In vivo degradation of binary magnesium alloys – a long-term study

Abstract

Bioresorbable magnesium materials are widely investigated because of their promising properties as orthopedic devices. Pure magnesium (99.99%) and two binary magnesium alloys (Mg2Ag and Mg10Gd) were used to investigate the degradation behavior, the bone adherence and bone-implant interface mechanics of these materials in growing Sprague-Dawley® rats in a long-term study of 36 weeks. In vivo micro-computed tomography (μCT) scans were performed at specific time points to observe the longitudinal degradation of each alloy within the same animal. Pin volume and surface, gas volume and degradation rates were calculated. The results showed a slower degradation of pure magnesium and Mg2Ag in comparison to the fast disintegrating Mg10Gd. Changes in bone morphology were determined by high resolution ex vivo μCT scans and bone sections stained with Toluidine blue. Pure magnesium and Mg2Ag were well integrated and surrounded by bony tissue 24 weeks after implantation. On the contrary, Mg10Gd remnants were surrounded by fibrous and bone tissue. Push-out tests revealed higher bone-implant-interface strengths of pure magnesium pins compared to Mg2Ag and Mg10Gd. Mg10Gd induces less beneficial tissue reactions, while Mg2Ag showed adequate biodegradation and no adverse reactions in bone healing process which might be promising as an orthopedic device.