Improved biodegradable magnesium alloys through advanced solidification processing

The potential of using external fields to reduce the cost of emerging magnesium alloys used for the manufacture of medical implant devices while maintaining biocompatibility and mechanical performance is explored. Zirconium (Zr) is often added to high performance magnesium alloys as a grain refiner which is expensive, and there is uncertainty about whether or not Zr is harmful to the biocompatibility of the alloy. This is a significant barrier to the adoption of alloys that contain Zr because of the need to undertake cytotoxicity and haemocompatibility testing, as well as evaluation of long-term clinical effects. An alternative approach is to investigate methods to minimise or eliminate the need for Zr addition. External fields applied during solidification of the alloy provide an opportunity to produce a refined microstructure without the addition of Mg-Zr master alloy presenting a distinct advantage both from biodegradation and biocompatibility perspectives. Preliminary work evaluates the effect of ultrasonic treatment on microstructure and mechanical properties of Mg-Zn-Ca alloys with and without Zr and then compares their in-vivo corrosion performance to that of WE43. A framework for future research is proposed along with opportunities for the development of lower cost alloys with at least equal biocompatibility, mechanical and corrosion performance. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.