In vivo biomechanics of the fingerpad skin under local tangential traction

Abstract

Small patches of fingerpad glabrous skin in human subjects were tested in vivo for their biomechanical properties under tangential loading and for large deformations. These conditions included stretching and shearing the skin at a length scale of 0.3 mm using an apparatus comprising a pair of piezoelectric benders arranged to increase the stiffness/free deflection tradeoff when compared to ordinary cantilevered benders. It was then possible to test the skin with up to 80% of tangential strain. With feedback control, it was also possible to create isotonic and isometric testing conditions. The results showed much variability across subjects and it was seen that the glabrous skin exhibited nonlinear stiffening in tangential traction. The skin was consistently more elastic across the ridges than along the ridges regardless of the location of the sample on the fingerpad. The skin behaved visco-elastically but relaxed about twice as fast than it crept. Finally, it was found that under large deformation, there was consistently an 80% of hysteretic loss for a wide range of loading conditions.

Anticipatory vibrotactile cueing facilitates grip force adjustment

“…It can be surmised from these observations that the initial dynamics of the interaction are dominated by the tissue mechanics characterized by the typical nonlinear stiffening of the finger tissues undergoing large deformation [13,18] and that this initial phase of 30 ms is followed by mechanical events precipitated by the neural response that can vary greatly among individuals. For example, one participant recorded a maximum pad deformation of approximately 4 mm on average, but for another participant this deformation was smaller than 1 mm.…”

Two Finger Grasping Simulation with Cutaneous and Kinesthetic Force Feedback

“…The force/deformation behavior of the fingertips in the lateral, or shearing, direction, is studied in [22]. Actually, the stress/strain behavior of the fingertip under shearing forces is non linear, in fact in [23] the authors experimentally quantified the anisotropic and hysteretic behaviour of the fingertip deformation under the application of tangential forces. In this paper we consider a linear relationship between the resultant wrench and the platform displacement.…”

The Spatial Spectrum of Tangential Skin Displacement Can Encode Tactual Texture

“…The finger is a soft, highly deformable object which, besides its complex detailed geometry, exhibits several types of nonlinearities that are manifest at different length scales of interaction with surfaces [16], [17], [18], [19], [20]. Even under the extremely simplified assumption of linear viscoelasticity and perfectly clean contacts free of foreign bodies and liquids, the contact of deformable bodies with rough surfaces gives rise to theories of considerable complexity that are unlikely to yield simple interaction models [21].…”