ABA-type block copolymers composed of 2-hydroxyethyl methacrylate (HEMA), a hydrophilic monomer, and styrene (St), a hydrophobic monomer, were synthesized by the coupling reaction of telechelic oligomers used as prepolymers. These block copolymers may be represented as microphase-separated structures. It is therefore possible to change the balance between hydrophilicity and hydrophobicity in the level of an assembled order of macromolecules. In response to the relative composition of the copolymers, three typical morphological patterns were observed in electron microscopic photographs: dispersed domains of continuous St chains in the region of HEMA chains, alternate HEMA and St lamellae and finally, dispersed phases of continuous HEMA chains in the region of St chains. The effect of the hydrophilic and hydrophobic microdomains of the copolymers on the mode of interaction between polymers and platelets was studied by the microsphere column method. In the case of homopolymers and random copolymers, a significant degree of platelet adhesion and aggregation was observed. However, the degree of platelet adhesion and deformation was suppressed on the surfaces of the block copolymers containing 0.608 and 0.347 mole fractions of HEMA whose microdomains were hydrophilic-hydrophobic lamellae and isolated hydrophilic islands in hydrophobic areas, respectively. These results show that the microphase-separated structures were antithrombogenic and prevented platelet adhesion and deformation. On the basis of the results obtained, the interaction between platelets and polymer surfaces was described in terms of the effect of hydrophilic and hydrophobic microdomains.
Bovine serum albumin and r-globulin were adsorbed, respectively, on films of ABA-type block copolymers and blendmers composed of 2-hydroxyethyl methacrylate (HEMA) and styrene in a mixture of protein and 0.2 M of phosphate buffer solution (pH 7.4) under the condition of 1150 physiological concentration of the protein at 37°C. The morphologies and dimensions of the microphase separated structure of the block copolymers and blendmers containing hydrophilic domains of HEMA molecules and hydrophobic domains of styrene molecules were studied by electron microscopy with or without osmium tetroxide fixation. In the adsorption of plasma protein, either both the adsorbed plasma protein and the hydrophilic domains or only the adsorbed plasma proteins could be stained selectively with osmium tetroxide to control the fixation time. Therefore the areas of plasma protein adsorbed on the phase of microseparated structure were evaluated by comparing the micrographs with and without the adsorbed plasma proteins. These results show that bovine serum albumin is adsorbed on the hydrophilic domains escaping from the hydrophobic domains, and on the contrary that r-globulin is selectively adsorbed on the hydrophobic domains.
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