Symposium Organizers
Michael P. Sheetz Columbia University
Jay T. Groves University of California-Berkeley
Dennis Discher University of Pennsylvania
BB1: Spatial and Mechanical Signal Presentation by ECM
Session Chairs
Tuesday PM, April 18, 2006
Room 2007 (Moscone West)
9:45 AM - BB1.2
Structure-Function Micromechanics of Cell-Populated Fibrin Biomaterials: Role of Matrix Elasticity in Remodeling in vitro
Abigail Corrin 1 , Erica Freeman 1 , Bill Tawil 1 , Michael Shaw 1
1 Bioengineering, California Lutheran University, Thousand Oaks, California, United States
Show AbstractMechanotransduction of forces from the extracellular matrix (ECM) by fibroblasts is a critical mechanism in the orchestrated process of wound healing. The ability of the ECM to communicate external forces depends upon its elastic and viscoelastic response, which in turn is governed by its composition and architecture. Here, we have explored the underlying structure-function relationships in fibrin biomaterial scaffolds through a coupled experimental/analytical approach. Specifically, we have developed a rigorous micromechanics model for their elastic response based upon knowledge of their intrinsic material properties and geometric arrangements. Furthermore, we have validated the model through experiments with fibrin materials of varying structure and elastic response. Separately, we have developed a lumped-element model for the viscoelastic response of fibrin in terms of the intrinsic response of the fibrin and the viscous response of fluid flow within the hydrated network. Finally, we have explored the role of cell-mediated remodeling of the matrix in vitro. First, fibrinogen and thrombin solutions (Baxter BioScience) were diluted by adding TBS to the fibrinogen (5-34 mg/ml) and 30mM CaCl2 in TBS to the thrombin (1 U/ml). AlexaFluor 488 (Molecular Probes) fluorescently labeled fibrinogen was added at a concentration of 1:50 to 300µl constructs on coverslips, and, after 24 hours, examined using confocal fluorescent microscopy for fibril network pore size. Constructs were also prepared with/without human foreskin fibroblasts (ATCC NIH3T3) seeded at a density of 100K cells/ml. Here, 5 ml of diluted fibrinogen and 5 ml of diluted thrombin were added simultaneously to wells in a 6-well plate. Following 1 hour at 25°C, 2ml of TBS were added and placed in a 5% CO2 incubator at 37C for 24 hours prior to testing. To obtain the nominal Young’s Modulus, a 3mm circular, flat-ended glass punch was used to indent the constructs in vitro, with a displacement rate of 10mm/min and a final displacement, u, of 5mm. Three loading rates were used: 1, 10 and 100mm/min during the initial loading portion; the indenter was then held at a fixed displacement for 60 s to acquire stress relaxation data. As one example, for fibrin (17.3 mg/ml fibrinogen; 1.0 U/ml of thrombin) the nominal Young’s modulus decreased from 5.0 to 2.5 kPa for loading rates of 100 mm/min to 1.0 mm/min with an increase in relaxation time constants from 3 s-1 to 19 s-1. For all cell-populated constructs after 10-days in vitro, the Young’s modulus approached typical values for human skin explants. Confocal microscopy revealed that fibrin with higher levels of fibrinogen exhibited larger macrobundles of fibrils, which were concluded to govern the linear increase in fibrin stiffness with increasing fibrinogen concentration. This linear relationship is consistent with the model predictions that the number of fibrils, N, is increasing, rather than increasing in diameter.
10:00 AM - BB1.3
Bio-conjugate Bi-linker Mediated Selective Adhesion of one Week Grown Hippocampal Neuronal Cells on Solid Surfaces.
Anubhuti Bansal 1 , Siyuan Lu 1 , Anupam Madhukar 1 , Walid Soussou 1 , Ted Burger 1
1 , university of southern california, los angeles, California, United States
Show AbstractOptimizing coatings on abiotic surfaces for spatially-selective cell adhesion is at the core of successful implants. In particular, use of cell adhesion molecules (CAMs) conjugated to organic molecules appropriate for binding to the abiotic surface, as ligands for binding to specific receptors on cells of interest is receiving increased attention in the context of neural prosthesis. Motivated by the use of deep penetrating electrodes for cortical (hippocampal) stimulation and recording, in which the metal electrodes are deposited on hard non-conducting substrates, we have examined some issues relating to the surface functionalization of glass and alumina. We have modified these surfaces with an organic bi-linker APTS (Amino propyl triethoxy silane) conjugated to peptides that mimic the binding domain of the extra-cellular matrix proteins which bind to specific receptors on the neuron surface (IKVAV from Laminin) and on the astrocyte surface (KHIFSDSSE from NCAM). The typical length of these bi-linkers is on the scale of ~1nm, thus necessitating proper characterization of the as-received and bi-linker modified surface roughness. Atomic force microscopy (AFM) measurements were done on these surfaces to characterize the surface roughness over nano-scales. Large scale uniformity of the surface coverage was characterized by optical fluorescence microscopy via fluorescent organic dyes tagged to the surface bound CAMs. Hippocampal E16 neurons were then cultured on these well characterized CAM (IKVAV and KHIFSDDSSE) modified glass surfaces and allowed to grow for a period of one week. Whereas cell adhesion studies of such type carried out preciously have mainly focused on adhesion experiments that measure cell coverage after a few hours or a couple of days, our studies examine the adhesion of fully grown one week cultured neuronal cells. We observed selective coverage of neurons on IKVAV modified glass substrates and significantly low coverage on KHIFSDDSSE modified surfaces. Studies aimed at determining the optimal surface coverage of CAMs for higher specific cell coverage are underway.
10:15 AM - BB1.4
Dynamic Deformation and Boundary Slip over 3T3 Fibroblasts: An AFM Force Spectroscopy Study.
Gleb Yakubov 1 , Ben Maddison 2 , Ann-Marie Williamson 1
1 Unilever Corporate Research, Unilever Colworth, Sharnbrook United Kingdom, 2 Unilever Life Sciences, Unilever Colworth, Sharnbrook United Kingdom
Show AbstractThe transduction of mechanical stimuli depends on the dynamic mechanical properties of the tissue. The value of the force transduced depends on: speed and magnitude of the applied force, time span of the stimuli, its direction relative to the tissue boundary and the application length scale. We have used AFM colloid probe spectroscopy to evaluate dynamic mechanical properties of 3T3 fibroblasts adhered to a glass substrate. It was found that dynamic deformation depends on the size of probe and can not be described consistently using viscoelastic or poroelastic models. We have used probes that cover various length scales, an AFM tip (R=20 nm) and colloidal probes (R=2.5 and 30 um), to discriminate the relative contributions of different substructures within the cell to its dynamic mechanical properties. For these stimuli we have estimated the overall plastic deformation, which may relate to possible cytoskeleton rearrangement due to extensive mechanical impact. In addition data on effective boundary slip over cell membrane in soft contact deformation will be also presented.
