Recent Development in Liquid Metal Materials

Liquid Metal-Based Frequency and Pattern Reconfigurable Yagi Antenna for Pressure Sensing

In this work, a frequency- and pattern-reconfigurable Yagi antenna based on liquid metal (LM) switches is proposed for pressure sensing and health monitoring. The proposed antenna consists of a dipole radiator, a reflector, a director, a dielectric substrate, and four flexible LM switches. Benefitted from the switching effect of the LM switches under external pressure, the frequency and radiation pattern of the antenna can be reconfigured. When the LM switch is fully or partially turned on, the radiation directions of the antenna are bidirectionally end-shot and end-fired, respectively. The operating frequency of the antenna can be tuned from 2.28 GHz to 2.5 GHz. It is shown that a maximum gain of 6 dBi can be obtained. A sample was fabricated and measured, and the experimental results were in good agreement with the simulations. The reconfigurable antenna can be applied in wireless pressure-sensing and health-monitoring systems.

In Vitro Assessment of Gallium Nanoalloy Hydrogels for Antimicrobial and Wound Healing Applications

Chronic and recurring wounds pose a significant challenge in modern healthcare, leading to substantial morbidity. These wounds allow pathogens to colonize, potentially resulting in local and systemic infections. Current interventions need to be revised and become increasingly less reliable due to the emergence of antibiotic resistance. In the present study, we aim to address these issues by fabricating hydrogels impregnated with gallium-based nanoalloys for their antimicrobial activity. Gallium liquid metal nanoparticles (approximately 100 nm in diameter) were alloyed in different combinations with bismuth and silver ions through a galvanic replacement reaction. These multimetallic hydrogels showed favorable antibacterial activity against the Gram-positive Staphylococcus aureus and the Gram-negative Pseudomonas aeruginosa, as observed with fluorescence microscopy and inhibition assays. The multimetallic hydrogels showed no toxicity against murine macrophages or human dermal fibroblasts and enhanced in vitro wound healing. The development of these innovative gallium-based hydrogels represents a promising strategy to combat chronic wounds and their associated complications, offering an effective alternative to current antimicrobial treatments amidst rising antibiotic resistance.

A Review of Conductive Hydrogel-Based Wearable Temperature Sensors

Conductive hydrogel has garnered significant attention as an emergent candidate for diverse wearable sensors, owing to its remarkable and tailorable properties such as flexibility, biocompatibility, and strong electrical conductivity. These attributes make it highly suitable for various wearable sensor applications (e.g., biophysical, bioelectrical, and biochemical sensors) that can monitor human health conditions and provide timely interventions. Among these applications, conductive hydrogel-based wearable temperature sensors are especially important for healthcare and disease surveillance. This review aims to provide a comprehensive overview of conductive hydrogel-based wearable temperature sensors. First, this work summarizes different types of conductive fillers-based hydrogel, highlighting their recent developments and advantages as wearable temperature sensors. Next, this work discusses the sensing characteristics of conductive hydrogel-based wearable temperature sensors, focusing on sensitivity, dynamic stability, stretchability, and signal output. Then, state-of-the-art applications are introduced, ranging from body temperature detection and wound temperature detection to disease monitoring. Finally, this work identifies the remaining challenges and prospects facing this field. By addressing these challenges with potential solutions, this review hopes to shed some light on future research and innovations in this promising field.

Soft Bioelectronics for Heart Monitoring

Cardiovascular diseases (CVDs) are a predominant global health concern, accounting for over 17.9 million deaths in 2019, representing approximately 32% of all global fatalities. In North America and Europe, over a million adults undergo cardiac surgeries annually. Despite the benefits, such surgeries pose risks and require precise postsurgery monitoring. However, during the postdischarge period, where monitoring infrastructures are limited, continuous monitoring of vital signals is hindered. In this area, the introduction of implantable electronics is altering medical practices by enabling real-time and out-of-hospital monitoring of physiological signals and biological information postsurgery. The multimodal implantable bioelectronic platforms have the capability of continuous heart sensing and stimulation, in both postsurgery and out-of-hospital settings. Furthermore, with the emergence of machine learning algorithms into healthcare devices, next-generation implantables will benefit artificial intelligence (AI) and connectivity with skin-interfaced electronics to provide more precise and user-specific results. This Review outlines recent advancements in implantable bioelectronics and their utilization in cardiovascular health monitoring, highlighting their transformative deployment in sensing and stimulation to the heart toward reaching truly personalized healthcare platforms compatible with the Sustainable Development Goal 3.4 of the WHO 2030 observatory roadmap. This Review also discusses the challenges and future prospects of these devices.

