Biphasic calcium phosphate bioceramics: preparation, properties and applications

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Biphasic calcium phosphate (BCP) bioceramics belong to a group of bone substitute biomaterials that consist of an intimate mixture of hydroxyapatite (HA), Ca10(PO4)6(OH)2, and beta-tricalcium phosphate (β-TCP), Ca3(PO4)2, of varying HA/β-TCP ratios. BCP is obtained when a synthetic or biologic calcium-deficient apatite is sintered at temperatures at and above 700 °C. Calcium deficiency depends on the method of preparation (precipitation, hydrolysis or mechanical mixture) including reaction pH and temperature. The HA/β-TCP ratio is determined by the calcium deficiency of the unsintered apatite (the higher the deficiency, the lower the ratio) and the sintering temperature. Properties of BCP bioceramics relating to their medical applications include: macroporosity, microporosity, compressive strength, bioreactivity (associated with formation of carbonate hydroxyapatite on ceramic surfaces in vitro and in vivo), dissolution, and osteoconductivity. Due to the preferential dissolution of the β-TCP component, the bioreactivity is inversely proportional to the HA/β-TCP ratio. Hence, the bioreactivity of BCP bioceramics can be controled by manipulating the composition (HA/β-TCP ratio) and/or the crystallinity of the BCP. Currently, BCP bioceramics is recommended for use as an alternative or additive to autogeneous bone for orthopedic and dental applications. It is available in the form of particulates, blocks, customized designs for specific applications and as an injectible biomaterial in a polymer carrier. BCP ceramic can be used also as grit-blasting abrasive for grit-blasting to modify implant substrate surfaces. Exploratory studies demonstrate the potential uses of BCP ceramic as scaffold for tissue engineering, drug delivery system and carrier of growth factors.