Search

Mg-based alloys have been considered as potential structural materials for biodegradable implants in orthopedic and cardiovascular applications, particularly when combined with other biocompatible alloying elements. However, the performances of Mg-based alloys in in vitro conditions do not accurately reflect their behavior in an in vivo environment. As such, the present study aimed at evaluating the in vivo behavior of a novel Mg-5Zn-2Nd-0.13Y-0.35Zr alloy designated as ZE52 alloy. In vivo assessment was carried out using cylindrical disks implanted into the sub-cutaneous layer of the skin at the back midline of male Wistar rats for up to 11 weeks. Post-implantation responses evaluated included well-being behavior, blood biochemical tests and histology. The corrosion rate of the implants, expressed in terms of hydrogen gas formation, was evaluated by radiographic assessment and CT examination. Results of the well-being behavioral and blood biochemical tests indicated that the in vivo behavior of ZE52 alloy implants was similar to that of inert Ti-6Al-4V alloy implants introduced into a control group. Moreover, histological analysis did not reveal any severe inflammation, as compared to the reference alloy. However, significant sub-cutaneous gas cavities were observed, indicative of the accelerated degradation of the ZE52 alloy implants. The accelerated degradation was also manifested by the formation of alloy debris that was encapsulated within the gas cavities. Post-implantation gas bubble puncturing resulted in the complete degradation of the Mg-based implants, indicating that the inert nature of the gas prevented accelerated degradation of the alloy before it was naturally absorbed by the body.

The article In Vivo Evaluation of Mg-5%Zn-2%Nd Alloy as an Innovative Biodegradable Implant Materialwritten by Elkaiam et al. was originally published electronically on the publisher's internet portal (currently SpringerLink) on September 17, 2019 with open access. With the author(s)' decision to step back from Open Choice, the copyright of the article changed on October 3, 2019 to Biomedical Engineering Society 2019 and the article is forthwith distributed under the terms of copyright.

The efforts to develop structural materials for biodegradable metal implants have lately shifted their focus from Magnesium and Iron base alloys towards Zinc. This was mainly due to the accelerated corrosion rate of Mg that is accompanied by hydrogen gas evolution, formation of voluminous iron oxide products with reduced degradation rate in the case of Iron implants and the crucial role of Zn in many physiological processes. However the mechanical properties and degradation capabilities of pure zinc in physiological environment are limited and do not comply with the requirements of biodegradable implants. The present study aims at evaluating the effect of 4%Fe on the in-vitro and in-vivo behavior of pure Zinc. This was carried out in order to address the inherent disadvantages of pure zinc in terms of mechanical properties and biodegradability. The results obtained clearly indicate that the biocompatibility and mechanical properties of the new material system was in accord with the prospective requirements of biodegradable implants. However the corrosion degradation of the new alloy in in-vivo conditions was quite similar to that of pure zinc in spite of the significant micro-galvanic effect created by Delta phase Zn 11 Fe.

The disadvantage of current biodegradable metals such as Mg and Fe is the release of hydrogen gas in vivo that can cause gas embolism and the production of voluminous iron oxide that can cause inflammation, respectively. Such considerations have turned focus towards Zn as an alternative. This is based on the fact that Zn plays a crucial role in many physiological processes, as well as potentially being biocompatible and capable of with biodegradation. As such, the purpose of the present study was to evaluate the in vivo performance of pure Zinc and Zn-2%Fe implants. The use of iron as an alloying element was aimed at accelerating the corrosion rate of pure zinc by a micro-galvanic effect so as to maintain the post-implantation biodegradation characteristics of the implant. In vivo assessment was carried out using cylindrical disks implanted in the back midline of 16 male Wistar rats for up to 24 weeks. Post-implantation evaluation included monitoring the well-being of rats, weekly examination of hematological parameters: serum Zn levels, red and white blood cell counts and hemoglobin levels, X-ray radiography, histological analysis and corrosion rate assessment. The results obtained in terms of well-being, hematological tests and histological analysis of the rats indicate that the in vivo behavior of pure Zn and Zn-2%Fe implants was adequate and in line with the results obtained by the control group containing inert Ti-6Al-4V alloy implants. The corrosion rate of Zn-2%Fe alloy in in vivo conditions was relatively increased compared to pure Zn due to micro-galvanic corrosion.