Optimisation of Fe-Mn-C steels for biodegradable vascular implant applications

The demand for advanced clinical treatments for various soft and hard tissue injuries and diseases has led to the development of innovative biodegradable implant materials. Compared to their non-degrading counterparts, implants made of biodegradable polymers or metals degrade progressively after providing temporary support during the healing process of diseased tissue. Besides Mg- and Zn-based systems, Fe-alloys are attractive candidates for metal-based degradable medical devices [1]. For the latter, especially Fe-Mn-C steels are promising as they offer a favourable combination of high ductility, stiffness and strength together with excellent processability. This makes them especially suitable for ultra-thin cardiovascular stent designs with low blood flow disturbance and minimal foreign material insertion. For such use cases, understanding the correlation between processing, microstructure, and the resulting mechanical as well as degradation performance is essential for successful material development.

 

The presentation will give insight into the characterisation of promising Fe-Mn-C steels, which were fabricated by a tailored hot forging process route. The microstructure was analysed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods, including electron backscatter diffraction (EBSD). The steels were verified to be austenitic, having comparable grain size distributions in the hot forged condition. The mechanical properties that are relevant for vascular implants were characterised by uniaxial tensile and ultrasonic tests. For the investigated mechanical parameters, the Fe-Mn-C steels demonstrated superior performance compared to the benchmark medical steel AISI 316L [2]. The material in vitro degradation behaviours were characterized electrochemically in simulated body fluids under well-defined hydrodynamic flow conditions. Degradation surface analysis was performed using microscopy and spectroscopy methods to gain further insight into the degradation mechanisms. Additionally, a novel remotely controlled smart Fe-Mn-C implant design was developed in an interdisciplinary collaboration [3]. As a result of these studies, improved mechanical and degradation properties were achieved, which flatten the path to the intended vascular implant applications.

 

References

 

[1] H.S. Han, S. Loffredo, I. Jun, J. Edwards, Y.C. Kim, H.K. Seok, F. Witte, D. Mantovani, S. Glyn-Jones, Current status and outlook on the clinical translation of biodegradable metals, Mater. Today. 23 (2019) 57–71.

 

[2] M. Otto, J. Freudenberger, L. Giebeler, A. Weidner, J. Hufenbach, Developing austenitic high-manganese high-carbon steels for biodegradable stent applications: Microstructural and mechanical studies, Mater. Sci. Eng. A. 892 (2024) 145998.

 

[3] B. Rivkin, F. Akbar, M. Otto, L. Beyer, B. Paul, K. Kosiba, T. Gustmann, J. Hufenbach, M. Medina-Sánchez, Remotely Controlled Electrochemical Degradation of Metallic Implants, Small. 2307742 (2024) 1–14.