Covalent surface modification of a titanium alloy with a phosphorylcholine-containing copolymer for reduced thrombogenicity in cardiovascular devices.

Abstract

Our objective was to develop a surface modification strategy for a titanium alloy (TiAl6V4) to provide thromboresistance for surfaces in rigorous blood-contacting cardiovascular applications, such as that found in ventricular assist devices. We hypothesized that this could be accomplished by the covalent attachment of a phospholipid polymer, poly(2-methacryloyloxyethylphosphorylcholine (MPC)-co-methacryl acid) (PMA). TiAl6V4 was H2O plasma treated by radio frequency glow discharge, silanated with 3-aminopropyltriethoxysilane (APS), and ammonia plasma treated to increase surface reactivity. The TiAl6V4 surface was then modified with PMA via a condensation reaction between the amino groups on the TiAl6V4 surface and the carboxyl groups on PMA. The surface composition was verified by X-ray photoelectron spectroscopy, confirming successful modification of the TiAl6V4 surfaces with APS and PMA as evidenced by increased Si and P. Plasma treatments with H2O and ammonia were effective at further increasing the surface reactivity of TiAl6V4 as evidenced by increased surface PMA. The adsorption of ovine fibrinogen onto PMA-modified surfaces was reduced relative to unmodified surfaces, and in vitro ovine blood contact through a rocking test revealed marked reductions in platelet deposition and bulk phase platelet activation relative to unmodified TiAl6V4 and polystyrene controls. The results indicate that the PMA-modification scheme for TiAl6V4 surfaces offers a potential pathway to improve the thromboresistance of the blood-contacting surfaces of cardiovascular devices.