A Generic Strategy to Create Mechanically Interlocked Nanocomposite/Hydrogel Hybrid Electrodes for Epidermal Electronics

Stretchable electronics are crucial enablers for next-generation wearables intimately integrated into the human body.As the primary compliant conductors used in these devices,metallic nanostructure/elastomer composites often struggle to form conformal contact with the textured skin.Hybrid electrodes have been consequently developed based on conductive nanocomposite and soft hydrogels to establish seamless skin-device interfaces.However,chemical modifications are typically needed for reliable bonding,which can alter their original properties.To overcome this limitation,this study presents a facile fabrication approach for mechanically interlocked nanocomposite/hydrogel hybrid electrodes.In this physical process,soft microfoams are thermally laminated on silver nanowire nanocomposites as a porous interface,which forms an interpenetrating network with the hydrogel.The microfoam-enabled bonding strategy is generally compatible with various polymers.The resulting interlocked hybrids have a 28-fold improved interfacial toughness compared to directly stacked hybrids.These electrodes achieve firm attachment to the skin and low contact impedance using tissue-adhesive hydrogels.They have been successfully integrated into an epidermal sleeve to distinguish hand gestures by sensing mus-cle contractions.Interlocked nanocomposite/hydrogel hybrids reported here offer a promising platform to combine the benefits of both materials for epidermal devices and systems.

Ultralight Iontronic Triboelectric Mechanoreceptor with High Specific Outputs for Epidermal Electronics

The pursuit to mimic skin exteroceptive ability has motivated the endeavors for epidermal artificial mechanoreceptors.Artificial mechanoreceptors are required to be highly sensitive to capture imperceptible skin deformations and preferably to be self-powered,breathable,lightweight and deformable to satisfy the prolonged wearing demands.It is still struggling to achieve these traits in single device,as it remains difficult to minimize device architecture without sacrificing the sensitivity or stability.In this article,we present an all-fiber iontronic triboelectric mechanoreceptor(ITM)to fully tackle these challenges,enabled by the high-output mechano-to-electrical energy conversion.The proposed ITM is ultralight,breathable and stretchable and is quite stable under various mechanical deformations.On the one hand,the ITM can achieve a superior instantaneous power density;on the other hand,the ITM shows excellent sensitivity serving as epidermal sensors.Precise health status monitoring is readily implemented by the ITM calibrating by detecting vital signals and physical activities of human bodies.The ITM can also realize acoustic-to-electrical conversion and distinguish voices from different people,and biometric application as a noise dosimeter is demonstrated.The ITM therefore is believed to open new sights in epidermal electronics and skin prosthesis fields.

Breathable Kirigami‑Shaped Ionotronic e‑Textile with Touch/Strain Sensing for Friendly Epidermal Electronics

Flexible ionotronic devices have great potential to revolutionize epidermal electronics.However,the lack of breathability in most ionotronic devices is a significance barrier to practical application.Herein,a breathable kirigami-shaped ionotronic e-textile with two functions of sensing(touch and strain)is designed,by integrating silk fabric and kirigami-shaped ionic hydrogel.The kirigami-shaped ionic hydrogel,combined with fluffy silk fabric,allows the ionotronic e-textile to achieve excellent breathability and comfortability.Furthermore,the fabricated ionotronic e-textile can precisely perform the function of touch sensing and strain perception.For touch-sensing,the ionotronic e-textile can detect the position of finger touching point with a fast response time(3 ms)based on the interruption of the ion field.For strain sensing,large workable strain range(>100%),inconspicuous drift(<0.78%)and long-term stability(>10,000 cycles)is demonstrated.On the proof of concept,a fabric keyboard and game controlling sleeve have been designed to display touch and strain sensing functions.The ionotronic e-textile break through the bottlenecks of traditional wearable ionotronic devices,suggesting a great promising application in future wearable epidermal electronics.

Epidermal self-powered sweat sensors for glucose and lactate monitoring

Sweat could be a carrier of informative biomarkers for health status identification;therefore,wearable sweat sensors have attracted significant attention for research.An external power source is an important component of wearable sensors,however,the current power supplies,i.e.,batteries,limit further shrinking down the size of these devices and thus limit their application areas and scenarios.Herein,we report a stretchable self-powered biosensor with epidermal electronic format that enables the in situ detec-tion of lactate and glucose concentration in sweat.Enzymatic biofuel cells serve as self-powered sensing modules allowing the sweat sensor to exhibit a determination coefficient(R2)of 0.98 with a sensitivity of 2.48 mV/mM for lactate detection,and R2 of 0.96 with a sensitivity of 0.11 mV/μM for glucose detection.The microfluidic channels developed in an ultra-thin soft flexible polydimethylsiloxane layer not only enable the effective collection of sweat,but also provide excellent mechanical properties with stable performance output even under 30%stretching.The presented soft sweat sensors can be integrated at nearly any location of the body for the continuous monitoring of lactate and glucose changes during normal daily activities such as exercise.Our results provide a promising approach to develop next-generation sweat sensors for real-time and in situ sweat analysis.

