Ionic exchanges modulate the in vitro response of mesenchymal stem cells to biomimetic hydroxyapatite

INTRODUCTION: In vitro assays are a potent tool for the evaluation of biomaterial performance. However, in the case of bioactive materials, like calcium phosphates (CaPs) the ionic exchange with the cell culture medium can make cell cultures very tricky. This is particularly relevant in the case of biomimetic hydroxyapatite, which has high specific surface area (SSA) and high surface reactivity. These features support its excellent in vivo performance, but can make the in vitro results difficult to interpret. The aim of this study was to analyse to what extent the outcome of cell culture studies on biomimetic calcium deficient hydroxyapatite depend on cell culture conditions, and more specifically on the ratio between cell culture and material volume, a parameter often overlooked.