Composto, Russell J

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Now showing 1 - 10 of 16
  • 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, Dwayne
    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 <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).
  • 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 J
    The 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 J
    Self-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 J
    The 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 J
    Peri-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
    Competitive adsorption of plasma proteins on polysaccharide-modified silicon surfaces
    (2004-11-28) Ombelli, Michela; Costello, Lauren B; Meng, Qing Cheng; Composto, Russell J; Eckmann, David M
    The initial response of blood exposed to an artificial surface is the adsorption of blood proteins that triggers a number of biological reactions such as inflammation and blood coagulation. Competitive protein adsorption plays a key role in the hemocompatibility of the surface. The synthesis of nonfouling surfaces is therefore one of the major prerequisites for devices for biomedical applications. Polysaccharides are the main components of the endothelial cell glycocalyx and have the ability to reduce nonspecific protein adsorption and cell adhesion and, therefore, are generally coupled with a wide variety of surfaces to improve their biocompatibility. We have developed a procedure for covalently binding dextran and sodium hyaluronate (HA) on silicon wafers and we have been able to achieve a high level of control over the surface properties of the coatings. In the present research effort we focus on a detailed investigation of competitive bovine serum albumin (BSA) and bovine fibrinogen (Fg) adsorption on dextran- and HA-modified silicon surfaces. Polysaccharide based biomimetic layers preferentially adsorb BSA and, in general, strongly suppress protein adsorption with respect to bare silicon and APTES-activated silicon surfaces used as control.
  • Publication
    RGDS peptides immobilized on titanium alloy stimulate bone cell attachment, differentiation and confer resistance to apoptosis
    (2007-12-01) Secchi, Antonino G; Grigoriou, V; Composto, Russell J; Shapiro, Irving M; Ducheyne, Paul; Cavalcanti-Adam, E. A; Adams, Christopher S
    A major cause of implant failure in skeletal tissues is failure of osseointegration, often due to lack of adhesion of cells to the titanium (Ti) alloy interface. Since arginine- glycine-aspartic acid (RGD)-containing peptides have been shown to regulate osteoblast adhesion, we tested the hypothesis that, bound to a Ti surface, these peptides would promote osteoblasts differentiation, while at the same time inhibit apoptosis. RGDS and RGES (control) peptides were covalently linked to Ti discs using an APTS linker. While the grafting of both RGDS and RGES significantly increased Ti surface roughness, contact angle analysis showed that APTS significantly increased the surface hydrophobicity; when the peptides were tethered to Ti, this was reduced. To evaluate attachment, MC3T3-E1 osteoblast cells were grown on these discs. Significantly more cells attached to the Ti-grafted RGDS then the Ti-grafted RGES control. Furthermore, expression of the osteoblasts phenotype was significantly enhanced on the Ti-grafted RGDS surface. When cells attached to the Ti-grafted RGDS were challenged with staurosporine, an apoptogen, there was significant inhibition of apoptosis; in contrast, osteoblasts adherent to the Ti-grafted RGES were killed. It is concluded that RGD-containing peptides covalently bonded to Ti promotes osteoblasts attachment and survival with minimal changes to the surface of the alloy. Therefore, such modifications to Ti would have the potential to promote osseointegration in vivo.
  • Publication
    Sintering Metal Nanoparticle Films
    (2008-01-21) Wang, Howard; Huang, Liwei; Xu, Zhiyong; Xu, Congkang; Composto, Russell J; Yang, Zhihao
    We have carried out several measurements in order to understand the process of metal nanoparticle (MNP) film sintering. Small angle neutron scattering has been used to reveal the average diameters of silver and gold nanoparticles (Ag-NPs and Au-NPs) used in this study to be 4.6 and 3.8 nm, respectively, with a size distribution of ca. 20%. Spun- cast Ag-NP and Au-NP films have been sintered at temperature ranges of 80-160ºC and 180-210º, respectively, for various times. The resulting film composition, morphology and electric resistance have been revealed. Upon sintering, the organic content in MNP films reduces to less than 10% while the overall film thickness reduces to about the half of the as-cast film thickness. The resistance of sintered Ag-NP films can vary over more than 7 decades depending on the sintering temperature. The conductivity of Ag-NP films sintered at 150º is 2.4 times 10-8Ωm. The transport properties are affected by both the composition and morphology of sintered films.
  • Publication
    Dextran grafted silicon substrates : preparation, characterization and biomedical applications
    (2003-04-21) Eckmann, David M; Ombelli, Michela; Composto, Russell J
    Biodevices 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.