An Injectable In Situ Forming Collagen/Alginate/CaSO4 Composite Hydrogel for Tissue Engineering Applications: Optimization, Characterization and In Vitro Assessments

In situ injectable hydrogels are effectively employed to fill irregular cavitary bone defects with initiating bone growth in targeted areas. Herein, an injectable composited hydrogel composed of collagen and alginate cross-linked in situ using different concentrations of calcium sulfate (0.15, 0.3 and 0.6%, wt./v) was synthesized. Recently, CaSO₄ is frequently supported as a bone graft material for bone regeneration, owing to its biocompatibility and osteoconductive properties. Moreover, hydroxyapatite (Hap) after salinization-step by (3-Aminopropyl) triethoxysilane (APTES) was incorporated for further enhancing the osteoconductive property of injected hydrogels. All fabricated hydrogels were characterized by SEM, FTIR and XRD analyses. While physiochemical characteristics of hydrogels were assessed through swelling index, hydrolytic degradability and thermal stability measurements. In vitro bio-assessments, e.g., antimicrobial activity, cytotoxicity and cell adhesion tests using osteoblast-like cells (MG-63) were investigated. Results showed that addition of Hap offered better control of gelation time and formed uniform hydrogels, additionally improved significantly thermal stability, which leads to hindering of swelling index, prolonging hydrolytic degradability rates and significantly enhanced the antimicrobial activity of hydrogel; compared to hydrogel free-Hap. Hap-loaded Col–Alg–CaSO₄ hydrogel with the highest concentration of CaSO₄ recorded an enrichment of cell viability among all hydrogel samples. Notably, In vitro cell adhesion test showed that MG-63 cells adhered adequately with all hydrogels. The results support the approach of using an injectable Hap-loaded Col/Alg hydrogel cross-linked with CaSO₄ as an alter and novel technique to enhance bone tissue regeneration, host–implant integration, quick/simple technique and easier for clinical handling.