Experimental and theoretical investigation of chain length and surface coverage on fouling of surface grafted polypeptoids

Numerous strategies exist to prevent biological fouling of surfaces in physiological environments; our strategy focuses on the modification of surfaces with poly-N-substituted glycine oligomers (polypeptoids). We previously reported the synthesis and characterization of three novel polypeptoid polymers that can be used to modify titanium oxide surfaces, rendering the surfaces resistant to adsorption of proteins, to adhesion of mammalian and bacterial cells and to degradation by common protease enzymes. In this study, we investigated the effect of polypeptoid chain length on the antifouling properties of the modified surfaces. For these experiments we used poly(N-methoxyethyl) glycines with lengths between ten and fifty repeat units and determined the influence of chain length on coating thickness and density as well as resistance to protein adsorption and cellular adhesion. Short-term protein resistance remained low for all polymers, as measured by optical waveguide lightmode spectroscopy, while fibroblast adhesion after several weeks indicated reduced fouling resistance for the polypeptoid-modified surfaces with the shortest chain length polymer. Experimental observations were compared to predictions obtained from a molecular theory of polymer and protein adsorption. Good agreement was found between experiment and theory for the chain length dependence of peptoid grafting density, and for protein adsorption as a function of peptoid grafting density. The theoretical predictions provide specific guidelines for the surface coverage for each molecular weight for optimal antifouling. The predictions show the relationship between polymer layer structure and fouling.