Extended Data Fig. 4: Mechanical characterization of transducers, skin phantoms and human skin.

a, Mechanical bistability evaluation in healthy individuals. Measurements were performed in five skin locations (depicted on the left). The absolute value of current required to transition the armature between relaxed and compressed states was measured for n = 6 participants (three males, three females, ages 20–36 years). The indentation depth was adjusted by performing experiments with harnesses of varying heights. b–i, Characterization of force as a function of extension was performed using a motorized stage (ESM303, Mark-10) and a force gauge (M5-2, Mark-10) with a 10 N capacity. b, Experimental and simulated forces measured as a function of the longitudinal position of the armature for several applied current values (excluding PDMS–MNP diaphragm and skin compressive force). We defined the origin as where the base of the armature and the core are in contact and we determined this using the force meter. For experimental results, the solid lines and shaded areas correspond to the means and standard deviations, respectively (n = 8). The square markers correspond to the maximum recorded force for each current, averaged across all transducers. The inset shows the experimental setup. c, Forces measured as a function of the longitudinal position of the armature rod (excluding force from core) for 40:1, 45:1, 50:1 and 55:1 skin phantoms with thicknesses of d = 2 mm (inset shows experimental setup). d, Forces measured as a function of the longitudinal position of the armature rod for 35:1, 40:1, 45:1, 50:1 and 55:1 skin phantoms with thicknesses of d = 5 mm. e, Skin reactive forces measured as a function of the longitudinal position of the armature rod (excluding force from core) for the ventral aspect of the forearm for n = 6 subjects (three males, three females, ages 20–36 years; experimental setup shown in inset). f, Skin reactive forces measured for the dorsal aspect of the palm above the adductor pollicis for n = 6 subjects (three males, three females, ages 20–36 years; location indicated in inset). g, Skin reactive forces measured for the dorsal aspect of the palm above metacarpal III for n = 6 subjects (three males, three females, ages 20–36 years; location indicated in inset). h, Tensile-peeling-force measurements of the harness attached to the silicone–mesh composite adhesive mounted on the forearm of n = 4 subjects (two males, two females, ages 26–32 years). The horizontal line shows the holding force of the indentation actuator. i, Tensile peeling force for a Ø7 mm disc pre-rotated to 30° and mounted on the forearm of n = 4 subjects (two males, two females, ages 26–32 years) with 3M 9699 double-sided adhesive. The horizontal line shows the holding force of the torsion actuator.