Understanding and controlling the bone-implant interface.

A goal of current implantology research is to design devices that induce controlled, guided, and rapid healing. In addition to acceleration of normal wound healing phenomena, endosseous implants should result in formation of a characteristic interfacial layer and bone matrix with adequate biomechanical properties. To achieve these goals, however, a better understanding of events at the interface and of the effects biomaterials have on bone and bone cells is needed. Such knowledge is essential for developing strategies to optimally control osseointegration. This paper reviews current knowledge of the bone-biomaterial interface and methods being investigated for controlling it. Morphological studies have revealed the heterogeneity of the bone-implant interface. One feature often reported, regardless of implant material, is an afibrillar interfacial zone, comparable to cement lines and laminae limitantes at natural bone interfaces. These electron-dense interfacial layers are rich in noncollagenous proteins, such as osteopontin and bone sialoprotein. Several approaches, involving alteration of surface physicochemical, morphological, and/or biochemical properties, are being investigated in an effort to obtain a desirable bone-implant interface. Of particular interest are biochemical methods of surface modification, which immobilize molecules on biomaterials for the purpose of inducing specific cell and tissue responses or, in other words, to control the tissue-implant interface with biomolecules delivered directly to the interface. Although still in its infancy, early studies indicate the value of this methodology for controlling cell and matrix events at the bone-implant interface.