Skin-Preparation-Free, Stretchable Microneedle Adhesive Patches for High-Fidelity Electrophysiological Sensing and Exoskeleton Robot Control

Ensuring highly reliable and comfortable recording of electrophysiological (EP) signals is vital in various applications, from medical care to human-machine interaction. Recent research has tried to address this issue by developing soft epidermal electrodes that offer time-dynamic accommodation to skin deformation. Although these sensors are suitable for long-term use and are conformable, the signals acquired using these approaches highly rely on skin conditions, thus requiring a cumbersome skin preparation setup. Microneedle electrodes can overcome the limitation by eliminating the need for skin pretreatment by providing direct access to the epidermis. Nevertheless, existing rigid or flexible microneedle electrodes face challenges related to mechanical elasticity and electrical reliability, particularly during dynamic body movement, hindering their suitability for accurate EP sensing over a prolonged time.<br/> To address these issues, we have developed a stretchable microneedle adhesive patch (SNAP) for skin-preparation-free, reliable EP monitoring. SNAP comprises gold-coated silicon microneedle arrays, stretchable serpentine gold interconnects, and electrically conductive adhesives. The microneedle array, with a height of less than 200 μm, ensures virtually pain-free penetration of stratum corneum and maintains consistently low and stable skin contact impedance regardless of skin conditions. The elastic, adhesive and conductive platform, featuring a serpentine mesh, enables dynamic adaptation to tissue deformations while also enhancing the electrical skin interface through the provision of an additional conductive pathway. Through this design, SNAP offers remarkable skin penetrability and establishes a robust electromechanical skin interface, ensuring prolonged and precise EP signal monitoring across diverse skin conditions. Analytical and experimental outcomes validate that SNAP enhances wearer comfort during intensive exercise and significantly decreases contact impedance under uncleaned skin, outperforming clinical gel electrodes and flexible microneedle electrodes. Demonstration using the wireless SNAP system in a human-machine interface (HMI) to control a back-support exoskeleton robot underlines its potential for high-fidelity HMIs, even in challenging scenarios involving time-varying skin conditions. We foresee that this SNAP system can be applied to various EP sensing, suggesting new strategies for enhancing comfort, reliability, and utility in applications ranging from healthcare and medical diagnostics to cutting-edge human-robot interactions.