BMP-2 delivery mode modulates the activity of bioactive implant surfaces

Objectives: To investigate the osteoinductive efficacy of various types of BMP-2-containing biomimetic calcium phosphate coatings. The criterion for an optimal system is that it elicits a high osteogenic activity at a low drug dose within a short period of time. Methods: Initially, the osteoinductive efficacies of a crystalline and an amorphous type of calcium phosphate coating bearing adsorbed BMP-2 at three different loading concentrations (2.5 µg, 5.0 µg and 7.5 µg per implant) were tested at an ectopic (subcutaneous) ossification site in rats. Following surgery, the implants (titanium discs) were retrieved 1, 2 or 3 weeks later for histomorphometric analysis. The crystalline type of coating was more osteoinductive than the amorphous one, and the effect was dose dependent. Having ascertained this fact, BMP-2 was incorporated into the crystalline type of coating at three different concentrations (0.56 µg, 0.61 µg and 1.7 µg per implant). We also established a hybrid system: a crystalline coating bearing incorporated BMP-2 at different concentrations and adsorbed BMP-2 at a fixed dose. The implanted samples were retrieved at 2 and 5 weeks. Results: Two weeks after surgery, the amount of bone deposited around crystalline coatings bearing the highest dose of incorporated BMP-2 (1.7 µg per implant) was almost 3-fold higher than that associated with crystalline coatings bearing adsorbed BMP-2 at a 3-fold higher dose (5.0 µg per implant), namely, 5.83 mm3 vs. 1.98 mm3 per implant. Using the hybrid system, osteoinductive efficacy was further potentiated in a manner that was proportional to the incorporated dose of BMP-2. Conclusions: The osteoinductive efficacy of BMP-2 can be modulated by the structural quality of biomimetic calcium phosphate coatings. The biomimetic technique – with its scope for the incorporation of bioactive agents – holds tremendous potential for the control and improvement of osteogenesis in dental and orthopaedic implantology.