Thermal modulation of skin friction at the fingertip

Preliminary human studies show that reduced skin temperature minimises the risk of mechanically-induced skin damage. However, the mechanisms by which cooling enhances skin tolerance to pressure and shear remain poorly understood. We hypothesized that skin cooling below thermo-neutral conditions will decrease friction at the skin-material interface. To test our hypothesis, we measured the friction coefficient of a thermally pre-conditioned index finger sliding at a normal load (5N) across a plate maintained at three different temperatures (38, 24, and 16{square}). To quantify the temperature distribution of the skin tissue, we used 3D surface scanning and Optical Coherence Tomography to develop an anatomically-representative thermal model of the finger. Our data indicated that the sliding finger with thermally affected tissues (up to 8mm depth) experienced significantly (p<0.01) lower frictional forces at 16{degrees}C-plate temperature than at the 24{degrees}C [-23% ({+/-}19% SD)] and 38{degrees}C plate interactions [-35% ({+/-}11% SD)], respectively. This phenomenon occurred without changes in skin hydration during sliding. Accordingly, our experiments demonstrate thermal modulation of skin friction in the absence of skin-moisture effects. Our complementary experimental and theoretical results provide new insight into thermal modulation of skin friction that can be employed for developing thermal technologies to maintain skin integrity under mechanical loading.