Epidermal radio frequency electronics for wireless power transfer

Epidermal electronic systems feature physical properties that approximate those of the skin,to enable intimate,long-lived skin interfaces for physiological measurements,human–machine interfaces and other applications that cannot be addressed by wearable hardware that is commercially available today.A primary challenge is power supply;the physical bulk,large mass and high mechanical modulus associated with conventional battery technologies can hinder efforts to achieve epidermal characteristics,and near-field power transfer schemes offer only a limited operating distance.Here we introduce an epidermal,farfield radio frequency(RF)power harvester built using a modularized collection of ultrathin antennas,rectifiers and voltage doublers.These components,separately fabricated and tested,can be integrated together via methods involving soft contact lamination.Systematic studies of the individual components and the overall performance in various dielectric environments highlight the key operational features of these systems and strategies for their optimization.The results suggest robust capabilities for battery-free RF power,with relevance to many emerging epidermal technologies.

Theoretical and experimental study of 2D conformability of stretchable electronics laminated onto skin

Smoothly attaching the stretchable epidermal electronic devices(EEDs) onto the skin surface is highly desired to improve the measurement accuracy of electrophysiological signal.The paper presents an analytical approach to study interfacial mechanics of the 2D planar EEDs on the checkerboard buckling patterns of human skin.Energy variation method is proposed to determine a criterion whether EEDs laminate conformally onto the skin surface under undeformed and stretched cases.EEDs with low bending stiffness(thin,soft devices/backing layer),smooth and soft skin,and strong adhesion promote conformal contact.Furthermore,the adhesion energy at the EED/skin interface is measured by the homemade peeling experiment platform with different substrate thicknesses and areal coverages.The upper limit of the areal coverage for EED conformal contact with the skin is proposed with given EED/skin properties.Conformability of EEDs are validated by experiments with different substrate thickness,areal coverage and external loadings.It provides a design guideline for EED to conformally contact with the skin surface for more accurate biological signal monitoring.

Multimodal epidermal devices for hydration monitoring

Precise,quantitative in vivo monitoring of hydration levels in the near surface regions of the skin can be useful in preventing skinbased pathologies,and regulating external appearance.Here we introduce multimodal sensors with important capabilities in this context,rendered in soft,ultrathin,‘skin-like’formats with numerous advantages over alternative technologies,including the ability to establish intimate,conformal contact without applied pressure,and to provide spatiotemporally resolved data on both electrical and thermal transport properties from sensitive regions of the skin.Systematic in vitro studies and computational models establish the underlying measurement principles and associated approaches for determination of temperature,thermal conductivity,thermal diffusivity,volumetric heat capacity,and electrical impedance using simple analysis algorithms.Clinical studies on 20 patients subjected to a variety of external stimuli validate the device operation and allow quantitative comparisons of measurement capabilities to those of existing state-of-the-art tools.

Stretchable,breathable,and washable epidermal electrodes based on microfoam reinforced ultrathin conductive nanocomposites

Stretchable epidermal electronics allow conformal interactions with the human body for emerging applications in wearable health monitoring and therapy.Stretchable devices are commonly constructed on submillimeter-thick elastomer substrates with limited moisture permeability,thereby leading to unpleasant sensations during long-term attachment.Although the ultrathin elastomer membrane may address this problem,the mechanical robustness is essentially lost for direct manipulations and repetitive uses.Here,we report a stretchable,breathable,and washable epidermal electrode of microfoam reinforced ultrathin conductive nanocomposite(MRUCN).The new architecture involves ultrathin conductive silver nanowire nanocomposite features supported on a porous elastomeric microfoam substrate,which exhibits high moisture permeability for pleasant perceptions during epidermal applications.As-prepared epidermal electrodes show excellent electronic conductivity(8440 S·cm^(-1)),high feature resolution(~50μm),decent stretchability,and excellent durability.In addition,the MRUCN retains stable electrical properties during washing to meet the hygiene requirements for repetitive uses.The successful implementation in an integrated electronic patch demonstrates the practical suitability of MRUCN for a broad range of epidermal electronic devices and systems.

Perspective on gallium-based room temperature liquid metal batteries

Recent years have witnessed a rapid development of deformable devices and epidermal electronics that are in urgent request for flexible batteries.The intrinsically soft and ductile conductive electrode materials can offer pivotal hints in extending the lifespan of devices under frequent deformation.Featuring inherent liquidity,metal-licity,and biocompatibility,Ga-based room-temperature liquid metals(GBRTLMs)are potential candidates to fulfill the requirement of soft batteries.Herein,to illustrate the glamour of liquid components,high-temperature liquid metal batteries(HTLMBs)are briefly summarized from the aspects of principle,application,advantages,and drawbacks.Then,Ga-based liquid metals as main working electrodes in primary and secondary batteries are reviewed in terms of battery configurations,working mechanisms,and fiinctions.Next,Ga-based liquid metals as auxiliary working electrodes in lithium and nonlithium batteries are also discussed,which work as functional self-healing additives to alleviate the degradation and enhance the durability and capacity of the battery system.After that,Ga-based liquid metals as interconnecting electrodes in multi-scenarios including photovoltaics solar cells,generators,and supercapacitors(SCs)are interpreted,respectively.The summary and perspective of Ga-based liquid metals as diverse battery materials are also focused on.Finally,it was suggested that tremendous endeavors are yet to be made in exploring the innovative battery chemistry,inherent reaction mechanism,and multifunctional integration of Ga-based liquid metal battery systems in the coining future.