Effect of particles addition to solution of plasma electrolytic oxidation (PEO) on the properties of PEO coatings formed on magnesium and its alloys: A review

Degrading metal alloys are a new class of implant materials suitable for bone surgery. The aim of this study was to investigate the degradation mechanism at the bone-implant interface of different degrading magnesium alloys in bone and to determine their effect on the surrounding bone. Sample rods of four different magnesium alloys and a degradable polymer as a control were implanted intramedullary into the femora of guinea pigs. After 6 and 18 weeks, uncalcified sections were generated for histomorphologic analysis. The bone-implant interface was characterized in uncalcified sections by scanning electron microscopy (SEM), element mapping and X-ray diffraction. Results showed that metallic implants made of magnesium alloys degrade in vivo depending on the composition of the alloying elements. While the corrosion layer of all magnesium alloys accumulated with biological calcium phosphates, the corrosion layer was in direct contact with the surrounding bone. The results further showed high mineral apposition rates and an increased bone mass around the magnesium rods, while no bone was induced in the surrounding soft tissue. From the results of this study, there is a strong rationale that in this research model, high magnesium ion concentration could lead to bone cell activation.

Magnesium (Mg) and its alloys have been intensively studied as biodegradable implant materials, where their mechanical properties make them attractive candidates for orthopaedic applications. There are several commonly used in vitro tests, from simple mass loss experiments to more complex electrochemical methods, which provide information on the biocorrosion rates and mechanisms. The various methods each have their own unique benefits and limitations. Inappropriate test setup or interpretation of in vitro results creates the potential for flawed justification of subsequent in vivo experiments. It is therefore crucial to fully understand the correct usages of each experiment and the factors that need to be considered before drawing conclusions. This paper aims to elucidate the main benefits and limitations for each of the major in vitro methodologies that are used in examining the biodegradation behaviour of Mg and its alloys. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.