58S and 68S sol-gel glass-like bioactive coatings for enhancing the implant performance of AZ91D magnesium alloy

Magnesium alloys such as AZ91D, has been presented as potential material for temporary implant material since it has a mechanical performance suitable with bone tissue and also degrades in time. The fast degradation at early times of AZ91D alloy could be retarded applying bioactive sol-gel glass coatings. In this work, two compositions of known bioactive silica-glasses (58S and 68S) were synthetized by sol-gel method and deposited by dip coating to the magnesium substrates. The glasses were produced without using any nitrate precursor, avoiding the presence of remaining residual in the coatings that could be not beneficial to the body. The coatings presented an excellent bioactive response after immersion in Hanks' balanced salt solution (HBSS) at 37 °C, showing apatite related deposits after 72 h immersion detected by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Corrosion behaviour has been also analyzed, 58S presented as better protective features after 17 days of immersion. Cell attachment and proliferation tests demonstrate that both 58S and 68S coatings on AZ91D magnesium alloy are suitable as temporary implant materials.