Sweat Softens the Outermost Layer of the Human Finger Pad: Evidence from Simulations and Experiments

2020

Miscellaneous

hi

The softness of human finger pads renders them highly effective at grasping objects. It has recently been debated whether sweat secreted from the finger pad alters the softness of the stratum corneum, the outermost layer of skin. However, it is not feasible to mechanically test in vivo skin to understand the properties of only the stratum corneum layer. To address this open question, we created a finite element model of a finger pad touching a glass plate in COMSOL Multiphysics, and we tuned it to fit contact data for a particular human finger. The experimental data were collected using a previously developed apparatus that records gross contact area and normal force over time; one participant conducted a finger-pressing test 15 times at each of three moisture levels (dry, moderate, and highly moist). We then used repeated contact simulations to determine the most likely mechanical properties of the stratum corneum layer for each condition. Applying a one-term Ogden hyper-elastic model with a fixed strain hardening exponent (α=9), we found the best shear moduli (μ) by comparing the contact area as a function of normal force between the simulations and the experiments. Our results show that the stratum corneum of the highly moist finger is indeed significantly softer than that of the same finger when it is only moderately moist or dry.

@misc{Nam20-EHWIP-Sweat,
  title = {Sweat Softens the Outermost Layer of the Human Finger Pad: Evidence from Simulations and Experiments},
  author = {Nam, Saekwang and Kuchenbecker, Katherine J.},
  howpublished = {Work-in-progress poster presented at EuroHaptics},
  address = {Leiden, The Netherlands},
  month = sep,
  year = {2020},
  doi = {},
  month_numeric = {9}
}