Recently, highly stretchable and tough hydrogels that are photodegradable on‐demand have been reported. Unfortunately, the preparation procedure is complex due to the hydrophobic nature of the photocrosslinkers. Herein, a simple method is reported to prepare photodegradable double‐network (DN) hydrogels that exhibit high stretchability, toughness, and biocompatibility. Hydrophilic ortho‐nitrobenzyl (ONB) crosslinkers incorporating different poly(ethylene glycol) (PEG) backbones (600, 1000, and 2000 g mol−1) are synthesized. These photodegradable DN hydrogels are prepared by the irreversible crosslinking of chains by using such ONB crosslinkers, and the reversible ionic crosslinking between sodium alginate and divalent cations (Ca2+). Remarkable mechanical properties are obtained by combining ionic and covalent crosslinking and their synergistic effect, and by reducing the length of the PEG backbone. The rapid on‐demand degradation of these hydrogels is also demonstrated by using cytocompatible light wavelength (λ = 365 nm) that degrades the photosensitive ONB units. The authors have successfully used these hydrogels as skin‐worn sensors for monitoring human respiration and physical activities. A combination of excellent mechanical properties, facile fabrication, and on‐demand degradation holds promise for their application as the next generation of substrates or active sensors eco‐friendly for bioelectronics, biosensors, wearable computing, and stretchable 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.