Biodegradable magnesium alloys for tissue engineering and other applications: unexpected findings from a mouse model

Abstract

Magnesium and its alloys had been investigated for use as an absorbable implant since the beginning of the 20th century. However, rapid gaseous evolution hindered its further use. Renewed interest of it as biomaterial has re-emerged recently on orthopedic and cardiovascular applications, but the use on tissue engineering was rarely explored despite its good biocompatibility. Degradation properties and host response of AM50A, AM60B, AZ91 alloys and 99.95% Mg are investigated in this paper. Polished Mg and Mg alloys treated with concentrated NaOH and DMEM were implanted subcutaneously into a mouse for 6 months. X-ray investigations were conducted twice a week for the first two weeks and weekly thereafter, but there was no significant gas formation observed for AM50A, AM60B and AZ91D. After implant retrieval, some gas bubbles were detected under the fibrous layer covering the implants. This implies that a lack of gas pocket on an X-ray image is insufficient for the declaration of a lack of gaseous accumulation. Moreover it could be observed that the Mg alloys under investigation did not degrade fast in the body. In fact there was nearly no observable dimensional change for the alloys (except the 99.95% Mg) after implantation. AZ91, a commonly used alloy on literatures, was found with much more pitting corrosion than commercially available AM50A and AM60B alloys. This suggests that the use of AZ91 to illustrate the relatively better corrosion profile of another alloy may be misleading.