Osteogenic and anti-osteoclastogenic properties of tannic acid-modified sodium alginate/chitosan microspheres for bone defect repair

Abstract Background: The traditional treatment methods for bone defects have many deficiencies. Recently, bone tissue engineering has played an increasingly important role in designing new grafts with tissue-inducing activity. In the body, bone resorption and bone formation are in a dynamic balance, effectively regulating osteoblast and osteoclast differentiation, and contributing to the repair of bone tissue. Tannic acid (TA) is a substance with various biological properties, and it has been reported to effectively improve the performance of hydrogels as an active substance. However, it is still unclear how TA and sodium alginate (SA)/chitosan (CS) combine to form microspheres in bone tissue engineering. This study aims to investigate the effect of SA/CS/TA composite hydrogel microspheres on osteogenic and osteoclastic differentiation in vitro and in a bone defect model in vivo. Methods: In this study, we investigated the impact of SA/CS/TA microspheres on osteoclast and osteogenic differentiation in vitro. We used a spectrophotometer to measure the release of TA from SA/CS/TA microspheres, while live-dead cell staining was employed to verify the effect of these microspheres on osteoclast and osteoblast activity. Real-time polymerase chain reaction (qPCR) and Western blotting analysis were utilized to assess the expression of osteoclast and osteogenic differentiation-specific genes and proteins. TRAP, F-actin, ALP, and ARS staining were used to validate the effects of SA/CS/TA microspheres on TRAP, F-actin, ALP activity, and mineral deposition. Finally, we evaluated the impact of SA/CS/TA microspheres in vivo using a tibial bone defect model. Results: SA/CS/TA microspheres have been found to be non-cytotoxic to both BMMs and BMSCs, while effectively releasing TA. They are capable of inhibiting osteoclast formation and promoting osteogenic differentiation. Furthermore, the microspheres have also been shown to promote bone healing in rats with tibial bone defects. Conclusions: The application of SA/CS/TA microspheres has been found to effectively promote the osteogenic differentiation of BMSCs, inhibit the osteoclastic differentiation of BMMs, and accelerate the healing of bone defects, thus indicating a promising new direction for bone tissue engineering.