Biomimetic mineralization of poly(L-lactic acid) nanofibrous microspheres for bone regeneration

Simulating the hierarchical structure of natural bone, mineralized synthetic polymer fibrils such as poly(L-lactic acid) (PLLA) in the form of microspheres show considerable potential as injectable scaffolds for bone defect repair. However, the hydrophobicity of PLLA restricts the deposition of bone-like apatite on the surface of PLLA directly, limiting its application in osteogenesis. In this paper, after sodium trimetaphosphate (STMP) modification, nanofibrous PLLA microspheres were immersed into 2.5 times simulated body fluid (2.5 ×SBF) for 3 days to produce abundant bone-like apatite on the surface of microspheres. The bioactivity in vitro and bone repair ability in vivo of surface mineralized PLLA microspheres were evaluated. The results indicated that surface mineralized nanofibrous PLLA microspheres improved MSCs proliferation and bone-related gene expression, including OPN, RUNX-2 and OCN. After the surface mineralized nanofibrous PLLA microspheres were implanted into rat skulls to repair bone defects (5 mm) for 6 weeks, the micro-CT and histology results showed that the surface mineralized nanofibrous PLLA microspheres improved bone regeneration compared to pure nanofibrous PLLA microspheres. Our study provides a feasible strategy for the rapid preparation of biomimetic mineralized PLLA scaffolds, the novel mineralized microspheres showed considerable bone repair potential.