Injectable polysaccharide hydrogel embedded with hydroxyapatite and calcium carbonate for drug delivery and bone tissue engineering.

To meet the progressive requirements for bone regeneration purpose, injectable hydrogels have attracted increasing attention in tissue regeneration and local drug delivery applications. In this study, we report a facile method to prepare injectable and degradable polysaccharide-based hydrogels doubly integrated with hydroxyapatite (HAp) nanoparticles and calcium carbonate microspheres (CMs) under physiological condition. The mechanism of cross-linking is attributed to the Schiff-base reaction between amino and aldehyde groups of carboxymethyl chitosan (CMCS) and oxidized alginate (OAlg), respectively. Synchronously, tetracycline hydrochloride (TH) loaded CMs were fabricated by the precipitation reaction with an average diameter of 6.62 µm. To enhance bioactive and mechanical properties, nano-HAp and CMs containing TH were encapsulated into the polysaccharide-based hydrogel to form injectable gel scaffolds for imitation of bone niche. The gelation time, morphology, mechanical properties, swelling ratio and in vitro degradation of the gel scaffolds could be controlled by varying HAp and CMs contents. Moreover, the composite gel scaffolds had good sustained drug release and antibacterial properties, as confirmed by drugs release calculation and antibacterial evaluation. In addition, the gel scaffolds were found to be self-healing due to dynamic equilibrium of the Schiff-base linkages. These results suggested that the prepared composite gel scaffolds hold great potential for drug delivery and regeneration of irregular bone defects.