10:30 AM - BB1.5
Self-assembly of Heparin Binding Peptide Amphiphile Nanofibers to Form an Angiogenic Matrix for Tissue Regeneration.
Kanya Rajangam 1 , Heather Behanna 3 , Michael Hui 1 , Xiaoqiang Han 4 , James Hulvat 5 2 , Jon Lomasney 4 , Samuel Stupp 2 3 5
1 Biomedical Engineering, Northwestern University, Evanston, Illinois, United States, 3 Chemistry, Northwestern University, Evanston, Illinois, United States, 4 Pathology, Northwestern University, Evanston, Illinois, United States, 5 Institute for BioNanotechnology in Medicine, Northwestern University, Evanston, Illinois, United States, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show Abstract10:45 AM - BB1.6
Functional Bio/Nano Interfaces through Cell-Directed Assembly
Eric Carnes 1 , Carlee Ashley 1 , DeAnna Lopez 1 , Seema Singh 2 , Hongyou Fan 2 1 , C. Brinker 2 1
1 Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractOur discovery that the introduction of living cells (Saccharomyces cerevisiae) dramatically alters the evaporation driven self-assembly of lipid-silica nanostructures suggests that novel bio/nano interfaces can be formed that are useful for cellular interrogation at the nanoscale. Such structures are of interest for probing cellular responses to the onset of disease, understanding of cell-cell communication, and the development of cell-based bio-sensors. By utilizing cell-directed assembly, several novel bio/nano interfaces have been created. Laser scanning confocal microscopy, SEM, TEM, and in situ grazing incidence small angle x-ray scattering (GISAXS) experiments were performed to characterize these new interfaces. It was found that introducing bio-compatible metallic nanoparticles can lead to an interface that allows for the exploitation of metallic characteristics. For example, gold nanoparticles could allow sensitive probing of the cell surface using Surface Enhanced Raman Spectroscopy (SERS). Cell-directed assembly can be used to form other functional nano/bio interfaces where proteins can be introduced and then localized at the cell surface, providing a way to physically introduce foreign proteins in the membrane of a cell. This interface was investigated using the bacterial trans-membrane protein bacteriorhodopsin. Altogether, cell-directed assembly provides a new general synthetic approach allowing for the creation and investigation of functional bio/nano interfaces.
11:30 AM - BB1.7
Directly Measuring the Adhesive and Elastic Properties of Bacteria using a Surface Force Apparatus: Effect of Desiccation.
Cheol Ho Heo 1 , Raina Maier 1 , Joan Curry 2
1 Department of Soil, Water, and Environmental Science, University of Arizona, TUCSON, Arizona, United States, 2 Department of Soil, Water, and Environmental Science and BIO5 Institute, University of Arizona, TUCSON, Arizona, United States
Show AbstractBacterial adhesion is the first step of biofilm formation that plays various roles in the environment and human body. Examples of undesirable roles of biofilm formation include metal rust, sewage sludge and bacteria-related diseases. Desirable roles are biofiltration and bioremediation. Bacteria can survive even in harsh environments, for example in very dry conditions, with some specific survival strategies. Desiccation is one of the most severe stresses for bacterial cells. Dehydration may damage DNA and change properties such as the melting point of proteins. Therefore, bacteria have developed strategies to protect against dehydration such as synthesis and accumulation of sugars such as sucrose and trehalose and transformation from an active state to a dormant state. Evaporative deposition of bacteria on a surface shows that some bacteria aggregate to form two dimensional patterns which may be important for nutrient sharing and survival in dry conditions. Bacteria are increasingly being employed as a component in biosensors and biofilm reactors. It is important to understand the material properties of bacteria in dry conditions for these applications. For a decade, Atomic Force Microscopy (AFM) has been the primary tool used to study the adhesion and elastic properties of individual bacteria. In this work we show it is possible to use a Surface Forces Apparatus (SFA) to measure elastic and adhesive properties of small collections of surface bound bacteria. The measurements are conducted with incomplete, patterned bacterial films and we have developed a protocol to image the contact area with AFM after the experiment. Using the SFA, we measured the force profile between a Pseudomanas Aeruginosa PAO1 film and a bare mica surface. Pseudomonas Aeruginosa PAO1 is a ubiquitous gram-negative soil bacterium and is also an opportunistic pathogen. We repeated the measurement in the same contact position for up to ten days to determine the effect of desiccation on the film material properties. The thickness of the bacterial layer decreased during the first few days and reached a steady state value for the remainder of the experiment. The elasticity decreased and adhesiveness increased as the bacteria respond to the dry conditions.
12:30 PM - **BB1.10
Patterned Tissue Formation Through Spatially Patterned Gene Delivery.
Angela Pannier 1 , Tiffany Houchin 2 , Lonnie Shea 2
1 Interdepartmental Biological Services, Northwestern University, Evanston, Illinois, United States, 2 Chemical and Biological Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractGene delivery from tissue engineering scaffolds can promote regeneration by providing a support for cell adhesion and growth, while also inducing the expression of tissue inductive factors that can direct cellular processes, such as proliferation or differentiation. We are developing the design parameters for delivery of non-viral vectors from biomaterial scaffolds based on immobilization of the vector to the surface – a process termed substrate-mediated delivery or solid phase delivery. Plasmid is self-assembled with cationic polymers or lipids, and the resulting complexes are immobilized to a substrate. Cells cultured on the substrate have vectors directly in their local microenvironment, which can lead to efficient gene transfer with relatively small quantities of immobilized vector. These non-viral vectors can be immobilized to the substrate through complementary functional groups conjugated to the vector and substrate, or through nonspecific interactions between them. The interaction between the vector and surface must be balanced to provide for immobilization to the substrate, yet allow for cellular internalization. Self-assembled monolayers of alkanethiols on gold were used to investigate chemical groups involved in non-specific immobilization. Surface hydrophilicity and ionization were observed to mediate both the quantity of vector immobilized, and the extent of cellular transfection.In addition to reducing vector quantities, surface immobilization provides the opportunity to spatially regulate gene delivery through patterning of the vector onto the surface. Spatially patterned transgene expression may also be able to pattern cellular responses, which may facilitate the engineering of tissues with complex architectures. Towards this objective, patterned deposition of lipoplexes to a surface was achieved with a microfluidic networks, which was created using PDMS molds fabricated by soft lithography. Surface patterning of complexes was visually confirmed with rhodamine-labeled plasmid. HEK293T cells cultured on the substrate were transfected within the pattern. The activity of the complexes was correlated to deposition time, complex volume, and DNA concentration in the complex. Patterned deposition of the complexes resulted in patterned transgene expression within the cell population, with transfection efficiencies within the pattern comparable to non-patterned surfaces. A co-culture system involving primary neurons and accessory cells was employed to investigate the patterning of neurite outgrowth. This ability to pattern cellular responses within a developing tissue may be a powerful tool to organize tissue formation for numerous applications.
