Bioactive Ceramics

Abstract

Bioactive ceramics are mostly calcium phosphates or silica-based materials. The bioactivity property refers to the ability of the materials to bond directly to bone and enhance bone formation. The degree of bioactivity depends on the ability of the material to provide a controlled and continuous supply of chemical cues to stimulate cell function and tissue formation. The chemical composition, crystalline structure, and processing parameters of bioactive materials control the rate of new bone tissue formation and graft material resorption. Among calcium phosphate ceramics, stoichiometric hydroxyapatite has high chemical stability and low bioactivity. The decrease in calcium content in calcium-deficient hydroxyapatite enhances the solubility and bioactivity. Bioactive glass has amorphous silicate structure and is characterized by a high rate of bone bonding compared to hydroxyapatite. The bone-bonding ability of bioactive glass is attributed to the rapid transformation of the material surface into a hydroxyapatite in contact with physiological solution. The hydroxyapatite layer that forms in physiological solution on the surface of bioactive glass is highly bioactive compared to hydroxyapatite ceramic due to its unique characteristics. Bioactive ceramics prepared by the sol gel method are more bioactive than those prepared by sintering at high temperature. The enhanced bioactivity is attributed to the low preparation temperature and the high porosity which provides high surface area in contact with tissue fluids. Silica-calcium phosphate nanocomposite (SCPC) has a series of compositions in a multiphase bioactive ceramic system. Among these phases, b-NaCaPO4 ss and a-cristobalite ss are the most thermodynamically stable phases. SCPC formulations with a high content of silica are more bioactive than calcium phosphate-rich SCPC compounds, hydroxyapatite ceramic, or bioactive glass. The bioactivity property of the material is not dependent on the ionic diffusion from the bulk to the surface as is the case with bioactive glass. Formation of solid solutions in SCPC ceramic phases underlies the excellent bioactivity and resorbability properties. Silica xerogels has a highly porous matrix with a large number of silanol groups (Si-OH) on the material surface. The silanol groups nucleate the formation of a hydroxyapatite layer on the material surface after immersion in simulated body fluid. Bioactive ceramics are used as bone filling grafts in non-load-bearing applications in orthopedic and maxillofacial surgery. In a porous form, bioactive ceramic can be used as drug delivery systems to treat diseases and regenerate tissues.