Repair of bone defect in femoral condyle using microencapsulated chitosan, nanohydroxyapatite/collagen and poly(L-lactide)-based microsphere-scaffold delivery system

Bone repair ability of microencapsulated chitosan, nanohydroxyapatite/collagen (nHAC), and poly(L-lactide) (PLLA)-based microsphere-scaffold delivery system was investigated in present research, with nHAC/PLLA composite scaffold as a control. Chitosan microspheres (CMs) encapsulated with bone morphogenetic protein-2-derived synthetic peptide were incorporated into nHAC and PLLA-based matrix via a thermally induced phase separation method, in which dioxane was used as the solvent for PLLA. Compared with the rapid release from CMs, the synthetic peptide was delivered from CMs/nHAC/PLLA microsphere-scaffold composite in a temporally controlled manner, depending on the degradation of both incorporated CMs and PLLA matrix. MC3T3-E1 osteoblastic cells were seeded into nHAC/PLLA and CMs/nHAC/PLLA scaffolds, respectively, and in vitro cytocompatibility was tested by scanning electron microscopy and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The results indicated that, with the appearance of CMs in microsphere-scaffold composite, the osteoblasts exhibit better morphology and proliferation ability. In vivo tissue compatibility was evaluated by transplanting the scaffolds into rabbit femoral condyles with a defect 6 mm in diameter. After implanting for 4, 8, and 12 weeks, respectively, radiographic and histological observation revealed that the CMs/nHAC/PLLA composite can accelerate the regeneration of cancellous bone defect as compared with the nHAC/PLLA scaffold. The results demonstrated that the CMs/nHAC/PLLA possesses better biocompatibility, which should be attributed to both the incorporated chitosan component and the encapsulated bioactive synthetic peptide. The promising CMs/nHAC/PLLA microsphere-scaffold composite can be used as delivery system for multiple bioactive factors or as inductive implant scaffold for bone regeneration.