Photodegradable Non-Drying Hydrogel Substrates for Liquid Metal Based Sustainable Soft-Matter Electronics

The increasing interest in disposable electronics such as wearable patches, e-textiles, and smart packaging, warns emergence of another man-made disaster. A paradigm shift toward a more sustainable future through the development of soft material architectures that are robust and durable, but also degradable by external stimuli is proposed. Hydrogels, a class of soft polymers with exceptional properties, and high water content are rarely used as substrates, mainly due to lack of ink-adhesion and rapid dehydration. Herein, photodegradable hydrogels are tailor-made that are nondrying, robust, adhesive to ink, and permit triggerable degradation, making them suitable substrates for sustainable electronics. These hydrogels are prepared by reversible ionic crosslinking between sodium alginate and divalent cations (Ca2+) and light-responsive crosslinking of poly(acrylamide) (PAAm) chains through synthesized ortho-nitrobenzyl (ONB)-based crosslinkers. By displacing the water molecules in the hydrogels by immersion in glycerol, the drying problem and printability of conductive ink are addressed. It is demonstrated that digital printing of a liquid metal (LM)-based stretchable ink over the developed substrate, shows several body-worn printed wearable sensors, and demonstrates their degradation and recycling of the expensive metals. This work lays the foundation for the use of hydrogels as promising substrates for the next generation of environmentally friendly electronics.