Liquid metal-elastomer hybrids, particularly those combining gallium-indium-tin (GaInSn) alloys with polydimethylsiloxane (PDMS), have emerged as a transformative class of materials for stretchable electronics, soft actuators, and strain sensing applications. These composites leverage the unique properties of liquid metals—high electrical conductivity, fluidic behavior, and low toxicity—with the mechanical compliance, elasticity, and durability of elastomers. The resulting systems enable deformable circuits that maintain functionality under extreme strains, making them ideal for wearable electronics, soft robotics, and biomedical devices.

The foundation of these hybrids lies in the dispersion of GaInSn within the PDMS matrix. GaInSn, a eutectic alloy, remains liquid at room temperature while exhibiting negligible vapor pressure and high surface tension. When embedded in PDMS, the liquid metal forms percolating networks that sustain electrical conductivity even under deformation. The key challenge is achieving uniform dispersion without coalescence, which can be addressed through mechanical mixing, sonication, or surface modification of the liquid metal droplets. Oxidizing the surface of GaInSn with weak acids or exposure to air creates a thin oxide layer that stabilizes the droplets within the elastomer, preventing aggregation.

Encapsulation is critical for maintaining the integrity and performance of LM-elastomer hybrids. Unencapsulated liquid metal can leak or oxidize over time, degrading electrical performance. Common encapsulation methods include multilayer PDMS coating, thermoplastic polyurethane (TPU) films, or silicone-based barriers. Multilayer PDMS encapsulation involves spin-coating or casting additional PDMS layers around the hybrid structure, ensuring adhesion through covalent bonding or plasma treatment. TPU films offer superior mechanical robustness and flexibility, often applied via lamination or heat pressing. The choice of encapsulation depends on the application’s mechanical demands, environmental exposure, and required longevity. For instance, biomedical applications prioritize biocompatible materials like medical-grade silicones, while industrial applications may favor TPU for abrasion resistance.

Self-healing properties are a hallmark of advanced LM-elastomer hybrids. The fluidic nature of GaInSn allows for autonomous repair of conductive pathways when damaged. When a crack or cut occurs, the liquid metal flows to bridge the gap, restoring electrical continuity. The elastomer matrix can also exhibit self-healing if designed with dynamic covalent bonds or supramolecular interactions. For example, PDMS modified with reversible Diels-Alder adducts or hydrogen-bonding networks can undergo mending upon heating or at room temperature. Combining these mechanisms results in materials that recover both mechanical and electrical properties after damage. Self-healing efficiency is typically quantified by comparing pre- and post-damage conductivity or tensile strength, with some systems achieving over 90% recovery.

Strain sensing is one of the most promising applications of LM-elastomer hybrids. The composites exhibit piezoresistive behavior, where electrical resistance changes predictably with applied strain. The mechanism involves the deformation-induced rearrangement of liquid metal droplets, altering the percolation pathways. At low strains, resistance increases linearly as the conductive paths elongate. At higher strains, the formation of new connections through droplet contact can lead to non-linear responses. Sensitivity, measured by the gauge factor, ranges from 1 to 10 for most LM-elastomer sensors, depending on filler concentration and matrix stiffness. These sensors can detect strains exceeding 300%, making them suitable for monitoring human motion, structural health, or robotic movements.

In soft actuators, LM-elastomer hybrids enable electrically responsive deformation. By patterning conductive pathways within the elastomer, Joule heating can be localized to induce thermal expansion or phase changes in the matrix. For example, a bilayer structure with an LM-PDMS composite on one side and pure PDMS on the other will bend when heated due to differential expansion. Actuation strains of up to 40% have been reported with response times under one second, depending on power input and thermal conductivity. The self-healing capability further enhances durability, as accidental cuts or punctures do not permanently disable the actuator.

The fabrication of stretchable circuits using these hybrids involves techniques like direct writing, screen printing, or embedding preformed LM patterns. Direct writing utilizes syringe-based extrusion to deposit liquid metal traces onto or within PDMS substrates. After curing, the traces remain conductive and stretchable. Screen printing employs LM-filled inks to create circuits on elastomer sheets, offering scalability for mass production. Embedded circuits are fabricated by casting PDMS around prefabricated LM networks, often supported by sacrificial templates. Each method balances resolution, throughput, and mechanical performance, with embedded circuits generally offering superior durability.

Challenges remain in optimizing the interfaces between liquid metal and elastomer to prevent leakage under cyclic loading. Nanoparticle additives, such as silica or carbon black, can reinforce the matrix and improve interfacial adhesion. Additionally, environmental stability—particularly resistance to humidity and temperature fluctuations—requires further improvement for outdoor or industrial applications. Recent advances include the development of LM-elastomer composites with enhanced thermal conductivity for heat dissipation in stretchable electronics, as well as hybrid systems integrating multiple functionalities like sensing, actuation, and energy storage.

Future directions focus on multifunctional systems where LM-elastomer hybrids serve as sensors, actuators, and energy harvesters simultaneously. For instance, combining piezoresistive strain sensing with triboelectric layers could enable self-powered deformable devices. Advances in computational modeling are also aiding the design of these materials by predicting percolation thresholds, mechanical response, and self-healing kinetics. As the field progresses, LM-elastomer hybrids are poised to enable next-generation technologies where elasticity, conductivity, and durability are paramount.