In vitro and in vivo corrosion of the novel magnesium alloy Mg–La–Nd–Zr: influence of the measurement technique and in vivo implant location

For the evaluation of new magnesium-based alloys, many different in vitro and in vivo methods are used. It was the aim of the current study to perform in vitro and in vivo corrosion studies of the new alloy Mg-La-Nd-Zr for its evaluation as a promising new degradable material and to compare commonly used evaluation methods. Die casted and subsequent extruded cylindrical pins (Ø1.5 mm; length 7 mm, [Formula: see text]) were implanted subcutaneously ([Formula: see text]), intramuscular ([Formula: see text]) and intramedullary ([Formula: see text]) in female Lewis rats with a postoperative follow up of 8 weeks; subsequent μ-computed tomographical analyses (XTremeCT and μCT80) were performed as well as weight analysis prior to and after implantation. Cubes (5 mm  ×  4 mm  ×  4 mm; surface area, 1.12 cm(2); [Formula: see text]) were used for in vitro corrosion (HBSS and RPMI 1640 + 10% FBS medium) and cytocompatibility studies (L929 cells). First of all it could be stated that implant location strongly influences the in vivo corrosion rate. In particular, intramedullary implanted pins corroded faster than pins in a subcutaneous or intramuscular environment. Considering the different evaluation methods, the calculated ex vivo μCT-based corrosion rates resulted in comparable values to the corrosion rates calculated by the weight loss method, especially after chromatic acid treatment of the explanted pins. The in vitro methods used tend to show similar corrosion rates compared to in vivo corrosion, especially when a RPMI medium was used, and therefore are suitable to predict corrosion trends prior to in vivo studies. Regarding cytocompatibility, the novel magnesium alloy Mg-La-Nd-Zr showed sufficient cell viability and therefore can be considered as a promising alloy for further applications.