Collagen-induced platelet aggregation. Dependence on triple helical structure and fiber diameter

Abstract Collagen molecules adsorb irreversibly to glass to form a thick brush-like monomolecular layer. It was found that washed rabbit platelets suspended in Tyrode's solution adhere well to this collagen-covered glass surface. The adherent platelets do not, however, activate to add other platelets and no surface aggregates are formed if the supporting glass surface is plane. On similarly coated fine glass fibers of diameter smaller than that of the platelet, washed platelets adhere more rapidly the smaller the fiber diameter and adhesion induces platelet aggregation. In this respect, glass fibers with an adsorbed monolayer of triple helical collagen molecules simulates the native collagen fiber. Bare glass fibers or fibers with adsorbed denatured collagen or albumin do not induce platelet aggregation. Moreover, adherence rate is lower than that found on surfaces with adsorbed molecular collagen although a similar dependence on fiber diameter is seen. A necessary and sufficient requirement for platelet aggregation on collagen thus seems to be a surface chemistry based on the triple helical conformation and a fiber surface of sufficiently high surface curvature. On the other hand, the arrangement of the triple helical collagen molecules relative to each other on the surface is not important. On all the plane surfaces adherent platelets spread. On fibers, however, they do not. Platelets remain rounded whether the fiber is a native collagen fiber or a bare or monolayer covered glass fiber. Hence no correlation was found between the ability of adherent platelets to spread on a surface and the ability of a surface to induce platelet aggregation.