Coin-sized, fully integrated, and minimally invasive continuous glucose monitoring system based on organic electrochemical transistors.

Continuous glucose monitoring systems (CGMs) are critical toward closed-loop diabetes management. The field's progress urges next-generation CGMs with enhanced antinoise ability, reliability, and wearability. Here, we propose a coin-sized, fully integrated, and wearable CGM, achieved by holistically synergizing state-of-the-art interdisciplinary technologies of biosensors, minimally invasive tools, and hydrogels. The proposed CGM consists of three major parts: (i) an emerging biochemical signal amplifier, the organic electrochemical transistor (OECT), improving the signal-to-noise ratio (SNR) beyond traditional electrochemical sensors; (ii) a microneedle array to facilitate subcutaneous glucose sampling with minimized pain; and (iii) a soft hydrogel to stabilize the skin-device interface. Compared to conventional CGMs, the OECT-CGM offers a high antinoise ability, tunable sensitivity and resolution, and comfort wearability, enabling personalized glucose sensing for future precision diabetes health care. Last, we discuss how OECT technology can help push the limit of detection of current wearable electrochemical biosensors, especially when operating in complicated conditions.

D-Mannitol/Graphene Phase-Change Composites with Structured Conformation and Thermal Pathways Allow Durable Solar-Thermal-Electric Conversion and Electricity Output.

Durable electricity generation from a phase-change material (PCM)-assisted solar thermoelectric generator (STEG) through photo-thermal-electric conversion is a promising way to take advantage of the clean solar energy. However, due to the deficient and mismatched thermal charging and discharging rates in the PCMs, the previous PCM-supported STEGs usually exhibit inefficient solar-thermal-electric conversion (<1%) and limited electricity output. In this work, we report a structured D-mannitol/graphene phase-change composite fabricated by a radial ice-template assembly and infiltration strategy, in which radially aligned graphene nanoplates are bridged by graphitized polyimide that offers multidirectional and interlaced thermal highways for rapid thermal charging, while the sample conformation is further regulated by the ice-template mold, promising the optimal charging and discharging balance in the PCM. After being integrated with a solar concentrator and a thermoelectric device, this powerful STEG outputs tremendous power density, with the solar-thermal-electric conversion approaching 2.40%. The plenteous electricity supply is demonstrated to reliably charge a mobile phone under normal sunlight. This elaborate STEG design opens up opportunities for providing sufficient power guarantees for the self-powering of electronic devices in the wild.

Tropocollagen-Inspired Hierarchical Spiral Structure of Organic Fibers in Epoxy Bulk for 3D High Thermal Conductivity.

Polymers are usually considered thermal insulators; however, significant enhancements in thermal conductivity (k) have been observed in oriented fibers and films. Despite being advantageous in real-world applications, extending the linear thermal-transport advantage of polymers into the 3D space in bulk materials is still limited due to the spatially interfacial phonon-conduction barriers. Herein, inspired by the structure of tropocollagen, it is discovered that weaving hierarchically arranged poly(p-phenylene benzobisoxazole) (PBO) fibers with a spiral configuration into an epoxy matrix can yield a 3D continuous thermal pathway. This achieves both a through-plane k of 10.85 W m-1 K-1 and an in-plane k of 7.15 W m-1 K-1 . Theoretical molecular simulations in combination with classical nonlinear modeling attribute the above spatially thermally conductive achievement to not only the hierarchical molecular, spiral and weaving structure of PBO, but also the noncrystalline chains that carry overlapping phonon density of states, thus thermally bridging adjacent high-k crystals in the PBO fiber. Consequently, the interfacial thermal resistance among high-k PBO crystals is suppressed to be on the order of 10-10 m2 K W-1 in both the through-plane and in-plane directions. Other advantages include being lightweight, mechanically strong, flexible, and non-combustible. This material creates opportunities for organic polymers in high-performance thermal management applications.

Intrinsically Stretchable Organic Electrochemical Transistors with Rigid-Device-Benchmarkable Performance.

Intrinsically stretchable organic electrochemical transistors (OECTs) are being pursued as the next-generation tissue-like bioelectronic technologies to improve the interfacing with the soft human body. However, the performance of current intrinsically stretchable OECTs is far inferior to their rigid counterparts. In this work, for the first time, the authors report intrinsically stretchable OECTs with overall performance benchmarkable to conventional rigid devices. In particular, oxygen level in the stretchable substrate is revealed to have a significant impact on the on/off ratio. By employing stretchable substrates with low oxygen permeabilities, the on/off ratio is elevated from ≈10 to a record-high value of ≈104 , which is on par with a rigid OECT. The device remained functional after cyclic stretching tests. This work demonstrates that intrinsically stretchable OECTs have the potential to serve as a new building block for emerging soft bioelectronic applications such as electronic skin, soft implantables, and soft neuromorphic computing.

