A low-modulus, adhesive, and highly transparent hydrogel for multi-use flexible wearable sensors

Flexible materials have been widely applied in wearable sensors, but their high modulus and non-adhesion impede their widespread applications. In this work, a polyacrylic acid (PAA)-enhanced carboxymethyl cellulose (CMC) hydrogel (PEC hydrogel) was prepared via a two-step method to be utilized in flexible wearable sensors. The hydrogel presented a transparency of over 90 % (400–800 nm). Because of polymer chain entanglements and non-covalent interactions between PAA and CMC, the tensile properties of the hydrogel were enhanced, affording the PEC hydrogel with high stretchability (492 %) and low tensile strength (< 12.5 kPa). A hydrogel-based resistive strain sensor exhibited a wide sensing range (0–300 %, GF = 3.16), fast response time (125 ms), and excellent durability (over 1500 cycles from 0 % to 100 % strain). Owing to the introduction of polar groups, the hydrogel could be adhered to various substrates, and the peeling strength on pig skin (a replacement for human skin) was 53.97 N/m. Thanks to its low modulus, adhesion, and sensing performance, the hydrogel was assembled into a wearable strain sensor that accurately detected multiple human body movements. The hydrogel was also applied in a capacitive pressure sensor, which possessed a fast response time (100 ms) and high sensitivity. This work provides facile method for fabricating hydrogels used in Multi-use Flexible Wearable Sensors.