The Sampling Position Within, Not the Undulating Geometry of, Fingertip Skin Microstructure May Amplify the Sensation of Edges

The skin plays a role in conditioning imposed indentation at its surface into distributions of stress/strain that underlying mechanoreceptors convert into neural signals. Solid mechanics techniques may help explain how skin microstructure, in particular the intermediate ridges, influence the SA-I mechanoreceptors’ sensitivity to edge and curvature stimuli. This investigation isolates two facets of intermediate ridge microstructure, the stress/strain sampling position relative to the epidermal-dermal a) material boundary and b) undulating interface geometry. The objective of this study is to determine the relative importance of each for amplifying sampled stress/strain. The following finite element analysis finds that undulating interface geometry provides no amplification advantage. Rather, the imperative factor for amplifying stress/strain is the positioning of the sampling points in the stiffer, epidermal material just above the material boundary. These results may help explain the SA-I receptors’ positioning and inform the future design of man-made, electro-mechanical tactile sensors.