ABSTRACT:In order to elucidate the interaction between blood platelets and polymer surfaces of microdomain structure, block copolymers consisting of hydrophilic chains of 2-hydroxyethyl methacrylate (HEMA) and hydrophobic chains of dimethylsiloxane (DMS) were synthesized. Films of the HEMA-DMS block copolymers exhibiting hydrophilic-hydrophobic microphase-separated structures were found to enhance platelet adhesion more than homogeneous surfaces of poly(HEMA) or poly(DMS). Platelet adhesion to the block copolymer increased with morphological changes in microdomains so long as the HEMA composition of the block copolymer · was 0.90 to 0.58. Platelet adhesion also varied with morphological change in the microdomains caused by changing the casting solvents, though an identical copolymer was employed. These results indicated that platelet adhesion to the HEMA-DMS block copolymer was influenced by domain morphology rather than HEMA composition of the copolymers. In spite of the enhancement of platelet adhesion, the HEMA-DMS block copolymers effectively suppressed shape change and aggregation of adhered platelets. The HEMA-DMS block copolymers were considered to have good antithrombogenecity on the basis of inhibition of activation and aggregation of adhered platelets. KEY WORDS 2-Hydroxyethyl Methacrylate-Dimethylsiloxane Block Copolymer / Microdomain Structure / Platelet Adhesion / Antithrombogenecity / The antithrombogenic property of synthetic polymers is influenced remarkably by the balance between hydrophilicity and hydrophobicity of polymer surface. 1 We propose that the microdomain structure of polymer surfaces constructed of hydrophilic and hydrophobic sites of orderly assembled marcomolecules is the most important factor for designing effective antithrombogenic polymers. 2 We synthesized new amphiphilic block copolymers and comb type graft compolymers consisting of a hydrophilic monomer, 2-hydroxyethyl methacrylate (HEMA), and a hydrophobic monomer, styrene (St). 3 Films of HEMA-St block copolymers formed hydrophilic-hydrophobic microdomain structures on their surfaces. Platelet adhesion, an important process in the initial stage of thrombus formation, was studied in relation to block copolymer surfaces. The amount and deformation of adhered platelets were effectively suppressed on the surface of HEMA-St block and graft copolymers. This suppressing effect was found to be influenced by the shape and size of the microdomain rather than by the composition of the copolymers. 2 • 4 The copolymers having microdomain structures of alternate lemellae with about 0.05 µm in width exhibited 649

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