α-Tricalcium phosphate: Synthesis, properties and biomedical applications

Nowadays, alpha-tricalcium phosphate (alpha-TCP, alpha-Ca-3(PO4)(2)) is receiving growing attention as a raw material for several injectable hydraulic bone cements, biodegradable bioceramics and composites for bone repair. In the phase equilibrium diagram of the CaO-P2O5 system, three polymorphs corresponding to the composition Ca-3(PO4)(2) are recognized: beta-TCP, alpha-TCP and alpha'-TCP. alpha-TCP is formed by heating the low-temperature polymorph beta-TCP or by thermal crystallization of amorphous precursors with the proper composition above the transformation temperature. The alpha-TCP phase may be retained at room temperature in a metastable state, and its range of stability is strongly influenced by ionic substitutions. It is as biocompatible as beta-TCP, but more soluble, and hydrolyses rapidly to calcium-deficient hydroxyapatite, which makes alpha-TCP a useful component for preparing self-setting osteotransductive bone cements and biodegradable bioceramics and composites for bone repairing. The literature published on the synthesis and properties of alpha-TCP is sometimes contradictory, and therefore this article focuses on reviewing and critically discussing the synthetic methods and physicochemical and biological properties of alpha-TCP-based biomaterials (excluding alpha-TCP-based bone cements). (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.