Anisotropic Subcutaneous Response During Fingertip Normal and Tangential Loadings

The subcutaneous mechanical response of the fingertip is highly anisotropic due to the presence of a network of collagen fibers linking the outer skin layer to the bone. Yet, the impact of this anisotropy on the fingerpad deformation had not been studied until now. This issue is here tackled using a two-dimensional finite element model of a transverse section of the finger. Different hypotheses about the orientation of the fibers are considered: radial (physiologic), circumferential, and random (isotropic behavior). The three variants of the model are assessed using experimental observations of a finger leaning on a flat surface. Predictions relying on the physiological orientation of fibers align best with reality. Moreover, the orientation of fibers plays a crucial role in determining the distribution of internal strain and stress. These factors, combined with the abrupt shift in contact pressure during the transition from sticking to slipping, represent important sensory cues for partial slip detection. This is valuable information for the development of haptic devices.