PROTEOGLYCANS AT THE BONE-IMPLANT INTERFACE

The widespread success of clinical implantology stems from bone's abil ity to form rigid, load-bearing connections to titanium and certain bi oactive coatings. Adhesive biomolecules in the extracellular matrix ar e presumably responsible for much of the strength and stability of the se junctures. Histochemical and spectroscopic analyses of retrievals h ave been supplemented by studies of osteoblastic cells cultured on imp lant materials and of the adsorption of biomolecules to titanium powde r. These data have often been interpreted to suggest that proteoglycan s permeate a thin, collagen-free zone at the most intimate contact poi nts with implant surfaces. This conclusion has important implications for the development of surface modifications to enhance osseointegrati on. The evidence for proteoglycans at the interface, however, is somew hat less than compelling due to the lack of specificity of certain his tochemical techniques and to possible sectioning artifacts. With this caveat in mind, we have devised a working model to explain certain obs ervations of implant interfaces in light of the known physical and bio logical properties of bone proteoglycans. This model proposes that tit anium surfaces accelerate osseointegration by causing the rapid degrad ation of a hyaluronan meshwork formed as part of the wound-healing res ponse. It further suggests that the adhesive strength of the thin, col lagen-free zone is provided by a bilayer of decorin proteoglycans held in tight association by their overlapping glycosaminoglycan chains.