In Vivo Evaluation of Mg-5%Zn-2%Nd Alloy as an Innovative Biodegradable Implant Material.

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.

Correction to: In Vivo Evaluation of Mg-5%Zn-2%Nd Alloy as an Innovative Biodegradable Implant Material.

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.

Porous biodegradable EW62 medical implants resist tumor cell growth.

Magnesium alloys have been widely investigated for biodegradable medical applications. However, the shielding of harmful cells (eg. bacteria or tumorous cells) from immune surveillance may be compounded by the increased porosity of biodegradable materials. We previously demonstrated the improved corrosion resistance and mechanical properties of a novel EW62 (Mg-6%Nd-2%Y-0.5%Zr)) magnesium alloy by rapid solidification followed by extrusion (RS) compared to its conventional counterpart (CC). The present in vitro study evaluated the influence of rapid solidification on cytotoxicity to murine osteosarcoma cells. We found that CC and RS corrosion extracts significantly reduced cell viability over a 24-h exposure period. Cell density was reduced over 48 h following direct contact on both CC and RS surfaces, but was further reduced on the CC surface. The direct presence of cells accelerated corrosion for both materials. The corroded RS material exhibited superior mechanical properties relative to the CC material. The data show that the improved corrosion resistance of the rapidly solidified EW62 alloy (RS) resulted in a relatively reduced cytotoxic effect on tumorous cells. Hence, the tested alloy in the form of a rapidly solidified substance may introduce a good balance between its biodegradation characteristics and cytotoxic effect towards cancerous and normal cells.

Improved stress corrosion cracking resistance of a novel biodegradable EW62 magnesium alloy by rapid solidification, in simulated electrolytes.

The high corrosion rate of magnesium (Mg) and Mg-alloys precludes their widespread acceptance as implantable biomaterials. Here, we investigated the potential for rapid solidification (RS) to increase the stress corrosion cracking (SCC) resistance of a novel Mg alloy, Mg-6%Nd-2%Y-0.5%Zr (EW62), in comparison to its conventionally cast (CC) counterpart. RS ribbons were extrusion consolidated in order to generate bioimplant-relevant geometries for testing and practical use. Microstructural characteristics were examined by SEM. Corrosion rates were calculated based upon hydrogen evolution during immersion testing. The surface layer of the tested alloys was analyzed by X-ray photoelectron spectroscopy (XPS). Stress corrosion resistance was assessed by slow strain rate testing and fractography. The results indicate that the corrosion resistance of the RS alloy is significantly improved relative to the CC alloy due to a supersaturated Nd enrichment that increases the Nd2O3 content in the external oxide layer, as well as a more homogeneous structure and reduced grain size. These improvements contributed to the reduced formation of hydrogen gas and hydrogen embrittlement, which reduced the SCC sensitivity relative to the CC alloy. Therefore, EW62 in the form of a rapidly solidified extruded structure may serve as a biodegradable implant for biomedical applications.

Increased corrosion resistance of the AZ80 magnesium alloy by rapid solidification.

Magnesium (Mg) and Mg-alloys are being considered as implantable biometals. Despite their excellent biocompatibility and good mechanical properties, their rapid corrosion is a major impediment precluding their widespread acceptance as implantable biomaterials. Here, we investigate the potential for rapid solidification to increase the corrosion resistance of Mg alloys. To this end, the effect of rapid solidification on the environmental and stress corrosion behavior of the AZ80 Mg alloy vs. its conventionally cast counterpart was evaluated in simulated physiological electrolytes. The microstructural characteristics were examined by optical microscopy, SEM, TEM, and X-ray diffraction analysis. The corrosion behavior was evaluated by immersion, salt spraying, and potentiodynamic polarization. Stress corrosion resistance was assessed by Slow Strain Rate Testing. The results indicate that the corrosion resistance of rapidly solidified ribbons is significantly improved relative to the conventional cast alloy due to the increased Al content dissolved in the α-Mg matrix and the correspondingly reduced presence of the ß-phase (Mg17 Al12 ). Unfortunately, extrusion consolidated solidified ribbons exhibited a substantial reduction in the environmental performance and stress corrosion resistance. This was mainly attributed to the detrimental effect of the extrusion process, which enriched the iron impurities and increased the internal stresses by imposing a higher dislocation density. In terms of immersion tests, the average corrosion rate of the rapidly solidified ribbons was <0.4 mm/year compared with ∼2 mm/year for the conventionally cast alloy and 26 mm/year for the rapidly solidified extruded ribbons.

In vivo behavior of biodegradable Mg-Nd-Y-Zr-Ca alloy.

The aim of the this study is to evaluate the in vivo behavior of Mg-1.5%Nd-0.5%Y-0.5%Zr implants with and without 0.4%Ca in comparison with inert Ti-6Al-4V reference implants. This was carried out by implanting cylindrical disks at the back midline of Wister male rats within the subcutaneous layer of the skin for up to 12 weeks. The degradation of magnesium-based implants in terms of hydrogen gas bubble formation was evaluated by radiography assessment; corrosion rate was analyzed by visual examination and weight loss measurements. The physiological response of the rats post-implantation was obtained by evaluating their wellbeing behavior and blood biochemical analysis including serum Mg, blood urea nitrogen, and serum creatinine. In addition, histological analyses of the soft tissue around the implants were carried out to assess local lesions relating to the implants such as inflammation, tissue necrosis, granulation, mineralization, and tumor development. The results obtained clearly indicate that apart from the normal degradation characteristics and subsequent formation of hydrogen gas bubbles, the in vivo behavior of Mg implants was adequate and comparable to that of Ti-6Al-4V reference alloy. In addition, it was evident that the corrosion degradation of the magnesium alloys was strongly related to the location of the implant within the animal's body. The addition of 0.4%Ca improves the biodegradation corrosion resistance of the tested magnesium implants.