pH-Regulated catechol-modified sodium alginate hydrogel with anti-freezing and high toughness for wearable strain sensor.

Hydrogel-based flexible electronic devices have garnered significant attention due to their excellent mechanical properties, high electrical conductivity, and signal sensitivity. Nevertheless, internal water molecules crystallize inevitably at low temperatures, impairing the performance of hydrogels. Designing anti-freezing and tough hydrogels to meet long-term stability requirements is extremely challenging. A double physically crosslinked PVA/SA-g-DA/Fe hydrogel was fabricated using a two-step method. The coordination mode between catechol groups and ferric ions was modified by adjusting pH of soaking solution, subsequently regulating antifreeze performance and mechanical properties of the hydrogels. The obtained PVA/SA-g-DA/Fe hydrogel is stretchable, tough, and has a remarkable freeze tolerance (-42.21 °C). The hydrogels can be assembled into a strain sensor to monitor various human activities accurately at normal and low temperatures. This study proposes a strategy for designing hydrogels for supporting signal detection in cold environments.