been demonstrated [1]. The ability to map electromechanical properties in aqueous media points the way to the electromechanical characterization of biological systems in native-like conditions.Here, we extend liquid PFM for imaging of biological systems in aqueous media. We performed solution PFM imaging of a number of model biosystems including one-dimensional assemblies of biomolecules (amyloid fibrils) and living cells (myocytes and breast adenocarcinoma cells). In the case of imaging of biomolecular assemblies, lysozyme and insulin fibrils were prepared by heating native proteins in acidic media and imaged on conductive ITO glass in distilled water. The fibrils were electromechanically active in solution and showed amplitude response linear with applied voltage, consistent with piezoelectric effect. Imaging of living cells grown on ITO glass was attempted in electrolyte-free media to reduce propagation of the electric field from the tip apex that results in the uniform biasing of the liquid and dramatic loss of resolution. Electrolytes were substituted for isotonic glucose to achieve cell viability for the period of PFM experiment. In these conditions, the response signals from adenocarcinoma cells were weak with only cell boundaries being resolved. On the contrary, strong PFM amplitude and phase responses were observed in the case of myocytes, consistently with their much higher electrophysiological activity in vivo. Thus, PFM can be used as a tool for characterization of complex electromechanical responses related to electrophysiological activity in biological systems. Research was supported through CNMS user proposals #2005-075 and #2006-049, and NSF #CMS-0619739.1. B.J. Rodriguezet. al, Phys. Rev. Lett. 96, 237602 (2006).
9:45 AM - OO7.3
A Bacterium’s Sense of ``Touch."
Ruchirej Yongsunthon 1 2 , Brian Lower 3 , Vance Fowler 4 , Emily Alexander 4 , Steven Lower 2
1 , Corning Incorporated, Corning, New York, United States, 2 , Ohio State University, Columbus, Ohio, United States, 3 , Pacific Northwest National Laboratory, Richland, Washington, United States, 4 , Duke University, Durham, North Carolina, United States
Show Abstract10:00 AM - OO7.4
Damage Modes in Dental Enamel under Simulated Dentition Loads – the Importance of Interface between Enamel Rods.
Hanson Fong 1 , Lois Lee 1 , Shane White 4 , Michael Paine 3 , Martha Somerman 2 , Malcolm Snead 3 , Mehmet Sarikaya 1
1 Materials Sci & Eng, University of Washington, Seattle, Washington, United States, 4 Endodontics, University of California at Los Angeles, Los Angeles, California, United States, 3 Center for Craniofacial Molecular Biology, University of Southern California, Los Angeles, California, United States, 2 Periodontics, University of Washington, Seattle, Washington, United States
Show AbstractMammalian dental enamel is an eloquent example of nature's ability to produce a biological material that is well adapted for its function. Evidence of the overall functionality of this material is in its ability to withstand a lifetime of complex stresses under complex fatigue conditions. Key structural features of the mammalian tooth include the presence of a bilayer composite consisting of two dissimilar tissues: hard enamel on the outside and tough dentin on the inside. We studied the mechanism(s) of mechanical coupling across this unique biological bilayer system by simulating the stresses the tooth is subjected to during mastication processes. The simulation was carried out by performing mechanical indentation in single static loading as well as cyclic fatigue loading on occlusal surfaces of healthy human molars (extracted wisdom teeth) and healthy human molars with enamel replaced by porcelain, a common ceramic dental restorative material. After loading, damage modes were assessed by preparing cross-sections of the tested regions and observed by scanning electron microscopy. The results revealed a significant difference in patterns of crack propagation between the two materials in both loading conditions. In static loading, the porcelain was damaged predominantly in cone cracks, which was predicted by established models on hard/soft bilayer composites [1]. Dental enamel, on the other hand, revealed that crack propagation was primarily controlled by the anisotropic microstructure. Specifically, cracks were found to follow the interface of enamel rods. In fatigue test, the damages found in porcelain were cone cracks with significant coalescence of microcracks around the contact region, which resulted in the surface material debonding from the bulk. The natural enamel, on the other hand, exhibited quasistatic yielding with crack lengths, again, approximating the rods without any material removal. These results demonstrate that the anisotropic nature of the hierarchically structured enamel with weaker interfacial strength between rods is well designed for containing crack propagation and thereby preserving the longevity of the tooth as a mastication tool.This work was supported NIDCR/NIH DE015109 and T32 DE07023-29 and carried out at the NSF-MRSEC Shared Experimental Facilities at the UW.1.B. R. Lawn, J. Am. Ceram. Soc., 81, 1977 (1998).
10:15 AM - OO7.5
Modeling the Aragonite-Protein Interface in Nacre: Weak Nonbonded Interactions Play a Significant Role on Mechanics of Nacre Proteins.
Pijush Ghosh 1 , Dinesh Katti 1 , Shashindra Pradhan 1 , Rahul Bhowmik 1 , Kalpana Katti 1
1 Civil Engineering, North Dakota State University, Fargo, North Dakota, United States
Show AbstractNacre is a laminated bio-nanocomposite of exceptional mechanical properties that exhibits a unique combination of high strength and fracture toughness. It comprises of 95% inorganic phase in the form of aragonite tablets and about 5% organic. Nacre exhibits a work of fracture about 3 orders of magnitude higher than that of monolithic ceramics and 3000 times that of pure aragonite. The reasons of its extraordinary mechanical properties were previously thought to be a result of its hierarchical morphology and microstructural nuances. However, our previous study using finite element model of nacre predicted that the organic phase has significantly high stiffness as compared to ordinary polymer, which is necessary for high strength of nacre. This was confirmed by our previous study using molecular dynamics that shows the presence of significant nonbonded interactions between aragonite and protein. The proximity of mineral (aragonite) to protein was shown to impart very high stiffness to protein with a help of steered molecular dynamics (SMD). The stiffer mechanical response of protein resulted in several fold greater dissipation of energy during unfolding of protein in the proximity of aragonite. In addition, the observed behavior was found to be dependent on the rate of deformation of protein. We also describe the effect of varying velocity of pulling during SMD on the mechanics at the organic-inorganic interface in nacre. In this work we present the specific molecular mechanisms responsible for enhanced mechanical behavior of nacre protein in the proximity of aragonite. These results shed light on the extraordinary ability of organic components of nanocomposites to function as a strong mortar-material while retaining a capability to undergo larger deformation necessary for toughness.
10:30 AM - **OO7.6
Mechanical Performance of Orthotropic Stalks, Stems and Tubes with a Graded Microstructure.
Ulrike G.K. Wegst 1
1 Dept of Materials Science & Engineering, Drexel University, Philadelphia, Pennsylvania, United States
Show Abstract11:00 AM - OO7: Tissues
BREAK
11:30 AM - **OO7.7
Biomechanics of Human Stratum Corneum.
Reinhold Dauskardt 1 , Kemal Levi 1
1 , Stanford University, Stanford, California, United States
Show AbstractThe outermost layer of skin, the stratum corneum (SC), provides mechanical protection and a controlled permeable barrier to the external environment while subject to highly variable conditions including changing temperature, humidity, mechanical and abrasive contact. The biomechanical properties of the SC are crucial for its mechanical and biophysical function, its cosmetic “feel” and appearance, and play a central role in skin damage processes of skin chapping and cracking. We describe a thin-film mechanics approach to characterize and model the biomechanical function of human SC. Techniques involving both in-plane and out-of-plane mechanical and intercellular delamination characterization are described. We demonstrate how environmental, enzymatic and chemical treatments to systematically manipulate and influence components of the SC tissue including intercellular lipids, corneodesmosomes and intracellular keratin affect resulting mechanical properties. In addition to stress-strain and viscoelastic properties, we describe novel thin-film methods to probe the resistance to time dependent intercellular delamination and the stresses that arise naturally in SC as a result of treatment or environmental conditions. We finally demonstrate how damage processes in human skin can be quantitatively modeled and predicted based on thin-film biomechanics and cracking processes. We believe that this represents a new approach to characterize and model the fundamental biomechanics of human SC.
12:00 PM - OO7.8
Nanoscale Oscillatory Deformation of Cartilage.
Lin Han 1 , Jacqueline Greene 1 , Han-Hwa Hung 5 , Eliot Frank 5 , Christine Ortiz 1 , Alan Grodzinsky 2 3 4
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 5 Center for Biomedical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Biological Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractArticular cartilage contains a fibrillar network of collagen, ~ 60% of tissue dry weight (mostly type II with fibril diameter ~ 30 – 80 nm). Gaps between fibrils (>~ 100 nm) are filled with negatively charged proteoglycans (PG, ~ 35% dry weight). Both collagen and PG significantly contribute to cartilage compressive stiffness. Here, we studied time-dependent AFM-based dynamic nanoindentation of cartilage over a wide range of deformation amplitudes (~ 2 – 100 nm) and frequencies (f ~ 1 – 1000 Hz) using different probe tip geometries. Disks of bovine calf cartilage, 0.5mm thick, were harvested from the middle zone of the femoropatellar groove; PG-depleted samples were prepared by digestion in 1mg/mL trypsin and 0.1U/mL chondroitinase ABC, 24 hrs each. Sinusoidal loading was performed using both a neutral colloidal spherical probe tip (end radius R ~ 2.5 μm, spring constant k ~ 0.58N/m) and a neutral pyramidal probe tip (R ~ 50 nm, k ~ 0.58N/m) applying after a 1 minute ramp-and-hold tip displacement to ~ 1 μm offset indentation depth. Effective dynamic stiffness E was calculated using Hertz model for small amplitude loading. At ~ 2 nm amplitude using the spherical tip, E increased nonlinearly for both nontreated (153±10 to 512±43 kPa, n ≥ 6 different positions, mean±SEM) and digested (108±10 to 235±9 kPa) cartilage samples as f increased from 1 to ~ 300 Hz, due to poroviscoelastic behavior. E further increased to 338±48 kPa for the digested cartilage, but did not change for nontreated cartilage (513±16 kPa) at f = 1000 Hz. These different trends at higher f may be due to a reduction in the characteristic poroelastic relaxation time caused by PG removal. Similar frequency dependence was observed with the pyramidal probe tip. With both tips, PG removal caused a ~ 40% decrease in E. There was no significant change in E for the untreated sample when the amplitude increased from ~ 2 to 100 nm. Interestingly, while E measured via the spherical tip was constantly lower for the digested sample at all f, digestion did not alter E for the pyramidal tip at 1 – 30 and ~ 1000 Hz. As pyramidal tip end-radius is on the order of collagen fibril diameter, this tip is more likely probing the properties of the solid fibrils, which may not be significantly affected by removing PG; the spherical tip measures micro-scale stiffness related to both fibrils and PGs. Hence, nanoscale dynamic loading of cartilage using different tip geometries and PG removal enabled a unique study of cartilage dynamic deformation mechanisms and matrix structure (collagen fibril diameter, pore size) and composition.
