Abstract: Biocompatible polymeric materials capable of providing in situ release of nitric oxide (NO) included diazeniumdiolated fumed silica as a filler in a multilayer polymer structure to release NO upon contact with water (blood). The blood-contacting polymer surface is preferably multi-layered so that the NO-releasing layer, containing the diazeniumdiolated fumed silica, is shielded from blood contact by one or more top (or base) coats. When in contact with blood, the NO released at the surface of the polymer prevents platelet activation and adhesion to the surface, thereby reducing platelet consumption, risk of thrombus formation and other clinical complications associated with interactions between blood and foreign materials.