Modeling of the use of AFM in the study of polyurethane samples with a carbonized surface

Abstract

One of the most important characteristics of polyurethane endoprostheses used in modern medical practice is the quality of their surface. As a rule, such products are coated with a special carbonized nanolayer to improve biocompatibility with living tissue. In terms of mechanical properties, these layers are not as flexible as polyurethane and are prone to brittle microdamage. Therefore, a reliable determination of the presence and distribution of microcracks in the nanocarbon layer on the surface of an endoprosthesis is an important factor for assessing the biocompatibility and possible injury to living tissues in the contact zone. The article presents the results of computer simulation of an AFM probe contact interaction with polyurethane samples having a carbonized nanocoating. The main goal of the study was to find an answer to the question whether it is possible to determine the presence of microdamages in polyurethane hidden under a carbonized coating using atomic force microscopy, and to classify them. Obviously, their presence can significantly aggravate the damaging effect of surface cracks on living biological tissue during the deformation of an endoprosthesis. Three cases of local microdamages that can occur in such samples are considered: a) there is a vertical crack in the carbon nanolayer, no damage in polyurethane; b) a cohesive damage of polyurethane (a vertical crack) was added to the vertical crack in the nanolayer; c) an adhesive delamination between the layer and polyurethane (a horizontal crack) was added to the vertical crack in the nanolayer. Computer modeling has shown that using atomic force microscopy, it is possible to quite accurately determine the presence of microcracks in the surface carbon nanolayer, while microdamages of the polyurethane itself, hidden under it, have a much weaker effect on nanoindentation.