Long-term in vitro degradation and in vivo evaluation of resorbable bioceramics

An essential criterion for the selection of resorbable bioceramics is their ability to degrade inside human body within a reasonable time frame. Furthermore, if the bioceramic can release beneficial ions, such as strontium, as it degrades, recovery time might be shortened. The present study demonstrates that strontium-containing calcium sulfate (Sr,Ca)SO₄ can fulfill these criteria. A long-term in vitro degradation analysis for 12 weeks using sintered (Sr,Ca)SO₄ discs in phosphate buffered solution (PBS) was conducted. The sintered (Sr,Ca)SO₄ disc was then implanted into defects in the distal femur of rats. The degradation rate of (Sr,Ca)SO₄ discs showed a strong dependence on the Sr content. Similar results were observed between the long-term in vitro degradation analysis and the in vivo evaluation. The sintered (3.8%Sr,Ca)SO₄ disc lost more than 80% of its initial weight after soaking in PBS with shaking at 37 °C for 12 weeks. After 12 weeks in vivo, the remaining volume of the (3.8%Sr,Ca)SO₄ disc within the bone defect was ~25%. Over the same time period, new bone was formed at a relative volume of 40%. This study demonstrates the potential of (Sr,Ca)SO₄ bioceramic, and the benefits of using a long-term degradation test during the evaluation of resorbable bioceramics.