12:15 PM - OO7.9
Sub-surface Observations of Plastic Deformation in the Mammalian Lung.
Maricris Silva 1 , Zhijia Yuan 2 , Zhenguo Wang 2 , Jae Kim 1 , Yingtian Pan 2 , Andrew Gouldstone 1
1 Materials Science and Engineering, SUNY Stony Brook, Stony Brook, New York, United States, 2 Biomedical Engineering, SUNY Stony Brook, Stony Brook, New York, United States
Show AbstractIn previous abstracts we have shown that the mammalian lung can exhibit quasi-plastic mechanical properties. It was postulated that this behavior was due to the onset of atelectasis, or local alveolar collapse. In addition, it was shown that indentation was an effective way to characterize atelectasis, as a function of inflation pressure, or gas composition. However, the mechanisms remain unclear, mainly due to the lack of sub-surface observation. In this talk, we will discuss how we have addressed this need, with in-situ images of sub-surface lung deformation using Optical Coherence Tomography (OCT). Rat lungs were inflated to various physiologic pressures, and indented using both spherical and cylindrical (“rib-like”) indenters, and atelectasis observed in-situ. In addition, deformation patterns were compared to FEM models that incorporated lung parenchyma and surface pleural membrane. By comparing the models and experiments, we are able to draw robust conclusions concerning the mechanical criteria for atelectasis, namely the effects of hydrostatic pressure or shear, on alveolar collapse.
12:30 PM - OO7.10
Age-related Architectural Variations in Individual Human Cartilage Aggrecan Macromolecules.
Hsu-Yi Lee 1 , Laura Daher 2 , Laurel Ng 4 , Peter Roughley 5 , Alan Grodzinsky 1 3 4 , Christine Ortiz 2 4
1 Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Biological Engineering Division, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 5 Joint Diseases Laboratory, Shriners Hospital for Crippled Children, Montreal, Quebec, Canada, 3 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractAggrecan, the most abundant proteoglycan in the extracellular matrix of all cartilaginous tissues, enables the tissue to perform its biomechanical function in articular joints. Electrostatic repulsion forces between the highly negatively charged sulfate glycosaminoglycan (GAG) chains of aggrecan are known to provide >50% of the equilibrium compressive modulus of cartilage. Embedded within the collagen network, aggrecan also protects collagen from proteolytic cleavage by collagenases. Structural variations of aggrecan have been found as a function of age which are associated with age-related degeneration of cartilage function, a hallmark of the disease osteoarthritis (OA). Therefore, the correlation between aggrecan structure and age has been one of the important topics for OA studies. Here, we utilized tapping mode atomic force microscopy (AFM) in ambient conditions to directly image individual aggrecan macromolecules extracted from newborn and adult (38 yr) human articular cartilage and sparsely adsorbed on 3-aminopropyltriethoxysilane functionalized mica substrates. Nanometer-scale resolution of individual GAG chains was achieved, as well as the C- and N-terminal domains of the core proteins. An image processing program was created to automatically trace the contours of single aggrecan macromolecules and its constituent GAG polymer chains. The measured aggrecan core protein trace length and end-to-end length of newborn human aggrecan (473±95 and 366±96 nm, mean±std, respectively) were both larger than that of adult human aggrecan (348±113 and 242±82 nm, respectively). By using the worm-like chain model to calculate the persistence length, newborn aggrecan was found to be stiffer than adult aggrecan by a factor of 1.6 (262 and 164 nm, respectively). Moreover, the length of newborn aggrecan GAG chains was ~ 1.5 longer than that of the adult aggrecan, in agreement with the known age-related change in the hydrodynamic size of human articular aggrecan in other studies. The percentage of full length aggrecan (containing both G1 and G3 domain) observed from newborn aggrecan monolayers (44.6%) was also higher than that of adult aggrecan monolayers (9.8%). This reflects the fact that progressive C-terminal truncation of the core protein by proteolytic enzymes takes place with increasing maturation. Continuing research is aimed at the study of age-related variations of aggrecan nanomechanical properties and their correlation with aggrecan structure.
12:45 PM - OO7.11
Mechanical Response of Molecular Collagen and Influence of Mineral Proximity in Natural Bone.
Rahul Bhowmik 1 , Kalpana Katti 1 , Dinesh Katti 1
1 Civil Engineering, North Dakota State University, Fargo, North Dakota, United States
Show AbstractBone is a highly complex structure which primarily consists of hydroxyapatite (HAP) and collagen. It has unique mechanical properties which depend upon its structural hierarchy. The hierarchy in structure starts from molecular scale, and spans over several orders of length scales to macroscopic scale. At the nanoscale level, molecular collagen interacts with specific surface of hydroxyapatite through telopeptides. In this work the influence of mineral on the mechanical properties of collagen is analyzed by steered molecular dynamics simulations. It has been performed by pulling the collagen molecule in close proximity and in absence of HAP at constant velocity. Simulations results have shown that collagen require more energy to deform in close proximity of HAP as compared to collagen in absence of HAP. Different reasons which are responsible for the observed features in load-deformation plots of collagen in close proximity and in absence of HAP have been investigated. It has been observed that the mineral influences the interaction between collagen and water. Also, the load-carrying behavior of collagen has been analyzed at different velocities. It has been performed by pulling the collagen in close proximity and in absence of HAP at different velocities. The energy which is required to deform the collagen molecule in close proximity and in absence of HAP decreases with decrease in velocity.
OO8/AA7: Joint Session: Nanomechanics and Tribology of Biological Materials
Session Chairs
Virginia L. Ferguson
Michelle L. Oyen
Wednesday PM, November 28, 2007
Room 208 (Hynes)
2:30 PM - **OO8.1/AA7.1
From Sharks to Gummi-Bears.
Susan Enders 1
1 , Max Planck Institute, Stuttgart Germany
Show AbstractNanoindentation and Nanotribology have been proven to be valuable tools for testing relatively stiff biological materials and polymers. But as always, the devil lies in the detail. For instance, biological samples are almost always composite materials, but only the properties of one particular component are of interest. This component often exists only in very small quantities and cannot easily be separated from the surrounding material. Second, bio-materials are extremely sensitive to desiccation. Testing can only be done under physiological conditions, for which equipment and methods are usually not designed for. Third, the majority of biological samples exhibit modulus and hardness values in the kPa-MPa range in which the accuracy of the measurements is limited.In my talk I will present and discuss experiments addressing all of the three problems above. Measurements on cartilage of fish are examples for tests under physiological conditions. The influence of sample preparation will be shown on samples of rubber-like proteins of insects.One conclusion from our tests on biomaterials is that still a lot of work has to be done to determine the influence of surface identification, viscoelasticity and adhesion on testing compliant materials. As a first step in this direction nanoindentation studies on polymers with different moduli will be presented, with focus on the initial contact identification during indentation testing and surface deformation outside the contact area.
3:00 PM - OO8.2/AA7.2
Nanoindentation Deformation Partitioning Reveals Insight into Mineral-modulus Relationships in Bone.
Virginia Ferguson 1
1 Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, United States
Show AbstractNanoindentation testing of bone is highly sensitive to minute changes in bone composition (i.e., relative amounts of mineral, organic, and water) and microstructural organization. Biological variability, a critical factor in the study of mineralized tissues, is present within a single sample of bone between adjacent, closely spaced sites. Two dimensional indentation arrays were placed within a single region (e.g., osteonal or interstitial) in PMMA-embedded human subchondral bone. The relationship between indentation modulus and mineral volume fraction shows a familiar positive correlation, as has been previously reported for mechanical properties collected via larger scale testing methods, but with substantial variability in both modulus and mineral volume fraction. Elastic indentation modulus (spherical tip, R=5 microns) varied significantly with little change in mineral volume fraction within the spacing of several microns. Similarly, Berkovich indentations demonstrated that creep deformation at the maximum applied load (Pmax) varied spatially between adjacent indentation sites as well as within any single value for mineral volume fraction. These Berkovich data at each indentation site are deconvoluted into elastic, plastic, and viscous components to reveal the relationships of each with mineral volume fraction. Such partitioning of deformation measurements permits insight into one potential source of biological variability in bone physical properties and clarifies the relationship between local mechanical properties and mineralization.
