The study will examine the results of the use of biological materials (allogeneic arterial grafts, allogeneic venous graft, autologous vein, biological bovine decellularized graft) as a bypass grafts for reconstructive interventions in patients with critical lower limb ischemia due to atherosclerotic peripheral arterial disease in the short-term and long-term postoperative periods. Histological analysis of allogeneic grafts will be carried out at various time points of graft preservation with a Roswell Park Memorial Institute 1640 cell medicum with 400mcg/ml gentamicin and 20mcg/ml fluconazole at a temperature of +4C. The physical properties of allogeneic grafts from postmortem donors (tensile and tear strength) will be evaluated at various conservation time periods (1 week, 2 weeks, 3 weeks, 4 weeks, 5 weeks, 6 weeks). Markers of endothelial dysfunction (IL-6, endothelin-1, 6-keto-prostaglandin F1alfa, eNOS) will be evaluated in patients with critical ischemia who undergo bypass procedures with arterial and venous allografts at various time points (before surgery, 7 days, 1 month, 3 months, 6 months, 1 year after).