Dextran Grafted Silicon Substrates: Preparation, Characterization And Biomedical Applications
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Dextran Grafted Silicon Substrates: Preparation, Characterization And Biomedical Applications Michela Ombelli, David M. Eckmann1 and Russell J. Composto2 Department of Chemistry, University of Perugia, Perugia, I-06123, Italy 1 Department of Anesthesia and The Institute for Medicine and Engineering, University of Pennsylvania, Philadelphia, PA, 19104-4283, U.S.A. 2 Department of Materials Science and Engineering and Center for Bioactive Materials and Tissue Engineering, University of Pennsylvania, Philadelphia, PA 19104-6272, U.S.A. ABSTRACT 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.
INTRODUCTION The polysaccharide dextran exhibits outstanding biocompatibility [1], and in recent years, a large number of studies have highlighted surface-bound dextran as a protein-binding and cellresistant coating for biomaterials. Many different anchoring methods have been investigated with the aim of obtaining highly controllable attachment strategies that require a small number of steps during synthesis and avoid toxic reagents [2,3]. We used the methods proposed by Dai et al. for coating silicon wafers with dextran [4] which involves low residual toxicity reagents and mild aqueous reaction conditions. In this method, the oxidation of glucose units by periodate produces hemialdals capable of reacting with amine groups previously anchored on silicon wafers through the deposition of a 3aminopropyltriethoxysilane (APTES) self-assembled monolayer. This Schiff-base linkage is then reduced by sodium cyanoborohydride to a secondary amine. The thickness, wettability, roughness and gas bubble adhesion properties of the coatings were investigated as a function of dextran molecular weight (in the range 1-100 kDa) and polydispersity index [5]. We found that glass tubes coated with low-dispersity dextran with a
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