The bioactivity mechanism of magnetron sputtered bioglass thin films

Smooth and adherent bioactive coatings with ∼0.5 μm thickness were deposited onto Si substrates by the radiofrequency-magnetron sputtering method at 150 °C under 0.4 Pa 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.