EGaIn-enhanced PDMS dielectric composites for flexible tactile sensors with three-dimensional force sensing

Flexible tactile sensors capable of detecting three-dimensional forces are critical for advanced applications in robotics, prosthetics, and human–machine interfaces. However, existing multilayer or isotropic composite designs often suffer from increased stiffness, poor conformability, and crosstalk between sensing channels. Here, we present a monolithic flexible sensor features a composite sensing layer comprising 6-acrylamidohexanoic acid (6-AHA) surface-modified eutectic gallium–indium (EGaIn) microdroplets, uniformly dispersed within a polydimethylsiloxane (PDMS) matrix. Surface modification enhances the dispersion of microdroplets and interfacial compatibility, thereby improving both the mechanical flexibility and dielectric performance of EGaIn/PDMS. Designed with four orthogonal arranged interdigital electrodes, the capacitive structure enables independent measurement of normal and tangential forces. Finite element simulations and experimental characterization reveal that deformation and reorientation of EGaIn microdroplets under external loading induce anisotropic dielectric responses and localized electric field redistribution, enabling effective decoupling of normal and tangential forces within a compact architecture. The sensor exhibits high sensitivity to both normal and tangential forces (∼0.085 %/N), acceptable response (<310 ms), low hysteresis, and excellent repeatability under cyclic loading. Although response speed and long-term reliability remain limited by matrix viscoelasticity, this work provides a scalable route for fabricating monolithic three-dimensional tactile sensors with high sensitivity and directional resolution, providing opportunities for applications in wearable electronics, robotic manipulation, and electronic skins.