BB2: Regulating Patterning: Tissue, Cell, and Molecular Levels
Session Chairs
Tuesday PM, April 18, 2006
Room 2007 (Moscone West)
2:30 PM - BB2.1
Micropatterned Silk Films for Cell Growth.
Maneesh Gupta 1 2 , David Phillips 2 , Tina Caserta 3 , Laura Sowards 2 , Lawrence Drummy 2 , Madhavi Kadakia 3 , Rajesh Naik 2
1 Biomedical Engineering, Wright State University, Dayton, Ohio, United States, 2 Materials and Manufacturing Directorate, Air Force Research Laboratory, WPAFB, Ohio, United States, 3 Biochemistry and Molecular Biology, School of Medicine Wright State University, Dayton, Ohio, United States
Show AbstractIn the past several years, there has been extensive research regarding the use of silk based scaffolds for tissue engineering applications. Silk based biomaterials are known to have excellent mechanical properties as well as biocompatibility. Furthermore, silk can easily be processed into a variety of geometries such as films, sponges, hydrogels, fibers, and mats. Recently, there has also been considerable interest in the application of microfabrication techniques to develop patterned and textured surfaces for cell growth. These techniques have been used to study the effects of surface topography on cell growth and adhesion and also for the creation of spatially organized cell growth. We have developed a method for fabricating patterned silk films using a soft lithography technique. This method utilizes a protocol for dissolution of Bombyx Mori cocoons in ionic liquids (1-butyl-3-methylimidazolium chloride) previously developed in our laboratory. Through this method we are able to impart a wide range of features (0.5µm-500µm) into optically clear, freestanding silk films. Films with patterned channels of varying sizes were fabricated and have been tested as scaffolds for cell culture in terms of differential growth, adhesion, and alignment. Silk films patterned through this technique have the potential to be used in numerous tissue engineering applications requiring not only the excellent mechanical and biological properties of silk, but also higher order spatial organization of cells directed by the silk film surface topography.
2:45 PM - BB2.2
Early-stage Mineralization Kinetics of Extracellular Protein Networks: use of the AFM to Probe the Elastic Modulus of Biomimetic Materials.
Seo-Young Kwak 1 , Karthikeyan Subburaman 2 , Elaine DiMasi 1 , Nadine Pernodet 2 , Miriam Rafailovich 2 , Nan-Loh Yang 3
1 National Synchrotron Light Source, Brookhaven National Laboratory, Upton, New York, United States, 2 Materials Science and Engineering, State University of New York, Stony Brook, New York, United States, 3 Department of Chemistry, City University of New York, Staten Island, New York, United States
Show AbstractBones and teeth are biocomposites that require controlled mineral deposition during their self-assembly to form tissues with unique mechanical properties. Extracellular matrix proteins are understood to be pivotal for biomineral formation. We have studied the adsorption of the hydrophobic extracellular proteins fibronectin and elastin, on negative-charged sulfonated polystyrene (SPS) spin-coated films on silicon. These proteins self-assemble into fibers with ~2 micron cross section, and organize further into networks with characteristic mesh sizes in the range 10-50 μm. The hierarchical organization has been used as a template to study the time- and length-scale dependencies of calcium carbonate mineralization. Supersaturated solutions were prepared by a free drift method and a flow cell method to compare differences in time dependence and the maintenance at constant driving force [1]. By using atomic force microscopy to image the networks and to probe the protein modulus using a new lateral force characterization method, very early mineralization stages are probed. The protein fibers increase height and stiffness when exposed to mineral solution. In early stage of mineralization, AFM height measurements suggest that the entire fiber surface is coated with mineral. At a later stage the films show localized and isolated particles on specific sites, especially the cross-linked sites of the elastin network, well-known to be hydrophilic. In contrast, on fibronectin network, isolated particles are also observed, but have no specific site. We conclude that properties of protein templates such as surface charge and hydrophobicity can determine the patterning and morphology of minerals.1. M. Travaille, Soft Interactions, Solid Results-nucleation of calcite on organic monolayers, Thesis, NSRIM institute, University of Nijmegan, 2004.
3:15 PM - BB2.4
Immunological Synapse Arrays: Templating the Structural Organization of Cell Surface and Intracellular Signaling Proteins in T cells Using Multi-component Patterned Protein Substrates.
Darrell Irvine 1 , Junsang Doh 2
1 Materials Science and Engineering and the Biological Engineering Division, MIT, Cambridge, Massachusetts, United States, 2 Chemical Engineering, MIT, Cambridge, Massachusetts, United States
Show Abstract3:30 PM - BB2.5
Studies of Cell-material Interactions on Protein Modified Biomaterial by Surface Characterization and Cell Morphology.
Meng-Jiy Wang 1 , Katherine Baria 1 , Dan Bader 1 , David Lee 1
1 Engineering, Queen Mary University of London, London United Kingdom
Show Abstract3:45 PM - BB2.6
Rewiring the T cell Signaling Network Using Solid-state Nanostructures.
