Elastic and Stretchable Double Network Hydrogel as Printable Ink for High-Resolution Fabrication of Ionic Skin.

A hydrogel that combines both printability and adaptability, high elasticity, and stretchability can provide ideal mechanical properties, and also render complex and accurate construction for ionic skin. However, it is extremely challenging. Here, we propose a colloidal-based double-network (DN) hydrogel as printable inks for high-precision fabrication of ionic skins. Particularly, polyacrylamide (PAAm), as the covalent network that can maintain the long-term material integrity, was combined with gelatin colloidal network to improve the injectability and printability of the resulting DN hydrogels. The DN design cooperatively provides the hydrogels with higher toughness values and deformability than what single colloidal or PAAm network can achieve. Further design of ionic skin based on capacitor microarray was demonstrated to serve as a sensitive and stable capacitor that can respond to external stimuli, thereby allowing to sense the body movements such as finger bending, laugh, and wrist pulse by translating mechanical changes into electric signals. Therefore, this study provides a novel strategy for the design and preparation of high-resolution ionic skins as the wearable sensor.