The bioactivity mechanism of magnetron sputtered bioglass thin films

► RF-sputtering: an efficient solution for synthesizing bioactive glass thin films. ► Electrostatic interactions between charged surface and ions from stagnant solution. ► Heterogeneous-type nucleation of apatite from the SBF solution on the glass surface. ► Peculiarities of hydroxyapatite nucleation process and biomineralisation kinetics. Smooth and adherent bioactive coatings with ∼0.5μm thickness were deposited onto Si substrates by the radiofrequency-magnetron sputtering method at 150°C under 0.4Pa of Ar atmosphere using a bioglass powder as target with a composition in the SiO2–CaO–MgO–P2O5–CaF2–B2O3–Na2O system. The bioactivity of the as-prepared bioglass samples was assessed by immersion in simulated body fluid for different periods of time up to 30 days. Grazing incidence X-ray diffraction, Fourier transform infra-red spectrometry and energy dispersive spectroscopy revealed that important structural and compositional changes took place upon immersing the samples in SBF. Whilst the excellent biomineralisation capability of the BG thin films was demonstrated by the in vitro induction of extensive and homogenous crystalline hydroxyapatite in-growths on their surfaces, a series of bioactivity process kinetics peculiarities (derogations from the classical model) were emphasised and thoroughly discussed.