Jay Groves 1
1 , UC Berkeley, Berkeley , California, United States
Show Abstract4:30 PM - BB2.7
Calcium Phosphate Bioceramics with Tailored Crystallographic Texture for Controlling Cell Activity
Hyunbin Kim 1 , Renato Camata 2 , Gregory Rohrer 3 , Yogesh Vohra 2
1 Dept of Materials Science and Engineering, University of Alabama at Birmingham, Birmingham, Alabama, United States, 2 Dept of Physics, University of Alabama at Birmingham, Birmingham, Alabama, United States, 3 Dept of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractThe excellent biocompatibility and bioactivity of calcium phosphate nanostructured surfaces offer a promising pathway for controlling key bioengineering processes such as cell cycle regulation, gene transfer, and patterned cell growth. The ionic dissolution products from these materials are known to affect, for example, the cell cycle of cells responsible for bone tissue formation. This effect may be genetically mediated as expression of various families of genes has been shown to be upregulated by Ca+ ions. These include genes for cell-signaling molecules, growth factors, DNA synthesis and repair, and extracellular matrix proteins. Among the many nanoscale physical characteristics of calcium phosphates that may influence cell activity, its crystallographic texture is one of the least investigated. Yet, crystallographic texture is known to be one of the essential microstructural features that determine the properties of polycrystralline materials. Naturally occurring calcium phosphates often exhibit preferred orientations resulting from highly specific biological processes. Texturing has also been observed in synthetic calcium phosphates that are coated onto metallic implants in dentistry and orthopedics to improve implant integration with adjacent bone tissue. Despite the fact that crystallographic texture is one the dominant features that determine the properties of polycrystalline ceramics and is commonly observed in naturally occurring calcium phosphates, its impact on the bioactivity of calcium-phosphate materials has so far received very little attention. This is due in part to the experimental difficulty in controlling texture in these materials through conventional fabrication methods. Recent studies have shown, however, that the crystallographic texture of calcium phosphates significantly affect protein and cell adhesion. This suggests that calcium phosphates with surfaces exhibiting tailored crystallographic texture may enable a new level of control of processes such as cell adhesion, differentiation, and proliferation. In this paper we present how we have used pulsed laser deposition to produce calcium phosphate coatings with controlled crystallographic texture. The orientation distributions of crystalline grains in the coatings were investigated using an X-ray pole-figure diffractometer. Increased laser energy density of a KrF excimer laser in the 4–7 J/cm2 range leads to the formation of hydroxyapatite grains with the c-axis preferentially aligned perpendicularly to the substrates. This preferred orientation is most pronounced when the plume direction of incidence is normal to the substrate. Texture formation of hydroxyapatite grains in the coatings is associated with the highly directional and energetic nature of the ablation plume. Anisotropic stresses, transport of hydroxyl groups, and dehydroxylation effects during deposition all seem to play important roles in the texture development.
4:45 PM - BB2.8
Design of Hepatocellular Microenvironment Using Protein Microarrays
Ji Youn Lee 1 , Alexander Revzin 1
1 Deparatment of Biomedical Engineering, University of California, Davis, California, United States
Show AbstractCellular interactions with the surrounding matrix proteins, neighboring cells and soluble factors define state of cell differentiation or proliferation. Our lab is interested in designing cellular microenvironment in a combinatorial fashion to enable rapid identification of inducers of cellular differentiation based on a small cell population. Microfabrication, surface engineering and microarraying will be employed to recreate multiple scenarios of cell microenvironment on the same substrate and to identify most potent microenvironment stimuli of differentiation. This presentation will describe the design of hepatocellular microenvironment using protein microarrays. Protein arrays were printed by high-throughput robotic microarrayer (ca. 150 μm individual spot diameter) or by semi-manual arryer (ca. 500 μm individual diameter) on silane- and PEG gel-modified glass substrates. Printed arrays contained three types of ligands: collagen type I, fibronectin, and poly-L-lysine. After incubating with micropatterned glass substrates, model hepatocytes, HepG2 cells, formed into clusters corresponding in size to imprinted islands of cell-adhesive ligands. In cells cultured on a redundant array of a single ligand such as collagen, liver-specific function could be evaluated by albumin ELISA assay of cell culture media. However, in the case of hepatocytes residing on a mixed array of ligands such traditional approaches were no longer applicable. To help untangle cell function without losing the microenvironment context we employed a laser capture microdissection (LCM) tool to extract hepatocytes in a location-specific fashion. Extracted cells were then analyzed for the expression of liver-specific genes such as albumin, alpha1-AT, prealbumin, and α-fetoprotein using quantitative real-time RT-PCR technique. In conclusion, this work describes protein micropatterning-based approaches for in vitro studies of cellular interactions and also provides a method for evaluation of cell function in the context of the local engineered microenvironment.
5:00 PM - **BB2.9
Topographic Cues that Model the Native Basement MembraneDifferentially Impact Corneal Epithelial Cell Behaviors.
Paul Nealey 1 , Christopher Murphy 2
1 Chemical and Biological Engineering, University of Wisconsin, Madison, Wisconsin, United States, 2 School of Veterinary Medicine, Univeristy of Wisconsin, Madison, Wisconsin, United States
Show AbstractA fundamental question in the design of corneal prosthetics is how surface topography regulates cell behavior. Our previous and ongoing work has focused on defining the topography of native basement membranes and determining the “phenotypic impact” of biologically relevant length scales on cell behaviors. We have found that the native corneal basement membrane contains features from 20 to 400 nanometers in size. We fabricated silicon surfaces that contain feature sizes ranging from 400 to 4000 nm in pitch (groove width + ridge width) as well as planar regions. The smallest feature sizes on these chips were 70 nm ridges on a 400 nm pitch. Thus, we are able to replicate on a single chip features of biologically relevant size, as well as larger, micron sized features that provide a link to the bulk of the literature. We find that nanometer length features affect the behavior of epithelial and neuronal cell lines differently than do micron scale features. Specifically, primary human corneal epithelial cells (hCECs) cultured in Epilife® medium (Cascade Biologics) align and elongate parallel to micron scale features, but perpendicular to nanometer length features. Adhesion of SV40-transformed hCECs under shear flow was dramatically enhanced when cells were cultured on nanometer length features over cells cultured on micron length features. hCEC proliferation and migration was decreased on surfaces with nanometer length scale features. PC12 cell neuritogenesis was dramatically enhanced on nanometer length features under sub-optimal conditions. When cultured in 5 ng/ml NGF for 3 days, cells plated on 400 and 800 nm pitch extended ~3 times as many neurites as cells on flat and micrometer length features. Remarkably, for each of these findings a transition in the cellular response to topography occurs at approximately 1200 to 1600 nm pitch (ridge widths of 400 to 900 nm). Cells plated onto features smaller than this transition zone demonstrate differences in behavior from cells plated onto features larger than this zone. Thus, biologically relevant nanometer length features may be important regulators of cellular behavior. These studies have relevance to our fundamental understanding the role that topographic cues play in the normal development and maintenance of the corneal epithelium. Furthermore, this knowledge may contribute to the genesis of novel strategies in tissue engineering and advance the development of ocular prosthetics.
5:30 PM - **BB2.10
Switching the Functional States of Proteins by Force.
Viola Vogel 1
1 Laboratory for Biologically Oriented Materials, Dept. of Materials, Swiss Federal Institute of Technology, ETH, Zurich Switzerland
Show Abstract
Symposium Organizers
Michael P. Sheetz Columbia University
Jay T. Groves University of California-Berkeley
Dennis Discher University of Pennsylvania
BB3: Regeneration and Wound Healing
Session Chairs
Wednesday AM, April 19, 2006
Room 2007 (Moscone West)
9:30 AM - BB3.1
Using an Atomic Force Microscope to Probe the Interactions between a Malignant Cell and Functionalized Colloid Particles: A Model of the Drug Delivery System.
