Functionally graded bioactive coatings: reproducibility and stability of the coating under cell culture conditions

This work sought to provide a basic protocol for treatment of functionally graded bioactive glass coatings (FGC) that reliably adhere to titanium alloy (Ti6Al4V) prior to in vivo evaluation. The effect of the fabrication process on glass structure and reproducibility of the coating's properties, and the effect of cell culture conditions on the integrity of the coating were assessed. The structure of FGCs was compared to that of the as cast glass used as a top coating. X-ray diffraction (XRD) showed that the fabrication process resulted in 5.9+/-3.0 vol.% crystallization, while glass as cast was amorphous. Glass as cast and coatings behaved similarly in simulated body fluid (SBF): an amorphous layer rich in phosphate formed, and it crystallized, over 4 weeks, into apatite-like mineral (Fourier transform infrared spectroscopy (FTIR), XRD, scanning electron microscopy (SEM)). Reproducibility of the fabrication process was tested from three batches of coatings by measuring thickness and crystallinity. MC3T3-E1.4 mouse pre-osteoblast cells were cultured and induced to mineralize on FGCs, either as made or pre-conditioned in SBF. The sub-surface glass silica network in FGCs was compromised by cell culture conditions. A crystalline phosphate was formed during pre-conditioning (XRD, FTIR, and SEM). SBF-pre-conditioning stabilized the coatings. Thus incubation in SBF is recommended to produce a stable coating.