Xanthan gum toughen ionically conductive hydrogels for flexible and artificial epidermis sensors with multifunctionality and self-healability

Abstract

Conductive hydrogels that possess hydrophobic interaction have gained much attention in fields like strain sensors, soft robotics, tissue engineering, human-machine interaction, and biomedical sensors due to their excellent stretchability and effective energy dissipation mechanism. However, their use is limited due to poor mechanical performance, low sensing ability, lack of response time, and deficiency of self-healing capability. To overcome these limitations, acrylamide-co-butylacrylate/xanthan gum-based hydrophobically associated conductive hydrogels were designed. Amphiphilic sodium dodecyl sulfate was employed both as a cross-linker and a micelle-forming agent, while LiCl make the hydrogel as an ionic conductive material. The obtained hydrogels show fracture stress and fracture strain of 661kPa and 1100% respectively. The measured conductivity was 0.21Sm−1 and the strain sensing of the designed hydrogel reached up to 800%. Similarly, the designed hydrogels show remarkable sensitivity (Gauge factor = 28.8 at an applied strain of 800%) which is useful in the detection of a wide range of human motions. Finger, wrist, elbow, and knee joint movement can be easily detected with these hydrogels. Furthermore, the hydrogel can detect speaking, facial expressions, and pressure sensing. The designed hydrogels showed an excellent response and recovery time of 0.15 s and 0.13 s respectively. During multiple stretching and un-stretching cycles for 140 s, the designed hydrogels show continuous linear response without any current drop or fracture. Therefore the as-fabricated hydrogel presents a novel opportunity for its application in various fields such as flexible conductive material, strain sensors, human motion detection devices, and tissue engineering.