Resorption of calcium phosphate materials: Considerations on the in vitro evaluation

Literature is quite abundant concerning the resorption of calcium phosphates. However, articles on in vitro acellular dissolution tests are scarcer, although these immersion experiments are often considered a first step in establishing a predictive dissolution test and understanding the resorption mechanisms. Also, the comparison of results obtained after immersion in model fluids reveals large discrepancies. The first part of this paper is a literature review focused on in vitro aging of apatite, dicalcium phosphate dihydrate (DCPD) and beta tricalcium phosphate (β-TCP). In the second part, experimental findings obtained by immersing DCPD and β-TCP samples in TRIS and PBS solutions for different times demonstrate the influence of the immersion conditions and possible artefacts induced by the experimental protocols. Suggestions are provided to improve the design of in vitro experiments. In addition, the interest to follow-up at the same time and at a local scale physico-chemical, microstructural and mechanical properties is discussed.