3:15 PM - OO8.3/AA7.3
Dynamic Oscillatory Compression of Individual Cartilage Chondrocytes.
BoBae Lee 1 , Lin Han 1 , Eliot Frank 2 , Alan Grodzinsky 3 4 5 , Christine Ortiz 1
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Center for Biomedical Engineering, MIT, Cambridge, Massachusetts, United States, 3 Electrical Engineering and Computer Science, MIT, Cambridge, Massachusetts, United States, 4 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States, 5 Biological Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractChondrocytes are continuously loaded and unloaded as articular cartilage is deformed during ambulatory motion (from 1 Hz, walking, up to 1 kHz from higher harmonics of impact loading). While static compression of cartilage inhibits chondrocyte synthesis of the tissue’s extracellular matrix (ECM), oscillatory compression is known to stimulate ECM synthesis in animal and human cartilages. Thus, knowledge of the dynamic mechanical properties of living chondrocytes can help to understand how chondrocytes within their native dense ECM respond to physiological mechanical stimuli. In this study, we report the nanoscale dynamic mechanical properties (i.e. complex modulus and phase angle) of single chondrocytes cultured in vitro for increasing periods of time, measured using atomic force microscopy (AFM)-based nanoindentation. The effect of frequency (1-316 Hz), culture duration (freshly isolated (day 0) and cultured bovine chondrocytes (day 7, 14, 21, and 28)), and tip length scale and geometry was investigated (both pyramidal (end radius, Rtip~50 nm) and colloidal spherical (Rtip~2.5 μm) probe tips were employed). Each cell was first pre-indented to 1 μm in a microfabricated silicon well and then a small sinusoidal displacement (~5 nm amplitude) was applied via an external wave generator. Dynamic loading data were analyzed via Fast Fourier Transform by fitting the measured force and displacement to a sinusoidal function to obtain the magnitude and phase of the complex modulus. The complex moduli at each culture day varied with frequency for the spherical probe tip. On day 0, the magnitude increased from 1.52±0.26 kPa at 1 Hz (mean±SEM) to 12.1±1.73 kPa at 316 Hz. The magnitude at each frequency increased gradually with culture duration; e.g., from 13.6±2.07 kPa for day 7 to 21.9±6.63 kPa for day 28 at 316 Hz. Similarly, the phase angle changed with frequency and culture period. For day 0 chondrocytes, the phase angle increased from 18.8±3.78 deg at 1 Hz to 65.8±2.06 deg at 316 Hz. At 100 Hz, the phase angle for day 7 and day 28 cells was 29.5±2.15 deg and 43.8±3.41 deg, respectively. There was a significant effect of frequency on the magnitude and phase angle of the complex modulus at 316 Hz for both probe tips at each culture day (p<0.05, ANOVA with post-hoc Tukey-Kramer test). Similar trends were obtained with the pyramidal tip, but the values were slightly lower. Interestingly, a semi-log plot of the complex modulus vs. frequency showed sharp change at 100Hz, suggesting that different loading mechanisms may exist for higher frequency loading. Thus, the mechanical properties of single chondrocytes depended on frequency, but were not strongly dependent on culture duration in this study. This is first dynamic loading of chondrocytes to our knowledge. Also, the increase in magnitude and phase with frequency is indicative of intracellular energy dissipation; further work is needed to distinguish between visco- and poroelastic dissipation mechanisms.
3:30 PM - OO8.4/AA7.4
Analyzing Structure-Property Linkages in Bone using Spherical Nanoindentation and Raman Spectroscopy.
Siddhartha Pathak 1 , Melanie Patel 1 , Surya Kalidindi 1 , Hayden-William Courtland 3 , Karl Jepsen 3 , Haviva Goldman 2
1 Department of Materials Science and Engineering, Drexel University, Philadelphia, Pennsylvania, United States, 3 Department of Orthopaedics , Mount Sinai School of Medicine , New York, New York, United States, 2 Department of Neurobiology & Anatomy, Drexel University College of Medicine, Philadelphia, Pennsylvania, United States
Show AbstractBone is a composite material whose mechanical performance is strongly dependent on the complex details of its internal hierarchical structure. Using Raman spectroscopy (RS), in combination with a novel nanoindentation analysis technique, we seek to improve our understanding of the linkages of bone’s composition to its local properties at the lamellar level, thus enhancing our ability to predict bone fracture risk.Femora from three different mouse strains, known to differ in their whole-bone mechanical properties (A/J, C3H/HeJ [C3H], and C57BL/6J [B6], 16 wks of age) were embedded in PMMA, sectioned transversely below the third-trochanter and surface polished to 0.05µm. RS (data mapped across 60 x 60 μm ROI at 2 μm intervals) was used to assess the compositional details across the postero-lateral cortex of each sample. Specifically, the mineral to matrix ratio (defined as the phosphate to CH2-wag peak intensity ratio) was calculated to provide a measure of the degree of mineralization of the bone matrix. Nanoindentations (20µm apart, in a single row) were carried out across this same cortex with a 13.5 µm radius spherical diamond tip. In order to better elucidate trends in elastic and post-elastic behavior at the lamellar level in bone, we have developed and utilized a technique for translating nanoindentation generated load-displacement curves into indentation stress-strain (ISS) curves. These ISS curves were used in combination with our RS ratios to study property–composition relationships in these mice bone. Our results demonstrate inter-strain differences in nanomechanical properties which are consistent with those reported in macro-mechanical testing of these mouse strains. Specifically our experiments show a strong correlation between the mineral to matrix ratios obtained from RS and the elastic modulus values obtained from the ISS curves. The modulus values, which are low for regions of lower mineralization, increase across the cortex as the indenter encounters bone of higher mineralization. By using ISS curves we are able to obtain these modulus values from the loading segment itself, where the spherical indenter is pressed on to a flat, undeformed bone surface. The resulting modulus is therefore more accurate than a modulus calculated using unloading curves, which would reflect a surface altered by prior indentation. Moreover, examination of the ISS curves taken at a 40µm distance from the actively forming periosteal surface of each strain demonstrate that all three have similar slopes during (elastic) loading, but vary in post yield behavior; A/J demonstrates the highest hardening slope, while B6 demonstrates the lowest. Our combined property-compositional analysis of bone represents a significant advancement in the characterization of mechanical behavior of bone .As such this study constitutes a crucial first step in the formulation of a rigorous framework for establishing structure-property linkages in bone.
3:45 PM - OO8.5/AA7.5
Nanoindentation as Tool to Investigate Micro-mechanical Properties in the Hierarchical Structure of Biological Materials.
Christoph Sachs 1 , Helge Fabritius 1 , Dierk Raabe 1
1 Microstructure Physics and Metal Forming, Max-Planck-Institut fuer Eisenforschung, Duesseldorf Germany
Show AbstractIn biological materials like arthropod exoskeletons or bone the mechanical properties vary with the length scale due to their hierarchical organization. The exoskeleton of our model organism, the American lobster, represents a chitin-protein-based fibrous nano-composite hardened with nanoscopic particles of amorphous or crystalline calcium carbonate. Chitin protein nanofibrils cluster to form mineralized fibers which are arranged in horizontal planes where the long axes of the fibers are all oriented in the same direction. Theses planes are stacked and gradually rotate around the normal axis, leading to a plywood structure at the microscale. The organism adjusts the mechanical properties to its requirements on the macroscopic level by changing the stacking height of the planes and the grade of mineralization of the fibers. To examine the elastic properties of the fibers on the microscopic level, we performed nanoindentation on cross-sections of air-dried test specimens. Our results show a pronounced orientation dependency of the elastic properties of the fibers as well as differences between the two mechanically relevant layers of the exoskeleton, the endocuticle and the exocuticle, which are correlated with a different stacking height and grade of mineralization.
4:00 PM - OO8/AA7:Bio
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4:30 PM - **OO8.6/AA7.6
The Role of Non-Collagenous Bone Proteins in Determining the Nanomechanics of Mouse Bones.
Adrian Mann 1
1 , Rutgers University, Piscataway, New Jersey, United States
Show AbstractThe main constituents of mammalian bones are apatite crystals and collagen fibers, however there are also a number of non-collagenous proteins present in bone. These included osteopontin which is important in osteoporosis, osteocalcin which is taken to be an indicator of healthy bone and fibrillin which may play a direct role in determining bone mechanics because of its elastic properties. Using wildtype and knockout mouse models we have been studying the effects of these proteins on the nanomechanics of cortical femora bone. The changes in the nanomechanics can be related to changes in the apatite phase of the bone using micro-Raman spectroscopy. Each of the proteins has a statistically significant effect on the nanomechanics of the bones, but the nature of the effect varies for each protein. In young bones from wildtype mice the hardness and elastic modulus of the cortical bone are much higher than in the osteopontin knockout mice. This suggests that osteopontin is important in the early development and formation of bone, as well as in the loss of bone in older mice due to osteoporosis. Osteocalcin, in contrast, seems only to affect the hardness of cortical bone and not the elastic modulus. Specifically, bones from osteocalcin knockout mice show a statistically significant increase in hardness compared to wildtype mouse bones. The Raman data for these bones shows a possible link between hardness and the degree of carbonate for phosphate substitutions in the apatite. Lastly, the absence of fibrillin 2 is found to cause a significant reduction in the hardness and elastic modulus of the mouse bones, though this is seen predominantly in the central part of the cortical bone midway between the periosteal and endosteal regions. There is no discernible change in the Raman spectra with the presence/absence of fibrillin 2, which suggests the mechanical properties are directly affected by fibrillin 2 rather than indirectly through a change in the apatite phase during bone development and remodeling. In summary, the results show that the non-collagenous bone proteins are very important in determining the nanomechanics of cortical bone, but each of the proteins plays a distinctly different role. In some cases the bone’s formation and modeling is modified while in other cases the protein directly affects the bone’s mechanics.
