Long-term in vivo degradation behaviour and biocompatibility of the magnesium alloy ZEK100 for use as a biodegradable bone implant

Magnesium alloys are the focus of research as resorbable materials for osteosynthesis, as they provide sufficient stability and would make surgery to remove implants unnecessary. The new degradable magnesium alloy ZEK100 was developed to improve the stability and corrosion resistance by alloying with zinc, rare earth metals and zirconium. As the implants were degraded to only a limited extent after 6 months implantation in a previous in vivo study the present study was conducted to evaluate the long-term degradation behaviour and biocompatibility in the same animal model over 9 and 12 months. Five rabbits each with intramedullary tibia implants were examined over 9 and 12 months. Three legs were left without an implant to serve as negative controls. Numerous examinations were performed in the follow-up (clinical examinations, serum analysis, and radiographic and in vivo micro-CT investigations) and after death (ex vivo micro-CT, histology, and implant analysis) to assess the in vivo degradation and biocompatibility. It could be shown that favourable in vivo degradation behaviour is not necessarily associated with good biocompatibility. Although ZEK100 provided a very high initial stability and positive biodegradation, it must be excluded from further biomedical testing as it showed pathological effects on the host tissue following complete degradation.