Biodegradable Fe-based alloys for use in osteosynthesis: outcome of an in vivo study after 52 weeks.

This study investigates the degradation performance of three Fe-based materials in a growing rat skeleton over a period of 1 year. Pins of pure Fe and two Fe-based alloys (Fe-10 Mn-1Pd and Fe-21 Mn-0.7C-1Pd, in wt.%) were implanted transcortically into the femur of 38 Sprague-Dawley rats and inspected after 4, 12, 24 and 52 weeks. The assessment was performed by ex vivo microfocus computed tomography, weight-loss determination, surface analysis of the explanted pins and histological examination. The materials investigated showed signs of degradation; however, the degradation proceeded rather slowly and no significant differences between the materials were detected. We discuss these unexpected findings on the basis of fundamental considerations regarding iron corrosion. Dense layers of degradation products were formed on the implants' surfaces, and act as barriers against oxygen transport. For the degradation of iron, however, the presence of oxygen is an indispensable prerequisite. Its availability is generally a critical factor in bony tissue and rather limited there, i.e. in the vicinity of our implants. Because of the relatively slow degradation of both pure Fe and the Fe-based alloys, their suitability for bulk temporary implants such as those in osteosynthesis applications appears questionable.

Degradation performance of biodegradable Fe-Mn-C(-Pd) alloys.

Biodegradable metals offer great potential in circumventing the long-term risks and side effects of medical implants. Austenitic Fe-Mn-C-Pd alloys feature a well-balanced combination of high strength and considerable ductility which make them attractive for use as degradable implant material. The focus of this study is the evaluation of the degradation performance of these alloys by means of immersion testing and electrochemical impedance spectroscopy in simulated body fluid. The Fe-Mn-C-Pd alloys are characterized by an increased degradation rate compared to pure Fe, as revealed by both techniques. Electrochemical measurements turned out to be a sensitive tool for investigating the degradation behavior. They not only show that the polarization resistance is a measure of corrosion tendency, but also provide information on the evolution of the degradation product layers. The mass loss data from immersion tests indicate a decreasing degradation rate for longer times due to the formation of degradation products on the sample surfaces. The results are discussed in detail in terms of the degradation mechanism of Fe-based alloys in physiological media.