In vivo assessment of frictional pain from skin surface to brain activation

Skin pain induced by friction is common in various skin–product interactions. In this study, interactions between residual limb skin and prosthetic sockets were taken into account to investigate the underlying mechanism of skin pain induced by interfacial friction. Subjective evaluation, in vivo tribological behaviors, and neurophysiological responses of the brain were studied systematically. The results demonstrated that frictional pain was subjected to a combination of the friction coefficient and the mechanical characteristics of the anatomic regions and contact materials. The impact of friction on skin pain should be assessed on the basis of the selection of anatomic regions and contact materials. Stronger frictional stimulation can induce higher neural signals to be converted by nociceptors, leading to greater potential for T cells to be modulated and processed by the spinal dorsal horn. The main types of brain activation associated with frictional pain were found in the primary somatosensory cortex, secondary somatosensory cortex, and prefrontal cortex. Negative brain activation was evoked, and the activation area decreased during frictional pain. Compared with no pain stimulation, an increase in γ-band oscillations of electroencephalogram (EEG) signals was observed under mild- or moderate-pain conditions. This study is helpful for understanding the mechanisms of frictional pain from the skin surface to the brain to avoid further skin injury in various skin–product interactions and to provide theoretical guidance for the use of prosthetics.