Fig 1.
(a) Illustration of the skin cross-section and its mechanoreceptors. (b) Depth assumption of a 2D microstructure and (c) Natural configuration of a 3D microstructure according to [3].
Fig 2.
A simplified elastic model mimicking a cut-away cube of the human fingertip.
Inset: exterior measurements and measurement of a single intermediate ridge.
Fig 3.
Depth configuration of (a) the 2D ridged model and (b) the 3D ridged model.
The epidermis, dermis, and subcutaneous layers are shown in white, green, and blue colors, respectively. The gray plane represents an example of a solid indenter (2×2mm2). The apexes of dermal papillae exhibit the same structure and measurements as those of intermediate ridges.
Fig 4.
Viscous parameters calibration.
(a) The displacement history of an indenter. (b) Profiles of the absolute contact force from the model and experimental data from [17]. (c) Profiles of normalized contact force in relaxation periods showing a good match between the model results and experimental data.
Fig 5.
Line load validation test, 50 micrometers.
(a) Illustration of three tested restraint conditions. Black triangles represent fixed boundary conditions (an assumption). (b) Surface deflection of the models under each restraint condition when compared with experimental data from Srinivasan et al. (1989). (c) Surface deflection of the models with different thicknesses of cutaneous tissue.
Fig 6.
SED distributions along the z-axis of an intermediate ridge.
(a) the 2D ridged model and (b) the 3D ridged model. The white square denotes the range of the indenter. Only the dermis is shown. The maximum SED of the scale bar at the left is set at 0.00019 MPa.
Fig 7.
3D distribution of SED at the tips of dermal papillae underlying the indenter.
(a) the 2D ridged model and (b) the 3D ridged model.
Fig 8.
Summary of the normalized SED distribution at the SA-I receptor location and FA-I receptor location, corresponding to the indenter.
The indenters are as follows (from left to right): a solid bar indenter, a gap indenter, a 90-degree-rotated gap indenter, and a solid circle indenter. The scale bar shows a gradient from white to red as the normalized SED increases from 0.6 to 1.0. Values under 0.6 are not plotted.
Fig 9.
Top view of the dermis part of the 3D ridged model during vibration by a 50-Hz stimuli.
(a) Displacement profile of a 50 Hz vibratory indenter. Distribution of SED at FA-I locations at (b) t = 0.001 s, (c) t = 0.005 s, and (d)t = 0.1 s. The white square depicts the range of the indenter.
Fig 10.
SED response at a FA-I location as a function of frequency, and a comparison of the 3D model and the 2D model.
Fig 11.
Comparison of 3D model and the mean spike rates of FA-I, adapted from [23].