5:00 PM - OO8.7/AA7.7
In vitro Dynamic Response of Porcine Brain Tissue in Uniaxial Compression and Indentation.
Asha Balakrishnan 1 , Thibault Prevost 1 , Simona Socrate 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show Abstract5:15 PM - OO8.8/AA7.8
Viscoelastic Behavior of a Centrally Loaded Circular Film Being Clamped at the Circumference.
Kai-Tak Wan 1 , Michelle Oyen 2 , Kuo-Kang Liu 3
1 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Engineering Department, Cambridge University , Cambridge United Kingdom, 3 Institute of Science and Technology in Medicine, Keele University, Stoke-on-trent United Kingdom
Show AbstractWednesday, Nov. 28Transferred Poster AA8.6 to AA7.8/OO8.8 @ 4:15 PMViscoelastic Behavior of a Centrally Loaded Circular Film Being Clamped at the Circumference. Kai-Tak Wan
5:30 PM - OO8.9/AA7.9
Nanoindentation of PuraMatrix-Collagen Hydrogels.
Jessica Kaufman 1 , Catherine Klapperich 1 2
1 Biomedical Engineering, Boston University, Boston, Massachusetts, United States, 2 Manufacturing Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractHydrogels composed of PuraMatrix(3DM, Cambridge, MA) and collagen have similar chemical and physical properties to native extracellular matrix. This makes them well suited for tissue engineering applications, in particular for mimicking the environment of soft tissues such as nerve. Mechanical testing of these artificial extracellular matrices poses several challenges. The hydrogels are often made in small amounts and are difficult to test using traditional methods. These very soft hydrogels, with a reduced modulus of 67.5 +/- 16.9 kPa (n=6), must be tested while hydrated to maintain their mechanical properties. Displacement controlled nanoindentation experiments with a 50 micron flat punch tip were performed on a Hysitron TriboIndenter. The indents were first used to calculate the contact stiffness and corresponding reduced modulus. The data were then fit using a 5-parameter Wiechert model to obtain the viscoelastic properties of these hydrogels. These methods indicate that biomaterials in the low-kPa range can be quickly and reliably tested using nanoindentation. The mechanical properties determined here will be used to analyze the cellular response to a material library of PuraMatrix-collagen hydrogels.
5:45 PM - OO8.10/AA7.10
The Graded Structure and Mechanical Properties of the Natural Armor of Polypterus Senegalus.
Ju Ha Song 1 , Benjamin Bruet 1 , Ilan Kalai 3 , Gadi Pelled 3 , Dan Gazit 3 , Mary Boyce 2 , Christine Ortiz 1
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , Hebrew University-Hadassah Medical Campus, Jerusalem Israel, 2 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractPolypterus senegalus are descendants of ancient fish that lived approximately 60 million years ago. Their body is covered by a natural armor consisting of mineralized scales which geometrically interlock and adhere to one another through a connective biomacromolecular fibrillar adhesive. This natural armor protects the fish from predators and harsh environments yet enables the fish to retain great flexibility in their body motion, using a whipping type motion to generate high speed movement. Each scale has a complex shape with “in-plane” dimensions of roughly 2.5 mm by 2.5 mm and a thickness that varies from 0.6 mm to 0.8 mm. Microcomputed tomography (μCT) was used to obtain full three-dimensional constructs of both a single scale and multiple interlocking scales and provided information on the density distribution, the flexible joints between two scales, and the scale-to-scale and scale-to-body interfaces. Optical micrography reveals the cross section to consist of four layers (from outer to inner): ganoine (8 ~ 20 μm thick), dentin (25 ~ 80 μm thick) isopedine (35 ~ 50 μm thick), and bone (200 ~ 500 μm thick). Material properties were reduced from instrumented nanoindentation data using a combination of Oliver-Pharr analysis and three-dimensional elastic-perfectly plastic finite element simulations giving (modulus, yield strength) pairs of (68.4 ± 2.0 GPa, 3.0GPa) for the ganoine, (29.9 ± 4.0 GPa, 750MPa) for the dentin, (17.7 ± 2.0 GPa, 265MPa) for the isopedine, and (17.6 ± 3.2 GPa, 225 MPa) for bone. Subsequently, the validity of the material property fit to the load-depth data was checked by comparison of simulation predictions of the residual depth profile after unloading to that measured by AFM. The properties are observed to transition from a very stiff and high yield strength outer layer to a more compliant lower strength bone region. The gradation in structure and properties is hypothesized to provide a penetration resistant yet tough protection to the fish. To understand the role of the graded layers macroscopically, the material properties for each layer were integrated into microindentation simulations of the scale which model the graded surface structure. In particular, a parametric study considering different thickness ratios of the various subsurface layers on the micro-hardness of the scale was conducted which also revealed the underlying stress and strain distribution in the layers and at the layer interfaces during indentation loading events. The computational analysis showed the load transfer and stress redistribution along the graded interfaces, which show the ratio of outer ganoine layer thickness to dentin thickness to provide a microhardness to resist penetration while minimizing the stress experienced in the layers and at the layer interfaces, giving the possibility of natural geometric optimization.
OO9: Poster Session II
Session Chairs
Virginia L. Ferguson
Carl Frick
Conrad R. Stoldt
John Zhang
Thursday AM, November 29, 2007
Exhibition Hall D (Hynes)
9:00 PM - OO9.1
The Role of Organics in the Mechanics of the Human Dentin-Enamel-Junction (DEJ).
Marta Baldassarri 1 2 , Lucia Pallotto 3 , Enrico P. Tomasini 4 , Elia Beniash 1 2 , Lorenzo Scalise 4
1 , Forsyth Institute, Boston, Massachusetts, United States, 2 , Harvard School of Dental Medicine, Boston, Massachusetts, United States, 3 , University of Padova, Padova Italy, 4 , Politechnic University of Ancona, Ancona Italy
Show AbstractTeeth are comprised of an outer layer of hard enamel (95% w/w mineral, <1 % w/w organics and ~4% water) and an underlying softer dentin tissue (70% w/w mineral, 20% organics and 10% water). These two materials are coupled at an interface called the dentin-enamel junction (DEJ). Previous studies have shown that under stress cracks generated in enamel are stopped at the DEJ, preventing catastrophic failure of the tooth. Here we present a new experimental study on the role of organics in the compressive mechanical properties and cracks patterns at the DEJ.Ten sections (1.5x1.5x3 mm) with long axis normal to the tooth surface were cut from five human incisor crowns. Each specimen comprised of enamel (1.5x1.5x1 mm) and dentin (1.5x1.5x2 mm). Five samples were treated with cold-plasma for 4 hours, using PlasmaPrepII (SPI), to achieve a maximal removal of organic material. The other five were not treated and used as controls. Specimens were stored in PBS at 4 degrees C until mechanical testing. Compression tests were performed along the long axis of the samples. Loading was applied at the enamel side using a piezoactuator (PI, P239.90) with a spherical tip. Load steps of 6 N were applied every 5 s up to sample breakage and load values were monitored with a load cell (LEANE FN3060). Displacement generated on the sample along the axis transversal to the load direction was measured with a laser (KEYENCE LC-2320; 0.5 μm of resolution), pointed at the DEJ (measuring point diameter: ~180 μm). Statistical analyses (t-test) were used to compare the Compressive Strength (σc) and the Yield Stress (σY) of the specimens and the Young’s modulus at the DEJ (E) in treated vs. untreated samples. SEM studies were performed to determine changes in the crack propagation patterns between treated and untreated specimens.Both σc and σY were lower in the treated (48±15 MPa and 1.5±.8 MPa respectively) compared to the untreated samples (104±9 MPa and 13±2 MPa respectively). E values at the DEJ were dramatically lower in the treated (0.76±.3 GPa) compared to the untreated specimens (8.2±1.5 GPa). All values (σc, σY and E) were significantly different between treated and untreated samples (p<0.0001 for all three analyses). The SEM studies showed that in the untreated samples the damage was primarily in the enamel tissue, whereas in the treated specimens cracks propagated through the junction breaking apart not only enamel but also dentin.Our data show that presence of organics contributes to significantly higher Compression Strength and Yield Stress of teeth, with damage limited to enamel. In contrast, when organics are removed, the tooth is less resistant, with cracks propagating through dentin and the tissue is more porous, with consequent decrease of the Young’s Modulus at the DEJ. We believe that the primary role of organics at the DEJ is to stop cracks preventing possible failure of the tooth.
9:00 PM - OO9.10
The Role of Substrate Mechanics on Mesenchymal Cell Differentiation.
Tatyana Miranova 1 , Vladimir Jurukovski 1 , Miriam Rafailovich 1 , Marcia Simon 1 , Nadine Pernodet 1
1 Materials Science and Engineering, Stony Brook University, Stony Brook, New York, United States
Show AbstractWe are exploring the effects of the surface mechanical properties on the differentiation of adult mesenchymal cells. Silicon substrates were coated with monodisperse (mw/Mn<1.1) polybutadiene (PB) films, where the mechanical properties of the films were controlled simply by the film thickness, while the surface chemistry and energy were completely unchanged. The mechanical properties of the films were measured using scanning modulation force microscopy and large changes in modulus were found as the film thickness was varied from 8-200 nm. The adult mesenchymal cells were plated on these substrates and incubated for one month, with and without inducing media. The cells with inducing media differentiated and produced differentiation products after two weeks incubation time. The amount of product was larger on the harder substrates. In the cultures without inducing media, no products were observed as expected, on the thick (low modulus) films. However, a large coating of crystals was observed after one week in cultures with cells on the hard PB covered subsubstrates. EDAX analysis is being carried out confirm the identity of the secreted materials.
