Research and development of the small caliber artificial blood vessel with antithrombogenicity

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The surface of block type copolymers having microphase separated structure of alternating lamellar type shows the excellent antithrombogenicity through the suppression of platelet adhesion and platelet activation. By using the microsphere-column method which was developed by us, adhesion of platelets on sample materials was examined in vitro. On the surface of homopolymer such as PHEMA or polystyrene, a large amount of platelets adhered, aggregated and extensively activated to form thrombus. On the contrary, platelet adhesion was significantly suppressed on the block type copolymer such as HEMA-St, FAA-St. It was indicated that the surface free energy gap between microdomains consisted of HEMA and St, or FAA and St was the determinant factor in formation of organized and stable layer of adsorbed proteins which gave intense influence to platelet adhesion and activation. In addition, prolonged platelet aggregation time (PAT) clearly indicates that the activation of adhered platelets was effectively inhibited on the surfaces with microphase separated structure.In ex vivo experiment (rabbit A-V shunt), duration of graft patency made of block type copolymers was distinguishably longer than of graft made of homopolymer. Time-course change in number and function of circulating platelets was remarkable in case of graft made of homopolymer. On the other hand, in case of block copolymer, the number and function of circulating platelets were maintained in the normal range after shunt formation. From these results, the excellent antithrombogenicity and hemocompatibility of the block type copolymers was confirmed. In coronary by-pass experiment in dogs, 1.5 mm internal diameter prosthetic tube coated with HEMA-St was kept it patency as long as four weeks.