A Universal Mechanochemistry Allows On-Demand Synthesis of Stable and Processable Liquid Metal Composites.

Gallium-based liquid metal (LM) is regarded as one of the most promising candidates for the new-generation jigsaw of stretchable electronics. Nonetheless, the obstacle for the LM application lies in its high surface tension and easy fluidity which leads to great difficulty in handling and processing. Herein, a cross-mechanochemistry between liquid metal and inorganic solid, mediated via the coordination binding between the empty electronic orbits of the former and the lone electron pair of the latter is reported. The mechanism is validated via density functional theory calculation and electron energy loss spectroscopy, and experimentally proven to be universally applicable for various liquid metals and inorganic solids. With the unique mechanochemistry, simple ball milling allows on-demand transformation of the liquid metal into a low-surface-tension liquid, semi-solid paste, or even solid powder. The overcoming of the intrinsic high surface tension of the liquid metal with this approach unleashes the freedom to easily process the liquid metal composites into polymer composites or as direct molding processable paste and printable electronic ink.

Pushing OECTs toward Wearable: Development of a Miniaturized Analytical Control Unit for Wireless Device Characterization.

Organic electrochemical transistors (OECTs) have emerged as a next-generation biosensing technology because of their water-stability, cost-effectiveness, and ability to obtain high sensitivity at low operation voltage (mV). However, a miniaturized readout unit that can wirelessly characterize the overall performance of an OECT is still missing, which hinders the assembling of truly wearable OECT systems for continuous health-monitoring applications. In this work, we present a coin-sized analytical unit for remote and wireless OECT characterization, namely, a personalized electronic reader for electrochemical transistors (PERfECT). It has been verified that PERfECT can measure the transfer, output, hysteresis, and transient behavior of OECTs with resolution and sampling rate on par with the bulky equipment used in laboratories. PERfECT is also capable of characterizing other low-voltage transistors. An integrated board for multiplexed OECT characterizations (32 channels) has also been demonstrated. This work provides a missing building block for developing next-generation OECT-based bioelectronics for digital wearable applications.

Highly thermoconductive yet ultraflexible polymer composites with superior mechanical properties and autonomous self-healing functionality via a binary filler strategy.

It is still a formidable challenge to develop ideal thermal dissipation materials with simultaneous high thermal conductivity, excellent mechanical softness and toughness, and spontaneous self-healing. Herein, we report the introduction of sandwich-like boron nitride nanosheets-liquid metal binary fillers into an artificial poly(urea-urethane) elastomer to address the above issue, which confers the composite elastomer with a unique thermal-mechanical-healing combination, including a low modulus, high in-plane thermal conductivity and high mass loading of rigid fillers but self-recoverability and room-temperature self-healing.

A Multidirectionally Thermoconductive Phase Change Material Enables High and Durable Electricity via Real-Environment Solar-Thermal-Electric Conversion.

A solar thermoelectric generator (STEG) that generates electricity from sunlight is expected to be a promising technology for harvesting and conversion of clean solar energy. The integration of a phase-change material (PCM) with the STEG even more enables engines to durably generate power in spite of solar radiation flux. However, its photothermal conversion and output electricity is still limited (<15 W/m2) by the PCM's deficient thermal management performance, i.e., restricted thermal conductivity and nonuniform heat-transfer behavior under concentrated sunlight radiation. In this study, a biomimetic phase-change composite, with centrosymmetric and a multidirectionally aligned boron nitride network embedded in polyethylene glycol, is tailored for the STEG via a radial ice-template assembly and infiltration strategy, which behaves in a highly and multidirectionally thermoconductive way and enables a rapid transfer of heat flux and uniform temperature distribution with respect to even a spot-like heat source. As a consequence, a powerful STEG is tactfully designed via the integration of this high-thermal-management characteristic and maximum collection of solar beams, for durable and real-environment solar-thermal-electric conversion, with its photothermal energy conversion efficiency of up to 85.1% and a high peak power density of 40.28 W/m2.

Metal-Level Robust, Folding Endurance, and Highly Temperature-Stable MXene-Based Film with Engineered Aramid Nanofiber for Extreme-Condition Electromagnetic Interference Shielding Applications.

