HAp granules encapsulated oxidized alginate–gelatin–biphasic calcium phosphate hydrogel for bone regeneration

•Encapsulation of HAp granules into oxidized alginate–gelatin–biphasic calcium phosphate hydrogel complex.•Fabrication and characterization of granules loaded hydrogel complex.•In vitro experiments for the evaluation of bio-compatibility.•In vivo experiment in critical defect zone of rabbit femoral using both hydrogel and granules loaded hydrogel complex.•HAp granules encapsulated hydrogel complex revealed higher bone formation than hydrogel complex alone. Bone repair in the critical size defect zone using 3D hydrogel scaffold is still a challenge in tissue engineering field. A novel type of hydrogel scaffold combining ceramic and polymer materials, therefore, was fabricated to meet this challenge. In this study, oxidized alginate–gelatin–biphasic calcium phosphate (OxAlg–Gel–BCP) and spherical hydroxyapatite (HAp) granules encapsulated OxAlg–Gel–BCP hydrogel complex were fabricated using freeze-drying method. Detailed morphological and material characterizations of OxAlg–Gel–BCP hydrogel (OGB00), 25wt% and 35wt% granules encapsulated hydrogel (OGB25 and OGB35) were carried out for micro-structure, porosity, chemical constituents, and compressive stress analysis. Cell viability, cell attachment, proliferation and differentiation behavior of rat bone marrow-derived stem cell (BMSC) on OGB00, OGB25 and OGB35 scaffolds were confirmed by MTT assay, Live–Dead assay, and confocal imaging in vitro experiments. Finally, OGB00 and OGB25 hydrogel scaffolds were implanted in the critical size defect of rabbit femoral chondyle for 4 and 8 weeks. The micro-CT analysis and histological studies conducted by H&E and Masson's trichrome demonstrated that a significantly higher (***p