Chameleon-Inspired\nStrain-Accommodating Smart Skin

Abstract

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