Skin preparation-free, stretchable microneedle adhesive patches for reliable electrophysiological sensing and exoskeleton robot control.

High-fidelity and comfortable recording of electrophysiological (EP) signals with on-the-fly setup is essential for health care and human-machine interfaces (HMIs). Microneedle electrodes allow direct access to the epidermis and eliminate time-consuming skin preparation. However, existing microneedle electrodes lack elasticity and reliability required for robust skin interfacing, thereby making long-term, high-quality EP sensing challenging during body movement. Here, we introduce a stretchable microneedle adhesive patch (SNAP) providing excellent skin penetrability and a robust electromechanical skin interface for prolonged and reliable EP monitoring under varying skin conditions. Results demonstrate that the SNAP can substantially reduce skin contact impedance under skin contamination and enhance wearing comfort during motion, outperforming gel and flexible microneedle electrodes. Our wireless SNAP demonstration for exoskeleton robot control shows its potential for highly reliable HMIs, even under time-dynamic skin conditions. We envision that the SNAP will open new opportunities for wearable EP sensing and its real-world applications in HMIs.

A temperature-responsive intravenous needle that irreversibly softens on insertion.

The high stiffness of intravenous needles can cause tissue injury and increase the risk of transmission of blood-borne pathogens through accidental needlesticks. Here we describe the development and performance of an intravenous needle whose stiffness and shape depend on body temperature. The needle is sufficiently stiff for insertion into soft tissue yet becomes irreversibly flexible after insertion, adapting to the shape of the blood vessel and reducing the risk of needlestick injury on removal, as we show in vein phantoms and ex vivo porcine tissue. In mice, the needles had similar fluid-delivery performance and caused substantially less inflammation than commercial devices for intravenous access of similar size. We also show that an intravenous needle integrated with a thin-film temperature sensor can monitor core body temperature in mice and detect fluid leakage in porcine tissue ex vivo. Temperature-responsive intravenous needles may improve patient care.

Wireless, AI-enabled wearable thermal comfort sensor for energy-efficient, human-in-the-loop control of indoor temperature.

The conventional heating, ventilation, and air conditioning (HVAC) systems are based on a set-point control approach that only considers the temperature of the environment without reflecting the thermophysiological status of the occupant. This approach not only fails to fully satisfy individual thermal preferences, but it also makes an HVAC operation energy-inefficient. One possible solution is to control the indoor thermal condition based on an accurate prediction of the occupant's thermal comfort to prevent any unnecessary energy consumption. Here, we present an artificial intelligence (AI) wearable sensor-based human-in-the-loop HVAC control system that is operated on a real-time basis reflecting the thermophysiological condition of the occupant to automatically improve their thermal comfort while reducing the energy consumption of the building. The wristband-type, AI-based, three-point wearable temperature sensor offers excellent thermal comfort prediction accuracy (93.9%), enabling a human-centric HVAC control operation. A proof-of-concept demonstration of closed human-in-the-loop HVAC control using the AI-enabled wearable sensor system confirms both the accuracy of the thermal comfort prediction and the energy-efficiency of this approach, demonstrating its potential as a new solution that improves the occupant's thermal comfort and provides building energy savings.

Self-Cooling Gallium-Based Transformative Electronics with a Radiative Cooler for Reliable Stiffness Tuning in Outdoor Use.

Reconfigurability of a device that allows tuning of its shape and stiffness is utilized for personal electronics to provide an optimal mechanical interface for an intended purpose. Recent approaches in developing such transformative electronic systems (TES) involved the use of gallium liquid metal, which can change its liquid-solid phase by temperature to facilitate stiffness control of the device. However, the current design cannot withstand excessive heat during outdoor applications, leading to undesired softening of the device when the rigid mode of operation is favored. Here, a gallium-based TES integrated with a flexible and stretchable radiative cooler is presented, which offers zero-power thermal management for reliable rigid mode operation in the hot outdoors. The radiative cooler can both effectively reflect the heat transfer from the sun and emit thermal energy. It, therefore, allows a TES-in-the-air to maintain its temperature below the melting point of gallium (29.8 â„ƒ) under hot weather with strong sun exposure, thus preventing unwanted softening of the device. Comprehensive studies on optical, thermal, and mechanical characteristics of radiative-cooler-integrated TES, along with a proof-of-concept demonstration in the hot outdoors verify the reliability of this design approach, suggesting the possibility of expanding the use of TES in various environments.

Design Strategy for Transformative Electronic System toward Rapid, Bidirectional Stiffness Tuning using Graphene and Flexible Thermoelectric Device Interfaces.

Electronics with tunable shape and stiffness can be applied in broad range of applications because their tunability allows their use in either rigid handheld form or soft wearable form, depending on needs. Previous research has enabled such reconfigurable electronics by integrating a thermally tunable gallium-based platform with flexible/stretchable electronics. However, supercooling phenomenon caused in the freezing process of gallium impedes reliable and rapid bidirectional rigid-soft conversion, limiting the full potential of this type of "transformative" electronics. Here, materials and electronics design strategies are reported to develop a transformative system with a gallium platform capable of fast reversible mechanical switching. In this electronic system, graphene is used as a catalyst to accelerate the heterogeneous nucleation of gallium to mitigate the degree of supercooling. Additionally, a flexible thermoelectric device is integrated as a means to provide active temperature control to further reduce the time for the solid-liquid transition of gallium. Analytical and experimental results establish the fundamentals for the design and optimized operation of transformative electronics for accelerated bidirectional transformation. Proof-of-concept demonstration of a reconfigurable system, which can convert between rigid handheld electronics and a flexible wearable biosensor, demonstrates the potential of this design approach for highly versatile electronics that can support multiple applications.