A monolithically integrated in-textile wristband for wireless epidermal biosensing.

Textile bioelectronics that allow comfortable epidermal contact hold great promise in noninvasive biosensing. However, their applications are limited mainly because of the large intrinsic electrical resistance and low compatibility for electronics integration. We report an integrated wristband that consists of multifunctional modules in a single piece of textile to realize wireless epidermal biosensing. The in-textile metallic patterning and reliable interconnect encapsulation contribute to the excellent electrical conductivity, mechanical robustness, and waterproofness that are competitive with conventional flexible devices. Moreover, the well-maintained porous textile architectures deliver air permeability of 79 mm s-1 and moisture permeability of 270 g m-2 day-1, which are more than one order of magnitude higher than medical tapes, thus ensuring superior wearing comfort. The integrated in-textile wristband performed continuous sweat potassium monitoring in the range of 0.3 to 40 mM with long-term stability, demonstrating its great potential for wearable fitness monitoring and point-of-care testing.

Wet-Adaptive Electronic Skin.

Skin electronics provides remarkable opportunities for non-invasive and long-term monitoring of a wide variety of biophysical and physiological signals that are closely related to health, medicine, and human-machine interactions. Nevertheless, conventional skin electronics fabricated on elastic thin films are difficult to adapt to the wet microenvironments of the skin: Elastic thin films are non-permeable, which block the skin perspiration; Elastic thin films are difficult to adhere to wet skin; Most skin electronics are difficult to work underwater. Here, a Wet-Adaptive Electronic Skin (WADE-skin) is reported, which consists of a next-to-skin wet-adhesive fibrous layer, a next-to-air waterproof fibrous layer, and a stretchable and permeable liquid metal electrode layer. While the electronic functionality is determined by the electrode design, this WADE-skin simultaneously offers superb stretchability, wet adhesion, permeability, biocompatibility, and waterproof property. The WADE-skin can rapidly adhere to human skin after contact for a few seconds and stably maintain the adhesion over weeks even under wet conditions, without showing any negative effect to the skin health. The use of WADE-skin is demonstrated for the stable recording of electrocardiogram during intensive sweating as well as underwater activities, and as the strain sensor for the underwater operation of virtual reality-mediated human-machine interactions.

Anti-Fatigue Hydrogel Electrolyte for All-Flexible Zn-Ion Batteries.

Hydrogel electrolytes are widely explored in Zn metal batteries for application in wearable electronics. While extensive studies have been conducted on optimizing the chemical structure and boosting the tensile elasticity, the mechanical stability of the hydrogel under repeated deformation is largely overlooked, leading to unsatisfactory performance at large cycling capacity. This work systematically analyzes the compressive fatigue-resistance properties of the hydrogel electrolyte, revealing the critical roles of the salt and copolymer matrix on crack initiation and propagation. It shows that, on the premise of homogeneous Zn deposition, an improved anti-fatigue property is essential to achieve high-capacity Zn metal anodes. The optimal Zn(ClO4 )2 -polyacrylamide/chitosan hydrogel electrolyte (C-PAMCS) exhibits an unprecedented lifespan of 1500 h for Zn//Zn cells at a current density of 10 mA cm-2 and a high areal capacity of 10 mAh cm-2 . The potential application of C-PAMCS is exemplified in all-flexible Zn-ion batteries enabled by a flexible current collector consisting of a Ag nanowires embedded elastomer. This study provides the rationale under hydrogel electrolyte engineering toward advanced Zn-ion battereis and the application in flexible devices.

Wafer-patterned, permeable, and stretchable liquid metal microelectrodes for implantable bioelectronics with chronic biocompatibility.

Implantable bioelectronics provide unprecedented opportunities for real-time and continuous monitoring of physiological signals of living bodies. Most bioelectronics adopt thin-film substrates such as polyimide and polydimethylsiloxane that exhibit high levels of flexibility and stretchability. However, the low permeability and relatively high modulus of these thin films hamper the long-term biocompatibility. In contrast, devices fabricated on porous substrates show the advantages of high permeability but suffer from low patterning density. Here, we report a wafer-scale patternable strategy for the high-resolution fabrication of supersoft, stretchable, and permeable liquid metal microelectrodes (µLMEs). We demonstrate 2-µm patterning capability, or an ultrahigh density of ~75,500 electrodes/cm2, of µLME arrays on a wafer-size (diameter, 100 mm) elastic fiber mat by photolithography. We implant the µLME array as a neural interface for high spatiotemporal mapping and intervention of electrocorticography signals of living rats. The implanted µLMEs have chronic biocompatibility over a period of eight months.

Permeable superelastic liquid-metal fibre mat enables biocompatible and monolithic stretchable electronics.

Stretchable electronics find widespread uses in a variety of applications such as wearable electronics, on-skin electronics, soft robotics and bioelectronics. Stretchable electronic devices conventionally built with elastomeric thin films show a lack of permeability, which not only impedes wearing comfort and creates skin inflammation over long-term wearing but also limits the design form factors of device integration in the vertical direction. Here, we report a stretchable conductor that is fabricated by simply coating or printing liquid metal onto an electrospun elastomeric fibre mat. We call this stretchable conductor a liquid-metal fibre mat. Liquid metal hanging among the elastomeric fibres self-organizes into a laterally mesh-like and vertically buckled structure, which offers simultaneously high permeability, stretchability, conductivity and electrical stability. Furthermore, the liquid-metal fibre mat shows good biocompatibility and smart adaptiveness to omnidirectional stretching over 1,800% strain. We demonstrate the use of a liquid-metal fibre mat as a building block to realize highly permeable, multifunctional monolithic stretchable electronics.