Tribological behavior of orthopedic foams/artificial skin systems: the effect of morphology, mechanical properties and surface free energy

The discomfort associated to the use of orthosis results mainly from friction between the coating material, in this case the foams, and human skin. Although, nowadays the use of such devices is common, there is few information concerning the influence of the properties of the foams in the tribological behavior of the orthosis. In this study it was investigated the effect of the morphology, mechanical properties and surface free energy in the values of friction coefficients of orthopedic foams/artificial skin systems. The artificial skin was characterized using different techniques such as, atomic force microscopy (AFM) for analyzing the topography and the sessile drop method to determine its wettability. Seventeen different commercial orthopedic foams were selected, and characterized concerning the morphology of their cells by scanning electron microscopy (SEM), surface free energy from wetting measures (sessile drop method) and mechanical properties through compressiondecompression tests. Nanotribological tests were performed between the artificial skin and the foam, with the application of various loads. The results show that the increase in cell size and in the Young's modulus of the foams leads to a reduction in friction coefficients. In contrast, the increase in the surface free energy origins an increase in the friction coefficient. Key-words: friction, artificial skin, orthopedic foams, morphology, mechanical properties and surface free energy.