Dynamics of hydrated polyurethane biomaterials: Surface microphase restructuring, protein activity and platelet adhesion.

Microphase separation is a central feature of segmented polyurethane biomaterials and contributes to the biological response to these materials. In this study we utilized atomic force microscopy (AFM) to study the dynamic restructuring of three polyurethanes having soft segment chemistries of interest in biomedical applications. For each of the materials we followed the changes in near surface mechanical properties during hydration, as well as fibrinogen activity and platelet adhesion on these surfaces. Both AFM phase imaging and force mode analysis demonstrated that these polyurethane biomaterials underwent reorientation and rearrangement resulting in a net enrichment of hard domains at the surface. Fibrinogen activity and platelet adhesion on the polyurethane surfaces were found to decrease with increasing hydration time. The findings suggest that water-induced enrichment of hydrophilic hard domains at the surface changes the local surface physical and chemical properties in a way that influences the conformation of fibrinogen, changing the availability of the platelet-binding sites in the protein. This work demonstrates that the hydrated polyurethane biomaterial interface is a complex and dynamic environment where the surface chemistry is changing, altering the activity of fibrinogen and affecting blood platelet adhesion.