Bioinspired Liquid Metal Based Soft Humanoid Robots

The pursuit of constructing humanoid robots to replicate the anatomical structures and capabilities of human beings has been a long-standing significant undertaking and especially garnered tremendous attention in recent years. However, despite the progress made over recent decades, humanoid robots have predominantly been confined to those rigid metallic structures, which however starkly contrast with the inherent flexibility observed in biological systems. To better innovate this area, the present work systematically explores the value and potential of liquid metals and their derivatives in facilitating a crucial transition towards soft humanoid robots. Through a comprehensive interpretation of bionics, an overview of liquid metals' multifaceted roles as essential components in constructing advanced humanoid robots-functioning as soft actuators, sensors, power sources, logical devices, circuit systems, and even transformable skeletal structures-is presented. It is conceived that the integration of these components with flexible structures, facilitated by the unique properties of liquid metals, can create unexpected versatile functionalities and behaviors to better fulfill human needs. Finally, a revolution in humanoid robots is envisioned, transitioning from metallic frameworks to hybrid soft-rigid structures resembling that of biological tissues. This study is expected to provide fundamental guidance for the coming research, thereby advancing the area.

Fabrication of Poly(ionic liquid) Hydrogels Incorporating Liquid Metal Microgels for Enhanced Synergistic Antifouling Applications

Hydrogels are ideal for antifouling materials due to their high hydrophilicity and low adhesion properties. Herein, poly(ionic liquid) hydrogels integrated with zwitterionic copolymer-functionalized gallium-based liquid metal (PMPC-GLM) microgels were successfully prepared by a one-pot reaction. Poly(ionic liquid) hydrogels (IL-Gel) were obtained by chemical cross-linking the copolymer of ionic liquid, acrylic acid, and acrylamide, and the introduction of ionic liquid (IL) significantly increased the cross-linking density; this approach consequently enhanced the mechanical and antiswelling properties of the hydrogels. The swelling ratio of IL-Gel decreased eight times compared to the original hydrogels. PMPC-GLM microgels were prepared through grafting the zwitterionic polymer PMPC onto the GLM nanodroplet surface, which exhibited efficient antifouling performance attributed to the bactericidal effect of Ga3+ and the antibacterial effect of the zwitterionic polymer layer PMPC. Based on the synergistic effect of PMPC-GLM microgels and IL, the composite hydrogels PMPC-GLM@IL-Gel not only exhibited excellent mechanical and antiswelling properties but also showed outstanding antibacterial and antifouling properties. Consequently, PMPC-GLM@IL-Gel hydrogels achieved inhibition rates of over 90% against bacteria and more than 85% against microalgae.

Tripling of the scattering vector range of X-ray reflectivity on liquid surfaces using a double-crystal deflector

The maximum range of perpendicular momentum transfer (q z) has been tripled for X-ray scattering from liquid surfaces when using a double-crystal deflector setup to tilt the incident X-ray beam. This is achieved by employing a higher-energy X-ray beam to access Miller indices of reflecting crystal atomic planes that are three times higher than usual. The deviation from the exact Bragg angle condition induced by misalignment between the X-ray beam axis and the main rotation axis of the double-crystal deflector is calculated, and a fast and straightforward procedure to align them is deduced. An experimental method of measuring scattering intensity along the q z direction on liquid surfaces up to q z = 7 Å-1 is presented, with liquid copper serving as a reference system for benchmarking purposes.

In Situ and Operando X-ray Scattering Methods in Electrochemistry and Electrocatalysis

Electrochemical and electrocatalytic processes are of key importance for the transition to a sustainable energy supply as well as for a wide variety of other technologically relevant fields. Further development of these processes requires in-depth understanding of the atomic, nano, and micro scale structure of the materials and interfaces in electrochemical devices under reaction conditions. We here provide a comprehensive review of in situ and operando studies by X-ray scattering methods, which are powerful and highly versatile tools to provide such understanding. We discuss the application of X-ray scattering to a wide variety of electrochemical systems, ranging from metal and oxide single crystals to nanoparticles and even full devices. We show how structural data on bulk phases, electrode-electrolyte interfaces, and nanoscale morphology can be obtained and describe recent developments that provide highly local information and insight into the composition and electronic structure. These X-ray scattering studies yield insights into the structure in the double layer potential range as well as into the structural evolution during electrocatalytic processes and phase formation reactions, such as nucleation and growth during electrodeposition and dissolution, the formation of passive films, corrosion processes, and the electrochemical intercalation into battery materials.

