A flexible omnidirectional rotating magnetic array for MRI-safe transdermal wireless energy harvesting through flexible electronics.

Magnetic resonance imaging (MRI)-safe implantable wireless energy harvester offers substantial benefits to patients suffering from brain disorders, hearing impairment, and arrhythmias. However, rigid magnets in cutting-edge systems with limited numbers of rotation axis impose high risk of device dislodgement and magnet failure. Here, a flexible omnidirectional rotating magnetic array (FORMA) and a flexible MRI-safe implantable wireless energy-harvesting system have been developed. Miniaturized flexible magnetic balls 1 millimeter in diameter achieved by molding three-dimensional printed templates can rotate freely in elastomer cavities and supply a magnetic force of 2.14 Newtons at a distance of 1 millimeter between an implantable receiver and a wearable transceiver. The system can work stably under an acceleration of 9g and obtain a power output of 15.62 decibel milliwatts at a transmission frequency of 8 megahertz. The development of the FORMA may lead to life-long flexible and batteryless implantable systems and offers the potential to promote techniques for monitoring and treating acute and chronic diseases.

Fully printed and self-compensated bioresorbable electrochemical devices based on galvanic coupling for continuous glucose monitoring.

Real-time glucose monitoring conventionally involves non-bioresorbable semi-implantable glucose sensors, causing infection and pain during removal. Despite bioresorbable electronics serves as excellent alternatives, the bioresorbable sensor dissolves in aqueous environments with interferential biomolecules. Here, the theories to achieve stable electrode potential and accurate electrochemical detection using bioresorbable materials have been proposed, resulting in a fully printed bioresorbable electrochemical device. The adverse effect caused by material degradation has been overcome by a molybdenum-tungsten reference electrode that offers stable potential through galvanic-coupling and self-compensation modules. In vitro and in vivo glucose monitoring has been conducted for 7 and 5 days, respectively, followed by full degradation within 2 months. The device offers a glucose detection range of 0 to 25 millimolars and a sensitivity of 0.2458 microamperes per millimolar with anti-interference capability and biocompatibility, indicating the possibility of mass manufacturing high-performance bioresorbable electrochemical devices using printing and low-temperature water-sintering techniques. The mechanisms may be implemented developing more comprehensive bioresorbable sensors for chronic diseases.

Flexible Thermoelectric Devices with Flexible Heatsinks of Phase-Change Materials and Stretchable Interconnectors of Semi-Liquid Metals.

Flexible thermoelectric (TE) devices offer great potential for wearable thermal management and self-powered systems, but heat dissipation and electrical interconnection remain key challenges. In this study, we address these issues by integrating flexible TE devices with phase-change material (PCM) heatsinks and stretchable semi-liquid metal (semi-LM) interconnectors. The effectiveness of PCMs with varying melting points for temperature regulation in different environmental conditions is demonstrated, delivering cooling effects exceeding 10 °C. Furthermore, the utilization of semi-LMs instead of LMs enables excellent stretchability and efficient heat dissipation. Moreover, the TE devices generate power with a density of 7.3 µW/cm2 at an ambient temperature of 22 °C, making it an ideal power source for a wearable self-powered sensing system. Successful integration into garments and armbands confirms the practicality and adaptability of these flexible thermoelectric devices, establishing them as critical components for future wearables with superior resilience to daily wear and tear.

In Situ Formation of Conductive Epidermal Electrodes Using a Fully Integrated Flexible System and Injectable Photocurable Ink.

In situ fabrication of wearable devices through coating approaches is a promising solution for the fast deployment of wearable devices and more adaptable devices for different sensing demands. However, heat, solvent, and mechanical sensitivity of biological tissues, along with personal compliance, pose strict requirements for coating materials and methods. To address this, a biocompatible and biodegradable light-curable conductive ink and an all-in-one flexible system that conducts in situ injection and photonic curing of the ink as well as monitoring of biophysiological information have been developed. The ink can be solidified through spontaneous phase changes and photonic cured to achieve a high mechanical strength of 7.48 MPa and an excellent electrical conductivity of 3.57 × 105 S/m. The flexible system contains elastic injection chambers embedded with specially designed optical waveguides to uniformly dissipate visible LED light throughout the chambers and rapidly cure the ink in 5 min. The resulting conductive electrodes offer intimate skin contact even with the existence of hair and work stably even under an acceleration of 8 g, leading to a robust wearable system capable of working under intense motion, heavy sweating, and varied surface morphology. Similar concepts may lead to various rapidly deployable wearable systems that offer excellent adaptability to different monitoring demands for the health tracking of large populations.

A flexible wearable device coupled with injectable Fe3O4 nanoparticles for capturing circulating tumor cells and triggering their deaths.

Elimination of circulating tumor cells (CTCs) in the blood can be an effective therapeutic approach to disrupt metastasis. Here, a strategy is proposed to implement flexible wearable electronics and injectable nanomaterials to disrupt the hematogenous transport of CTCs. A flexible device containing an origami magnetic membrane is used to attract Fe3O4@Au nanoparticles (NPs) that are surface modified with specific aptamers and intravenously injected into blood vessels, forming an invisible hand and fishing line/bait configuration to specifically capture CTCs through bonding with aptamers. Thereafter, thinned flexible AlGaAs LEDs in the device offer an average fluence of 15.75 mW mm-2 at a skin penetration depth of 1.5 mm, causing a rapid rise of temperature to 48 °C in the NPs and triggering CTC death in 10 min. The flexible device has been demonstrated for intravascular isolation and enrichment of CTCs with a capture efficiency of 72.31% after 10 cycles in a simulated blood circulation system based on a prosthetic upper limb. The fusion of nanomaterials and flexible electronics reveals an emerging field that utilizes wearable and flexible stimulators to activate biological effects offered by nanomaterials, leading to improved therapeutical effects and postoperative outcomes of diseases.

