Composto, Russell J
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Publication Dextran grafted silicon substrates : preparation, characterization and biomedical applications(2003-04-21) Eckmann, David M; Ombelli, Michela; Composto, Russell JBiodevices used in the cardiovascular system suffer from well-known problems associated with surface-induced gas embolism and thrombosis. In order to improve the biocompatibility of these devices, biomimetic coatings show good promise. We recently synthesized a coating layer of dextran, a relatively simple and well characterized neutral polysaccharide, with the purpose of mimicking the cells' glycocalyx layer, that prevents non-specific cells-protein interactions. Systematic physical chemical characterization was performed on coatings obtained both from commonly used polydisperse dextrans and low-dispersity dextrans in the 1-100 kDalton molecular weight range. We have combined standard surface analysis techniques, such as ellipsometry, contact angle measurements and AFM, with less traditional vibrational spectroscopy techniques in the characterization of our biomimetic coatings. FTIR, micro-FTIR and micro-Raman spectroscopies were utilized to correlate the conformational and molecular aspects of the grafted poly- and monodisperse dextran chains to their attractive biological properties.Publication Breakdown of Dynamic Scaling in Thin Film Binary Liquids Undergoing Phase Separation(2004-05-06) Chung, Hyun-joong; Composto, Russell JThe kinetics of phase separation in thin polymer blend films displaying discrete and bicontinuous domain morphologies are examined. For discrete domains, the correlation length ξ grows as t1/3, in agreement with a coalescence model. By plotting ξ/d vs t/ti (initiation time), universal growth behavior is obtained for thickness values (d) from 1000 to 190 nm. In contrast, bicontinuous domains grow with a decreasing exponent, 0.62 to 0.28, as d decreases from 900 to 90 nm (i.e., no universal growth). This slowing down with reduced dimensionality suggests suppression of lateral hydrodynamic pumping.Publication Self-Assembled Charged Hydrogels Control the Alignment of Filamentous Actin(2009-01-01) Park, Jung Hyun Hyun; Goldman, Yale E.; Composto, Russell J; Sun, YujieWe demonstrate a novel route to control attachment of filamentous actin (F-actin) on hydrogel films. By incorporating an amine-terminated silane, the hydrogel surface charge and surface topography are varied. With increasing silane content, F-actin reorients from perpendicular to parallel to the hydrogel surface, ceases to wobble, and forms mainly elongated or cyclic structures. F-Actin coverage reaches a maximum at 2.5 vol% silane and declines at higher silane content. This biphasic behavior is explained by the simultaneous increase in surface charge and the self-assembly of a micron scale pattern of positively charged islands. Our approach provides guidelines for constructing nanoscale tracks to guide motor proteins underlying nano-engineered devices such as molecular shuttles.Publication Adhesion of MC3T3-E1 cells to RGD peptides of different flanking residues: Detachment strength and correlation with long-term cellular function(2007-04-01) Lee, Mark H; Adams, Christopher S; Shapiro, Irving M; Boettiger, David; Composto, Russell J; DeGrado, William F; Ducheyne, PaulWe synthesized a series of RGD peptides and immobilized them to an amine-functional self-assembled monolayer using a modified maleimide-based conjugate technique that minimizes nonspecific interactions. Using a spinning disc apparatus, a trend in the detachment strength (τ50) of RGD peptides of different flanking residues was found: RGDSPK ≻ RGDSVVYGLR ≈ RGDS ≻ RGES. Using blocking monoclonal antibodies, cellular adhesion to the peptides was shown to be primarily α√-integrin-mediated. In contrast, the τ50 value of the cells on fibronectin (Fn)-coated substrates of similar surface density was 6-7 times higher and involved both α5β1 and ανβ3 integrins. Cellular spreading was enhanced on RGD peptides after 1 h when compared to RGE and unmodified substrates. However, no significant differences were observed between the different RGD peptides. Long-term function of MC3T3-E1 cells was also evaluated by measuring alkaline phosphatase (ALP) activity and mineral deposition. Among the four peptides, RGDSPK exhibited the highest level of ALP activity after 11 days and mineralization after 15 days and reached comparable levels as Fn substrates after 15 and 24 days, respectively. These findings collectively illustrate both the advantages and limitations of enhancing cellular adhesion and function by the design of RGD peptides.Publication Effect of Nano-to Micro-Scale Surface Topography on the Orientation of Endothelial Cells(2004-11-29) Uttayarat, P.; Lelkes, Peter I.; Composto, Russell JThe effect of grating textures on the alignment of cell shape and intracellular actin cytoskeleton has been investigated in bovine aortic endothelial cells (BAECs) cultured on a model cross-linked poly(dimethylsiloxane) (PDMS). Grating-textured PDMS substrates, having a variation in channel depths of 200 nm, 500 nm, 1 µm and 5 µm, were coated with fibronectin (Fn) to promote endothelial cell adhesion and cell orientation. As cells adhered to the Fn-coated surface, the underlying grating texture has shown to direct the alignment of cell shape, F-actin and focal contacts parallel to the channels. Cell alignment was observed to increase with increasing channel depths, reaching the maximum orientation where most cells aligned parallel to channels on 1-µm textured surface. Immunofluorescence studies showed that F-actin stress fibers and vinculin at focal contacts also aligned parallel to the channels. Cell proliferation was found to be independent of grating textures and the alignment of cell shape was maintained at confluence.Publication Early-stage compositional segregation in polymer-blend films(2003-06-23) Wang, H.; Douglas, Jack F; Satija, S. K.; Composto, Russell J; Han, C. C.The existence of a transient period during the surface enrichment of a binary polymer blend by one