Autogenous bone grafting, allogeneic bone grafting and xenogeneic bone grafting are common clinical approaches for bone defect repair. However, their application is limited by problems such as insufficient donor availability, increased surgical trauma and immune rejection. In contrast, synthetic calcium phosphate ceramic repair materials have a physicochemical structure similar to that of natural bone tissue. Their porous micro-nano morphology and surface bioactive ions endow them with excellent osteoconductive and osteoinductive properties, which render them broad application prospects in bone defect repair therapy.

Calcium phosphate ceramics are a category of bioceramics with favorable bioactivity and osteoconductivity, which have garnered extensive attention. Based on differences in calcium-to-phosphorus ratios, calcium phosphate ceramics are classified into three types: hydroxyapatite (HA), tricalcium phosphate (TCP) and biphasic calcium phosphate (BCP).

Hydroxyapatite

Hydroxyapatite (HA) is a naturally mineralized form of calcium apatite with a calcium-to-phosphorus (Ca/P) ratio of 1.67. As the primary inorganic component of human bone, it accounts for approximately 50% of bone mass and exhibits excellent osteoconductive properties. HA boasts the highest stability and lowest solubility among all components of calcium phosphate ceramics. Similar to cancellous bone, HA has relatively low initial mechanical strength and is more vulnerable to tensile and shear forces; however, its compressive strength can reach up to 100 MPa, and it has a higher elastic modulus than natural bone. Despite its favorable mechanical strength and cell adhesion capacity, HA’s poor degradability impedes material resorption and ingrowth of autologous bone.

Schematic diagram of material factors related to bone inductive properties

It can be concluded that the calcium phosphate ceramics can be endowed with osteoinductive properties by optimizing the material characteristics including ionic microenvironment, macro-microporous structure, morphological features and nanostructures. These material properties can directly or indirectly regulate the osteogenic induction process. Based on these findings, the osteogenic efficiency of calcium phosphate ceramics can be further improved via the optimization of their physicochemical properties, which contributes to an in-depth and extensive understanding of the osteogenic mechanism of such materials.

Reference: Lu D, Zhang C, Duan RQ, et al. Osteoinductive properties of calcium phosphate ceramic bone repair materials[J]. Chinese Journal of Tissue Engineering Research, 2023, 27(7):1103-1109.