9:00 PM - OO9.11
Paper-Based Microfluidic Devices: An Inexpensive, Portable, and Lightweight Platform for Detection.
Scott Phillips 1 , Andres Martinez 1 , George Whitesides 1
1 Chemistry & Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
Show Abstract9:00 PM - OO9.12
Single Molecule Analysis of DNA/Protein Interactions: The Nanopore Shift Assay.
Meni Wanunu 1 , Devora Cohen-Karni 1 , Yong Yu 1 , Zhiping Weng 1 , Amit Meller 1
1 Biomedical Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractTranscription factors (TFs) are an important class of gene regulatory proteins. They recognize short doubled stranded DNA stretches (up to 20 bp) with high specificity and affinity. Established methods for studying the interactions of TFs with DNA include Electrophoretic Mobility Shift Assay (EMSA) and chromatin immunoprecipitation with microarray detection (ChIP-chip). EMSA can resolve short DNA stretches, but is inherently low throughput and time consuming. ChIP-chip can provide genome-wide binding information in living cells, but suffers from low spatial resolution and high cost. We have recently developed a novel approach for analyzing DNA/TF interactions at the single-molecule level. Our method utilizes solid-state nanopores comparable in size to double-stranded DNA cross-section, to analyze TF binding with high throughput. TF-bound and unbound DNA molecules display distinct differences in the measured ion current patterns, enabling ultra fast detection and screening of TF binding. We present results demonstrating the feasibility of our approach using the TF SP1, which contain zinc finger motif, and map its interactions, with genomic DNA fragments. Future studies will allow us to study interactions between multiple TFs and neighboring binding sites on the same DNA molecule in a single experiment , hence obtaining information on the cooperativity of binding.
9:00 PM - OO9.13
Analysis of Human Spleen Contamination.
Martin Kopani 1 , Martin Weis 2 , Jan Jakubovsky 3
1 Department of Pathology, Comenius University, School of Medicine, Bratislava Slovakia, 2 Department of Physics, Slovak University of Technology, Faculty of Electrical Engineering and Information Technology, Bratislava Slovakia, 3 Department of Pathology, Comenius University, School of Medicine, Bratislava Slovakia
Show AbstractBesides carbon, oxygen and nitrogen, numerous other elements and their compounds are significant in the body of humans and other animals [1]. Accumulation of some elements and their compounds is recognized by clinical and biochemical evaluation. The physical-chemical properties and topical characteristics of elements in tissues may play a crucial role in evaluation their effect on human body. The 57Fe Mössbauer measurement was used for evaluation of iron–oxide biomagnetic nanoparticles composition and properties. Absorption spectra of the powder spleen recorded at 77K and 300K were measured and subsequently analyzed. From fitted data is possible obtain material composition as well as discuss the mean particle size (received from decrease hyperfine field in comparison with bulk value).Energy-dispersive X- ray microanalysis (EDX) in combination with scanning electron microscopy (SEM) has been caried out on 5 samples of human spleen. Tissue probes have been prepared by common methods.In the specimens from the adult human spleen, the EDX microanalysis showed the presence of silicon in macrophages of the red pulp. Evaluation of the same specimens in polarized light microscopy did it not uncover. The particles in the spleen were 10-30 μm large. Silicon, silicon-aluminium and silicon-calcium particles by EDX were found. Spectral lines of magnesium, aluminium, silicon, sulphur, calcium, potassium and iron were also identified in various parts of the red pulp. X-ray diffraction revealed beta-SiO2 and Fe2O3 particles in the human spleen.Crystals of SiO2 1-5 μm large are considered to be pathogenic. Shalaeva et al. [9] demonstrated that from the point of silicosis there is no substantial difference between amorphous and crystalline SiO2. Our measurements indicated both, its crystalline and amorphous phase. Our specimens contained silicon, from the viewpoint of silicosis pathogenesis, of inert nature and people whose spleens were investigated, did not show manifestations of silicosis. Thus we assume that the silicon must have got into the organism from the external environment. As a foreign material, it was excluded from the blood stream by the spleen clearance function [10]. We suppose that the presence of silicon in the mentioned tissues is consequence of the cleaning function of human spleen.This work was supported by grant of Slovak Research and Development Agency No. APVT-20-003104.
9:00 PM - OO9.2
Nanoindentation Mapping and Modeling of Mineralized Tissue Interfaces.
Michelle Oyen 1 , Ching-Chang Ko 2
1 Engineering Dept., Cambridge University, Cambridge United Kingdom, 2 School of Dentistry, University of North Carolina, Chapel Hill, North Carolina, United States
Show AbstractRecent developments in instrumentation have increased the use of contact mechanical testing techniques (“nanoindentation”) for the examination of mechanical responses in a variety of materials including mineralized biological tissues. In the current work, nanoindentation arrays with hundreds of individual indentation tests are performed near features of interest in dental applications, such as the dentine-enamel junction in teeth and the interface between bone and titanium dental implants. Experimental results demonstrate variability in local elastic response, with point-to-point variation particularly prominent in bone samples. No clear distinction was found between bone samples harvested at three different time-frames following implantation. Intrinsic variability in indentation response is examined by modeling indentation events at different length-scales relative to a material’s microstructural features. The implications for local mechanical property variation are considered further by generating two-dimensional axisymmetric finite element models of the indented regions, with point-to-point property variations in the FE model based directly on the indentation experimental results. While this study emphasized elastic responses, there is substantial scope for characterizing inelastic deformation using the approaches developed in the current work.
9:00 PM - OO9.3
Modeling Cytoskeletal Assembly and Organization in Engineered Muscle Cells.
Po-Ling Kuo 1 , Chinlin Guo 2 , Kevin Parker 1
1 School of Engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 Engineering & Applied Sciences, California Institute of Technology, Pasadena, California, United States
Show AbstractSynchronized contraction of myocytes depends on a proper alignment of myofibrils. As myocytes mature, the myofibrils appear to be arranged from an irregularly dispersed pattern into tightly organized bundles spanning the length, rather than the width, of the cells. However, how myocytes develop such a form and its role in contractile function remains a mystery. We hypothesized that the spatial organization of myofibrils prefers to be anisotropic and this anisotropy results from the competition between two processes taking place at different time scale: the interactions between the focal adhesive complex (FAC) and the contractile apparatus (the fast process), as well as a mutual alignment between adjacent nascent myofibrils (the slow process). We implemented these two processes into a mathematical model and simplified our simulation into 2D myocytes fully spreading on given geometries. We modeled the kinetics of the following field variables at discretized positions within the cell: (1)the density of bound and unbound integrins; (2)the local traction exerted on the FAC; (3)the orientation and density of actomyosin filaments immediately resulting from the fast process; (4)the resultant orientation and parallel bundling of the nascent myofibrils. All variables are in dimensionless units. All time-scales are normalized with respect to that of nascent myofibril bundling. The assembly/disassembly of actomyosin filaments was assumed to occur instantaneously and we approximated each filament as a force vector with strength proportional to both fiber length and density of the connected FACs. The temporal change of traction at a given FAC was determined by integrating the tension contributed from all connected filaments, plus the amplification resulting from parallel bundling of local myofibrils. Redistribution of FAC was calculated based on studies indicating that FAC assembly is dependent upon exerted traction. The instant network of the actomyosin filaments was then updated according to FACs and served as a structural template to regulate bundling and orientation of nascent myofibrils. The myofibrils were also assumed to impose torques upon neighboring myofibrils and influence their orientations. Our model predicted an anisotropic pattern of cytoskeletal assembly in myocytes. When there is a geometric heterogeneity in which the longest cellular axis can be defined without ambiguity, myofibrillar architecture always follows the longest axis of myocytes. In the absence of a preferentially long axis, as in circular myocytes, myofibrils exhibit an unrepeatable distribution, but may eventually evolve to a symmetry breaking pattern. Our results also suggest that the functional goal of this anisotropic differentiation of myocytes is to maximize their contractile tension and perhaps establish a means of orchestrating the structural organization of the myocardium.
9:00 PM - OO9.4
Characterizing Mechanical Interaction between Myocytes and Substrates.
Po-Ling Kuo 1 , Nicholas Geisse 1 , Sean Sheehy 1 , Kevin Parker 1
1 School of Engineering & Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractMechanical crosstalk between myocytes and their surrounding environment, as well as adjacent myocytes may play a role in proper differentiation of myocardium and repairing process of myocardial injury. Here we reported an in vitro system to characterize the mechanical interaction between myocytes and substrate. Polydimethylsiloxane (PDMS) molds containing complementary pattern of cellular shape, size and distance between cells were fabricated by soft lithography. The molds were used to micropattern fibronectin islands on the surfaces of polyacrylamide gels embedded with fluorescence beads. The stiffness of substrate was adjusted to be comparable with living tissue (~8kPa). Freshly harvested neonatal rat ventricular myocytes were cultured on these substrates, where the cells spread and assumed the shape of the adhesive island after 24 hours in culture. Consecutive images of beads immediately beneath the beating myocytes were paired to measure displacements of beads. Changes of bead position along the axis perpendicular to the surface of substrate were estimated and 3D matrix strains were reconstructed. The spatiotemporal maps of the contractile tractions exerted on the substrate by myocytes were solved using an inverse problem approach. We found that the contraction of myocytes generates significantly rotational movement (curls) of extracellular matrix. This rotational movement is maximized at the ends of longitudinal axis of myocytes and may contribute to the structural organization of myocardium during differentiation. Our preliminary results also suggested that the matrix strain (divergence) may serve as a mean of long range coupling between myocytes.
