Characterization and analysis of osteopontin-immobilized poly(2-hydroxyethyl methacrylate)

The central issue impeding improved performance of biomaterial devices is the foreign body reaction. This thesis work investigates the hypothesis that immobilized osteopontin (OPN) can modulate the foreign body response in vivo. The ability to immobilize molecules that modulate inflammation and enhance wound healing would generate a new class of “stealth” biomaterials that mimic nature by controlling the proteins at interfaces with precision. Specifically, an immobilized OPN layer might alter the traditional foreign body capsule associated with implanted biomaterials by inhibiting the production of nitric oxide by infiltrating macrophages, providing survival signals for endothelial cells, and facilitating the creation of new blood vessels. Poly(2-hydroxyethyl methacrylate) (poly(HEMA)), a highly hydrated polymer with free hydroxyl groups, possesses the inherent ability to resist rapid protein adsorption and cell adhesion and was thus chosen as an ideal model surface on which to investigate the concept of precision biomaterials.; Osteopontin-immobilized poly(HEMA) surfaces were created using a carbonyldiimidazole-based attachment method as well as through a type 1 collagen affinity coating. Surface analysis results verified progression of surface chemistry and presence of protein on the poly(HEMA) surface. Time-of-flight secondary ion mass spectrometry data also suggested that each immobilization method presented OPN on the surface in a distinctive manner. Radio-iodination of OPN quantified the amount of OPN bound using both immobilization methods and established that binding was dose-dependent in both cases. A cell adhesion assay verified that, once immobilized, OPN retained its cell-adhesive properties and also demonstrated that OPN immobilized via a type 1 collagen affinity coating exhibited significantly greater adhesion than CDI-immobilized OPN, presumably through interaction of cells with both proteins. Surface plasmon resonance data probed the interaction of OPN with type 1 collagen and revealed several potential factors for the manipulation and disruption of OPN binding. Lastly, several animal experiments implied that immobilized OPN does not have a pronounced affect on either foreign body capsule thickness or capsule vascularity. Preliminary work, however, using a valve calcification model suggests a promising therapeutic application for OPN immobilized via a type 1 collagen affinity coating.