Strontium-Containing Apatite/Poly Lactide Composites Favoring Osteogenic Differentiation and in Vivo Bone Formation

Strontium was shown to enhance bone growth; however, its oral administration may lead to severe side effects. The application of strontium in orthopedic biomaterials may therefore be an alternative to achieve targeted and sustained strontium treatment to the surgery site in aid of bone growth locally. In this study, strontium-containing composites were prepared by introducing various levels of strontium into amorphous apatite and extruding the obtained apatite powders into polylactide in a weight ratio of 1:1. Strontium substitution increased apatite dissolution and enhanced the degradation behavior of the resulting composites. Sustained and dose-dependent strontium release from the composites was observed for up to 24 weeks in simulated physiological solution, indicating that strontium release can be tuned by its substitution level in the embedded apatite. Strontium-containing composites enhanced the osteogenic differentiation of murine mesenchymal stromal cells in vitro in a dose-dependent fashion. After heterotopic implantation with the combination of rhBMP-2, bone formation on strontium containing composites was enhanced. These results suggest that strontium-releasing composites provide a local ion-rich (i.e., Sr2+ as well as Ca2+ and PO43-) environment that favors osteogenic differentiation and in vivo bone formation.