TISSUE-RESPONSE TO TITANIUM IMPLANTS IN THE RAT TIBIA - ULTRASTRUCTURAL, IMMUNOCYTOCHEMICAL AND LECTIN-CYTOCHEMICAL CHARACTERIZATION OF THEBONE-TITANIUM INTERFACE

Although many aspects of the bone response to materials such as titani um are understood, less is known about the nature of the bone-implant interface. In the present study, we have used morphological techniques to examine the tissue response to titanium implants, and (immuno)cyto chemistry to identify and characterize the organic moieties present at the bone-implant interface. Miniature titanium screws were implanted into rat tibiae. Animals were sacrificed at 1 day to 5 months post-imp lantation and tissues were processed for scanning and transmission ele ctron microscopy, lectin-gold cytochemistry for glycoconjugates, and p rotein A-gold immunolabeling for non-collagenous bone and plasma prote ins. Other rats were injected with H-3-proline, 4 days prior to sacrif ice, to examine bone matrix deposition. New bone formation was observe d soon after implantation, first as cancellous bone, which then remode led relatively quickly into more compact bone. Radioautography confirm ed bone matrix deposition in the vicinity of the implant. The presence of osteoblasts, osteoid or mineralized matrix against the implant sur face indicates that bone deposition can occur both toward, and at the surface of, and then away from, the implant. Tissue components at the bone-implant interface included cells, cell debris and/or organic mate rial with a variable appearance and thickness. A portion of the implan t surface was covered with a layer (cement line/lamina limitans) rich in glycoconjugates that was intensely immunolabeled for osteopontin an d alpha(2)HS-glycoprotein. Osteocalcin, fibronectin and albumin showed no preferential accumulation at the bone-implant interface. In conclu sion, based on structural and compositional similarities between cemen t lines in bone and the bone-titanium interface, the host response to biomaterials may be similar to those osteogenic processes occurring at natural bone interfaces.