## 1 Introduction  
To date, a sufficient number of methods of plasma modification of polymers, for improving their biomedical characteristics, have been proposed. One way or another, the treatment affects wettability, free surface energy, chemical structure, and surface topography. As a result, sorption of \"good\" proteins (e.g., albumin [1, 2]) can be improved, which, in turn, affects cell adhesion [3, 4]; in certain cases, the amount of \"bad\" proteins, such as fibrinogen, responsible for thrombosis, is reduced [5, 6]. Antibacterial properties may be enhanced due to changes in relief structure [7], wettability [8], and surface chemistry [9]. However, the stiffness of the modified surface often increases. Under certain treatment conditions, when the elastic modulus of the modified layer exceeds that of the polymer material, the surface loses its stability, forming a wrinkled topography. The chaotic structure of the wrinkles has a positive antibacterial effect [10]. This phenomenon has also been found in applications in metrology [11], the development of smart materials [12], and flexible electronics [13]. However, the application of such materials is associated with mechanical loads that provoke the following defects in the treated surfaces: strain-induced cracks and folds [14; 15; 16; 17]. Under cyclic loads, even tiny nanocracks propagate to a considerable depth [18], damaging both the polymer and the surrounding tissues; the formed defects become centers of bacterial growth [10].  
Low-energy treatment of the polymer in gaseous plasma, such as argon [19], nitrogen [20], or oxygen [21], is one of the solutions to the problem of the destruction of the modified surface. Note that treatment in plasma of inert gas affects not only the physicochemical properties of the surface, but may reduce the internal stresses in the modified layer [22]. Another way of improving the deformability of coatings is by creating discontinuous (island-like) coatings by plasma chemical deposition of certain species. In particular, the deposition of carbon [23] is of interest. The carbon structure of the coating depends on the choice of carbon-containing reaction gas, treatment, and substrate; diamond-like carbon films [24], fluorocarbons [25], nanotubes, nanofibers, and nanodiamonds [26] may be achieved. The initial stage of coating growth is the nucleation of cores (grains, islets [26]) of the further uniform layer. This stage is of the greatest interest, as it potentially allows deformable heterogeneous coatings with promising properties to be obtained.  
Polyurethanes are widespread polymers in many applications; their physical and mechanical properties are determined by the peculiarities of manufacturing. This is a two-phase system consisting of hard blocks in a softer matrix. The aim of this work was to study the changes in the surface properties of polyurethane under the action of argon/acetylene plasma; as a result, carbon-containing nanostructures are formed on the surface. The sorption activity of albumin, as well as the surfaces of the materials in the tensile state, was investigated. The effect of argon post-treatment on modified surfaces is discussed (it is known that argon increases surface activity and may relieve internal stresses in the modified layer).