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 interface 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 effect of friction coefficient and the mechanical characteristics of anatomic regions and contact materials. The impact of friction on skin pain should be assessed based on the selection of anatomic regions and contact materials. Stronger frictional stimulation can induce higher neural signals to be converted by nociceptors, leading to a higher potential of T-cell to be modulated and processed by the spinal dorsal horn. The main brain activation associated with frictional pain were found in the primary somatosensory cortex, secondary somatosensory cortex, and prefrontal cortex. The brain negative activation was evoked, and the activation area decreased during frictional pain. Compared with no pain stimulation, an increase in γ oscillations of EEG signals was observed in mild or moderate pain conditions. This study is helpful for understanding the mechanisms of frictional pain from the skin surface to brain response and to avoid further skin injury in various skin-product interactions as well as to provide theoretical guidance for the use of prosthetics.