An oriented Fe3+-regulated lignin-based hydrogel with desired softness, conductivity, stretchability, and asymmetric adhesiveness towards anti-interference pressure sensors

The development of conductive, soft, ultra-stretchable, and asymmetrically adhesive hydrogels is difficult and essential for both wearable electronics and anti-adhesion tissue dressings. In particular, there is still no simple, effective and universal approach to construct an asymmetrically adhesive multifunctional hydrogel. Here, we first synthesized lignosulfonate sodium (LS)-doped PAA hydrogels with uniform adhesion (adhesive strength: -30.5 kPa), conductivity (-0.45 S/m), stretchability (up to -2250%), and low compressive modulus (-20 kPa). In the second step, an oriented soaking of Fe3+ onto the upper surface of the resultant composite hydrogel renders the upper surface non-adhesive. This novel strategy masterfully delivers asymmetric adhesion behavior to the upper and bottom surfaces of the same hydrogel (-0 kPa adhesive strength for the upper surface; strong adhesive strength of -27 kPa for the bottom surface). The asymmetric adhesive hydrogel has proven to adhere well onto the human skin and achieve waste-barrier. Importantly, this hydrogel assembled pressure sensor demonstrates excellent anti-interference and wearable comfort.

Automated summary

The research successfully achieved asymmetric adhesion behavior on the upper and bottom surfaces of the same hydrogel by synthesizing lignosulfonate sodium-doped PAA hydrogel and orienting soaking Fe3+ onto the upper surface. The hydrogel exhibits conductivity, stretchability, and low compressive modulus, and adheres well onto human skin.