Dynamic hofmeister effect-engineered thermosensitive ionic conductive hydrogel with 3D plasticity and environmental...

Wearable devices made of ionic conductive hydrogels have drawn great attention within the scientific community, but there has been a crucial issue in making multimodal sensors as most of the existing hydrogel based sensors could only detect one kind of signal. in this study, we presented a new 3D printable hydrogel (named as GSA-PNIPAM@Fe³⁺/AS) made of a semi-interpenetrating polymer network which was synthesized by photocuring a three-component mixture of gelatin, sodium alginate, and N-isopropylacrylamide followed by soaking it successively in sodium ferric ethylenediaminetetraacetate and ammonium sulfate solutions. Using the Hofmeister effect, we reduced the hydration layer around the gelatin which helped form a triple-helix structure and led to a closely cross-linked, swell-resistant network so the resulting hydrogel had excellent properties such as a toughness of 661 kJ m^-3, a compressive modulus of 30 MPa, an ionic conductivity of 1.78 S m^-1, and long-lasting resistance to swelling over a long time and after being submerged in water for 12 days, the equilibrium swelling ratio reached a plateau at 80%. moreover, the hydrogel showed outstanding responsiveness within a wide temperature range from -10 to 50 °C. sensors made from this hydrogel could accurately record multidimensional human movement both on land and underwater, keep monitoring body temperature all the time, and distinguish underwater Morse code signals for aquatic communication. This research clarified a flexible method for creating multimodal wearable sensors intended to work in various difficult environments thus increasing the usefulness of flexible electronic devices.