9:00 PM - OO9.5
Engineering Contractility of Myocardial Sheets.
Adam Feinberg 1 , William Adams 1 , Mark Bray 1 , Sean Sheehy 1 , Kevin Parker 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractWe have developed an in vitro assay to study structure-function relationships in myocardium; combining ultrastructural analysis with functional readout of contractile force. Rather than recapitulating the whole heart, or even an entire ventricle, we have focused on evaluating the deformation of 2-dimensional (2D) myocardial sheets that mimic the lamellar layers of the ventricular wall. This myocardial sheet is integrated into a free-standing, thin film of polydimethylsiloxane (PDMS) elastomer. Thus, we have created a biological and synthetic, bilaminate structure, referred to as a muscular thin film (MTF). The orientation of cardiomyocytes within the 2D myocardium is engineered using microcontact printing of FN in order to recapitulate the uniaxial alignment of native myocardium. Cell aspect ratio is controlled by altering the width and spacing of FN lines in order to mimic normal (7:1) and cardiac disease states (5:1 and 11:1). Measurements of cell borders shows that a change in cell aspect ratio from 3:1 to 6:1 to 8:1 was produced by changing FN coverage from isotropic to lines/spacings of 20 μm and 10 μm respectively. The MTF curves during contraction and the contractile stress generated by the 2D myocardium is quantified based on a modified Stoney’s equation and the known physical and mechanical properties of the PDMS. For physiologic experiments, the MTFs are fashioned into cantilevers, mounted in normal Tyrode’s solution in an organ bath maintained at 37C and electrically stimulated to contract. Using this system, we have verified excitation-contraction coupling by correlating MTF deformation to electrical stimulation. Altering cardiomyocyte orientation from unaligned to uni-axially aligned produced peak systolic stresses of ~0.5 kPa to ~10 kPa respectively, a 20-fold increase. This difference in contractility was similar to the remodeling that occurs at the myocardial infarct border zone. Additionally, we have used immunofluorescent staining of the Z-disks to quantify individual sarcomere alignment at the sub-micron scale. Preliminary results show that increased peak systolic stress corresponds to an increased number of aligned sarcomeres and a decreased distribution width of sarcomere orientation angles. Thus, we can engineer myocardial sheets (MTFs) with specific contractile properties by controlling microcontact printing parameters. The next step will be engineering MTFs with tissue microstructures that mimic normal, pressure-overload and dilated cardiomyopathy disease states in order to better understand the biomechanics of maladaptive hypertrophy and develop therapeutic strategies.
9:00 PM - OO9.6
Finite Deformation of a Biotic-Abiotic Thin Film in a Fluid.
William Adams 1 , Adam Feinberg 1 , Kevin Parker 1
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States
Show AbstractQuantitative characterization of the traction applied by a living tissue onto a substrate has become a problem of biological interest for which there are few in vitro tools. Experimentally, we have developed a method of creating a thin polymer film as a substrate for cell culture. The millimeter-scale film is free-standing within a fluid medium. Harvested muscle cells cultured on the film contract and produce measurable deformation. Through cellular engineering techniques, we confine the contraction of the tissue to lie within a plane.We have used a two dimensional mechanical model of the deformation of the thin film immersed in a fluid as a means to quantify the traction applied by the tissue onto the film. We assume the time-evolution of the geometry of the thin film is known from experimental measurements. The thin film is modeled with finite elasticity as an inextensional plate with finite thickness. The surrounding fluid medium is modeled as an unsteady, incompressible, irrotational flow with time-dependent boundary conditions. The deformation of the film imposes local moving boundary conditions while the fluid is at rest at the remote boundaries. With a Reynolds number near unity and with geometrically-complicated boundary conditions, analytical approaches to solving the velocity field of the fluid are extremely limited. Therefore, the theoretical elasticity components are combined with a computational solution of Laplace’s equation using a finite element method to find the velocity potential of the fluid. Ultimately, the hydrodynamic pressure on the thin film is related to the time-evolution of the velocity potential through a Bernoulli equation. This solution to the equations of motion of the fluid incorporates both the pressure-gradient across the membrane from the induced flow as well as the added mass effect of accelerating the proximate fluid medium during deformation. The coupled finite elasticity and fluid mechanical models of the thin film and the fluid are solved to find the traction applied by the cultured cells as a function of time.This methodology is both computationally and experimentally inexpensive. The methods are generalized and applicable to any contractile tissue or material. This modeling has the potential to be used in many in vitro systems as a means to quantitatively understand the mechanical behavior of live biological structures at the tissue scale.
9:00 PM - OO9.7
Comparison of Fracture Energy of Structure Modified Diamond-like Carbon Films by Thermal Annealing and Si Incorporation with the Four Point Bending Test.
Heon Woong Choi 1 2 , David M. Gage 2 , Reinhold. H Dauskardt 2 , Kwang-Ryeol Lee 3 , kyu Hwan Oh 1
1 Materials Science and Engineering, Seoul National University, Seoul Korea (the Republic of), 2 Materials Science and Engineering, Stanford University, Stanford, California, United States, 3 Future Convergence Technology Laboratory, Korea Institute of Science and Technology, Seoul Korea (the Republic of)
Show Abstract9:00 PM - OO9.8
Fiber Spinning as a Gateway into Micro and Nano Worlds.
Alexander Lobovsky 1 , Mohammad Behi 1
1 , United Materials Technologies, LLC, Westfield, New Jersey, United States
Show AbstractLately new discoveries made in the field of nano-technology and bio-scaffolding pose a new challenge of handling and orienting substances on the scale of 10-E6 to 10-E9 m.The shaped fibers with their nano and micro sized geometric features and variety of materials present a flexible and inexpensive solution.Polymeric fibers have been made in various cross-sections in order to enhance their properties and performance. The desired properties may range from stiffness, luster and dirt hiding capabilities to attraction and retention of dust in filtering applications to increase in surface area and permeability for hollow fiber membranes.Modern spinneret capillary manufacturing technology such as EDM (Electrical Discharge Machining) allows quick and inexpensive fabrication of elaborate capillaries shapes, thus giving us an ability to create hundreds capillary designs. As a result testing of over 400 capillary designs and studying polymer flow effects in capillaries we have developed technology to produce practically any fiber shape.In addition a number of various product prototypes were fabricated with the spun shaped fibers that verified fiber shape efficacies and improved product performance.Combining fiber shape technology with multi-component fiber spinning offers even greater opportunities for new products with unique properties. This presentation gives dozens of examples of fiber shapes and discusses their potential applications.
9:00 PM - OO9.9
Aromatic Thermosetting Copolyester (ATSP) / UHMWPE Blends with Improved Wear Properties and Biocompatibility.
Yongqing Huang 2 , James Economy 1
2 , DuPont CR&D, Wilmington, Delaware, United States, 1 Materials Science and Engineering, University of Illinois at Urbanan-Champaign, Urbana, Illinois, United States
Show Abstract
Symposium Organizers
Virginia L. Ferguson University of Colorado
John X.-J. Zhang The University of Texas-Austin
Conrad Stoldt University of Colorado
Carl P. Frick Abbott Vascular
OO10: Nanomaterials Interfaced with Biology
Session Chairs
Reed Ayers
Rebekah Drezek
John Zhang
Thursday AM, November 29, 2007
Room 206 (Hynes)
9:30 AM - OO10.1
Towards Conductive Nanowires by Seeded-growth of Gold Nanocrystals on the Filamentous Biological Templates.
Fuke Wang 1 , Penghe Qiu 1 , Chuanbin Mao 1
1 Chemistry & Biochemistry, University of Oklahoma, Norman, Oklahoma, United States
Show AbstractThe preparation of conductive nanowire is still a challenge in the development molecular-scale devices. Here we reported the synthesis of gold nanowires by using a filamentous virus as a template. The nanoparticle seeds were first assembled along the virus, followed by crystal growth into nanowires. A genetically engineered virus with controlled surface charge density was used as the template to align the gold nanoparticle seeds with the sizes of 2.6, 13, and 50 nm. The nano-seeds with large sizes (13 and 50 nm) were found to be aligned continuously into a line along the filamentous virus, while the gold seeds with a relative smaller size than the diameter of the viral templates (~7 nm) were aligned with equal inter-dot spacing with high density on the surface of the viral templates. In the subsequent growth, the one-line aligned gold seeds (13 and 50 nm) were difficult to grow into the gold nanowires while continuous gold nanowires were formed from the aligned 2.6 nm gold seeds on the virus. To have a better understanding of the process, techniques such as UV-vis spectra, SEM, TEM and AFM were applied to illustrate the mechanism of nanowire formation. Furthermore, the conductive and related properties are now under investigation in our lab.
9:45 AM - OO10.2
Do Cells Exposed to Au Nanoparticles Recover?
Tatsiana Mironava 1 , Asya Bakhtina 2 , Xiaohua Fang 1 , Miriam Rafailovich 1 , Nadine Pernodet 1
1 , SUNY, Stony Brook, New York, United States, 2 Chemistry, Polytechnic University, Brooklyn, New York, United States
Show AbstractWe have shown previously that human dermal fibroblasts are significantly affected by the presence of Au-nanoparticles with different sizes, mostly in term of cell proliferation, cell migration and protein secretion. However, an essential question remains, if the nanoparticles are removed, can the cells recover from the adverse influence and resume their normal proliferation and functions? We set up a series of experiments where the cells were exposed to different dose of nanoparticles, the media was then removed and replaced by fresh media without nanoparticles, and we found a critical dosage existed beyond which the cells were not able to recover. The dependence on nanoparticle size and exposure time will be presented as well.
