Preparation, Properties, and Applications of Smart Liquid Metal Hydrogel Composites: A Review.

Smart liquid metal (LM) hydrogel composites are an emerging class of flexible functional composites. They are fabricated by structurally integrating highly conductive and fluidic LMs with flexible and biocompatible hydrogels, thereby combining the advantages of both components. Three main preparation strategies include patterning LMs on hydrogel surfaces, injecting LMs into the interior of hydrogels, and directly mixing LMs with hydrogels. Smart LM hydrogel composites exhibit outstanding comprehensive performance of excellent electrical conductivity, self-healing capability, mechanical strength, adhesiveness, and biocompatibility, as well as multiresponsive behaviors to external stimuli, including strain, light, magnetic field, temperature, and humidity. Benefiting from these superior properties, smart LM hydrogel composites have found wide applications in cutting-edge fields such as wearable devices, disease therapy, actuators, electromagnetic interference shielding, and triboelectric nanogenerators. This review systematically correlates the structure-property-application relationships of smart LM hydrogel composites, with an emphasis on the synergistic enhancement mechanisms of LMs on the electrical conductivity, self-healing performance, mechanical properties, adhesiveness, biocompatibility, and intelligent responsiveness of hydrogels. Various application scenarios of smart LM hydrogel composites are also summarized. Smart LM hydrogel composites are expected to achieve more development in intelligent systems through optimizing structural design, tuning interfacial interactions, and expanding multifunctional integrated systems.