The role of friction on skin wetness perception during dynamic interactions between the human index fingerpad and materials of varying moisture content

Mechanosensory inputs arising from dynamic interactions between the skin and moisture, such as when sliding a finger over a wet substrate, contribute to the perception of skin wetness. Yet, the exact relationship between the mechanical properties of a wet substrate, such as friction, and the resulting wetness perception, remains to be established under naturalistic haptic interactions. We modelled the relationship between mechanical and thermal properties of substrates varying in moisture levels (0.49x10-4; 1.10x10-4; 2.67x10-4 ml mm-2), coefficient of friction (0.783, 0.848, 1.033, 0.839, 0.876, 0.763), and maximum thermal transfer rate (Qmax, ranging from 511 to 1260 W m-2 K-1), and wetness perception arising from the index finger pad's contact with such substrates. Forty young participants (20M/20F) performed dynamic interactions with 21 different stimuli using their index finger pad at a controlled angle, pressure, and speed. Participants rated their wetness perception using a 100 mm visual analogue scale (very dry to very wet). Partial least squares regression analysis indicated that coefficient of friction explained only ~11% of the variance in wetness perception, while Qmax and moisture content accounted for ~22% and 18% of the variance, respectively. These parameters shared positive relationships with wetness perception, such that the greater the Qmax, moisture content, and coefficient of friction, the wetter the perception experienced. We found no differences in wetness perception between males and females. Our findings indicate that while the friction of a wet substrate modulates wetness perception, it is still secondary to thermal parameters such as Qmax