No abstract

While several stretchable batteries utilizing either deterministic or random composite architectures have been described, none have been fabricated using inexpensive printing technologies. In this study, the authors printed a highly stretchable, zinc‐silver oxide (Zn‐Ag2O) battery by incorporating polystyrene‐block‐polyisoprene‐block‐polystyrene (SIS) as a hyperelastic binder for custom‐made printable inks. The remarkable mechanical properties of the SIS binder lead to an all‐printed, stretchable Zn‐Ag2O rechargeable battery with a ≈2.5 mA h cm−2 reversible capacity density even after multiple iterations of 100% stretching. This battery offers the highest reversible capacity and discharge current density for intrinsically stretchable batteries reported to date. The electrochemical and mechanical properties are characterized under different strain conditions. The new stress‐enduring printable inks pave ways for further developing stretchable electronics for the wide range of wearable applications.

The hybrid device, screen-printed on two sides of the fabric, is designed to scavenge biochemical energy from the wearer's sweat using a biofuel cell module, and to store the harvested bioenergy into the supercapacitor module for subsequent use.

Despite the fast development of various energy harvesting and storage devices, their judicious integration into efficient, autonomous, and sustainable wearable systems has not been widely explored. Here, we introduce the concept and design principles of e-textile microgrids by demonstrating a multi-module bioenergy microgrid system. Unlike earlier hybrid wearable systems, the presented e-textile microgrid relies solely on human activity to work synergistically, harvesting biochemical and biomechanical energy using sweat-based biofuel cells and triboelectric generators, and regulating the harvested energy via supercapacitors for high-power output. Through energy budgeting, the e-textile system can efficiently power liquid crystal displays continuously or a sweat sensor-electrochromic display system in pulsed sessions, with half the booting time and triple the runtime in a 10-min exercise session. Implementing “compatible form factors, commensurate performance, and complementary functionality” design principles, the flexible, textile-based bioenergy microgrid offers attractive prospects for the design and operation of efficient, sustainable, and autonomous wearable systems.

Recent advances in wearable sensor technologies offer new opportunities for improving dietary adherence. However, despite their tremendous promise, the potential of wearable chemical sensors for guiding personalized nutrition solutions has not been reported. Herein, we present an epidermal biosensor aimed at following the dynamics of sweat vitamin C after the intake of vitamin C pills and fruit juices. Such skin-worn noninvasive electrochemical detection of sweat vitamin C has been realized by immobilizing the enzyme ascorbate oxidase (AAOx) on flexible printable tattoo electrodes and monitoring changes in the vitamin C level through changes in the reduction current of the oxygen cosubstrate. The flexible vitamin C tattoo patch was fabricated on a polyurethane substrate and combined with a localized iontophoretic sweat stimulation system along with amperometric cathodic detection of the oxygen depletion during the enzymatic reaction. The enzyme biosensor offers a highly selective response compared to the common direct (nonenzymatic) voltammetric measurements, with no effect on electroactive interfering species such as uric acid or acetaminophen. Temporal vitamin C profiles in sweat are demonstrated using different subjects taking varying amounts of commercial vitamin C pills or vitamin C-rich beverages. The dynamic rise and fall of such vitamin C sweat levels is thus demonstrated with no interference from other sweat constituents. Differences in such dynamics among the individual subjects indicate the potential of the epidermal biosensor for personalized nutrition solutions. The flexible tattoo patch displayed mechanical resiliency to multiple stretching and bending deformations. In addition, the AAOx biosensor is shown to be useful as a disposable strip for the rapid in vitro detection of vitamin C in untreated raw saliva and tears following pill or juice intake. These results demonstrate the potential of wearable chemical sensors for noninvasive nutrition status assessments and tracking of nutrient uptake toward detecting and correcting nutritional deficiencies, assessing adherence to vitamin intake, and supporting dietary behavior change.

This work demonstrates a stretchable and flexible lactate/O 2 biofuel cell (BFC) using buckypaper (BP) composed of multi-walled carbon nanotubes (MWCNTs) as the electrode material. Free-standing BP, functionalized with a pyrene-polynorbornene homopolymer, is fabricated as the immobilization matrix for lactate oxidase (LOx) at the anode and bilirubin oxidase (BOx) at the cathode. This biofuel cell delivers an open circuit voltage of 0.74 V and a high-power density of 520 µW cm-2. The functionalized BP electrodes are assembled onto a stretchable screen-printed current collector with an "island-bridge" configuration, which ensures conformal contact between the wearable BFC and the This article is protected by copyright. All rights reserved. 2 human body and endows the BFC with excellent performance stability under stretching condition. When applied to the arm of the volunteer, the BFC can generate a maximum power of 450 µW. When connected with a voltage booster, the on-body BFC is able to power a light emitting diode under both pulse discharge and continuous discharge modes during exercise. This demonstrates the promising potential of the flexible BP-based BFC as a self-sustained power source for next generation wearable electronics. Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

Tracking fluctuations of the cortisol level is important in understanding the body's endocrine response to stress stimuli. Traditional cortisol sensing relies on centralized laboratory settings, while wearable cortisol sensors are limited to slow and complex assays. Here, a touch‐based non‐invasive molecularly imprinted polymer (MIP) electrochemical sensor for rapid, simple, and reliable stress‐free detection of sweat cortisol is described. The sensor readily measures fingertip sweat cortisol via highly selective binding to the cortisol‐imprinted electropolymerized polypyrrole coating. The MIP network is embedded with Prussian blue redox probes that offer direct electrical signaling of the binding event to realize sensitive label‐free amperometric detection. Using a highly permeable sweat‐wicking porous hydrogel, instantaneously secreted fingertip sweat can be conveniently and rapidly collected without any assistance. By eliminating time lags, such rapid (3.5 min) fingertip assay enables the capture of sharp variations in cortisol levels, compared to previous methods. Such advantages are demonstrated by tracking cortisol response in short cold‐pressor tests and throughout day‐long circadian rhythm, along with gold‐standard immunoassay validation. A stretchable epidermal MIP sensor is also described for directly tracking cortisol in exercise‐induced sweat. The rapid touch‐based cortisol sensor offers an attractive, accessible, stressless avenue for quantitative stress management.

Circularly polarized light (CPL) as a massless physical force causes absolute asymmetric photosynthesis, photodestruction, and photoresolution. CPL handedness has long been believed to be the determining factor in the resulting product's chirality. However, product chirality as a function of the CPL handedness, irradiation wavelength, and irradiation time has not yet been studied systematically. Herein, we investigate this topic using achiral polymethacrylate carrying achiral azobenzene as micrometer-size aggregates in an optofluidic medium with a tuned refractive index. Azobenzene chirality with a high degree of dissymmetry ratio (±1.3 × 10 at 313 nm) was generated, inverted, and switched in multiple cycles by irradiation with monochromatic incoherent CPL (313, 365, 405, and 436 nm) for 20 s using a weak incoherent light source (≈ 30 μW·cm). Moreover, the optical activity was retained for over 1 week in the dark. Photoinduced chirality was swapped by the irradiating wavelength, regardless of whether the CPL sense was the same. This scenario is similar to the so-called Cotton effect, which was first described in 1895. The tandem choice of both CPL sense and its wavelength was crucial for azobenzene chirality. Our experimental proof and theoretical simulation should provide new insight into the chirality of CPL-controlled molecules, supramolecules, and polymers.