Microscopic and spectroscopic evidences for multiple ion-exchange reactions controlling biomineralization of CaO.MgO.2SiO2 nanoceramics

This study is focused on the mechanism of in vitro biomineralization on the surface of CaO.MgO.2SiO2 (diopside) nanostructured coatings by scanning electron microscopy, energy-dispersive X-ray spectroscopy and inductively coupled plasma spectroscopy assessments. A homogeneous diopside coating of almost 2 µm in thickness was deposited on a medical-grade stainless steel by coprecipitation, dipping and sintering sequences. After soaking the sample in a simulated body fluid (SBF) for 14 days, a layer with the thickness of 8 µm is recognized to be substituted for the primary diopside deposit, suggesting the mineralization of apatite on the surface. Investigations revealed that the newly-formed layer is predominantly composed of Ca, P and Si, albeit with a biased accumulations of P and Si towards the surface and substrate, respectively. The variations in the ionic composition and pH of the SBF due to the incubation of the sample were also correlated with the above-interpreted biomineralization. In conclusion, the multiple ion-exchange reactions related to Ca, Mg, Si and P were found to be responsible for the in vitro bioactivity of nanodiopside.