Temperature-Dependent Dynamic Friction of a Single Human Corneocyte at Nanoscale Contact: An Analytical Approach and Direct Measurement Using Lateral Force Microscopy for Haptic Design Insight.

Dynamic friction between human skin and a haptic surface is known to increase with the substrate temperature. When the substrate temperature reaches 60 °C, prolonged sliding contact for just 1 min can cause damage to the outer skin surface. However, the effect of the temperature on dynamic friction at the nanoscale interface between human skin cells and a nanosized probe remains inadequately quantified. This paper presents direct measurements of the dynamic friction of human skin corneocytes as a function of the AFM nanoprobe temperature, using atomic force microscopy (AFM). The lateral force microscopy (LFM) technique with a heated tip was employed to quantify the dynamic friction force of the corneocytes under a constant normal load of 10 nN and standard relative humidity (40% RH). The temperature of the heated tip was calibrated before each LFM experiment. The friction force, derived from the LFM signal data during each temperature scan, was compared to dynamic friction calculations based on a proposed analytical model. The results show that dynamic friction increases exponentially with sliding velocity as the temperature of the heated AFM tip rises, but the rate of increase slows at very high sliding velocities. These findings suggest that, in the nanoscopic contact regime at low haptic substrate temperatures (<35 °C) and normal humidity (40% RH), friction could significantly increase with increasing sliding velocities. In contrast, at higher temperatures (>35 °C) with faster sliding velocities, the finger may experience lubrication from skin hydration.