The role of osteoclasts in osteoinduction triggered by calcium phosphate biomaterials in mice

Objective Bone remodeling is mediated by the interaction between osteoblasts and osteoclasts, so does osteoinduction triggered by calcium phosphate (CaP) biomaterials. This study aims to investigate the role and function of osteoclasts in ectopic bone formation induced by CaP biomaterials. Methods Four kinds of mice, two outbred mouse strains (KM and ICR) and two inbred mouse strains (C57BL/6 and BALB/c), were chosen for the experiments. The hydroxyapatite/𝛽-tricalcium phosphate (HA/𝛽-TCP) biomaterials were implanted into the bilateral thigh muscle of each mouse, and then all mice ran on the treadmill to accelerate the ectopic bone formation. Five and ten weeks later, five mice in each group were euthanized and the samples were harvested for electron microscope scanning or histological identification: hematoxylin and eosin (HE), Masson-trichrome and tartrate-resistant acid phosphatase (TRAP) staining, respectively. The inflammation indexes, angiogenesis, and osteogenic ability were compared among the four kinds of mice, and the role of osteoclasts was analyzed based on this evidence. Results The number of multinucleated cells, the number of new blood vessels, and the area percentage of new bone tissues were higher in outbred mouse strains than in inbred mouse strains; and there were more TRAP-positive cells in the outbred mouse strains group. We believe that the monocytes from the peripheral blood could migrate into new bone tissues to form osteoclasts. Conclusion Bone induction could be triggered by CaP biomaterials in mice, and osteoclasts could maintain the dynamic balance between bone resorption and remodeling, and induce the production of new bone marrow tissues.