In Vivo Evaluation of ZnAg3—A New Bioabsorbable Material in Fracture Treatment Compared to Biodegradable Mg Alloys

Permanent implants, which are primarily used to treat fractures, are either removed during a subsequent procedure or remain in the body after being surgically inserted. Bioabsorbable implants are designed to be reabsorbed by the body, minimizing the risk of chronic infections or foreign body reactions. The qualification of a novel zinc-silver alloy containing 3.3 wt% silver (ZnAg3) as a bioabsorbable implant was investigated in this in vivo study on New Zealand white rabbits. The osteointegration of ZnAg3 pins and MAGNEZIX pins, which served as controls, was evaluated histomorphometrically and histologically at 4, 8, and 16-week intervals. The implant area and the osteoid area were measured in order to assess the degradation of the material as well as the bone formation. The histological evaluation included a cell count of osteogenic cells and a descriptive evaluation of the histological images. The animal trial was accompanied by frequent blood, urine, and X-ray tests. The results showed adequate degradation of ZnAg3 with an implant area of 93.92% ± 5.85% at week 16 and a sufficient number of osteogenic cells, allowing progressive osteointegration. In comparison, the MAGNEZIX pin degraded significantly faster and, after 16 weeks, diminished to 77.54% ± 13.59% of the original implant area. Furthermore, harmful hydrogen gas pockets were found, which correlated with reduced bone formation, represented by a lower cell count of osteoblasts after 4 weeks. ICP-OES measurements performed on the animals' blood samples did not reveal any increased metal ion concentrations above the tolerable level. Thus, ZnAg3 pins showed excellent results compared to MAGNEZIX pins, which are in clinical use as bioabsorbable implants.