## 3 Results
### Biocompatibility In Vitro and In Vivo
#### 3.6.2 Biocompatibility In Vivo  
Additional investigation of the biocompatibility was made by implantation of the studied alloys under the skin of mice. In order to study the body reaction to the alloy, histological techniques for the investigation of the cell structure of the subcutaneous tissue adjacent to the implants were used. Blood biochemical parameters were assessed as markers of systemic toxicity. The vital parameters of mice with implanted specimens were compared with those of the intact animals. A study of mouse subcutaneous tissue morphology showed that during 2 weeks after implantation, a fibrous capsule was formed around the alloy samples. The capsule was noticeably thicker around the Fe-Mn-5 Si specimens after ECAP (Figure 12). The tissue of the capsule is infiltrated with a large number of fibroblasts and macrophages, which indicates the activation of cellular effectors of the destruction of the alloy and accompanies a moderate typical response to a foreign body. In the tissue surrounding the specimens, a significant amount of dilated blood vessels was detected, which probably contributed to the cell implementation, alloy bioresorption and elimination of their biocorrosion products. Figure 11: Biocompatibility of the Fe-Mn-5 Si alloy after annealing and ECAP treatment by assessing the change in hemolysis (**a**) and LDH Release (**b**) in comparison with the control. Accunulations of biocorrosion products were best seen around the alloy after ECAP. In general, a comparative analysis indicates that the bioresorption of the specimens after ECAP proceeded more intensively in comparison with the alloy in the annealed state, causing a more active reaction from the animal body. After implantation of alloy specimens, the skin of mice had no sign of inflammation in the area of the surgery. Therefore, the detected soft-tissue reaction was regarded as a typical process associated with the formation of granulations, aimed at healing the damage in the area of implantation. As a rule, the presence of this type of cellular infiltrate is accompanied by the formation of an early granulation tissue, and after a while, the number of cells decreases markedly. As shown above, the accumulation of degradation products were observed in animal tissues after implantation of the studied alloy samples. It can be assumed that degradation products will enter the blood with the interstitial fluid and macrophages that phagocytized them. Degradation products accumulate in the excretory organs (liver, kidney etc.) and can induce toxic effects, which will lead to organ dysfunction and changes in biochemical markers. To study liver function, bilirubin and albumin were assessed in blood serum, and urea and creatinine were assessed for kidney function. The obtained data were compared with the results of intact animals in the control group (Table 5). Figure 12: Mouse subcutaneous tissue adjacent to Fe-Mn-5 Si alloy implants in the annealed state (**a,b**) and after ECAP treatment (**c,d**). IT—implant/tissue contact area; C—restrictive capsule; BV—blood vessels. CP—corrosion products; M—macrophages. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**Intact Animals**} & \multicolumn{5}{c}{**After Implantation of Fe-Mn-5 Si Alloy Samples**} \\ \cline{3-6}  & & **After Annealing** & \(p\) * & **After ECAP** & \(p\) * \\ \hline Bilirubin, \(\mu\)mol/L & 6 \(\pm\) 4 & 3 \(\pm\) 2 & 0.55 & 6 \(\pm\) 4 & 1.00 \\ \hline Urea, U/L & 4 \(\pm\) 4 & 6 \(\pm\) 2 & 0.69 & 6 \(\pm\) 4 & 0.75 \\ \hline Creatinine, U/L & 79 \(\pm\) 11 & 68 \(\pm\) 14 & 0.58 & 80 \(\pm\) 16 & 0.96 \\ \hline Albumin, g/L & 39 \(\pm\) 8 & 35 \(\pm\) 10 & 0.78 & 37 \(\pm\) 7 & 0.86 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Blood parameters of mice after implantation of the Fe-Mn-5 Si alloy samples after annealing and after ECAP in comparison with intact animals (2 weeks after implantation).