Surface modifying additives for improved device-blood compatibility

Copolymers composed of polar and nonpolar blocks, when blended with a base polymer in low concentrations, migrate to the base polymer surface during and after fabrication. Migration of these surface modifying additives (SMAs) dramatically changes the outermost surface molecular layers that comprise the region that determines biocompatibility. The blood compatibility of cardiopulmonary bypass and hemodialysis components have been improved by using SMA blended polymers or SMA coated surfaces. The particular SMAs used were a series of triblock copolymers with a general formulation of polycaprolactone-polydimethylsiloxane-polycaprolactone. X-ray fluorescence (XRF), fourier transform infrared (FTIR), refractive increments (RI), and gel permeation chromatography (GPC) were used to characterize the molecular weight of SMA and the bulk concentration of SMA after blending. Electron spectroscopy for chemical analysis (ESCA) proved that the surface of blended polymers was highly saturated with SMA. Results of in vitro experiments with human blood demonstrated that SMA blended polymers delay contact activation (kallikrein-like activity), reduce coagulation activity (thrombin-antithrombin [TAT] generation), and do not adversely affect complement activation (terminal complement complex [TCC] generation) or mononuclear cells activation (IL-1 beta production). Ex vivo canine AV shunt studies showed improvement of platelet compatibility of SMA blended polymers. Reduction of cellular and protein system activation by using components fabricated with SMA blood contacting surfaces can potentially result in reduced morbidity associated with extracorporeal circulation.