Influences of hydroxyapatite and ß-TCP on biomaterials bioactivity in vivo

Introduction: This study was undertaken to analyse the bioactivity pattern of a combination of HA and ß-TCP. For this purpose Straumanns BoneCeramic® (a combination of HA and ß-TCP in a 60:40 ratio in two different sizes (group A: 500 -1000 µm; group B: 400-700 µm in diameter)) was used.

Materials and Methods: Using a modified subcutaneous implantation model of Hafemann et al. 1999, 90 female 5-week-old Wistar rats were randomly divided into 3 groups of 30 animals each. Group 1 and 2 were treated with Straumanns BoneCermic® A and B. Group 3 was a Sham group (operation without biomaterial implantation). The biomaterials were explanted for further histological and histochemical analysis at 3, 10, 15, 30, or 60 days after implantation (6 animals per indicated time point).

Results: Both biomaterials showed a distinctive vascularisation and a mild degradation 60 days after implantation. At das 10 after implantation increased multinucleated tartrate-resistant acid phosphatase (TRAP)-positive cells with typical sealing zones appeared adjacent to the biomaterial. The number of osteoclasts increased continuously in group 2 up to day 60 after implantation, while in group 1 they reached their maximum at day 30 after implantation.

Conclusion: This in vivo study shows that both BoneCermic® A and B fulfil a range of requirements of being suitable synthetically derived bone substitutes. As shown previously ß-TCP based middle sized biomaterials activates a large number of osteoclasts already at day 10 after implantation, but undergo a fast degradation within the first 90 days after implantation. Pure HA-based biomaterials did not degrade as fast as ß-TCP, however showed a mild bioactivity. While the ß-TCP component of BoneCeramic® contributes to its bioactivity and to vascularization, the HA component may contribute to its stability. Ongoing in vivo research will show to what extend BoneCeramic® has an effect on bone healing and osteoconductivity.