Highly stretchable natural polymer agar reinforced conductive hydrogel for strain sensing and artificial skin applications.

In many areas, advances in soft robotics, human-machine interfaces, and healthcare technology are revolutionising the way humans engage with machines (inspection, etc.). Strain-sensitive conductive hydrogels have attracted considerable scientific interest due to their potential applications in various fields. Traditional hydrogels often face limitations such as significant hysteresis energy, low electrical conductivity, limited elasticity, slow response rates, and inadequate shape recovery. This research aims to design a conductive hydrogel with excellent strain-sensing properties to address these challenges. The hydrogel is strengthened with Agar (Ag), butyl acrylate (BA), and acrylamide (Amm), which function as hydrophobic and hydrophilic monomers, respectively. Ag-enhanced mechanical properties are significantly affected by their insertion into the polymeric system. The developed hydrogel demonstrated a fracture stress of 338 kPa and a remarkable fracture strain of 1224 % (for 0.04 % of Ag). The frequency sweep and strain amplitude tests of the rheological analysis confirmed the elastic properties of the hydrogel. Moreover, the developed hydrogel exhibits excellent electrical conductivity of 354 mSm-1 and demonstrates remarkable sensitivity to mechanical deformation. It responds effectively to both low (50 %) and high (700 %) strain levels and maintains exceptional anti-fatigue performance with continuous standing stretching at 400 % strain for 500 s. Additionally, it features a rapid response time of 110 ms, a recovery time of 120 ms, and a gauge factor of 11 at 700 % strain. The Ag4 hydrogel also demonstrates potential for use as electronic skin, effectively functioning when attached to different joints, such as the neck, elbows, and fingers. The hydrogel can function as an electronic pen when it comes into contact with a plastic pen cover.