In vivo characterization of magnesium alloy biodegradation using electrochemical H 2 monitoring, ICP-MS, and XPS

• Published in: Acta biomaterialia 2017-03, Vol.50, p.556
• Main Authors: Zhao, Daoli, Wang, Tingting, Nahan, Keaton, Guo, Xuefei, Zhang, Zhanping, Dong, Zhongyun, Chen, Shuna, Chou, Da-Tren, Hong, Daeho, Kumta, Prashant N, Heineman, William R
• Format: Article
• Language: English
• Subjects: Absorbable Implants; Alloys - chemistry; Animals; Electrochemical Techniques - methods; Hydrogen - analysis; Magnesium - chemistry; Mice, Nude; Photoelectron Spectroscopy; Spectrophotometry, Atomic; Tissue Distribution; X-Rays; Zinc - analysis
• ISSN: 1878-7568
• DOI: 10.1016/j.actbio.2017.01.024

The effect of widely different corrosion rates of Mg alloys on four parameters of interest for in vivo characterization was evaluated: (1) the effectiveness of transdermal H measurements with an electrochemical sensor for noninvasively monitoring biodegradation compared to the standard techniques of in vivo X-ray imaging and weight loss measurement of explanted samples, (2) the chemical compositions of the corrosion layers of the explanted samples by XPS, (3) the effect on animal organs by histology, and (4) the accumulation of corrosion by-products in multiple organs by ICP-MS. The in vivo biodegradation of three magnesium alloys chosen for their widely varying corrosion rates - ZJ41 (fast), WKX41 (intermediate) and AZ31 (slow) - were evaluated in a subcutaneous implant mouse model. Measuring H with an electrochemical H sensor is a simple and effective method to monitor the biodegradation process in vivo by sensing H transdermally above magnesium alloys implanted subcutaneously in mice. The correlation of H levels and biodegradation rate measured by weight loss shows that this non-invasive method is fast, reliable and accurate. Analysis of the insoluble biodegradation products on the explanted alloys by XPS showed all of them to consist primarily of Mg(OH) , MgO, MgCO and Mg (PO ) with ZJ41 also having ZnO. The accumulation of magnesium and zinc were measured in 9 different organs by ICP-MS. Histological and ICP-MS studies reveal that there is no significant accumulation of magnesium in these organs for all three alloys; however, zinc accumulation in intestine, kidney and lung for the faster biodegrading alloy ZJ41 was observed. Although zinc accumulates in these three organs, no toxicity response was observed in the histological study. ICP-MS also shows higher levels of magnesium and zinc in the skull than in the other organs. Biodegradable devices based on magnesium and its alloys are promising because they gradually dissolve and thereby avoid the need for subsequent removal by surgery if complications arise. In vivo biodegradation rate is one of the crucial parameters for the development of these alloys. Promising alloys are first evaluated in vivo by being implanted subcutaneously in mice for 1month. Here, we evaluated several magnesium alloys with widely varying corrosion rates in vivo using multiple characterization techniques. Since the alloys biodegrade by reacting with water forming H gas, we used a recently demonstrated, simple, fast and noninva