Role of blood coagulation components as intermediators of high osteoconductivity of electrically polarized hydroxyapatite.

The immediate interactions of an implanted hydroxyapatite (HA) surface and blood coagulation components were detected in vivo, and the mechanism of the enhanced osteoconductivity caused by electrical polarization was discussed. Fibrin was presented as being a key protein in the early stages of osteoconduction. Scanning electron microscope observation and immunohistochemical detection indicated that fibrin adsorption is accelerated on negatively charged surfaces (N-surfaces) and on positively charged surfaces (P-surfaces) of implanted polarized HA. The acceleration of fibrin adsorption is caused by the ionic and pH changes near the N- and P-surfaces by the attraction of calcium ions. The adsorbed fibrin formed a network scaffold for subsequent cell components, such as platelets and osseous cells. Near the N-surface, the higher concentration of calcium ions than that on the conventional nonpolarized surface (O-surface) and P-surface contributed to the adhesion of the platelets to the fibrin through integrin alpha(IIb)beta(3) and platelet activation. The activated platelets release a variety of growth factors that stimulate the osseous cells. These continuous reactions from the action of the fibrin adsorption as a trigger induced the early osteoconduction near the N-surface. The coagulation components played an important role at an early stage of the osteoconductive mechanism.