Digital Texture Voxels for Stretchable Morphing Skin Applications

Abstract

to survive throughout extreme hot dry or extremely humid weathers equally. [3] A truly fascinating example of stretchable camouflaging texture morphing skin is seen in cephalopods-the underwater invertebrates known as the masters of camouflage. These marine creatures control their skin morphology by stimulating cutaneous muscles known as papillae. These muscles generate complex texture patterns by pushing the overlying epidermal tissue upward and away from the mantle surface during their contraction. [4] Thanks to the large number of high-resolution texture muscles, cephalopods undergo complex morphology change. Overall, the skin of the cephalopod is a 3D display, where the papillae muscles control each voxel's extension on-demand by several millimeters out of the skin plane, create hierarchical textures, and collectively change the overall skin pattern. The generation of complex 3D shapes not only facilitates camouflage by pattern matching but also could enhance the swimming efficiency by controlling the hydrodynamic drag.The material systems required to achieve such morphological changes are extremely heterogenous and complex. The flexible and stretchable skin tissue of cephalopods is coupled to dermal shape-changing mechanisms, seamlessly embedded muscles, and integrated neurological sensing and control. A few texture and morphology change technologies inspired by cephalopods' papillae have been recently proposed. Wang et al. [5] produce on-demand fluorescent patterns using electroactive and mechanoresponsive elastomers, where high electric voltage (>50 kV mm −1 ) induces surface roughness of a millimeter. Current material developments are underway to reduce the required voltage and increase the materials voltage breakdown strength of these materials. Pikul et al. [6] use pneumatically actuated elastomeric membranes coupled to rigid mesh to achieve programmable 3D texture morphing. This material produces complex preprogrammed morphological camouflage, yet their broad applicability is limited by the need for heavy, rigid, and noisy air compressor.In this study, we produce a new type of stretchable skin based on electromechanical digital texture voxels (DTVs) to emulate the 3D morphing display of cephalopods papillae. The DTVs provide surface roughness, which actively changes its amplitude from the sub-millimeter to more than a centimeter and requires only 0.02 V mm −1 for actuation. These surface actuators undergo giant and reversible extensions exceeding 2000% strain within a few seconds. The DTVs are made from Smart skins capable of on-demand dynamic texture morphing are attractive for several applications, ranging from haptic feedback devices [1] to drag control in aerial or underwater vehicles. [2] There are countless inspiring examples of biological creatures, which intelligently morph their skin patterns to achieve multifunctionality. For example, the leaves of the silver tree (Leucadendron argenteum) morph their hair-like texture

Spatiotemporally Programmable Surfaces via Viscoelastic Shell Snapping

“…[2,3] These examples have inspired numerous artificial materials and devices with tunable surface textures for a wide range of applications in aerospace, [4,5] human-computer interaction, [6][7][8] and soft robotics. [9][10][11][12][13][14][15] The actuation for textural morphing relies on either mechanical loads [4][5][6][7][8][9][10][16][17][18][19][20] or embedded stimuliresponsive materials. [13][14][15][21][22][23][24][25][26][27][28] Unlike the dynamic textural morphing in nature, most synthetic materials transform into only one targeted surface texture in response to a stimulus.…”

“…[ 2,3 ] These examples have inspired numerous artificial materials and devices with tunable surface textures for a wide range of applications in aerospace, [ 4,5 ] human–computer interaction, [ 6–8 ] and soft robotics. [ 9–15 ] The actuation for textural morphing relies on either mechanical loads [ 4–10,16–20 ] or embedded stimuli‐responsive materials. [ 13–15,21–28 ]…”

Cephalopod‐Inspired Stretchable Self‐Morphing Skin Via Embedded Printing and Twisted Spiral Artificial Muscles

“…Twisting was applied until the polymer line started coiling simultaneously; 4) the twisted portion of the fishing line was then manually formed into a flat Archimedean spiral on an adhesive substrate; 5) the muscle was then annealed at 150 °C for 3 h to retain the spiral shape; and 6) after cooling, the TSAMs were allowed to reach an equilibrium state for 48 h before electrothermal actuation. [9] Alternatively, silver paint, instead of copper wire, can be used to provide electrical conductivity to TSAMs. [39] Copper wire was used for the electrothermal actuation of TSAMs because of its excellent electrical conductivity, low cost, and ability to provide joule heating during electrothermal actuation of the TSAMs.…”

“…Additional details on the manufacturing and working mechanism of TSAMs are provided in Section S1 of the Supporting Information. [9,26] The embedded printing process for fabricating a liquidmetal electrode network is schematically depicted in Figure 2a. A printing mold was initially filled with the base elastomer at the bottom and the filling elastomer on the top.…”

Progresses in Tensile, Torsional, and Multifunctional Soft Actuators

“…[ 107 ] A coiled tensile artificial muscle with spiral architecture was designed into digital texture voxels for use as stretchable morphing skin. [ 142 ]…”