Synthesis of PLA coating on ZK41 Mg alloy for improved biodegradation resistance as an implant material

Magnesium (Mg) alloys are promising biodegradable biomaterials for implant applications due to their biodegradability, biocompatibility, and mechanical properties like those of natural bone tissue. Despite favourable properties, Mg alloys are rarely used as biodegradable implants because they corrode rapidly in physiological environments. This study employed dip-coated polylactic acid (PLA)-apatite polymer coatings on ZK41 Mg alloy to improve the system's integrity. The coating solutions were prepared using PLA with chloroform, dichloromethane, and a combination of both solvents to prevent degradation of the ZK41 alloy. Surface characteristics of the samples were examined using scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Rockwell hardness testing, and pH measurements. Results indicated that a compact, uniform PLA coating on ZK41 alloy could be achieved using a mixture of chloroform and dichloromethane. A hardness measurement of this sample showed better mechanical properties than the other samples. Additionally, in vitro biodegradation performance was assessed through immersion tests and tests in Hank's solution (HBSS) at 37 °C. The ZK41 alloy coated with PLA using chloroform and dichloromethane, with 25% higher hardness than pure ZK41 alloy, exhibited the highest adhesion strength and degradation resistance compared to the uncoated and coated with PLA + chloroform or PLA + dichloromethane samples. The uncoated ZK41 Mg alloy exhibited the highest degradation rate of 25.2 ± 1.44 mg/cm 2 after 14 days, whereas the PLA-coated sample with chloroform and dichloromethane showed the lowest rate at 7.32 ± 0.12 mg/cm 2 . This sample also shows the lowest evolution of H 2 gas after 24 hr immersion period.