β-tricalcium phosphate for bone substitution: Synthesis and properties

beta-tricalcium phosphate (beta-TCP) is one the most used and potent synthetic bone graft substitute. It is not only osteoconductive, but also osteoinductive. These properties, combined with its cell-mediated resorption, allow full bone defects regeneration. Its clinical outcome is sometimes considered to be unpredictable, possibly due to a poor understanding of beta-TCP physico-chemical properties: beta-TCP crystallographic structure is not fully uncovered; recent results suggest that sintered beta-TCP is coated with a Ca-rich alkaline phase; beta-TCP apatite-forming ability and osteoinductivity may be enhanced by a hydrothermal treatment; beta-TCP grain size and porosity are strongly modified by the presence of minute amounts of beta-calcium pyrophosphate or hydroxyapatite impurities. The aim of the present article is to provide a critical, but still rather comprehensive review of the current state of knowledge on beta-TCP, with a strong focus on its synthesis and physico-chemical properties, and their link to the in vivo response. Statement of significance The present review documents the richness, breadth, and interest of the research devoted to beta-tricalcium phosphate (beta-TCP). beta-TCP is synthetic, osteoconductive, osteoinductive, and its resorption is cell-mediated, thus making it one of the most potent bone graft substitutes. This comprehensive review reveals that there are a number of aspects, such as surface chemistry, crystallography, or stoichiometry deviations, that are still poorly understood. As such, beta-TCP is still an exciting scientific playground despite a 50 year long history and > 200 yearly publications. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd.