We have found that block and graft copolymers having hydrophilic-hydrophobic microphase separated structure often show good antithrombogenic activities. In this paper, block copolymers constructed with hydrophilic and hydrophobic chains were synthesized in order to clarify the role of microphase separated structure in interaction between polymer and blood platelets. On block copolymer surfaces, platelets adhered singly in a round shape compared with homopolymers. From the study of platelet function using aggregometer, it was revealed that the aggregating ability and the function of ATP release of platelets were not decreased after contacting with block copolymers. That is, block copolymers having microphase separated structure on their surfaces exhibited suppressing effect on deformation and activation of platelets which were not observed on homopolymer surfaces.
