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 formation of focal contacts. The contact structure and the reaction of the contact associated contractile cytoskeleton were studied using fibres of different flexibility/mobility: butyl-S-Sepharose (S), Polysulfone (PS) and Polyurethane (PU). Ultrastructural and immunocytochemical investigations were carried out to obtain information on the influence of tension on (1) the structure of the focal contacts; (2) the constricting cytoskeleton known to retract adherent collagen or fibrin fibres and (3) the cable-like bundles of actomyosin as observed in the clot. 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 C for 6 to 30 min while stirring for contact or activation with ADP or thrombin. Flexible fibres of the BM were found in deep invaginations of the plasmalemma associated with the constricting cytoskeleton. Focal contacts (mediated by fibrinogen as shown immunocytochemically) with fibres which were fixed in the texture or inflexible (PU) induce cable-like bundles of micofilaments containing myosin. These bundles pass across the cytoplasm and connect the contacts with the fibres or with other platelets, as demonstrated by computer-assisted 3-dimensional reconstruction. The model used indicates that retraction is possible as long as fibres are mobile and that cable-like bundles occur when the locomotion of platelets is blocked by immobile fibres. The interaction of platelets with textured BM reflects the situation during collagen or fibrin condensation. The findings may contribute to an understanding of platelet reactions on textured surfaces in grafts.