Thermal Transfer-Enabled Rapid Printing of Liquid Metal Circuits on Multiple Substrates.

Low-cost, rapid patterning of liquid metal on various substrates is a key processing step for liquid metal-based soft electronics. Current patterning methods rely on expensive equipment and specific substrates, which severely limit their widespread applications. Based on surface adhesion adjustment of liquid metal through thermal transferring toner patterns, we present a universal printing technique of liquid metal circuits. Without using any expensive processing steps or equipment, the circuit patterns can be printed quickly on thermal transfer paper using a desktop laser printer, and a toner on the thermal transfer paper can be transferred to various smooth substrates and polymer-coated rough substrates. The technique has yielded liquid metal circuits with a minimum linewidth of 50 µm fabricated on various smooth, rough, and three-dimensional substrates with complex morphology. The liquid metal circuits can maintain their functions even under an extreme strain of 800%. Various circuits such as LED arrays, multiple sensors, a flexible display, a heating circuit, a radiofrequency identification circuit, and a 12-lead electrocardiogram circuit on various substrates have been demonstrated, indicating the great potential of such a technique to rapidly achieve large-area flexible circuits for wearable health monitoring, internet of things, and consumer electronics at low cost and high efficiency.

Miniaturized soft centrifugal pumps with magnetic levitation for fluid handling.

Centrifugal pumps are essential mechanical components for liquid delivery in many biomedical systems whose miniaturization can promote innovative disease treatment approaches. However, centrifugal pumps are predominately constructed by rigid and bulky components. Here, we combine the soft materials and flexible electronics to achieve soft magnetic levitation micropumps (SMLMs) that are only 1.9 to 12.8 grams in weight. The SMLMs that rotate at a rotation speed of 1000 revolutions per min to pump liquids with various viscosities ranging from 1 to 6 centipoise can be used in assisting dialysis, blood circulation, and skin temperature control because of excellent biocompatibility with no organ damage. The development of SMLMs not only demonstrates the possibility to replace rigid rotating structures with soft materials for handling large volumes of fluids but also indicates the potential for fully flexible artificial organs that may revolutionize health care and improve the well-being of patients.

Water-Sintered Transient Nanocomposites Used as Electrical Interconnects for Dissolvable Consumer Electronics.

Rapid development of electronic technology shortens the development time for new products and accelerates the obsolescence of consumer electronics, resulting in the explosive growth of electronic waste that is difficult to recycle and hazardous to the environment and human health. Transient electronics that can dissolve in water may potentially be adopted to tackle the issues of electronic waste; however, promising approaches to yield large-scale and high-performance transient consumer electronics have not yet been developed. Here, the joint effect of galvanic corrosion and redeposition has been utilized to develop bimetallic transient nanocomposites, which can be printed and water-sintered to yield high-performance transient PCB circuits with excellent electrical conductivity and mechanical robustness. The entire sintering process requires no external energy and strict environmental conditions. The achieved PCB circuits offer a conductivity of 307,664.4 S/m that is among the highest in comparison with other printed transient circuits. The supreme performance of the transient circuits eventually leads to the first dissolvable smartwatch that offers the same functions and similar performance as conventional smartwatches and dissolves in water within 40 h. The joint effect of galvanic corrosion and redeposition between two metals with distinct activities leads to novel nanocomposites and processing techniques of transient electronics. The resulting high-performance transient devices may reshape the appearance of consumer electronics and reform the electronics recycling industry by reducing recycling costs and minimizing environmental pollution and health hazard.

Sub-thermionic, ultra-high-gain organic transistors and circuits.

The development of organic thin-film transistors (OTFTs) with low power consumption and high gain will advance many flexible electronics. Here, by combining solution-processed monolayer organic crystal, ferroelectric HfZrOx gating and van der Waals fabrication, we realize flexible OTFTs that simultaneously deliver high transconductance and sub-60 mV/dec switching, under one-volt operating voltage. The overall optimization of transconductance, subthreshold swing and output resistance leads to transistor intrinsic gain and amplifier voltage gain over 5.3 × 104 and 1.1 × 104, respectively, which outperform existing technologies using organics, oxides and low-dimensional nanomaterials. We further demonstrate battery-powered, integrated wearable electrocardiogram (ECG) and pulse sensors that can amplify human physiological signal by 900 times with high fidelity. The sensors are capable of detecting weak ECG waves (undetectable even by clinical equipment) and diagnosing arrhythmia and atrial fibrillation. Our sub-thermionic OTFT is promising for battery/wireless powered yet performance demanding applications such as electronic skins and radio-frequency identification tags, among many others.

Room-Temperature Ozone Sensing Capability of IGZO-Decorated Amorphous Ga2O3 Films.

In present work, we report a room-temperature ozone sensor using InGaZnO (IGZO)-decorated amorphous Ga2O3 (a-Ga2O3) thin films. The gas sensing tests demonstrate that the topmost IGZO modification can significantly promote the sensors' responsivity. Intriguingly, the sensing capability presents a first increasing and then decreasing tendency as the surface morphology of IGZO develops from dispersed particles to a continuous film. Finite difference time domain (FDTD) simulation results prove that IGZO nanoparticles can remarkably increase the surface density of photogenerated electrons, clearly manifesting a strong dependence on IGZO particle size and contributing to the boosted responsiveness. However, once IGZO particles coalesce into a thin film, the ozone sensor's responsivity starts to decrease even though the number of photogenerated carriers still increases. The smaller specific surface area of IGZO thin film is believed to be responsible for this phenomenon. The proposed ozone gas sensors own the merits of low cost, room-temperature detection, easy integration, and mass production, significantly expanding the application fields of a-Ga2O3 thin film.