Bimetallic-MOF Tunable Conductive Hydrogels to Unleash High Stretchability and Sensitivity for Highly Responsive Flexible Sensors and Artificial Skin Applications

Abstract

Metal−organic frameworks (MOFs) are widely applied in various fields, including energy storage, drug delivery, wastewater treatment, and much more. However, their use in hydrogels is limited due to their low dispersion which causes agglomeration in the hydrogel network and many properties of hydrogels are sacrifices. Similarly, conductive hydrogels have emerged as a promising material for skin-like sensors due to their excellent biocompatibility and mechanical flexibility. However, like MOFs, hydrogels also face challenges such as limited stretchability, low toughness, and susceptibility to fatigue, resulting in a low sensing range and large response time-reduced durability of the sensors. In this study, a highly stretchable, tough, and antifatigue conductive composite poly(dodecyl methacrylateacrylamide-2-(acryloyloxy)ethyl trimethylammonium chloride) bimetallic metal−organic framework [p(DA-AM-AETAC)BM-MOF] hydrogel was developed by integrating BM-MOFs into it. To achieve uniform dispersion of BM-MOFs within the hydrogel network, a positively charged surfactant, ethyl hexadecyl dimethylammonium bromide, was used. It facilitates the formation of hydrophobic interactions between the hydrogel matrix and the surface of the BM-MOFs. Furthermore, it can also interact with surfactant and polymer chains through physical interactions, significantly enhancing the mechanical properties of the hydrogel. The resulting BM-MOF-based hydrogels exhibited impressive stretchability (1588%) and toughness (537 kJ m −3 ), along with exceptional antifatigue properties. Moreover, it demonstrated a high conductivity of 1.3 S/m and high tensile strain sensitivity ranging from 0.5 to 700% with a gauge factor of 14.8 at 700% strain and response−recovery of 195−145 ms. The p(DA-AM-AETAC)BM-MOF hydrogel sensors displayed sensitive, reliable, and repetitive detection of a wide range of human activities, including wrist elbow rotation, finger bending, swallowing motion, speaking, as well as handwriting and drawing. Furthermore, the hydrogels also monitor the pressure and can mimic human skin. This highlights the potential of hydrogels as wearable strain, pressure, and artificial skin sensors for flexible devices.