Calcium Phosphate-Based Osteoinductive Materials

Calcium phosphate-based bone substitute materials (CaP-BSMs) in different forms (granules, blocks, composites) or as cements or coatings on orthopedic and dental implants are used in many medical and dental applications. They can also be used as scaffolds in tissue engineering for dentin or bone regeneration. CaPs are similar to bone in composition and having bioactive (ability to directly bond to bone, thus forming a uniquely strong interface) and osteoconductive (ability to serve as a template or guide for the newly forming bone) properties. Interconnecting porosity (macroporosity and microporosity) similar to that of bone can be introduced by chemical or physical methods. The bioactive property promotes formation of a carbonate hydroxyapatite layer, which attracts protein to which cells bind or adhere, proliferate, and differentiate, leading to matrix production and biomineralization or formation of new bone. CaP materials, by themselves, are not osteoinductive (i.e., do not have the ability to induce de novo bone formation as evidenced by bone formation nonskeletal sites such as subcutaneous or intramuscular sites). However, osteoinductive properties can be introduced to CaP materials by two methods: (1) designing the CaPs with appropriate geometry, topography, combined appropriate macroporosity/microporosity and concavities that will allow the entrapment and concentration of circulating growth factors or osteoprogenitor cells responsible for bone formation or (2) combining CaP with growth factors (BMPs, mesenchymal cells) or bioactive proteins (collagen, OPs, or peptides based on osteonectin and bone sialoprotein). In the latter case, microporosity/ macroporosity, composition, and particle size affect the efficacy of the CaP scaffold or carrier. Introducing osteoinductive property to Cal? materials will enhance their application in bone repair and regeneration for medical and dental applications. Two ways of introducing osteoinductive properties to CaP-BSMs include (1) designing the CaPs with appropriate geometry, topography, combined macroporosity/microporosity and concavities or that will entrap and concentrate the circulating growth factors or (2) combining CaP with growth factors (BMPs, mesenchymal cells) or bioactive proteins (collagen, OPs, or peptides based on osteonectin and bone sialoprotein). In the latter case, microporosity/macroporosity, composition, and particle size affect the efficiency of the CaP scaffold or carrier. The concept of introducing osteoinductive properties to biomaterials is an exciting one. However, it has the appropriate architectural features of the materials or scaffolds with 'intrinsic' osteoinductivity, and the reproducibility of producing these features in the manufactured is yet to be determined. In the case of 'engineered' osteoinductivity, the properties of the scaffolds or carriers, the mode of incorporating the osteogenic factors, their dosage, and controlled release rate have yet to be determined and optimized. Nevertheless, such materials would potentially replace the use of autografts and allografts with their attendant shortcomings. © 2008 American Chemical Society.