Multi-Functional Initiator and Poly(carboxybetaine methacrylamides) for Building Biocompatible Surfaces Using "Nitroxide Mediated Free Radical Polymerization" Strategies

Biomaterials generally suffer from rapid nonspecific protein adsorption, which initiates many deleterious host responses, and complex chemistries that are employed to facilitate cellular interactions. A chemical approach that, based upon current literature, combines a nonfouling architecture with a biomemtic cell-adhesive end-group, is presented. Namely, surface-initiated polymerization of zwitterionic [poly (carboxybetaine methacrylamide)] brushes, with controlled charge densities and phosphonate head groups. Nitroxide mediated free radical polymerization (NMFRP) was employed for various reasons: reduces presence of potentially cytotoxic organometallic catalysts common in atom transfer radical polymerization (ATRP); and it allows a phosphonate end-group instead of the common brominated end-group. Thermally oxidized silicon wafers were covalently functionalized with diethyl-(1-(N-(1-(3-(trimethoxysilyl)propylcarbamoyl)ethoxy)-N-tert-butylamino)ethyl)phosphonate. NMFRP was used to graft zwitterionic carboxybetaine methacrylamide monomers of varying inter-charge separation. The resulting thin films were characterized using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) and X-ray photoelectron (XPS) spectroscopy, ellipsometry, water contact angle analysis, and thermo gravimetric analysis (TGA). The effect of spacer group on the surface charge density was determined using zeta potential techniques. It is thought that this stratagem will facilitate the ability to tailor systematically both the interior and terminal polymer properties, providing a platform for further understanding how these conditions affect protein adsorption as well as cell-surface interactions. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1051-1060,2011