Cathy McNamee 1 , Nayoung Pyo 1 , Saaya Tanaka 1 , Ko Higashitani 1
1 Department of Chemical Engineering, Kyoto University, Katsura, Kyoto, Kyoto, Japan
Show AbstractAnti-cancer drugs may be delivered to malignant cells at the required rate and concentration for effective treatment, if we use the Drug Delivery System (DDS). Here, the drugs are embedded in carriers, which have surface functionalities specific only to the malignant cells. The effective operation of the DDS requires we know the surface properties of a melanoma cell, the carrier surface functionality groups to which the cell is specific, and the optimum conditions for administering the drugs. The problem is that these properties are still unknown. In this study, we investigated these subjects by measuring with the Atomic Force Microscope (AFM) the adhesion force between functionalised cantilever colloid probes, which modeled the DDS carrier, and a living melanoma B16F10 cell. The success of a DDS is thought to be influenced by the force used in administrating the drug, the position where the drug is administrated on a cell, and the residential time of a drug at a cell. There appears to be no study that investigates the single importance of each of these points. In order to explore the importance of the force strength, we varied the pushing force of the colloid probe to the cell, and noticed that the magnitude of the pushing force did not appear to affect the adhesion, as long as the force was small enough not to damage the cell. Next, we investigated the difference in the adhesion force between the cell and colloid probe, when we measured at the cell nucleus and near the edge of the cell. We found no relation between the cell surface position and the adhesion force. Finally, the influence of the adhesion time of the probe at the cell surface was examined, by varying the adhesion time from 10 to 60 min. A large dependence was seen, where the largest adhesion was noted for longer times. Next, we varied the type of carrier, in order to find the functionality with the highest specificity to the malignant cell. As carriers containing hydrophobic, polyethylene glycol (PEG), or positive surface groups appear to show specificity to non-malignant cells, it was thought that a malignant cell may respond in a similar manner. We tested the effect of charge, hydrophobicity, and polymer presence on a DDS carrier on its degree of specificity to the melanoma cell. We surprisingly found that negatively charged surfaces, hydrophobic, and PEG modified surfaces all had similar low adhesive force values. Additionally, there was no observable dependence on the degree of hydrophobicity of the probe surface to a B16F10 cell. Only the particle that was modified to give a positive charge was seen to give strong adhesive forces with the B16F10 cell. In conclusion, carriers with short-chained PEG or hydrophobic groups do not show an increased specificity towards a melanoma cell – this is a result in opposition to current beliefs. Thus, the optimum delivery of a drug to such cells appears to occur when we use positively charged DDS carriers and long residence times.
9:45 AM - BB3.2
Improved Biomaterials from a Cellular Point of View
Venu Varanasi 1 , Eduardo Saiz 2 , Hengameh Yousifzedah 1 , Tiffany Vallortigara 1 , Peter Loomer 1 , Antonio Tomsia 2 , Grayson Marshall 1 , Sally Marshall 1
1 Preventive and Restorative Dentistry, University of California, San Francisco, San Francisco, California, United States, 2 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractBioactive glasses are coated onto titanium-alloy prostheses to improve their osseointegration. In this study, an experimental bioactive glass (used to coat titanium) was compared with uncoated titanium alloy and commercial Bioglass for its relative cyto compatibility and bioactivity. An experimental bioactive glass (6P55, Table 1, Lawrence Berkeley National Laboratory, Berkeley, CA) was prepared using melt derived powders (SEM COM). These powders were placed onto a Pt crucible and fired to 1400 1500oC using a standard high temperature furnace. The melt was then poured into a graphite mold to make cylindrical rods or rectangular bars. The experimental glass and Bioglass (45S5, Table 1, Mo-Sci, St. Louis, MO) were cut using a conventional low-speed saw, while titanium alloy (Ti6Al4V, Goodfellow) was cut using a conventional lathe. All samples had a surface area of approximately 3 cm2 and were polished to 25 micrometers using a conventional metallographic polishing. Samples were then placed in a 12-well tissue culture polystyrene (TCPS) plate and sterilized using gamma irradiation for 16 h.Table 1. Composition of experimental and commercial bioactive glass.GlassSiO2Na2OK2OCaOMgOP2O545S54524.524.56.06P5554.512.04.015.08.56.0Mouse pre-osteoblast cells (MC3T3.E1.4) were seeded at 50,000 cells cm -2 on each substrate in tissue culture media. After 12 h, non adhering cells were removed by discarding the residual media, and the number of adherent cells were determined using the MTT assay (CellTiter96, Promega, Madison, WI), in which ells were incubated overnight, and their reaction with formazine dye was quantified using a spectrophotometer (Spectramax, Molecular Devices, Sunnyvale, CA). All experiments were performed in triplicate.All results are reported relative to control (TCPS). Optical microscopy revealed adherent cell layers on the surface of the bioactive glasses (titanium is not transparent, thus, could not be visually analyzed for cellular attachment). Cells on TCPS had an elongated morphology whereas cells on 6P55 and 45S5 were rounded .Results from the MTT assay revealed that more cells were adherent to the bioactive glasses than on control or Ti6Al4V. Cell numbers on 6P55 and 45S5 were 140% and 120% higher than the control, whereas cell numbers on Ti6Al4V were10% lower than control.Support. NIH/NIDCR Grants R01DE11289 and T32DE07306 (VV).
10:00 AM - BB3.3
Biphasic Polymeric Shell-Core 3D Fiber Deposited Scaffolds Enhance Chondrocyte Redifferentiation.
