a biomaterial with a thromboresistant surface and a method for forming same are provided . the thromboresistant surface is comprised of a distinct coating layer of a chitosan - based membrane and a biologically active material . the biologically active material is capable of converting the chitosan membrane coating from a highly thrombogenic to an essentially non - thrombogenic one . the biologically active material can be a polymeric substance , such as polyvinyl alcohol , forming a polymeric blend with the chitosan , or , can be a biological substance , such as serum albumin , embedded in or attached to the chitosan membrane which has been activated with a treatment of glutardialdehyde . the thromboresistant biomaterial is suitable for use in vascular grafts having an inside diameter of less than 6 millimeters .