Bone grafts are used in a wide array of clinical settings to augment bone repair and regeneration. This article reports a new method for the elaboration of a hybrid biomaterial in the form of sponge based on collagen gel, CaCO₃ from recycled Rapana thomasiana seashell, and Na₂HPO₄·2H₂O. Practically, collagen acts as a matrix through which calcium and phosphate ions are diffusing during in situ hydroxyapatite synthesis. The organic–inorganic interactions among biomaterial components have been studied by infrared spectroscopy, and the surface morphology was investigated by scanning electron microscopy technique. Moreover, the developed biomaterials were studied for in vitro biocompatibility with MG63 human osteoblasts. The results obtained demonstrated that the developed hybrid material does not exhibit a significant cytotoxicity and supports cell proliferation. Consequently, it holds great promise for applications in bone tissue engineering.