Bone is formed by cells called osteoblasts, which arise from progenitor cells in a multistep process. At bone defect (injury) sites, osteoblast progenitors are recruited from thin cell layers surrounding the bone surface and tissue inside the bone (periosteum and bone marrow, respectively). That is, resected or injured bone sites induce the chemoattraction of multipotent progenitor cells that originally reside in the marrow or periosteum, and these cells become osteoblasts at the defect site through a series of controlled differentiation steps. These progenitor cells are referred to as stromal or mesenchymal stem cells (MSCs).

When metals or their alloys are implanted at bone defect sites, corrosion may inhibit the differentiation of MSCs around the implanted metals, resulting in encapsulation of the implants by scar tissue or a fibrous membrane, with the thickness of the membrane proportional to the degree of metallic corrosion. In contrast, when alumina (Al₂O₃) ceramics or titanium devices are implanted into bone defects, the MSCs around the ceramics can undergo osteogenic differentiation. This results in functional regeneration of the bone tissue around the materials with minimal scar tissue or fibrous membrane formation. Still, the interface between the bone and the implant is not strong, and will detach easily upon shear and load stress.