Control of degradation rate of Mg alloys using silica sol-gel coatings for biodegradable implant materials

Silica sol-gel coatings were deposited on AZ31B and AZ91D magnesium substrates with the aim of controlling the degradation rate, corrosion attack and further dissolution of magnesium alloys for temporal implants. Two different silica sols were prepared with and without colloidal silica particles (MTL and TG sols) and deposited by dip-coating on both alloys. The coatings were characterised in SBF using three different in vitro tests; hydrogen evolution, pH variation and potentiodynamic polarization curves. The results show that the corrosion behaviour depends on the alloy and on the coating composition. Coatings on AZ91D-MTL were able to block the degradation of the alloy during 8 days of immersion in SBF, whereas coatings AZ91D-TG only maintain their stability during 3 days. Mg(OH)(2) and hydroxyapatite (HAp) were identified as the compounds precipitated on AZ31B samples, not appearing on AZ91D samples. The electrochemical tests confirm the promising corrosion results obtained for coated AZ91D samples. Graphical Abstract Suitable silica sol-gel coatings were deposited on Mg alloys showing a great potential to control the degradation rate, corrosion attack and further dissolution of the magnesium alloys. [GRAPHICS] .