Control of Corrosion Resistance and Osteoclastic Resorbability of Bioresorbable Carbonate Apatite Coating for Biodegradable Mg Alloys through Carbonate Content

To investigate the effect of carbonate content on the corrosion resistance and osteoclastic resorbability of carbonate apatite (CAp) coatings for biodegradable Mg alloys, polarization, electrochemical impedance, and osteoclast precursor cell culture tests were conducted for CAp-coated pure Mg (Mg) and Mg-4Y-3RE (WE43) containing approximately 11, 17, and 18 wt % carbonate. In Hanks' solution, the polarization resistance (Rp) was higher than in a 0.9% NaCl solution, and the CAp coatings improved the Rp of Mg by 7 to 15 times. The Rp of CAp-coated Mg increased by approximately 1.5 times in a 0.9% NaCl solution and 2 times in Hanks' solution with increasing carbonate content, indicating a reduction in coating defects. For CAp-coated Mg, osteoclasts only survived on the higher carbonate content coating. For WE43, the coating with a higher carbonate content exhibited a higher number of mature osteoclasts and approximately a 1.5-fold increase in the resorbed area by osteoclasts. These findings demonstrate that the carbonate content in the CAp coating allows for adjustment of the corrosion rate of biodegradable Mg alloys to suit the affected part of the body. It was also found that once osteoclasts are induced, the CAp coating with a higher carbonate content is resorbed more quickly by the osteoclasts.