10:30 AM - **OO10.5
Optical Molecular Imaging for Assessment of Nanomaterial Interactions In Vivo.
Rebekah Drezek 1
1 Bioengineering, Rice University, Houston, Texas, United States
Show AbstractAdvances in optical imaging technologies offer new and appealing approaches to directly monitoring the biological interactions of engineered nanomaterials in vivo. A variety of photonics-based approaches may be employed with selection of the most appropriate technology determined by the properties of the nanomaterials as well as the field of view, resolution, and imaging depth required. This talk will first overview the potential of optical imaging strategies for direct observation of nanomaterial and other biomaterial interactions in vivo using our work imaging gold nanoshells in a variety of biological systems as a case study. Metal nanoshells consist of a dielectric core coated with a thin metallic layer, typically gold. These particles provide an ideal material for many biomedical imaging and therapy applications because the optical resonance can be precisely tuned to desired wavelengths throughout the near infrared (NIR) spectral region where light penetration through tissue is deepest by varying the core/shell thickness ratio. In vitro and in vivo experiments will be presented highlighting several relevant optical spectroscopic and direct imaging approaches. The use of in vivo optical imaging to provide a facile approach to real-time monitoring in order to optimize treatment protocols as nanomaterial surface properties and targeting are modified will be demonstrated. Imaging of several additional classes of scattering, absorbing, and/or emissive nanomaterials under development at Rice will also be described. Finally, we will present results from a recent study on the influence of surface coating on quantum dot biological interactions to demonstrate the additional information quantitative optical techniques can provide over and above what may be obtained through conventional methods for assessment of nanomaterial cytotoxicity.
11:00 AM - OO10:Nanomatls
BREAK
11:30 AM - **OO10.6
The Detection and Characterization of Nanoparticulate Heavy Metals in Epithelial Tissues in Patients with Nephrogenic Fibrosing Dermopathy.
Reed Ayers 1 , John Chandler 1 , Jim Ranville 1 , Whitney High 2
1 Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 Dermatology, University of Colorado Health Sciences, Aurora, Colorado, United States
Show AbstractCertain diseases have been associated with the administration of heavy elements as contrast agents to patients undergoing medical imaging procedures. Recently, the presence of gadolinium (Gd) administered as a paramagnetic contrast agent for MRI contrast studies was associated with the incidence of Nephrogenic Fibrosing Dermopathy (NFD), also called Nephrogenic Systemic Fibrosis (NSF). To determine specific causation, Gd and other metallic nanoparticles in various tissues must be detected directly and characterized in-situ. This is done to develop specific mechanisms for the chemical modification of the metal elements as the result of a biologic response. Fixed biopsies embedded in paraffin were sectioned at 3-5 microns thick, deparaffinized by hand (xylene and 100% ethyl alcohol), placed on carbon planchettes, and allowed to air dry. Deparaffinized tissues were examined using a field emission SEM (FE-SEM) to directly detect and image the presence of Gd as well as other metals. Backscatter electron (BSE) imaging (20kV) was used to discern metal particles within tissues. Energy dispersive spectroscopy (EDS) (15kV) was used to verify the specific elements present. This allowed for the spatial characterization of the nanoparticles within the tissues but due to the physical limitations of SEM/EDS, quantification of the amount of metal was not possible. Mass concentration of the metal elements was determined using inductively coupled plasma mass spectrometry (ICP-MS) on digested tissues. Thick tissue sections, >30 micorns, were used for ICP-MS to provide enough mass for detection. These sections were taken from the histology blocks adjacent to the thin sections used in the FE-SEM. Gadolinium was detected in skin, heart, lung and liver tissues. The highest concentrations were found in heart and skin; both had average tissue concentrations greater than 200 micrograms/gram (100-450 micrograms/gram range). In skin, gadolinium nano-particulates were readily seen near cell body locations in autopsy samples and within the cells in biopsy samples. The cells where gadolinium was most easily found were along blood vessels. In the cells the agglomerates appear granular with a size of less than 100 nm. They are diffused throughout the cell but as of this time not associated with any particular cell structure. Subsequent work using TEM will examine that aspect as well as the specific ultrastructure and chemistry of the nanoparticles. In this investigation, gadolinium was detected in the tissues of a number of patients with NSF. Although neither dispositive of a pathophysiologic mechanism, nor proof of causation, the detection and quantification of gadolinium within tissues of NSF patients is supportive of the epidemiologic association between exposure to gadolinium containing contrast material and development of the disease.
12:00 PM - OO10.7
Size Dependent Cytotoxicity of Gold Nanoparticles.
Yu Pan 1 , Willi Jahnen-Dechent 1 , Sabine Neuss 2 , Annika Leifert 3 , Monika Fischler 3 , Ulrich Simon 3 , Günter Schmid 4 , Wolfgang Brandau 5 , Fei Wen 3
1 Biomedical Engineering Biointerface Lab, RWTH Aachen University, Aachen Germany, 2 Pathology, RWTH Aachen University, Aachen Germany, 3 Inorganic Chemistry, RWTH Aachen University, Aachen Germany, 4 Inorganic Chemistry, University Duisburg-Essen, Essen Germany, 5 Radiochemistry, University Hospital Essen, Essen Germany
Show AbstractGold nanoparticles are widely used in biomedical engineering. The recent literature however, contains conflicting data regarding the cytotoxicity of gold nanoparticles. Against this background we undertook a systematic study of water soluble gold nanoparticles stabilized by triphenylphosphine derivatives ranging in size from 0.8 nm to 15 nm to exclude the ligand chemistry as a possible confounder of cytotoxicity. All the gold nanoparticles were characterized by electron microscopy, atomic absorption spectroscopy (AAS), UV/VIS spectroscopy and CHN analysis to determine the physicochemical parameters. We tested the cytotoxicity of these particles in four cell lines representing major functional cell types with barrier and phagocyte function both in logarithmic phase and in stationary phase. We proved that all the cell lines were most sensitive to gold particles of ∼1.4 nm size resulting in IC50 values ranging from 40-200 µM. In contrast, gold particles of 15 nm size and Tauredon®, (gold thiomalate) were non-toxic at up to 60-fold and 100-fold higher concentration, respectively. To estimate if the cytotoxic Au compounds caused preferentially apoptotic or necrotic cell death we performed annexin V and propidium iodide double staining. The cellular response was strictly size-dependent in that 1.4 nm particles caused rapid cell death by necrosis within 12 hours, while closely related particles of 1.2 nm diameter effected programmed cell death by apoptosis.
12:15 PM - OO10.8
Reductive Degradation of Worm Micelles for Drug Delivery Applications
Karthikan Rajagopal 1 , Dennis Discher 1
1 Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractThursday, Nov 29Transferred OO11.5 @ 2:30 PM to OO10.8 @ 11:15 AMReductive Degradation of Worm Micelles for Drug Delivery Applications. Karthikan Rajagopal
12:30 PM - OO10.9
Interfacing Silicon Nanowires with Mammalian Cells.
Woong Kim 1 , Jennifer Ng 2 , Miki Kunitake 3 , Bruce Conklin 2 , Peidong Yang 1 3
1 Materials Sciences Division, Lawrence Berkeley National Lab, Berkeley, California, United States, 2 , Gladstone Institute of Cardiovascular Disease, San Francisco, California, United States, 3 Chemistry, University of California, Berkeley, California, United States
Show AbstractWe present a direct interface of silicon nanowires with mammalian cells such as mouse embryonic stem (mES) cells and human embryonic kidney (HEK 293T) cells. The cells were cultured on a silicon (Si) substrate with a vertically aligned SiNW array on it. The penetration of the SiNW array into individual cells naturally occurred during the cell incubation. The cells survived up to several days on the nanowire substrates. The longevity of the cells was highly dependent on the diameter of SiNWs. Furthermore, successful maintenance of cardiac myocytes derived from mES cells on the wire array substrates was observed and gene delivery using SiNW array was demonstrated. Our results suggest that the nanowires can be potentially utilized as a powerful tool in studying intra- and inter-cellular biological processes.
12:45 PM - OO10.10
Pharmacokinetics of Soluble Carbon Nanotubes in Mice.
