applied sciences  
Biocompatibility and Degradation of Fe-Mn-5 Si Alloy after Equal-Channel Angular Pressing: In Vitro and In Vivo Study  
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A.A. Baikov Institute of Metallurgy and Materials Science of the Russian Academy of Sciences,  
119334 Moscow, Russia; [EMAIL_ADDRESS] (O.R. ); [EMAIL_ADDRESS] (N.M.); [EMAIL_ADDRESS] (L.S. ); [EMAIL_ADDRESS] (E.L.); [EMAIL_ADDRESS] (O.C. ); [EMAIL_ADDRESS] (S.D.) N.N. Blokhin National Medical Research Center of Oncology (N.N. Blokhin NMRCO) of the Ministry of Health of the Russian Federation, 115478 Moscow, Russia; [EMAIL_ADDRESS] (E.K. ); babaevgualy  
on Fe [4; 5; 6], such as alloys of the Fe-Mn-Si system. For the vast majority of alloys with SME, such as Ti-Ni, including those based on Fe (Fe-Pt, Fe-Ni-Co-Ti, etc. ), SME occurs due to thermoelastic martensitic phase transformation. The SME in Fe-Mn-Si alloys arises as a result of stress-induced \(\gamma\) (fcc) \(\rightarrow\)\(\varepsilon\) (hcp) martensitic transformation, followed by reverse transformation on heating. The SMEs of the Fe-Mn-Si system have been constantly studied since their discovery [7; 8; 9]. This system is expected to be a promising alternative to Ti-Ni based shape memory alloys. One of its important advantages is degradation, which helps to avoid repeated surgical intervention to remove the implant, reducing the risk of side effects due to long-term use. The effective use of Fe-based bioresorbable SME alloys in medicine requires them to meet relevant criteria. Bioresorbable materials for biomedical applications are expected to have a mechanical strength of \(\geq\)200 MPa with a corresponding elongation of \(\geq\)10% [10]. It is fair to note that Fe-Mn-Si alloys with SMA have satisfactory strength and ductility, despite the fact that Si impairs the ductility of the material. For example, the Fe-30 Mn-6 Si alloy has a tensile strength of 453 MPa and a relative elongation of 16.5% [6]. At the same time, in Fe-Mn-Si alloys, Young's modulus is quite high compared to that of the human bones, which adversely affects the biomechanical compatibility of the implanted device and the bone [11]. However, Young's modulus can gradually decrease with increasing degradation time [12], as well as with the application of appropriate processing [13; 14; 15]. So far, several studies on the degradation and biocompatibility of Fe-based SMA have been reported [4; 6; 16]. In [6], the corrosion resistance of Fe-Mn-Si alloy with SME, Fe-Mn alloy and pure Fe was studied by the method of potentiodynamic polarization in the Hanks solution. It was found that the Fe-Mn-Si alloy exhibited the lowest corrosion potential and the highest corrosion current density, indicating the lowest corrosion resistance among the studied materials. In [17], this behavior was explained by the lower corrosion resistance of the austenitic and martensitic phases in the Fe-Mn-Si alloy compared to the ferrite of pure Fe. Fe-Mn-Si alloys exhibit satisfactory in vitro degradation characteristics compared to pure Fe [13; 18]. The in vitro cytotoxicity test carried out in [6] demonstrated satisfactory biocompatibility of Fe-Mn-Si alloys. Studies [19; 20] showed biocompatibility in vivo with the preservation of the mechanical integrity of the Fe-Mn-Si alloy. At the same time, [21] reported on the weight loss of the Fe-Mn-Si implant after a two-week implantation in the rat tibia without specifying the exact corrosion rate in vivo. However, their corrosion rate is much lower than that of the Mg-based alloys. After confirming acceptable degradation and biocompatibility in Fe-based SMA alloys, attempts to change the composition of these alloys in order to increase the corrosion rate required for the manufacture of bioresorbable implants were made [12; 22; 23].