Lorenzo Moroni 1 , Joost de Wijn 1 , Jeanine Hendriks 1 2 , Roka Schotel 2 , Clemens van Blitterswijk 1
1 Polymer Chemistry and Biomaterials, Twente University, Bilthoven Netherlands, 2 , CellCoTec, Bilthoven Netherlands
Show AbstractIntroductionIn tissue engineering polymers are used as three dimensional (3D) porous matrices for tissue repair. These constructs have to be biocompatible, possibly biodegradable, offer mechanical support, and provide the appropriate chemistry for cells to form the proper tissue [1]. A way to control the distribution and morphology of seeded cells is to make multiphase scaffolds, where different materials are regionally present. We present here a novel system to create 3D fibrous scaffolds with shell-core fiber architecture, where one polymer supplies the mechanical properties, and the other is a coating providing the surface properties of a construct. In our study, 3D fiber deposited (3DF) scaffolds with a shell of 1000PEOT70PBT30 and a core of 300PEOT55PBT45 were examined for cartilage regeneration.Materials and Methods300PEOT55PBT45 and 1000PEOT70PBT30 copolymers were obtained from Isotis S.A. The polymers were mixed in a 50/50 weight ratio blend. Scaffolds were fabricated as described elsewhere [2]. The blend was inserted in a syringe, heated above its melting temperature and extruded on a stage in a CAD/CAM pattern, by applying pressure (5 bars).Bovine primary chondrocytes were seeded and cultured on 300/55/45 and 1000/70/30-300/55/45 shell-core cylindrical scaffolds (Ø=4mm; h=4mm). After 21 days DNA and GAG were measured.Cells morphology was analyzed by scanning electron microscopy (SEM). The dynamic stiffness of the constructs was measured by dynamic mechanical analysis (DMA). A t-test was performed to determine significant (p<0.05) differences.Results and DiscussionDNA and GAG were not significantly different in the shell-core constructs compared to the 300/55/45 scaffolds. SEM analysis revealed a maintained rounded morphology of chondrocytes in the shell-core constructs, while cells were spread in the 300/55/45 scaffolds (figure 1). This suggests a higher cell redifferentiation capacity of the shell-core constructs. DMA showed a significant increase of the dynamic stiffness after 21 days for both the scaffolds. The dynamic stiffness of the shell-core construct was considerably higher (p<0.1) than the dynamic stiffness of 300/55/45 (figure 2).Conclusions Shell-core scaffolds with different physicochemical properties can be tailor-made to influence cell response. Chondrocytes cultured on 1000/70/30-300/55/45 3DF scaffolds maintained rounded cell morphology, showing comparable DNA and GAG amount, and a higher dynamic stiffness compared to 300/55/45.References 1. Hutmacher DW. J Biomater Sci Polym Ed 2001;12(1):107-24.2. Moroni L, de Wijn JR, van Blitterswijk CA. Biomaterials 2005, doi:10.1016/j.biomaterials.2005.07.023AcknowledgementsThis project was funded by EC Intelliscaf GSRD_2002_00697.
10:15 AM - BB3.4
Mechanical Properties of Wild Type and Mutant Caenorhabditis Elegans using a Closed Loop Piezoresistive Cantilever Indentation System.
Sung Jin Park 1 , Miriam Goodman 2 , Beth Pruitt 1
1 Department of Mechanical Engineering, Stanford University, Stanford, California, United States, 2 Department of Molecular & Cellular Physiology, Stanford University, Stanford, California, United States
Show Abstract10:30 AM - BB3.5
Fibronectin Coated Silica Nanowires for Introducing Compound into Mammalian Cells.
Daqing Zhang 1 , Lidong Wang 2 , Miles Beaux 2 , Devananda Gangadean 2 , Katarzyna Dziewanowska 3 , Gregory Bohach 3 , David McIlroy 2
1 Physics, California State University, Fresno, Fresno, California, United States, 2 Physics, Univerity of Idaho, Moscow, Idaho, United States, 3 Microbiology, Molecular Biology and Biochemistry, University of Idaho, Moscow, Idaho, United States
Show AbstractThe controlled delivery of biologically-active molecules to the inside of mammalian cells has broad and significant applications such as drug delivery and cell biology research. However, most chemical compounds cannot permeate through the cell membrane, i.e., endocytosis into the cell is prohibited. A method for sidestepping this obstacle is the use of nanomaterials as carriers for delivery of compounds into cells. In this study, a process was developed for introducing silica based nanowires into bovine mammary gland epithelial cells (MAC-T) that exploits receptor/ligand interactions employed by several intracellular bacteria. Fibronectin was used as a molecular bridge to induce internalization of the nanowires into the viable MAC-T cells. The bonding mode of fibronectin to silica based nanowires has been examined using x-ray photoelectron spectroscopy. Examination of the Si 2p, O 1s, and C 1s core level states before and after exposure of the nanowires to fibronectin showed that bonding of fibronectin primarily involves the Si sites on the nanowire surface. Imaging of the MAC-T cells after exposure to the fibronectin coated silica nanowires with a scanning electron microscope operated in the secondary electron imaging mode (SEI) and backscattered electron imaging mode (BEI) verified that the fibronectin coated nanowires are internalized by the MAC-T cells. Further studies to tailor the interface of the nanowires to facilitate the desired chemical bonds with specific chemical structures are under way.
10:45 AM - BB3.6
Enzymatic Cross-linking of Short Synthetic Peptides to Chondrocyte Membrane and to Cell Membrane-associated Extracellular Matrix: Towards Mechanotransduction.
Marsha Ritter Jones 1 , Phillip Messersmith 1
1 Biomedical Engineering, Northwestern University, Evanston, Illinois, United States
Show Abstract11:30 AM - BB3.7
Sequential Bone Response to Immediately Loaded Mini-Implants, in vivo Study.
Glaucio Guimaraes 2 1 , Liliane Morais 2 1 , Marc Meyers 1 , Carlos Elias 2
2 Mechanical Engineering and Materials Science, Engineering Institute of Engineering, Rio de Janeiro Brazil, 1 Mechanical and Aerospacial Engineering, UCSD, La Jolla, California, United States
Show Abstract11:45 AM - BB3.8
Growth and Shape Stability of a Biological Membrane Adhesion Complex in the Binder Diffusion Mediated Regime.
Vivek Shenoy 1
1 , Brown University, Providence , Rhode Island, United States
Show AbstractWe examine the process of expansion of a focal adhesion complex by whicha biological membrane containing mobile binders adheres to a substratewith complementary binders. Attention is focused on the situation, commonamong living cells, in which the mean mobile binder density is insufficientto overcome generic resistance to close approach of the membrane to itssubstrate. In order for the membrane to adhere, binders must be recruitedfrom adjacent regions to join an adhesion patch of density adequate foradhesion, thereby expanding the size of the patch. The specific configurationexamined is the expansion of a circular adhesion zone for which diffusivebinder transport driven by a chemical potential gradient is the mechanismof binder recruitment. An aspect of the process of particular interestis the stability of the circular shape of the expanding front. It is foundthat the adhesion front radius increases as $\sqrt{t}$ where t is thetime elapsed since nucleation, and that the circular shape becomes unstableunder sinusoidal perturbations for radii large compared to the nucleationsize, as observed in recent experiments.Ref: V. B. Shenoy and L. B. Freund, Proc. Nat. Acad. Sci. vol. 102, 3213-3218 (2005)
12:00 PM - **BB3.9
Application of Mechanical Forces for Controlled Differentiation of Human Embryonic Stem Cells.
