Ex Vivo and In Vitro Investigation of Biodegradable Magnesium-Gadolinium Implants

Biodegradable magnesium-based implants are playing an increasingly important role in the area of orthopaedic implants as they eliminate the need for a second surgery to remove the implant, consequently reducing the chance of patients’ harm as well as the financial burden. There is a need for degradable magnesium-based implants to be fully characterized in terms of microstructure, corrosion performance in vitro and in vivo due to the implants’ performance differences in these different environments. Two magnesium gadolinium alloys (Mg-5 weight % Gd and Mg-10 weight % Gd) in the shape of M2 screws have been investigated with regards to their microstructure and their degradation performance over 1 - 56 days period in vitro via both weight loss and volume loss measurements. Investigations were performed via optical microscopy, scanning electron microscopy / backscatter electrons microscopy, electron backscatter diffraction and micro computed tomography (µCT). Ex vivo analysis on the same Mg-xGd alloys at 4, 8, 12 weeks was performed via synchrotron radiation µCT and histology towards their degradation performance in Sprague Dawleys' tibia and bone-to-implant interaction. In order to gain knowledge about the bone-to-implant interaction parameters bone-to-implant-contact area and bone volume density around the implant have been investigated. Additionally, in situ synchrotron radiation µCT imaging of the implant failure during the increase of force on the implant was performed (push-out experiments). After detailed exploration and correlation of in vitro and ex vivo results, it is suggested that both Mg-xGd alloys are suitable as materials for bone implants.