Chameleon-Inspired Strain-Accommodating Smart Skin

Abstract

Stimuli-responsive color-changing hydrogels, commonly colored using embedded photonic crystals (PCs), have potential applications ranging from chemical sensing to camouflage and anti-counterfeiting. A major limitation in these PC hydrogels is that they require significant deformation (>20%) in order to change the PC lattice constant and generate an observable chromatic shift (∼100 nm). By analyzing the mechanism of how chameleon skin changes color, we developed a strain-accommodating smart skin (SASS), which maintains near-constant size during chromatic shifting. SASS is composed of two types of hydrogels: a stimuli-responsive, PC-containing hydrogel that is patterned within a second hydrogel with robust mechanical properties, which permits strain accommodation. In contrast to conventional “accordion”-type PC responsive hydrogels, SASS maintains near-constant volume during chromatic shifting. Importantly, SASS materials are stretchable (strain ∼150%), amenable to patterning, spectrally tunable, and responsive to both heat and natural sunlight. We demonstrate examples of using SASS for biomimicry. Our strategy, to embed responsive materials within a mechanically matched scaffolding polymer, provides a general framework to guide the future design of artificial smart skins.

Mechanochromism of Structural‐Colored Materials

“…The color of the obtained photonic hydrogel could be modulated by the magnetic strength during assembly as well as the size of Fe 3 O 4 @C nanospheres. By introducing different polymer matrix, sphere‐chains‐based mechanochromic 1DPCs have been developed considerably, with remarkable properties such as shape‐memory, [ 66 ] and multiresponsiveness, [ 39,65 ] for the application of organic detection and data storage. [ 65,66 ]…”

“…Among these adjustable parameters, mechanochromism was mainly achieved by changing the interplanar spacing ( d ), which can be easily altered via the tuning the intersphere spacing, [ 10,39,42 ] as well as the deformation of elastic nanospheres. [ 48–51 ]…”

“…The magnetically induced assembly of superparamagnetic nanoparticles is an efficient method to form 1D ordered spheres chains. [ 39,64–66 ] Specifically, the superparamagnetic particles, usually Fe 3 O 4 nanospheres, were dispersed in the monomer liquid, in which they were driven by magnetic force to be oriented along the magnetic field line when exposed to the external magnetic field. After the alignment by magnetic field, the ordered array of nanospheres was fixed by polymerization.…”

“…[ 10 ] In addition, although the color shift is a predominant method to achieve mechanochromic behavior, [ 34–36 ] increasing efforts have been made to develop mechanochromism based on polarization and transparence. [ 11,37,38 ] As one of the rapidly developing intelligent materials with multiresponse, [ 34,39,40 ] mechanochromic structural‐colored materials have become promising in various applications, such as mechanical sensing, [ 11,41 ] colorful displays, [ 10,42 ] anti‐counterfeiting, [ 26,37 ] and healthcare materials. [ 43,44 ]…”

Hydrogel-Based Colloidal Photonic Crystal Devices for Glucose Sensing

“…Photonic structures exist in many natural beings, and bionics has become a hot spot for CPC research [103]. Recent studies on biomimicking chameleon skin showed that CPC structures might have more potential applications in military, biomedicine, electroskin, and smart wearable devices [104,105]. Moreover, with the development of material science and technology, especially 3D/4D printing technology [106], there may be more potential for the development of new structures of CPCs.…”