The concept of using degradable metals in orthopedics originated over 100 years ago; however, due to a lack of adequate corrosion control, clinical use of these materials was short-lived. Recently however, advances in corrosion control have made degradable metals such as magnesium (Mg) alloys viable as craniofacial and orthopedic devices. Magnesium alloys exhibit a unique combination of strength and degradation, providing advantages over permanent metals and degradable polymers. However, difficulties remain assessing their in vivo degradation and biological effect. For this reason, we have developed a 3D model to assess degrading Mg alloys and their effect on surrounding cells and tissue in vivo.
Method:
Scaffolds consisted of Mg alloy rods within a collagen sponge seeded with human bone marrow stromal cells (hBMSC). Two commercially available Mg alloys were compared, 99.9% pure Mg and AZ31. Scaffolds were implanted subcutaneously in mice and explanted upon sacrifice eight weeks post-operative. Alloy degradation was assessed with micro-computed tomography (microCT). Biological effect of the degrading implant was assessed through histological staining.
Result:
MicroCT analysis showed greater volume loss for pure Mg when compared to AZ31 after eight weeks in vivo. Localized regions of pitting corrosion were observed on some samples. Hematoxylin and Eosin staining revealed normal tissue organization surrounding the alloys, with human cell localization at the alloy-tissue interface. Von Kossa and Alizarin Red staining showed a thin calcium and phosphate rich layer surrounding the alloys.
Conclusion:
In conclusion, this model can be used as an efficient method to screen Mg alloys based on corrosion behavior and subsequent biological effect, allowing candidate alloys for craniofacial and orthopedic device applications to be identified.