Polymer-based electromagnetic interference (EMI) shielding materials possess many irreplaceable advantages than metals, such as superior flexibility, easy processing, and low density. However, impeded by their limited mechanical properties, inferior temperature resistance and unsatisfactory electrical conductivity, it is still challenging to extend their shielding applications under some extreme conditions, i.e., <-50 or >200 °C. Herein, we report an ultrathin, highly robust, superflexible, and temperature-stable film via engineering a worm-like aramid nanofiber (ANF) into the rod-like microscopic configuration, followed with self-assembly with Ti3C2Tx (MXene) into a hierarchical brick-and-mortar architecture. With stiff and symmetric aromatic rings fully straightened and well packed into a crystalline form in the backbone, this rod-like ANF enables an augmented network with effective energy dissipation, resulting in the metal-like mechanical properties, i.e., unprecedented tensile strength (300.5 MPa), high Young's modulus (13.6 GPa), and excellent folding endurance (>10 000 times). More significantly, this MXene/ANF composite film with outstanding specific EMI shielding effectiveness (8814.5 dB cm2 g-1) and flame retardancy performs a broad range of operations in the temperature range from -100 °C (355 MPa) to 300 °C (136 MPa), in which >99% electromagnetic waves could be eliminated; this promises its potential EMI shielding applications even in some extreme conditions.

Highly Thermoconductive, Thermostable, and Super-Flexible Film by Engineering 1D Rigid Rod-Like Aramid Nanofiber/2D Boron Nitride Nanosheets.

Polymer-based thermal management materials have many irreplaceable advantages not found in metals or ceramics, such as easy processing, low density, and excellent flexibility. However, their limited thermal conductivity and unsatisfactory resistance to elevated temperatures (<200 °C) still prevent effective heat dissipation during applications with high-temperature conditions or powerful operation. Therefore, herein highly thermoconductive and thermostable polymer nanocomposite films prepared by engineering 1D aramid nanofiber (ANF) with worm-like microscopic morphologies into rigid rod-like structures with 2D boron nitride nanosheets (BNNS) are reported. With no coils or entanglements, the rigid polymer chain enables a well-packed crystalline structure resulting in a 20-fold (or greater) increase in axial thermal conductivity. Additionally, strong interfacial interactions between the weaved ANF rod and the stacked BNNS facilitate efficient heat flux through the 1D/2D configuration. Hence, unprecedented in-plane thermal conductivities as high as 46.7 W m-1 K-1 can be achieved at only 30 wt% BNNS loading, a value of 137% greater than that of a worm-like ANF/BNNS counterpart. Moreover, the thermally stable nanocomposite films with light weight (28.9 W m-1 K-1 /103 (kg m-3 )) and high strength (>100 MPa, 450 °C) enable effective thermal management for microelectrodes operating at temperatures beyond 200 °C.

Green Production of Regenerated Cellulose/Boron Nitride Nanosheet Textiles for Static and Dynamic Personal Cooling.

Personal cooling technology using functional clothing that could provide localized thermal regulation instead of cooling the entire space is regarded as a highly anticipated strategy to not only facilitate thermal comfort and human health but also be energy-saving and low-cost. The challenge is how to endow textiles with prominent cooling effect whenever the wearer is motionless or sportive. In this study, high content of edge-selective hydroxylated boron nitride nanosheets (BNNSs) up to 60 wt % was added into a biodegradable cellulose/alkaline/urea aqueous solution, and then regenerated cellulose (RCF)/BNNS multifilaments were successfully spun in a simple, low-cost, and environmentally friendly process, which was demonstrated to serve as both static and dynamic personal cooling textile. Typically, excellent axial thermal conductivity of RCF/BNNS filament rendered that body-generated heat could directly escape from skin to the outside surface of the textile by means of thermal conduction, achieving a much better static personal cooling result through continuous thermal radiation. Besides, synergistic effect between excellent heat dissipation capability and good hygroscopicity also resulted in much better dynamic cooling effect once the wearer is doing some sports, whose efficiency was even better than commercial hygroscopic textiles such as cotton and RCF.

Gradient Polydopamine Coating: A Simple and General Strategy toward Multishape Memory Effects.

Multi shape memory polymers (multi-SMPs) exhibit many potential applications such as aerospace, soft robotics, and biomedical devices because of their unique abilities. Although many works are done to broaden the preparations of multi-SMPs, the desire to a simple and versatile strategy as well as more complex shapes still exists. Moreover, a light-induced SMP shows more advantages than a thermal-induced one in many practical working circumstances. Herein, inspired by strong adhesion and efficient photothermal conversion of polydopamine (PDA) coating, we report a more simple and facile approach to prepare light-induced multi-SMPs by introducing a gradient PDA coating on a dual-SMP through time-controlled dipping. The photothermal converting properties with varying thicknesses of PDA under the tunable near-infrared light source are investigated. Then, light-induced multishape memory effects based on gradient PDA coatings are illustrated, where three designs of multi-SMPs - rectangle, triangle, and cross are prepared and demonstrated. Also, the evolutions of coating morphology during shape shifting are carefully studied. Finally, we present few complex designs of patterns and shapes as well as a design of potential application for the highly controllable smart devices. This strategy demonstrates a very simple and general strategy to design and prepare the light-induced multi-SMPs with complex shapes based on any thermal-responsive dual-SMPs.