TEXTURED BIOMATERIALS AS A MODEL FOR STUDYING FORMATION OF FOCAL CONTACTS AND REARRANGEMENT OF THE CONTRACTILE CYTOSKELETON IN PLATELETS

Fibres of textured biomaterials (BM) enable platelets to adhere with f ormation of focal contacts. The contact structure and the reaction of the contact associated contractile cytoskeleton were studied using fib res of different flexibility/mobility: butyl-S-Sepharose (S), Polysulf one (PS) and Polyurethane (PU). Ultrastructural and immunocytochemical investigations were carried out to obtain information on the influenc e of tension on (1) the structure of the focal contacts; (2) the const ricting cytoskeleton known to retract adherent collagen or fibrin fibr es and (3) the cable-like bundles of actomyosin as observed in the clo t. Fibre network from S spheres and 0.3 mm thick frozen sections of PS or PU were incubated with citrated PRP or with washed platelets at 37 degrees C for 6 to 30 min while stirring for contact or activation wi th ADP or thrombin. Flexible fibres of the BM were found in deep invag inations of the plasmalemma associated with the constricting cytoskele ton. Focal contacts (mediated by fibrinogen as shown immunocytochemica lly) with fibres which were fixed in the texture or inflexible (PU) in duce cable-like bundles of micofilaments containing myosin. These bund les pass across the cytoplasm and connect the contacts with the fibres or with Other platelets, as demonstrated by computer-assisted 3-dimen sional reconstruction. The model used indicates that retraction is pos sible as long as fibres are mobile and that cable-like bundles occur w hen the locomotion of platelets is blocked by immobile fibres. The int eraction of platelets with textured BM reflects the situation during c ollagen or fibrin condensation. The findings may contribute to an unde rstanding of platelet reactions on textured surfaces in grafts.