Biomimetic Surfaces via Dextran Immobilization: Grafting Density and Surface Properties
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Biomimetic Surfaces via Dextran Immobilization: Grafting Density and Surface Properties Davide Miksa,1 Elizabeth R. Irish,2 Dwayne Chen,1 Russell J. Composto,2 David M. Eckmann1 Departments of 1Anesthesia and 2Material Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104 ABSTRACT 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 θ1h>θ2,4h>θ0.5h). INTRODUCTION Evermore pressing needs to control the biochemical interactions at the tissue/material interface have prompted scientist to consider polysaccharides and proteoglycans, which are native to the cellular glcocalyx,1 as coatings for biomaterials.2-4 Although different aspects of such coatings have been studied in the past, the wettability and spatial organization at the biomaterial surface are still recognized as the limiting factors in biocompatibility. It is therefore essential to develop surface synthetic techniques that will afford reproducible control over the surface morphology of the biomaterial coating. Furthermore, it is imperative to characterize those surfaces with the necessary resolution and under conditions that are relatable to their proposed working environment so that their performance can be directly attributed to their structural and functional properties. It has, therefore, been the goal of the present study to create dextran coated surfaces having varying grafting density between dextran and the substrate. Since increased surface roughness can promote protein adhesive as well as micro-embolic events, smooth silicon wafers with a SiO2 surface layer were chosen as the starting point for further modification. The well established chemistry of organo-silane self-assembled monolayers (SAMs)5 afforded an amine functionalized SiO2 surface onto which dextran was immobilized via reductive amination. Although there are several techniques that allow surface characterization at the molecular level, the authors have focused on atomic force microscopy (AFM) and H2O contact angle as the primary modes of analysis. AFM also offered the possibility to conduct force of adhesion measurements, which provided further insight in the dextran-substratum, and dextran-probe interactions.
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EXPERIMENTAL Materials. All reagents and solvents were used as received unless otherwise stated. Aminopropyltriethoxysilane (APTES), sodium periodate, 99% (NaIO4), sodium cyanoborohydrate (NaBH3CN), and dimethylformamide were purchased from Sigma-Aldrich Co. Dextran from Leuconostoc ssp (Mw = 110,000, Mw/Mn = 1.52) was supplied by Fluka Chemie. Deuterium oxide (D2O, 99.9%) for 1H NMR measurements was obtained from Cambridge Isotope Laboratories, Inc. H2SO4 (96%
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