Somen Saha 1 , Sean Palecek 1 , Juan de Pablo 1
1 , University of Wisconsin, Madison, Wisconsin, United States
Show AbstractHuman embryonic stem cell (hESC) self-renewal and differentiation are regulated by extrinsic signals in the cell microenvironment, including chemical factors and mechanical forces. We have investigated the regulation of spontaneous differentiation under mechanical strain and have studied directed differentiation of hESCs along the keratinocyte lineage.Mechanical forces induce proliferation and/or differentiation in many cell types, but the role of mechanotransduction on human embryonic stem cell differentiation is unknown. Above a threshold of 5%, we have found that cyclic strain inhibits hESC differentiation without selecting against survival of differentiated or undifferentiated cells. Mechanical inhibition of hESC differentiation could not be traced to secretion of chemical factors into the media, suggesting that mechanical forces may directly regulate hESC differentiation. We found that though mechanical forces play a role in regulating hESC differentiation, they must act synergistically with chemical signals. These findings imply that mechanics may be involved in early embryonic developmental processes, and that application of mechanical forces may be useful, in combination with chemical and matrix-encoded signals, for control of differentiation of hESCs for therapeutic applications. One potential application of hESCs that we have started to explore is concerned with skin grafting and tissue engineering; such an application would require directing the commitment and differentiation of hESCs into the keratinocyte lineage in vitro. We have identified soluble chemical and extracellular matrix factors that permit isolation of epidermal keratinocytes from hESCs and have subsequently expanded the isolated keratinocyte population down keratinocyte lineage by inducing them to stratify and terminally differentiate. We have found that embryoid body formation is not necessary to generate keratinocytes; direct transfer of hESC colonies to keratinocyte growth medium permits keratinocyte differentiation. With further studies to optimize generation and purification of hESC-derived keratinocytes, these cells could provide a source of epidermal cells for skin tissue engineering applications, in vitro or in vivo.
12:30 PM - **BB3.10
Oriented Collagen Films for Wound-Healing Applications
Gerald Fuller 1 , Jayakumar Rajadas 1 , An Goffin 1
1 , Stanford University, Stanford, California, United States
Show AbstractIt is well-known that infants are able to heal wounds with an absence of scarring. In addition, infant skin is characterized by collagen with a much higher degree of orientation compared with adult skin. This paper presents a means of processing well-oriented collagen films to produce artificial skin for the purpose of promoting wound healing. The method involves a means of spreading solubilized collagen on the surface of water and manipulating the orientation of the protein through compression and dessication of the film. Direct optical measurements of molecular orientation is accomplished through dichroism and birefringence and monitors the kinetics of this process.
BB4: Engineering Matrix Assembly and Signaling
Session Chairs
Wednesday PM, April 19, 2006
Room 2007 (Moscone West)
2:30 PM - BB4.1
Imaging Mechanotrandsuction: Mechanical Mapping of Living Cell Surfaces.
Sunyoung Lee 1 , Jelena Mandic 1 , Krystyn Van Vliet 1
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractCell surfaces comprise a variety of molecules through which signal transduction and extracellular matrix (ECM) interactions are mediated. The capacity to mechanically image cell surfaces in real-time provides the potential to map the dynamic molecular response of the cell to both chemical and mechanical cues that modulate cell function. Such quantitative mapping of cell-environment interactions is critical to the design of synthetic ECM and materials that induce cell phenotypes via a combination of substrate stiffness, ECM ligand presentation, and soluble biomolecules. Here, we demonstrate an engineering approach termed functionalized force imaging, enabled by nanoscale intermolecular forces between ligand-functionalized scanning probe microscope cantilevers and molecular receptors presented by the living cell surface. The spatial distribution and binding avidity of key molecular receptors on living cells are mapped in real-time and at the single cell level. We validate this approach in microvascular endothelial cells, mechanically responsive cells important in wound healing and cancer progression, and demonstrate how the real-time organization and binding capacity of receptors for soluble molecules (growth factors) and ECM adhesion peptides are altered significantly by external chemical and mechanical stimuli. This general cell surface imaging approach thus provides a means to visualize the mechanotransduction processes directly at the cell-ECM interface.
2:45 PM - BB4.2
Role of Particle Shape in Phagocytosis.
Julie Champion 1 , Samir Mitragotri 1
1 Chemical Engineering, University of California Santa Barbara, Santa Barbara, California, United States
Show AbstractPhagocytosis is a principal component of the body’s innate immunity in which macrophages internalize large (> 0.5 um) targets such as pathogens and senescent cells. Examples of targets include pathogens such as E. Coli and Bacillus Anthacis, senescent cells such as aged erythrocytes, and airborne particles such as dust and pollen, all of which vary widely in both shape and size. It has been well documented that mechanical features of biological materials influence cell function and motility. To date, however, there exists no comprehensive understanding of the role of target geometry in phagocytosis despite its well recognized relevance to macrophage function. Previous work has used only spherical particles which not only discount the role of particle shape in phagocytosis but also create an inaccurate picture of the role of particle size since all parameters that describe size (volume, surface area etc.) scale with particle radius, leaving one wondering as to which parameter is of fundamental consequence in phagocytosis. To fill this void, we created polystyrene particles of six different shapes: spheres, elliptical disks, oblate ellipsoids, prolate ellipsoids, rectangular disks, and UFO shapes. Collectively, these novel particles possess volumes, surface areas, curvatures, and maximum lengths that span several orders of magnitude. We report, using these particles and alveolar macrophages, that particle shape, not size, plays a critical role in initiation of phagocytosis. We found that internalization velocity directly correlates with particle shape. Our results demonstrate that the target shape at the point of macrophage attachment decisively determines whether cells will proceed with phagocytosis or simply spread on the particle. Size primarily impacts the completion of phagocytosis in cases where particle volume exceeds the cell volume. Dependence of phagocytosis on particle shape is a new and remarkable example of cell behavior being dictated by the physical environment.
3:00 PM - **BB4.3
From Surface Arrays to Biomaterials - New Tools for Controlling Human Embryonic Stem Cells.
Laura Kiessling 1 2 , Ratmir Derda 1 , Brendan Orner 2 , Lingyin Li 1 , Rachel Lewis 3 , James Thompson 3
1 Chemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States, 2 Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin, United States, 3 Anatomy, University of Wisconsin-Madison, Madison, Wisconsin, United States
Show AbstractHuman embryonic stem (ES) cells hold promise because of their ability to give rise to any human cell type. A significant barrier to the study and use of human ES cells is the difficulty of maintaining them in a pluripotent state. The signals that promote human ES cell self-renewal in culture are different than those required for mouse ES cells; strategies to identify conditions for culturing and differentiating human ES cells are needed. To solve this problem, we have developed surface arrays composed of self-assembled monolayers; these chemically-defined surfaces that can be screened for their ability to control human ES cell fates. From these arrays, surfaces that promote human ES cell propagation have been discovered. Moreover, we show that these surfaces can guide the design of multivalent biomaterials as substrates for human ES cell culture. We envision that this general approach can be used to identify materials that promote selective propagation and/or differentiation of a variety of cell types.
