PSI - Issue 18

S.V. Slovikov et al. / Procedia Structural Integrity 18 (2019) 198–204 S.V. Slovikov and O.A.Staroverov / Structural Integrity Procedia 00 (2019) 000–000

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Diagrams 1 and 3 shown in Fig. 1(с) are characteristic of knitted meshes of appropriate weight and porosity, even with slightly different weaving. The aponeurosis of the abdominal cavity is modeled by creating a thin shell with a diameter of 300 mm inside which created pressure corresponding to the pressure in the IAP from 1 kPa to 7 kPa. The installed mesh was modeled with a thin membrane with a diameter of 80 mm. Internal pressure is applied uniformly over both areas. It is assumed that when restoring aponeurotic tissue, the method of non-tensioned hernioplasty is used, that is, there are no forces and corresponding strains in the aponeurotic tissue under the mesh. In practice, the situation is less dangerous and depends on the state of the tissue splicing process. But the analysis assumes that the normal state is when strain in the tissues of the aponeurosis is as close as possible to the fields of strain in the surgical mesh. The strain in the meridian direction seems to be critical if the axis passing through the centers of the studied areas is taken as the polar direction. When installing both “light” and “heavy” meshes and a pressure of 1 kPa: the strain field in the meridian direction is uniform and amounts to 1.5 - 2%; at 2 kPa: 2.5% in around the borders and 3% in areas remote from the borders. At a pressure of 3 kPa, zones of increased deformation begin to appear when using a “heavy” mesh. The field of meridian membrane strains using a “heavy” mesh with a diameter of 80 mm and a pressure of 4 kPa are presented in Fig.2. In this case, due to the greater rigidity of the mesh on soft tissues, increased strains occur, which can lead to the emergence of new tissue defects. Without a mesh, the strain at 4 kPa is 6%, and with the “heavy” mesh installed, it reaches 11%. Thus, with the mechanical behavior of the materials described by the diagrams presented in Fig. 1c, areas of increased strains on the aponeurotic tissue occur up to 11%, which can lead to accelerated wear over time, since, presumably, the fibers with such values of strain unfold almost completely ( this is evident from the change in the slope of the stretching diagram of the aponeurosis) in the plates, the fibers of which are located coaxially with the meridian direction.

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Fig. 2. (a) field of meridian strain when using a “heavy” surgical mesh and pressure of 4 kPa; (b) field of meridian strain when using of a “light” surgical mesh and pressure of 4 kPa; (c) field of meridian strain with the use of a “light” grid and a pressure of 6 kPa.

With the same pressure value of 4 kPa, but using the “light” mesh, the strain fields are obtained as shown in Fig. 2b. The strain field with the use of a “light” grid and a pressure of 6 kPa is shown in Fig. 2c. At this pressure, the stiffness of the tissues of the aponeurosis becomes greater than the stiffness of the mesh. There are increased strains in the area of the mesh, and if this does not lead to the destruction of the mesh, it will have a negative effect on the restored living tissues in the area of the hernial defect. The actual strain field on living organisms is certainly much more complicated as shown, for example, when analyzing the use of various meshes for rabbits by Simón-Allué et al. (2018). Podwojewski et al. (2014), Tran et al. (2014) use the Vic 3D video system (the digital image correlation method) on the abdominal cavity under pressure. At the same time, for an approximate analysis and understanding of the effect of the established mesh on the strain of soft tissues, it is possible to use the presented approximate modeling. As it is known, the structure of the abdomen area includes skin, subcutaneous fat, tissue of aponeurosis, muscles, peritoneum (Hanley et al., 1999). The tissues of the aponeurosis and muscles carry load. Apparently, in the region of