Keiji Fujimoto

Polyurethane surface modification by graft polymerization of acrylamide for reduced protein adsorption and platelet adhesion

Surface modification of polyurethane by glow-discharge treatment and subsequent graft polymerization of acrylamide was studied. The modified hydrophilic surfaces were characterized by the measurements of dynamic contact angle and zeta potentials and examined for protein adsorption behaviour and platelet adhesion. Data from in vitro and ex vivo experiments indicated a reduction of protein adsorption and platelet adhesion for the hydrophillic graft polymers, the extent of which was correlated to polymer graft density.

Ex vivo and in vivo evaluation of the blood compatibility of surface-modified polyurethane catheters

Catheter model tubes were prepared from a medical-grade polyetherurethane and their outer surfaces modified by surface-graft polymerization of acrylamide and dimethyl acrylamide (DMAA). The surface-graft layer was characterized by means of dry staining, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, and protein adsorption. Ex vivo evaluation for the blood compatibility of the surface-modified polyurethane was carried out using the polyurethane tube as an arterio-venous shunt between the carotid artery and the jugular vein of rabbits. When the surface density of grafted polymer was in the range of 10-30 microg/cm2, the in vitro adsorption of IgG exhibited a minimum value and platelet adhesion to the grafted polyurethane surface was insignificant, in marked contrast with that to the virgin (nonmodified) surface. The in vivo blood compatibility of polyurethane was evaluated by implanting the catheter tube in the inferior vena cava of rabbits from the femoral vein after ligation of a distal site of the exposed femoral vein. After remaining there for predetermined periods of time, the implanted catheters were taken out together with the veins of the rabbits that had been heparinized and sacrificed just prior to excision of the veins. After exchange of the blood in the veins for saline, the excised veins were opened by cutting longitudinally to inspect for clot formations on the surfaces of the implanted catheters. Occlusion of the inferior vena cava was not observed for any of the catheters, nor was there any apparent damage or microembolizations in the lungs and kidneys. Many small-sized clots were observed on the surfaces of the nonmodified polyurethane tubes after a 2-week implantation whereas the catheter surfaces grafted with DMAA polymer chains had a much smaller number of clots. When the blood compatibility of polyurethane surfaces was graded for relative evaluation from one (marked clotting) to five (no clotting) based on the size and number of the clots, the evaluation results were as follows: 3.1 (virgin, 2 weeks), 4.0 (grafted, 1 week), 4.1 (grafted, 2 weeks), and 3.5 (grafted, 1 month).

Improvement in the Mechanical Properties of Artificial Blood Vessel Suitable for the Extracranial Cerebral Artery

Saphenous vein interposition grafts have been commonly used for the reconstruction of occlusive lesions in the extracranial cerebral vessels, such as carotid or vertebral arteries. In contrast, cerebral revascularization using an artificial blood vessel has not been so common. This is due to the fact that conventional artificial blood vessels have been too firm or too rigid for use in the neurosurgery. Another reason is that the long term patency rate of small caliber artificial blood vessels has usually been inferior to that found in autologous vein grafts. The purpose of this study was to develop a soft and compliant artificial blood vessel suitable for cerebrovascular surgery. This new artificial blood vessel is made of polyurethane, porous in structure (porous polyurethane). Thus, multiple small-sized pores exist both in the inner and outer surfaces, and in the wall of the porous polyurethane graft. To test its mechanical properties, we evaluated stress-strain curves and compliance. In comparison to expanded polytetrafluoroethylene graft (Goretex), which has been one of the most commonly used artificial blood vessels in the cardiovascular surgery, the mechanical properties of the porous polyurethane graft more closely resembled those of the common carotid artery in dogs. Thus, porous polyurethane graft was shown to be a soft and compliant new artificial blood vessel. This means not only that it can be maneuvered with technical ease for anastomosis but also that there is a reduction of compliance-mismatch between the host vessel and the artificial vessel. Compliance mismatch has been documented as a major factor in the inducement of intimal hyperplasia, which causes a delayed occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)