3:30 PM - BB4.4
Study of Cellular Biomechanics using Underwater Electrostatic Actuator.
Vikram Mukundan 1 , Beth Pruitt 1
1 Mechanical Engineering, Stanford University, Stanford, California, United States
Show Abstract3:45 PM - BB4.5
Mechanotransduction in Prokaryotic Cells? Modulating Bacteria Function Through Mechanically Tunable Substrates.
M. Thompson 1 , Jenny Lichter 1 , Michael Rubner 1 2 , Krystyn Van Vliet 1 2
1 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States, 2 Center for Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractMechanotransduction is studied chiefly in cells that contain nucleus-localized genetic machinery and cytoskeletal networks, as it is reasonable to assume that these eukaryotic cells have unique structures to sense and respond to mechanical cues. In previous studies of one such eukaryotic cell type, microvascular endothelial cells, we have demonstrated the use of weak polyelectrolyte multilayer thin films comprising poly(acrylic acid) and poly(allylamine hydrochloride) to modulate substrate elastic stiffness over several orders of magnitude and thereby also modulate cell attachment and proliferation. Here, we apply this same material system to the study of prokaryotic cells (Escheria coli bacteria) which lack such robust structural and signaling networks, in order to consider whether mechanotransduction requires the structural machinery though to be required of mammalian response. We demonstrate that the attachment, proliferation, and function of these prokaryotic cells are modulated independently by the mechanical stiffness and the surface charge density of the underlying thin films, and compare potential mechanotransduction mechanisms to those proposed for eukaryotic responses.
4:30 PM - BB4.6
Cellular Integration into Functional Hierarchical/Multiscale Devices
Carlee Ashley 1 , Eric Carnes 1 , DeAnna Lopez 1 , Helen Baca 1 , Hongyou Fan 2 1 , Seema Singh 2 , C. Brinker 2 1
1 Chemical and Nuclear Engineering , University of New Mexico, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show Abstract The incorporation of living cells into solid-state platforms or devices is important for a diverse range of applications including tissue engineering, array-based drug discovery, bio-sensing, and the powering of nanodevices. Here we report a cell-directed assembly approach to the 3-D incorporation of living cells in a uniformly nanostructured inorganic host that maintains cell accessibility, addressability, and viability in the absence of an external fluidic architecture. Using in-situ grazing incidence small angle x-ray scattering (GISAXS) along with transmission electron microscopy (TEM) and laser scanning confocal imaging, we investigated how amphiphilic phospholipids direct the formation of ordered biocompatible silica mesophases in the absence or presence of the eukaryotic organism, S. cerevisiae. We find that living S. cerevisiae profoundly alter the self-assembly pathway, each cell creating an extensive multilayered phospholipid vesicle around itself that interfaces coherently with the nanostructured silica host. In doing so, cells gain viability that extends well beyond the expected range, creating devices that can function for longer periods of time. This approach has recently been extended to Gram-positive and Gram-negative bacteria and other eukaryotic cells with comparable results. Using yeast and bacteria genetically-modified to express green fluorescent protein in response to an external stimulus (along with other viability probes), we show that this novel cell-directed hierarchical structure serves as a useful, physiologically relevant standalone environmental sensor. We also demonstrate the ability of living cells to rapidly and efficiently organize metallic nanocrystals and various functional proteins within their surrounding multilayered lipid vesicles, suggesting a new general synthetic approach wherein cells direct their self-integration into functional 3-D hierarchical/multiscale devices. A similar method involving integration of living cells onto pre-defined mesoporous silica minimizes osmotic stress and exposure to toxic components involved in our traditional cell-directed self-assembly approach and allows for the creation of patterned arrays. Incorporation of photoactive compounds into the silica mesophase provides the ability to generate optically-defined microarrays based on selective wetting. Similarly, ink-jet printing of mesoporous silica allows for an additional technique whereby cells can be selectively localized onto an inorganic host matrix, which is central to the development of functional bio-sensors.
4:45 PM - **BB4.7
Unique Biomaterial Requirements for Stem Cell Culture in Hydrogels.
Jennifer Elisseeff 1
1 , Johns Hopkins University, baltimore, Maryland, United States
Show AbstractA number of cell types have been encapsulated in three dimensional hydrogels for applications including musculoskeletal tissue engineering. We have compared tissue forming capabilities of differentiated chondrocytes, adult marrow-derived stem cells, and embryonic stem cells encapsulated in polyethylene glycol-based (PEG) hydrogels. Chondrocytes, the cells that comprise cartilage, are able to produce cartilage-like tissue in the PEG hydrogels when cultured in standard chondrocyte medium. Marrow-derived stem cells required growth factor exposure (transforming growth factor beta 1 or 3) to induce differentiation, although small amounts of differentiation can be observed in 3D hydrogels cultured without growth factor. Embryonic stem cell behavior in the hydrogels depended on the species, mouse or human. Mouse stem cells were able to differentiate in conditions similar to the adult stem cells, however human embryonic stem cells (hES) required coculture with differentiated cells or incorporation of adhesion peptides into the PEG hydrogel to induce differentiation. Human embryonic stem cells require unique signals to survive and differentiate when encapsulated in 3D hydrogels yet can be manipulated to produce homogenous cartilage tissue.
5:15 PM - **BB4.8
Bioactive Networks
Samuel Stupp 1
1 Materials Science & Engineering, Department of Chemistry, and Feinberg School of Medicine, Northwestern University, Evanston, Illinois, United States
Show AbstractMolecular design of artificial environments to interact with cells will lead to great advances in biology and regenerative medicine. An important opportunity is to create networks that form by self-assembly artificial extracellular matrices around cells to control their behavior through signaling. Bioactive supramolecular networks could deliver signals for cell survival, migration, proliferation, and differentiation of stem cells into defined lineages, and those systems would become key players in achieving regeneration of tissues and organs. One of the fundamental questions is what nanostructures are best to interact effectively with membrane receptors, or to program the delivery of proteins that trigger signal transduction pathways. This lecture describes the design of peptide amphiphile monomers that polymerize through self-assembly to create bioactive nanofibers designed for cell signaling. These nanostructures can present to cells high densities of epitopes and proteins with interesting biological consequences. This will be illustrated with systems designed toward targets such as the repair of the central nervous system, bone regeneration, the growth of blood vessels, and the formation of insulin producing organs to cure diabetes.