Microphase separation structure influences protein interactions with poly(urethane urea) surfaces

Microphase separation is an important characteristic of polyurethane copolymer biomaterials. An improved understanding of the effects of microphase structure on protein interactions with the polymeric biomaterial surface is essential for the development and application of new biomaterials intended for implantation into the body. In this study, an array of atomic force microscopy (AFM) techniques were used to visualize the phase separation structure in a hydrated poly(urethane urea) (PUU) material and to correlate that structure with molecular interactions at the molecular level. Sequential in situ AFM phase images showed that the hard domains present a dynamic environment and undergo rearrangement and enrichment at the surface when hydrated. Adhesion forces measured using a protein-modified AFM probe suggests that the PUU surface became less adhesive to protein with hydration time, consistent with other physical characterizations. Force measurements were used to quantify and correlate mechanical properties and local adhesion forces for bovine serum albumin, and results showed that low adhesion forces were primarily associated with polar hard domain regions. A nanogold-labeled protein conjugate was used to visualize individual protein adsorption to the separate microstructures on the PUU surface, with preferential protein adsorption seen on the more apolar hydrophobic soft segment regions. Together, the results suggest that the microphase separation structure mediates local surface microenvironments that influence biological interactions with the surface.