Printing technology can be used for manufacturing stretchable electrodes, which represent essential parts of wearable devices requiring relatively high degrees of stretchability and conductivity. In this work, a strategy for fabricating printable and highly stretchable conductors are proposed by transferring printed Ag ink onto stretchable substrates comprising Ecoflex elastomer and tough hydrogel layers using a water-soluble tape. The elastic modulus of the produced hybrid film is close to that of the hydrogel layer, since the thickness of Ecoflex elastomer film coated on hydrogel is very thin (30 µm). Moreover, the fabricated conductor on hybrid film is stretched up to 1780% strain. The described transfer method is simpler than other techniques utilizing elastomer stamps or sacrificial layers and enables application of printable electronics to the substrates with low elastic moduli (such as hydrogels). The integration of printed electronics with skin-like low-modulus substrates can be applied to make wearable devices more comfortable for human skin.

Conventional stretchable electronics entailing the adoption of a wavy design, a neutral mechanical plane, and a conformal contact between abiotic and biotic interfaces have shown diverse skin-interfaced applications. Despite such remarkable progress, there have been challenged to be evolved to intelligent skin prosthetics due to the absence of the monolithic integration of neuromorphic constituents into individual sensing and actuating components. Herein, we demonstrate a golden tortoise beetle-inspired stretchable sensory-neuromorphic system comprising an arti cial mechanoreceptor, an arti cial synapse, and an epidermal photonic actuator as three biomimetic functionalities that correspond to a stretchable capacitive pressure sensor, a resistive random-access memory, and a quantum dot light-emitting diode, respectively. This system features a rigid-island structure interconnected with a sinter-free printable conductor (stretchability ~ 160%, conductivity ~ 18,550 S/cm), which allows one to improve both areal density and structural reliability while avoiding the thermal degradation of heat-sensitive stretchable electronic components. Moreover, even in the skin deformation range, the system accurately recognizes various patterned stimuli via an arti cial neural network with training/inferencing functions. Our new bioinspired system is therefore expected to be an important step toward the implementation of intelligent wearable electronics.

Electrochromic devices (ECDs) are emerging as a novel technology for various applications like commercialized smart window glasses, and auto-dimming rear-view mirrors. Recently, the development of low-power, lightweight, flexible, and stretchable devices has been accelerated to meet the growing demand in the new wearable devices market. Silver nanowires (AgNWs) can become new primary transparent conducting electrode (TCE) materials to replace indium tin oxide (ITO) for ECDs. However, issues such as substrate adhesion, delamination, and higher resistance still exist with AgNWs. Herein, we report a high-performance stretchable flash-induced AgNW-network-based TCE on surface-treated polydimethylsiloxane (PDMS) substrates. A Xe flash light method was used to create nanowelded networks of AgNWs. Surface silane treatments increased the adhesion and durability of the films as well. Finally, ECDs were fabricated under the optimal conditions and examined under strained conditions to demonstrate the resistance and mechanical behaviours of the devices. Results showed a flexible and durable film maintaining a high level of conductivity and reversible resistance behaviour, beyond those currently achievable with standard ITO/PET flexible TCEs.