Elastic Membrane That Undergoes Mechanical Deformation Enhances Osteoblast Cellular Attachment and Proliferation

The main objective of this paper was to investigate the effect of transmission of force on bone cells that were attached to a deformable membrane. We functionalized a silastic membrane that measured 0.005 inches thickness and coated it with an extra cellular matrix (ECM) protein, fibronectin (FN). MC3T3-E1 osteoblast-like cells were cultured on the functionalized FN-coated membrane after which cell attachment and proliferation were evaluated. We observed an immediate attachment and proliferation of the bone cells on the functionalized membrane coated with FN, after 24 hours. Upon application of a mechanical force to cells cultured on the functionalized silicone membrane in the form of a dynamic equibiaxial strain, 2% magnitude; at 1-Hz frequency for 2 h, the osteoblast cells elicited slightly elevated phalloidin fluorescence, suggesting that there was reorganization of the cytoskeleton. We concluded from this preliminary data obtained that the engineered surface transduced applied mechanical forces directly to the adherent osteoblast cells via integrin binding tripeptide receptors, present in the FN molecules, resulting in the enhanced cellular attachment and proliferation

Biomimetic surfaces via dextran immobilization : grafting density and surface properties

Biomimetic surfaces were prepared by chemisorption of oxidized dextran (Mw = 110 kDa) onto SiO2 substrates that were previously modified with aminopropyl-tri-ethoxy silane (APTES). The kinetics of dextran oxidation by sodium metaperiodate (NaIO4) were quantified by 1H NMR and pH measurements. The extent of oxidation was then used to control the morphology of the biomimetic surface. Oxidation times of 0.5, 1, 2, 4, and 24 hours resulted in \u3c20, ~30, ~40, ~50 and 100% oxidation, respectively. The surfaces were characterized by contact angle analysis and atomic force microscopy (AFM). Surfaces prepared with low oxidation times revealed a more densely packed brushy layer when imaged by AFM than those prepared at low oxidation times. Finally, the contact angle data revealed, quite unexpectedly, that the surface with the greatest entropic freedom (0.5 h) wetted the fastest and to the greatest extent (THETAAPTES \u3e THETA1h \u3e THETA2,4h \u3e THETA0.5h)

Surface segregation amplification in miscible polymer blends near criticality

In atomic, small molecule or polymeric multicomponent materials, surface compositions naturally differ from the bulk because one component (or phase) will generally favor the surface region. Binary polymer blends represent a model system to investigate surface enrichment because segregation is enhanced by the small combinatorial entropy of mixing and amplified by chain connectivity (relative to small-molecule systems). Therefore, polymers are advantageous systems for probing the thermodynamic complexities underlying surface enrichment in mixtures. In this work, the surface excess of binary polymer blends is studied as a function of composition and temperature in the vicinity of the critical point. Although the surface excess away from criticality behaves as anticipated, it is found to grow slower than expected as criticality is approached from the one-phase region. These results suggest that the surface and bulk thermodynamics are coupled

Understanding morphology evolution and roughening in phase-separating thin-film polymer blends

Using forward recoil spectrometry and atomic force microscopy, the entire phase evolution is revealed for a critical thin-film blend deposited on a substrate undergoing symmetric wetting and phase separation. The three main stages are characterized by a trilayer structure, interphase coarsening, and surface roughening. Capillary fluctuations are shown to cause spontaneous rupturing of the interphase resulting in an interconnected network, which eventually forms encapsulated droplets. The surface roughness grows rapidly at first, remains relatively constant (ca. 12 nm), and then increases rapidly to a final macroscopic value of 245 nm, about half the original film thickness

Phase-Morphology Map of Polymer-Blend Thin Films Confined to Narrow Strips

Upon lateral confinement, a critical polymer-blend film at 200 degreesC has been directed to form tube, capsule, confined domain, and multiple domain configurations. A phase-morphology map is produced by varying the confinement width (W) and film thickness (h(0)), and interpreted using a single pore model. Using the known correlation length, capsule length, and W, the boundary, in terms of W/h(0), between configurations is predicted and found to be in good agreement with experiment. This morphology map has potential applications for microencapsulating drugs and self-assembled conducting wires

Mobile nanoparticles and their effect on phase separation dynamics in thin-film polymer blends

We present a systematic study of mobile nanoparticles (NP) and their effect on phase separation dynamics in polymer blend films. Starting with a homogeneous dispersion of silica NP in \tx{PMMA}:\tx{SAN} films, the NP are observed to partition into the PMMA-rich phase and stratify during phase separation. The correlation length ξ between phases grows as $\xi\sim t^{1/3}$ for blends containing 0, 2, and 5\un{wt}% NP. However, phase size decreases as the wt% of NP increases. This behavior agrees with a coalescence model, which incorporates an increase in viscosity due to the NP

Block copolymer adsorption from a homopolymer melt to an amine-terminated surface

Using neutron reflectometry, the adsorption of diblock copolymers from a neutral polystyrene (PS) matrix is studied as a function of substrate type and non-adsorbing block degree of polymerization. The block copolymer is poly(deutero styrene)-block-poly(methyl methacrylate) and the substrates are silicon oxide, SiOx, and SiOx functionalized with (3-aminopropyl)triethoxysilane (APTES). We have determined the equilibrium volume fraction-depth profiles for such films, and compared them with volume fraction profiles generated by self-consistent mean-field (SCMF) theory and find good agreement between the experimental and theoretical data. SCMF calculations show that the segmental interaction energy between PS matrix chains and APTES is two orders of magnitude stronger than that between PS and SiOx

Hierarchical Nanoparticle Topography in Amphiphilic Copolymer Films Controlled by Thermodynamics and Dynamics

This study systematically investigates how polymer composition changes nanoparticle (NP) grafting and diffusion in solvated random copolymer thin films. By thermal annealing from 135 to 200 °C, thin films with a range of hydrophobicity are generated by varying acrylic acid content from 2% (SAA2) to 29% (SAA29). Poly­(styrene-random-<i>tert</i> butyl acrylate) films, 100 nm thick, that are partially converted to poly­(styrene-random-acrylic acid), SAA, reversibly swell in ethanol solutions containing amine-functionalized SiO₂ nanoparticles with a diameter of 45 nm. The thermodynamics and kinetics of NP grafting are directly controlled by the AA content in the SAA films. At low AA content, namely SAA4, NP attachment saturates at a monolayer, consistent with a low solubility of NPs in SAA4 due to a weakly negative χ parameter. When the AA content exceeds 4%, NPs sink into the film to form multilayers. These films exhibit hierarchical surface roughness with a RMS roughness greater than the NP size. Using a quartz crystal microbalance, NP incorporation in the film is found to saturate after a mass equivalence of about 3 close-packed layers of NPs have been incorporated within the SAA. The kinetics of NP grafting is observed to scale with AA content. The surface roughness is greatest at intermediate times (5–20 min) for SAA13 films, which also exhibit superhydrophobic wetting. Because clustering and aggregation of the NPs within SAA29 films reduce film transparency, SAA13 films provide both maximum hydrophobicity and transparency. The method in this study is widely applicable because it can be applied to many substrate types, can cover large areas, and retains the amine functionality of the particles which allows for subsequent chemical modification