## 2 Materials and Methods  
Production of polyurethane. Polyurethane was made from a prepolymer (urethane prepolymer based on simple polyester and toluene diisocyanate) and crosslinking agent (hardener MOCA--13.2%, plasticizer polyfurite--84.7%, catalyst voranol--2.1%) in a mass ratio of 100:47. The components were heated to 80 \({}^{\circ}\)C and evacuated. The mixture was cured in a mold with an open top at 40 \({}^{\circ}\)C for 24 h. The initial elastic modulus measured by uniaxial mechanical test was 8 MPa, elongation at break--900%. Plasma treatment. The internal two-phase structure of polyurethane is naturally covered by a nanolayer of soft fraction [27]. Low-energy plasma treatment of such surface will only affect this soft layer. Therefore, the surface was pretreated (activated) in plasma of argon for 30 s; studies have shown the etching of the upper layer. Then this surface was treated in argon/acetylene plasma. The entire treatment cycle is the following: The chamber was evacuated to a pressure of 5 \(\times\) 10\({}^{-5}\) Torr. Argon pressure of 2 \(\times\) 10\({}^{-3}\) Torr was set and a glow discharge was ignited in a low-energy source of an electron beam. The accelerating voltage of electron source was set to 100 V and the discharge--1 A. After treatment in Ar plasma for 30 s, C\({}_{2}\)H\({}_{2}\) was pumped into the working chamber at a flow rate of 1 cm\({}^{3}\)/min. Samples were exposed to Ar/C\({}_{2}\)H\({}_{2}\) plasma for 30, 60 or 120 s.  
After Ar/C\({}_{2}\)H\({}_{2}\) modification, a portion of the samples was post-treated in argon plasma. For this reason, the C\({}_{2}\)H\({}_{2}\) flow was stopped and the Ar plasma treatment was continued for 30 s. The purpose of this post-treatment was the possible reactivation of the surface. Sorption of albumin. An aqueous solution of 1 mg/mL of human albumin (Biolot, Saint Petersburg, Russia) was used. The samples were thermostatted in the solution at 37 \({}^{\circ}\)C for 2 h. Concentration of albumin attached to the surface was determined by UV1080 spectrophotometer (Shimadzu, Kyoto, Japan) at 280 nm as the difference between control (clear solution) and experimental concentrations. Wetting and free surface energy. The wetting contact angle was determined by a sessile drop method. Water and diethylene glycol were used as test liquids (we did not use diiodmethane, since this and other solvents react with the polymer); the drop sizes were 2-3 mm. The free surface energy was calculated by the Owens\(-\)Wendt\(-\)Rabel\(-\)[PERSON] method as the sum of the dispersion (accounts van der Waals interactions) and polar (dipole interactions and energy of hydrogen bonds) components. It is known that surface activity of a plasma-treated surface falls to equilibrium for several days, thus the wetting measurements were conducted ten days after the treatment. Raman spectroscopy. Raman spectra were obtained on a Bruker Santerra dispersive spectrometer with the following parameters: wavelength of the excitation laser--532 nm; duration of accumulation--1 s; number of accumulations--1600; aperture--25 \(\times\) 1000 \(\upmu\)m. The power of radiation was limited to 0.2 mW preventing destruction of the soft polymer. The baseline was aligned using the adaptive method in the SpectraGryph software. Atomic force microscopy. The surfaces were examined by an atomic force microscope (AFM) Ntegra Prima (NT-MDT BV, Apeldoorn, the Netherlands) in dynamic and static indentation modes. Probes with calibrated tip geometry and stiffness \(k\) of the cantilever were used. Undeformed surfaces as well as materials in static tensile state were investigated. In the dynamic indentation regime the probe (\(k\) = 0.5 nN/nm, tip radius \(R\) = 4 nm) with high frequency (-0.5 kHz) presses the surface with a small force of -5 nN, which does not damage the coating. As a result, each point of the surface has its own force interaction curve; their study gives the physical and mechanical properties of the surface.