Reducing the Wear of the UHMWPE Used in the Total Hip ‎Replacement after Low-Pressure Plasma Treatment

This paper discusses the problem of evaluating the microhardness gradient effect on surface wear of an ultra-high molecular weight polyethylene (UHMWPE) films treated with low-pressure plasma. Its solution was first obtained on the basis of the well-known Archard's wear law, modified taking into account the use of approximating dependences of negative depth gradients of surfaces microhardness, calculated on the basis of experimental data obtained by the nanoindentation method for samples with different plasma processing times (from 3 to 12 minutes). The wear evaluation was carried out in the ANSYS and MATLAB software in accordance with the requirements of ISO 14242-1 using the method of numerical simulation developed by authors. The simulation results show that such an integral parameter as cumulative volume wear is significantly lower for specimens treated with low-pressure plasma as compared to untreated ones. It has been found that both linear and cumulative volume wear decrease with an increase in the plasma processing time of the sample. The largest reduction (4 times compared to untreated) has been obtained for samples with a hardness gradient obtained by plasma surface treatment for 12 minutes. This time can be considered the maximum possible for processing UHMWPE with low-pressure plasma, since further increase in this time enhances the sample surface roughness and, consequently, the coefficient of friction. The use of low-pressure plasma treated UHMWPE films in THR will significantly reduce their wear and the likelihood of osteolysis, and thus increase the THR lifespan.