Breathable Gelatin Conductive Hydrogels Using a Template Method and Reverse Use of Hofmeister Effect for Wearable Sensors

Hydrogel-based wearable sensing devices are attractive and have broad application prospects on motion intention recognition and health monitoring. The research on the aspect of their wearable comfort and the improvement of breathability is essential. In this paper, a breathable porous hydrogel film was prepared using a template method combined with the inverse Hofmeister effect. Different from conventional hydrogels that utilize the Hofmeister effect by using lyophilic ions for toughening, our approach involved the reverse application of the Hofmeister effect, the use of chaotropic ions, which induced a loosening effect within the hydrogel interior, thereby achieving a more uniform pore distribution. The prepared hydrogel film has excellent mechanical properties (elongation at break of 404%, tensile strength of 173 kPa), air permeability (9.96 mg·cm–2·h–1), and sensitivity (GF = 4.41). The film is used as a wearable sensor with high sensitivity and accuracy to monitor human finger, wrist, and large joint movements, human electrophysiological signals [electromyogram (EMG) and electrocardiogram (ECG)], small changes in vocal cord vibration, and manipulation of electronic devices for gaming. This work provides an approach for the preparation of breathable hydrogel films as wearable sensors.