Cortical Bone Response Towards Porous Composites of PLGA and Apatite Prepared from Calcium Complexes

Abstract

Apatites were prepared by varying the ligands of calcium complexes. Two lower crystallinity apatites were prepared from calcium-iminodiacetic acid (Ca-IDA) or calcium- aspartic acid (Ca-Asp) complexes and one higher crystallinity apatite from Ca-IDA complex. Cortical bone responses towards their PLGA composites including different apatites, namely, PLGA/IDA-HA(lower), PLGA/IDA-HA(higher) and PLGA/Asp-HA(lower), were evaluated after implantation into the cortical bone of rabbit tibiae.
Micro-CT observation showed no distinct differences among the three PLGA/apatite composites after 12 weeks of implantation. The original drill holes were partly closed and formation of primary woven bone was observed. Residue of decomposed PLGA was still observed inside the bone marrow.
The histological appearances of porous PLGA/apatite composite scaffolds after 12 weeks of implantation showed similar overall cortical bone response to different PLGA/apatite composites. The original drill hole was not completely filled with new bone. For PLGA/IDA-HA(higher) composite, the original bone defect was partly filled with new bone. Residue of degraded PLGA and remaining apatite was recognized. Both PLGA/IDA-HA(lower) and PLGA/Asp-HA(lower) showed residue of degraded PLGA inside the bone marrow. Remnant lower-crystallinity apatite was not clearly recognized.
In conclusion, apatites with different crystallinity were prepared through Ca-IDA and Ca-Asp complexes. The bone responses towards PLGA/apatite composites with different crystallinity were similar, but the degradation behavior of PLGA/apatite composite was different. It is suggested that the degradation of PLGA in PLGA/apatite composite influences new bone formation in addition to the release and dissolution of calcium from apatite.