NONTHROMBOGENIC POLYMER VASCULAR PROSTHESIS

Although many synthetic vascular grafts have been developed and evalua ted experimentally or clinically, none of them have met long-term pate ncy when applied as a small diameter vascular substitute. We have rece ntly developed a small caliber vascular graft (3 mm i.d.) using a nont hrombogenic polymer coating. The graft consists of three layered struc tures: Dacron for the outer layer, polyurethane in the middle layer, a nd a HEMA/styrene block copolymer (HEMA-st) coating for the inner laye r. HEMA-st is an amphiphilic block copolymer composed of 2-hydroxyethy l methacrylate and styrene which has demonstrated improved blood compa tibility over existing biomedical polymers in both in vitro and ex viv o experiments. Ten grafts were evaluated in a dog bilateral carotid re placement model. The grafts were electively retrieved at 7, 14, 30, 92 , and 372 days after implantation. All grafts were patent without dete ctable thrombi along the graft length including anastomotic sites. Sca nning electron micrographs of retrieved graft lumen showed fairly clea n surfaces covered with a homogenous protein-like layer without microt hrombi or endothelial cell lining. The thickness of the surface protei n layer measured by a transmission electron microscopy was what can be described as monolayer protein adsorption regardless of implantation periods of as much as 372 days. A stable monolayer adsorbed protein la yer formed on HEMA-st surfaces demonstrated nonthrombogenic activities in vivo and secure long-term patency of small caliber vascular grafts with the absence of an endothelial cell lining.