Functionalization of Titanium Oxide Surfaces by Means of Poly(alkyl-phosphonates)

Abstract

The use of a multiple attachment sites strategy is considered in order to improve the stability of monomolecular adlayers. The hypothesis was tested in the case of PEG-ylated compounds carrying phosphonate groups, known for their affinity toward titanium oxide surfaces. As a result, a new class of co- and terpolymers were synthesized by free-radical polymerization of three different monomers: dialkyl(methacryloyloxyalkyl)phosphonates, PEG methyl ether methacrylate, and/or butyl methacrylate monomers. Adlayers were formed following a simple dip-and-rinse protocol using diluted aqueous polymer solutions and were characterized by evaluating their thicknesses with variable angle spectroscopic ellipsometry (VASE) and their elemental compositions with X-ray photoelectron spectroscopy (XPS). The same techniques were used to determine changes of the adlayer as a function of exposure to electrolytes at different pH values and to monitor nonspecific protein adsorption upon serum exposures. The results indicated that the poly(alkyl-phosphonate)-based adlayers combine multiple site attachment of phosphonic groups and presentation of PEG side chains to the aqueous environment, resulting in both improved stability over a wide pH range in comparison to the tested reference surfaces and excellent resistance to protein adsorption when exposed to full human serum.