Ceramic coating for delayed degradation of Mg-1.2Zn-0.5Ca-0.5Mn bone fixation and instrumentation

Abstract Mg and its alloys possess a biodegradable nature that has recently made them attractive for potential applications in biomedical devices that are expected to degrade and bioresorb completely in-vivo after the healing of the body tissue. We have developed an Mg-Zn-Ca-Mn alloy containing biocompatible alloying elements, and a heat treatment process that is likely to improve mechanical stability and absorption properties during bone healing and reliably resorb following the healing of a reconstructed skeletal segment. Our objective in this work is to investigate the use of a composite ceramic-based coating to delay the degradation (weakening) of our strengthened alloy for several months to avoid loss of mechanical properties during the healing process. The heat-treated alloy samples were coated using plasma electrolytic oxidation (PEO) and a sol-gel (layer-by-layer) coating techniques to achieve improved corrosion resistance. The coated samples were characterized for their morphological and corrosion characteristics using scanning electron microscope (SEM), X-ray diffraction analysis (XRD), and in vitro corrosion testing methods. These in vitro corrosion studies showed a significant improvement in the corrosion resistance of the PEO/sol-gel coated alloy. The PEO/sol-gel coated alloy samples lost only approx. 3% of their strength, after 8 weeks of immersion in a corrosive environment, compared to 30% loss for the uncoated alloy samples under the same conditions. The results of this study suggest that it should be possible to maintain the mechanical integrity of Mg-based implants inside the body for the desired 6–9 month period and longer if that becomes useful.