We report an anisotropic conductive elastomer consisting of liquid metal microdroplets and magnetically aligned ferromagnetic microparticles within a silicone matrix. This composite exhibits both piezoconductive and piezoresistive effects within the same sample, depending on the direction of measurement relative to the direction of particle alignment. We harness these unique properties to demonstrate soft tactile logic devices and a range-adjustable rheostat. This work has the potential to advance the development of soft tactile sensors and flexible electronics.

Stretchable conductive composites (SCCs) are generally elastomer matrices filled with conductive fillers. They combine the conductivity of metals and carbon materials with the flexibility of polymers, which are attractive properties for applications such as stretchable electronics, wearable devices, and flexible sensors. Most conventional conductive composites that are filled with only one type of conductive filler face issues in mechanical and electrical properties. Recently, some studies introduced secondary fillers to create hybrid‐filler SCCs to solve these problems. The secondary fillers produce a synergistic effect with the primary fillers to enhance the electrical conductivity of the composites. They also improve the thermal conductivity and mechanical properties or impart composites with special functions like catalysis and self‐healing. Herein, the fabrication methods, stretchability enhancement strategies, and piezoresistivity of SCCs are analyzed, and their latest applications in stretchable electronics are introduced. Finally, the challenges and prospects of their development are discussed.

Nanoparticles (NPs) of gallium-based liquid metal (LM) alloys have potential applications in flexible electronics, drug delivery, and molecular imaging. They can be readily produced using top-down methods such as sonication. However, the sonication process generates heat that can cause dealloying of NPs through hydrolysis and oxidation of gallium. This limits the sonication power and period that can be applied for disrupting LM into smaller particles with high concentrations. Also, it remains challenging to achieve long-term colloidal stability of NPs in biological buffers. Here, we develop a dynamic temperature control system for improving the production performance of LM NPs. The enhanced performance is reflected by the significantly increased particle concentration, the decreased overall particle size, the prevention of the formation of oxide nanorods, and the versatility of producing NPs of different types of alloys. In addition, we design a brushed polyethylene glycol polymer with multiple phosphonic acid groups for effectively anchoring the NPs. More importantly, we discover that phosphate can effectively passivate the surface of NPs to further improve their stability. Using these strategies, the produced NPs remain stable in biological buffers for at least six months. Thus, the proposed methods can unleash the vast potential of LM NPs for biomedical applications.

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Soft crawling robots have potential applications for surveillance, rescue, and detection in complex environments. Despite this, most existing soft crawling robots either use nonadjustable feet to passively induce asymmetry in friction to actuate or are only capable of moving on surfaces with specific designs. Thus, robots often lack the ability to move along arbitrary directions in a two-dimensional (2D) plane or in unpredictable environments such as wet surfaces. Here, leveraging the electrochemically tunable interfaces of liquid metal, we report the development of liquid metal smart feet (LMSF) that enable electrical control of friction for achieving versatile actuation of prismatic crawling robots on wet slippery surfaces. The functionality of the LMSF is examined on crawling robots with soft or rigid actuators. Parameters that affect the performance of the LMSF are investigated. The robots with the LMSF prove capable of actuating across different surfaces in various solutions. Demonstration of 2D locomotion of crawling robots along arbitrary directions validates the versatility and reliability of the LMSF, suggesting broad utility in the development of advanced soft robotic systems.