Experimental assessment of friction coefficient between polypropylene and human skin using instrumented sclerometer

Prosthetic devices are used to restore as much as possible not only the functionality, but also the self-esteem of patients who have been submitted to amputation surgeries. Typically, lower limb prostheses need a socket to act as a link with the human stump, so the contact stresses at the socket–stump interface are critical for the recovery process and the subsequent comfort perception of the patient as well. In this work, a broad experimentation to establish the coefficient of friction (COF) between socket material (polypropylene) and human skin was developed with the aid of an instrumented sclerometer, which was adapted to put in contact a polypropylene probe with human forearms. Seven factors were considered, but only sweat and hair skin were found to have a significant effect on COF, which varied from 0.22 to 0.45 in the tests. Lower values of COF were obtained when sweat was present at the interface, while the absence of both sweat and hair skin led to the highest value. The results are believed to be relevant for developing reliable finite element (FE) models for socket–stump interaction since the relation between normal and shear stresses at the interface of two interacting bodies is strongly determined by the COF.