Michael McDevitt 1 , Debjit Chattopadhyay 1 , Jaspreet Jaggi 1 , Ronald Finn 1 , Pat Zanzonico 1 , Carlos Villa 1 , Diego Rey 2 , Juana Mendenhall 3 , Carl Batt 3 , Jon Njardarson 4 , David Scheinberg 1
1 Departments of Molecular Pharmacology and Chemistry, Medicine, Radiology, and Medical Physics, Memorial Sloan-Kettering Cancer Center, New York , New York, United States, 2 Biomedical Engineering, Cornell University, Ithaca, New York, United States, 3 Dept. of Food Sciences, Cornell University, Ithaca, New York, United States, 4 Dept. of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
Show AbstractHow nanomaterials interface with biological systems is a key question that may impact the emerging field of nanomedicine. The pharmacokinetic profile of these new materials is a prominent factor in determining their suitability for in vivo applications. Single-walled carbon nanotubes (CNT) are being investigated as platforms for the delivery of biological, radiological, and chemical payloads to target tissues. CNT are mechanically robust graphene cylinders comprised of sp2-bonded carbon atoms and possessing highly regular structures with defined periodicity. CNT exhibit unique mechanochemical properties that can be exploited for the development of novel drug delivery platforms. In order to evaluate the potential usefulness of this CNT platform, we undertook an imaging study to determine the pharmacokinetics of prototypical DOTA-functionalized CNT labeled with Y-86 in a mouse model. Methods: The [Y-86]-CNT construct was synthesized from amine-functionalized, water-soluble CNT by covalently attaching multiple copies of DOTA chelates and then radiolabeling with the cyclotron-produced positron-emitting metal-ion, Y-86. The constructs were characterized spectroscopically, microscopically, and chromatographically. The whole-body distribution and clearance of Y-86 were determined at 3 and 24 hours post-injection using positron emission tomography (PET). Results: The [Y-86]-CNT construct exhibited high specific activity and was 90% radiochemically pure. The Y-86 cleared the blood within 3 hours and distributed predominantly to the kidneys, liver, spleen and bone. Although the activity that accumulated in the kidney cleared with time, the whole-body clearance was slow. The differential uptake among these tissues was observed following intraveneous or intraperitoneal injection. Conclusions: The whole-body PET images indicated that the major sites of accumulation of activity resulting from the administration of [Y-86]-CNT were the kidney, liver, spleen, and, to a much less extent, bone. The mass amounts of the CNT construct that were administered per animal in this study were in the same range as those used in studies with targeting CNT constructs. Furthermore, the rapid blood clearance can be beneficial in the use of short-lived radionuclides in diagnostic applications.
OO11: Nanomaterials Interfaces with Biology
Session Chairs
Thursday PM, November 29, 2007
Room 206 (Hynes)
2:30 PM - OO11.1
Protein Adsorption on Gold Nanoparticles Passivated by Carboxylic Thiols.
Yuan Sun 1 , Malka Bromberg 2 , Sam Blass 2 , Frieda Dukesz 2 , Batya Herzberg 2 , Qi Wang 2 , Neer Asherie 2 , Anatoly Frenkel 2 , Nadine Pernodet 1 , Miriam Rafailovich 1
1 Materials Science and Engineering, State University of New York at Stony Brook, Stony Brook, New York, United States, 2 Physics, Yeshiva University, New York, New York, United States
Show AbstractWater-soluble gold nanoparticles passivated by 3-mercaptopropionic acid (MPA) and 6-mercaptohexanoic acid (MHA) were synthesized. From Transmission Electron Microscopy (TEM) we determined that the particle sizes were 9.8 ± 3.1 nm and 17.2 ± 6.2 nm for the MPA-gold and MHA-gold nanoparticles, respectively. When dissolved in plasma these particles adsorb serum proteins, which may facilitate their penetration into cells. Hence we will discuss the type and amount of protein adsorbed as a function of particle structure and chemistry, and the effect on cell proliferation and activity. Extended X-ray Absorption Fine Structure (EXAFS) and Light Scattering will be used to study the protein adsorption on these particles.
2:45 PM - OO11.2
Effects of Changes in Structural Hydration of Multiphasic Heterogeneous Calcium Phosphate Powders Created via Auto-ignition Combustion Synthesis.
Nina Vollmer 1 , Douglas Burkes 2 , John Moore 1 , Reed Ayers 1
1 Metallurgy and Materials Engineering, Colorado School of Mines, Golden, Colorado, United States, 2 , Idaho National Labs, Idaho Falls, Idaho, United States
Show AbstractCalcium phosphate (CaP) materials are commonly used in bone tissue engineering applications as they closely resemble the chemistry of bone and teeth. The inorganic component of mineralized tissue is multiphasic in nature, thus to better replicate those tissues, CaP materials should also be multiphasic. Combustion synthesis is a process that creates multiphasic CaP (HCaP) with low energy input over a relatively short time. The structure and chemistry of HCaP synthesized via auto-ignition combustion synthesis (AICS) varies greatly with respect to structural hydration. Product hydration was accomplished by modifying hydrogen and oxygen content in the combustion reaction by changing the amount of fuel, urea [ ] pre-reaction, and heating or sintering products post-reaction. The reaction equation for this specific system is given below. Calcium nitrate [ ], and ammonium nitrate [ ] are the components to form HCaP. Urea acts as a catalyst. Changes in the amount of urea dictate the amount of excess hydrogen to form water within the reaction. Excess products formed include water, carbon dioxide, nitrogen and oxygen. Salts of the reactants were mixed with 10 milliliters of de-ionized water in a pyrex beaker, heated on a hot plate for 20 minutes or until the reactants began to foam, and then placed in a muffle furnace at 1000°C until the foam ignited in a combustion reaction. This was noted by the progression of a combustion wave throughout the foam. Post-AICS, products were heated at 105°C for 8 hours and 24 hours and massed to determine water content of the product. Subsequently, the products were sintered at 1000°C for 8 hours and massed again. Porosity is measured using optical imaging followed by binarization of the images and pixel counting such that the ratio of black to white pixels gives relative surface porosity. The primary products formed using AICS are hydroxyapatite (HA), α-tricalcium calcium phosphate (TCP) and hydrated forms of tricalcium phosphate (HTCP). During low temperature heating, 105°C, water content decreases as time increases and the products began to densify. Initial results indicate that surface porosity decreases during the powder densification. XRD shows that peak intensity increases after low temperature heating, indicating an increase in crystallinity, grain orientation and peak intensity. XRD confirms that both crystalline and amorphous phases occur in the hydroxyapatite (HA), α-TCP and HTCP products. The amount of structural hydration does have an effect on CaP, and these effects are noted by an increase in density and decrease in porosity as structurally bound water is removed from the system. Future research will be dedicated to determining a hydration ratio (amount of urea in the reaction to the amount of water within the products) and a Ca:P ratio that result in optimal powder porosity, ductility and grain size generating a multiphasic HCaP implant biomaterial that accurately replicates natural bony tissue.
3:00 PM - OO11.3
Single Molecule Adsorption of Human Plasma Fibrinogen Studied with Atomic Force Microscopy and Photo-Electron Emission Microscopy.
Xianhua Kong 1 , Jacob Garguilo 1 , Glenn Edwards 2 , John Simon 3 , Robert Nemanich 4
1 Physics, North Carolina State University, Raleigh, North Carolina, United States, 2 Physics, Duke University, Durham, North Carolina, United States, 3 Chemistry, Duke University, Durham, North Carolina, United States, 4 Physics, Arizona State University, Tempe, Arizona, United States
Show Abstract3:15 PM - OO11.4
Effect of Chemistry on Thermo-mechanical Shape-memory Properties of Acrylate Networks.
David Safranski 1 , Ken Gall 1 2
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta , Georgia, United States, 2 George Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta , Georgia, United States
Show AbstractShape-memory acrylate networks are novel materials for both biomedical and industrial applications. The purpose of this study is to understand how the chemical structure dictates thermo-mechanical properties of shape-memory acrylate networks, specifically strain to failure and toughness. The strain to failure is useful because it is pivotal to know how much recovery strain the material experiences. To understand how the structure is related to mechanical properties, such as strain to failure, materials of differing chain stiffness ratio, C∞, are compared at varying percentages of cross-linker. First, a set of networks is characterized to understand the trends in the basic thermo-mechanical properties of the monomers once cross-linked. Thirty-one acrylates are separated into two groups: linear chain builders having one functional group, and cross-linkers having two or more functional groups. The networks are systematically synthesized by varying the linear chain builders with poly(ethylene glycol) dimethacrylate Mn~550 (PEGDMA550) as the cross-linker, and varying the cross-linker while holding tert-butyl acrylate constant as the linear chain builder. A dynamic mechanical analyzer evaluates the glass transition temperature, rubbery modulus, and spread of tan delta. Subsequently, strain to failure tests are performed at the glass transition temperature of each respective mixture. The linear chain builders with PEGDMA550 have glass transition temperatures ranging from -29 to 112 °C, and rubbery moduli from 2.75 to 17.5 MPa. The addition of sidegroups like methyl groups or large ringed structures close to the functional group increases the glass transition temperature. The cross-linkers co-polymerized with tert-butyl acrylate have glass transition temperatures ranging from -3 to 98 °C, and rubbery moduli from 6 to 130 MPa. As the functionality of the cross-linker increases, the rubbery modulus increases due to the increased cross-linking density. With this ‘library’ of networks, materials can be selected to independently vary the glass transition temperature and rubbery modulus. Based upon the initial screening results, networks with different C∞ are formed at varying percentages of cross-linker. C∞ values typically apply only for pure linear chain builders, not networks, and here we demonstrate how chemical cross-linking alters the impact of C∞ on strain to failure. The comparison of these networks yields insight into the relationship between chemical structure and mechanical properties leading to a relationship between C∞, percentage cross-linker, and strain to failure.
3:30 PM - OO11.5
Characterization Asprich Peptides AP1 and DEADAC2 and Their Effects on Calcite Morphology.
Katya Delak 1 2 , Jennifer Giocondi 3 , Chrisine Orme 3 , John Evans 1 2
1 Chemistry, New York University, New York, New York, United States, 2 Center for Biomolecular Materials Spectroscopy, New York University , New York, New York, United States, 3 Biosciences and Biotechnology Division, Lawrence Livermore National Laboratory, Livermore, California, United States
Show AbstractThursday, Nov 29Transferred OO11.6 @ 2:45 PM to OO11.5 @ 2:30 PMCharacterization Asprich Peptides AP1 and DEADAC2 and Their Effects on Calcite Morphology. Katya M. Delak