99 research outputs found
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)
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
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
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
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 SiO<sub>2</sub> 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
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