The osteogenesis and the biologic mechanism of thermo-responsive injectable hydrogel containing carboxymethyl chitosan/sodium alginate nanoparticles towards promoting osteal wound healing

With the development of minimally invasive orthopedics, injectable materials for bone repair are attracted more attention, especially for those wound with a small external mouth and sizeable internal cavity. In this work, the hydrogel with features of thermo-responsiveness, degradability and injectability was designed and fabricated. The hydrogel, named as FHCS, is composed of Pluronic F-127 (F127) loaded with carboxymethyl chitosan/sodium alginate nanoparticles (nCS) and nanohydroxyapatite (nHA). The hydrogel FHCS was non-toxic and good hemocompatible. It can enhance the ALP activity and extracellular matrix calcification of MC3T3-E1 due to the chitosan-based nanoparticle components (nCS). Moreover, FHCS-5 (containing 5 mg/mL nCS) showed relative high expression of osteogenic genes and protein markers. Osteal regeneration was observed treated by FHCS-5 hydrogel in a critical-size rat calvarial bone defect model. CT scanning showed that the whole defect was basically covered by new bone after FHCS-5 hydrogel. The results of H&E staining and Masson's trichrome staining on histological sections further confirmed that FHCS-5 hydrogel promoted new osteal formation and maturation, which up regulated the osteogenic related genes and proteins of ALP, OCN, OPN through BMP/Smad signaling pathway. Hence, this study suggests that FHCS-5 hydrogels have a promising application for non-loading bone regeneration.