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The availability of osteoinductive coatings on dental and orthopedic implants will result in an improved fixation of these devices. Those cases where implants are placed in poor-quality bone or where high failure rates are obtained are especially expected to gain from such coatings. This paper presents a novel, biological approach to obtain bioactive and osteoinductive coatings on bone-replacement implant materials. This so-called tissue engineering approach utilizes osteogenic bone marrow cells that are cultured on an implant material to form a bone-like tissue. The implant materials used herein included porous calcium phosphate scaffolds and metallic plates, the latter of which were coated with a biomimetic calcium phosphate coating to facilitate cellular attachment. Bone marrow cells were obtained from a variety of species, including humans, and were grown to facilitate cellular proliferation. The cells were subsequently seeded onto the implants and cultured for an additional week to facilitate osteogenic differentiation and extracellular matrix production. The resulting hybrid implants, encompassing the biomaterial carrier and cultured bone-like tissue, were subsequently implanted subcutaneously in nude mice for 4 weeks, followed by histological examination for de novo bone formation. The results revealed that newly formed bone was seen both in porous implants and on flat metallic surfaces. This bone tissue engineering approach, therefore, offers great potential to enhance bony healing around implants in a compromised bone bed.

The use of osteoinductive in vitro tissue-coated implants in orthopaedic and dental surgery (e.g. revision hip arthroplasty), could result in a better fixation of these implants. However, this tissue engineering technology has only proved to be effective in porous materials and not on flat implant surfaces. In this study we have demonstrated that calcium phosphate-coated titanium plates with a layer of cultured osteogenic cells and their extracellular matrix can initiate bone formation in vivo. Both primary and subcultured rat bone marrow cells were grown on to biomimetic calcium phosphate-coated titanium plates. After 7 d of culture, in the presence or absence of dexamethasone, the implants were subcutaneously implanted in nude mice for 4 wk. Control samples, which consisted of calcium phosphate-coated plates without cultured cells and porous calcium phosphate particles with or without cultured cells, were also implanted subcutaneously. At autopsy, no bone formation could be detected on any of the control samples without cells and samples with subcultured cells, which were primary cultured in medium without dexamethasone. In contrast, clear de novo bone formation could be observed on the calcium phosphate-coated plates and in the porous calcium phosphate particles with primary or subcultured cells, which had been continuously cultured in medium with dexamethasone. These results indicate that this hybrid technology offers great potential for the fixation of flat bone replacement implants (e.g. artificial hips) in inferior bone in the future.

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