Multimodal Adhesive E-skin for Robotic Platforms

Human skin offers multimodal sensing capabilities including tactile, thermal, and chemical detection, a capability that can be partially replicated using ionic hydrogels to create electronic skin (e-skin). However, for e-skin to properly function, it must firmly adhere to substrates. Adhesion to a diverse range of soft substrates, such as those found in soft robotics, remains a major challenge. Typical adhesives are rather soft such that they can adopt their shape to the surface roughness of the substrate, yet, their softness limits the mechanical properties of the resulting composites. Here, we present a double-network granular organogel (DNGOG) that integrates microfragments, which can interact with hydrophobic substrates with a secondary soft polymer network rich in ionic and hydrogen bonds. This architecture enables strong, reversible adhesion to a wide range of hydrophilic and hydrophobic substrates. The presence of ionic groups within the hydrogel facilitates metal–ligand coordination, whereas the much stiffer microfragments increase the stiffness of the material. Thereby, the DNGOG-based e-skin can combine an adhesive strength of 1.9 MPa with a tensile strength of 1.0 MPa, overcoming the long-standing adhesion-strength compromise of soft materials. We demonstrate adhesion across diverse substrates, including porcine skin, silicone rubber, thermoplastics, wood, glass and metals. The ionic conductivity of the DNGOG enables this material to sense multiple stimuli vital to humans such as their pulse, respiration, temperature, and sweat, as well as tactile feedback in soft robotic systems. This multifunctional platform offers a promising route toward next-generation wearable and robotic e-skin technologies.