of its components has been suggested by previous theoretical and experimental studies as well as computer simulations. Taking advantage of the high depth resolution of neutron reflectivity and the slow dynamics of polymers near their glass transition, we investigate this early-stage surface compositional enrichment in a phase separating polymer blend for the first time. Two stages of surface enrichment layer growth are observed. A rapid local surface enrichment at the chain segmental level occurs first, followed by a slower growth of a diffuse layer having a scale on the order of the bulk correlation length and the radius of gyration of the surface enriching polymer chains.Publication Self-assembled monolayers of omega-functional silanes: A platform for understanding cellular adhesion at the molecular level(2007-01-01) Boettiger, David; Ducheyne, Paul; Lee, Mark H; Composto, Russell JSelf-assembly represents a powerful and versatile strategy to create substrates with controlled molecular-level physicochemical characteristics. As a result, self-assembled monolayers (SAMs) of silanes continue to find use in a multitude of applications in biotechnology and nanotechnology, both as model substrates to study interfacial interactions and as a strategy to chemically graft bioactive molecules. In our work, SAMs of various functional groups have been used for fundamental studies of cellular interactions with peptides and proteins. Namely, cellular adhesion was quantitatively probed to elucidate the roles of non-specific forces arising from the substrate and to study the specific interactions of cellular receptors with adsorbed extracellular matrix (ECM) proteins, such as fibronectin, and grafted arginine–glycine–aspartic acid (RGD) peptides. Measurements of the cellular detachment strength using a spinning disc apparatus demonstrated that the terminal functionality of the silane SAM used as the substrate exerted significant effects and highlighted the importance of substrate selection in biological applications. Quantitative comparison of the various cellular interactions demonstrated that non-specific interactions can be much larger in magnitude than peptide- and protein-mediated adhesion. As adhesion is the first step in a cascade of events through which cellular interaction with a material surface occurs, this finding has implications on assays of long-term cellular function as well. The insight provided by these studies should help in the development of optimized protein and peptide microarrays, or biochips, as well as better bioactive materials for biomaterial/tissue engineering applications.Publication Dispersion of polymer-grafted magnetic nanoparticles in homopolymers and block copolymers(2008-07-01) Xu, Chen; Ohno, Kohji; Ladmiral, Vincent; Composto, Russell JThe dispersion of magnetic nanoparticles (NPs) in homopolymer poly(methyl methacrylate) (PMMA) and block copolymer poly(styrene-b-methyl methacrylate) (PS-b-PMMA) films is investigated by TEM and AFM. The magnetite (Fe3O4) NPs are grafted with PMMA brushes with molecular weights from M = 2.7 to 35.7 kg/mol. Whereas a uniform dispersion of NPs with the longest brush is obtained in a PMMA matrix (P = 37 and 77 kg/mol), NPs with shorter brushes are found to aggregate. This behavior is attributed to wet and dry brush theory, respectively. Upon mixing NPs with the shortest brush in PS-b-PMMA, as-cast and annealed films show a uniform dispersion at 1 wt%. However, at 10 wt%, PS-b-PMMA remains disordered upon annealing and the NPs aggregate into 22 nm domains, which is greater than the domain size of the PMMA lamellae, 18 nm. For the longest brush length, the NPs aggregate into domains that are much larger than the lamellae and are encapsulated by PS-b-PMMA which form an onion-ring morphology. Using a multi-component Flory–Huggins theory, the concentrations at which the NPs are expected to phase separate in solution are calculated and found to be in good agreement with experimental observations of aggregation.Publication The inhibition of Staphylococcus epidermidis biofilm formation by vancomycinmodified titanium alloy and implications for the treatment of periprosthetic infection(2008-08-01) Antoci, Valentin; Adams, Christopher S; Parvizi, Javad; Composto, Russell J; Davidson, Helen M; Freeman, Theresa A; Ducheyne, Paul; Wickstrom, Eric; Jungkind, Donald; Shapiro, Irving M; Hickok, Noreen JPeri-prosthetic infections are notoriously difficult to treat as the biomaterial implant is ideal for bacterial adhesion and biofilm formation, resulting in decreased antibiotic sensitivity. Previously, we reported that vancomycin covalently attached to a Ti alloy surface (Vanc-Ti) could prevent bacterial colonization. Herein we examine the effect of this Vanc-Ti surface on Staphylococci epidermidis, a Gram-positive organism prevalent in orthopaedic infections. By direct colony counting and fluorescent visualization of live bacteria, S. epidermidis colonization was significantly inhibited on Vanc-Ti implants. In contrast, the gram-negative organism Escherichia coli readily colonized the Vanc-Ti rod, suggesting retention of antibiotic specificity. By histochemical and SEM analysis, Vanc-Ti prevented S. epidermidis biofilm formation, even in the presence of serum. Furthermore, when challenged multiple times with S. epidermidis, Vanc-Ti rods resisted bacterial colonization. Finally, when S. epidermidis was continuously cultured in the presence of Vanc-Ti, the bacteria maintained a Vanc sensitivity equivalent to the parent strain. These findings indicate that antibiotic derivatization of implants can result in a surface that can resist bacterial colonization. This technology holds great promise for the prevention and treatment of periprosthetic infections.Publication Biomimetic surfaces via dextran immobilization : grafting density and surface properties(2004-04-12) Irish, Elizabeth R; Miksa, Davide; Composto, Russell J; Eckmann, David M; Chen, DwayneBiomimetic 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 <20, ~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 > THETA1h > THETA2,4h > THETA0.5h).