Electrophoretic Deposition of Nanohydroxyapatite on Homogenized Magnesium-Based Alloy for Biomedical Applications

Magnesium alloys are promising biodegradable implant materials. If successful, they do not require a second surgical operation for their removal. However, magnesium alloys suffer a fast degradation rate and loosen the structural integrity before the healing process ends. Among the phase compositions of magnesium alloy microstructure is the beta or intermetallic phase, which is nobler than the alpha phase and it can worsen the degradation conduct of magnesium alloys due to its galvanic effects. This study aimed to evaluate the effects of the beta phase on the degradation rate which hinders the clinical application of magnesium AZ91 alloy. Thus, homogenization heat treatment was carried out to reduce the beta phase. The influence of the beta phase and the hydroxyapatite powders were employed to slow down the initial degradation rate of magnesium AZ91 alloy. Samples were cut from magnesium grade AZ91 alloy ingot in 10 mm x 10 mm x 3 mm dimensions. The samples were prepared and divided into two; the first part was classified as an as received sample (sample a) while the second one was processed for homogenization heat treatment. The homogenization heat treatment was carried out at 410oC/10 h, cooled inside the furnace, and named a homogenized sample (sample b). The hydroxyapatite powder was synthesized using a simple wet chemical precipitation technique and deposited on sample b via electrophoretic deposition at different voltages with different deposition times. The hydroxyapatite powder, uncoated, and coated samples were characterized. Potentiodynamic polarization and immersion tests were carried out in simulated body fluid to estimate the degradation rate and in vitro bioactivity of Mg AZ91 respectively. The results revealed a significant drop in degradation rate from sample a (1.421 mm per year) to coated sample h (3.73 x 10-4 mm per year).