Bio-inspired stretchable and self-healable nanocomposite gelatin hydrogel with low silica nanoparticle content and brilliant angle/strain-independent structural colors

Abstract

Stretchable and self-healable structural-colored nanocomposite gelatin hydrogel with photonic structure of random dense/loose regions of non-close-packed silica nanoparticles (SiO2 NPs) is developed via convenient and scalable polymer-mediated assembly. The formation of the special photonic structure with overall low SiO2 NP content is characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The small-angle X-ray scattering test indicates the existence of short-range order, which is consistent with the TEM and SEM results. The dense photonic structure consisting of SiO2 NP chains and domains, and the loose structure consisting of abundant solitary SiO2 NPs, accounts for pronounced and uniform structural colors via combined effects of coherent scattering of light by dense structure, and Mie scattering of solitary NPs. These structural colors are independent of viewing angles and large mechanical strains. The dynamic physical and chemical bonding of the gelatin hydrogel network matrix enables self-healing functions and good deformability. Moreover, salt treatment of the structural-colored gelatin hydrogel networks enhances physical crosslinking and the mechanical strength of the hydrogel. The resilient, flexible and self-healable structural-colored nanocomposite hydrogel with low SiO2 NP content has great potential in wearable photonics, cosmetics, and various other color-related fields. This work also sheds light on enhancing non-iridescent structural colors through advanced photonic design.