Effects of Altering Magnesium Metal Surfaces on Degradation In Vitro and In Vivo during Peripheral Nerve Regeneration

Rigwed Tatu; Leon G White; Yeoheung Yun; Tracy Hopkins; Xiaoxian An; Ahmed Ashraf; Kevin J Little; Meir Hershcovitch; David B Hom; Sarah Pixley

doi:10.3390/ma16031195

Effects of Altering Magnesium Metal Surfaces on Degradation In Vitro and In Vivo during Peripheral Nerve Regeneration

Materials (Basel). 2023 Jan 30;16(3):1195. doi: 10.3390/ma16031195.

Authors

Rigwed Tatu^{1

2}, Leon G White^{3

4}, Yeoheung Yun³, Tracy Hopkins¹, Xiaoxian An⁵, Ahmed Ashraf¹, Kevin J Little⁶, Meir Hershcovitch⁶, David B Hom^{1

7}, Sarah Pixley¹

Affiliations

¹ Department of Pharmacology & Systems Physiology, College of Medicine, University of Cincinnati, Cincinnati, OH 45267, USA.
² PSN Labs (Plastics Services Network), Erie, PA 16510, USA.
³ Department of Mechanical Engineering, Department of Bioengineering, North Carolina Agricultural & Technical State University, Greensboro, NC 27411, USA.
⁴ Northrop Grumman, Baltimore, MD 21240, USA.
⁵ Division of Pharmaceutical Sciences, James L. Winkle College of Pharmacy, University of Cincinnati, Cincinnati, OH 45229, USA.
⁶ College of Medicine, University of Cincinnati, Cincinnati, OH 45267, USA.
⁷ Head & Neck Surgery, San Diego Medical Center, University of California, San Diego, CA 92103, USA.

Abstract

In vivo use of biodegradable magnesium (Mg) metal can be plagued by too rapid a degradation rate that removes metal support before physiological function is repaired. To advance the use of Mg biomedical implants, the degradation rate may need to be adjusted. We previously demonstrated that pure Mg filaments used in a nerve repair scaffold were compatible with regenerating peripheral nerve tissues, reduced inflammation, and improved axonal numbers across a short-but not long-gap in sciatic nerves in rats. To determine if the repair of longer gaps would be improved by a slower Mg degradation rate, we tested, in vitro and in vivo, the effects of Mg filament polishing followed by anodization using plasma electrolytic oxidation (PEO) with non-toxic electrolytes. Polishing removed oxidation products from the surface of as-received (unpolished) filaments, exposed more Mg on the surface, produced a smoother surface, slowed in vitro Mg degradation over four weeks after immersion in a physiological solution, and improved attachment of cultured epithelial cells. In vivo, treated Mg filaments were used to repair longer (15 mm) injury gaps in adult rat sciatic nerves after placement inside hollow poly (caprolactone) nerve conduits. The addition of single Mg or control titanium filaments was compared to empty conduits (negative control) and isografts (nerves from donor rats, positive control). After six weeks in vivo, live animal imaging with micro computed tomography (micro-CT) showed that Mg metal degradation rates were slowed by polishing vs. as-received Mg, but not by anodization, which introduced greater variability. After 14 weeks in vivo, functional return was seen only with isograft controls. However, within Mg filament groups, the amount of axonal growth across the injury site was improved with slower Mg degradation rates. Thus, anodization slowed degradation in vitro but not in vivo, and degradation rates do affect nerve regeneration.

Keywords: PEO anodization; bioabsorbable metal; in vitro vs. in vivo; magnesium; micro-CT; peripheral nerve regeneration.

Abstract

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