Emerging Functional Polymer Composites for Tactile Sensing

In recent years, extensive research has been conducted on the development of high-performance flexible tactile sensors, pursuing the next generation of highly intelligent electronics with diverse potential applications in self-powered wearable sensors, human-machine interactions, electronic skin, and soft robotics. Among the most promising materials that have emerged in this context are functional polymer composites (FPCs), which exhibit exceptional mechanical and electrical properties, enabling them to be excellent candidates for tactile sensors. Herein, this review provides a comprehensive overview of recent advances in FPCs-based tactile sensors, including the fundamental principle, the necessary property parameter, the unique device structure, and the fabrication process of different types of tactile sensors. Examples of FPCs are elaborated with a focus on miniaturization, self-healing, self-cleaning, integration, biodegradation, and neural control. Furthermore, the applications of FPC-based tactile sensors in tactile perception, human-machine interaction, and healthcare are further described. Finally, the existing limitations and technical challenges for FPCs-based tactile sensors are briefly discussed, offering potential avenues for the development of electronic products.

Liquid metal enabled conformal electronics

The application of three-dimensional common electronics that can be directly pasted on arbitrary surfaces in the fields of human health monitoring, intelligent robots and wearable electronic devices has aroused people's interest, especially in achieving stable adhesion of electronic devices on biological dynamic three-dimensional interfaces and high-quality signal acquisition. In recent years, liquid metal (LM) materials have been widely used in the manufacture of flexible sensors and wearable electronic devices because of their excellent tensile properties and electrical conductivity at room temperature. In addition, LM has good biocompatibility and can be used in a variety of biomedical applications. Here, the recent development of LM flexible electronic printing methods for the fabrication of three-dimensional conformal electronic devices on the surface of human tissue is discussed. These printing methods attach LM to the deformable substrate in the form of bulk or micro-nano particles, so that electronic devices can adapt to the deformation of human tissue and other three-dimensional surfaces, and maintain stable electrical properties. Representative examples of applications such as self-healing devices, degradable devices, flexible hybrid electronic devices, variable stiffness devices and multi-layer large area circuits are reviewed. The current challenges and prospects for further development are also discussed.

Electric current-assisted manipulation of liquid metals using a stylus at micro-and nano-scales

A novel methodology, based on wetting and electromigration, for transporting liquid metal, over long distances, at micro-and nano-scale using a stylus is reported. The mechanism is analogous to a dropper that uses 'suction and release' actions to 'collect and dispense' liquid. In our methodology, a stylus coated with a thin metal film acts like the dropper that collects liquid metal from a reservoir upon application of an electric current, holds the liquid metal via wetting while carrying the liquid metal over large distances away from the reservoir and drops it on the target location by reversing the direction of electric current. Essentially, the working principle of the technique relies on the directionality of electromigration force and adhesive force due to wetting. The working of the technique is demonstrated by using an Au-coated Si micropillar as the stylus, liquid Ga as the liquid metal to be transported, and a Kleindiek-based position micro-manipulator to traverse the stylus from the liquid reservoir to the target location. For demonstrating the potential applications, the technique is utilized for closing a micro-gap by dispensing a minuscule amount of liquid Ga and conformally coating the desired segment of the patterned thin films with liquid Ga. This study confirms the promising potential of the developed technique for reversible, controlled manipulation of liquid metal at small length scales.

Flexible Tactile Sensing Microfibers Based On Liquid Metals

High-performance and intelligent fibers are indispensable parts of wearable electronics in the future. This work mainly demonstrates the preparation of flexible intelligent liquid metal (LM) fibers with three core-sheath structures. An ultra-thin (10-50 μm), conductive, and highly flexible LM was deposited on the fiber core [carbon/polyethylene terephthalate (C/PET)--150-500 μm] along the fiber direction and then deposited on a polymer-protective layer [polyvinyl alcohol/epoxy resin (PVA/EP)--10 μm]. Four kinds of LM intelligent fibers were manufactured, including the C-LM-PVA fiber, C-LM-EP fiber, PET-LM-PVA fiber, and PET-LM-EP fiber. These LM intelligent fibers (diameter, 150-600 μm) were demonstrated with a high conductivity of 7.839 × 104 S·m-1. The changes in resistance in different torsion directions were measured, and these smart LM fibers could also be used as electrical heaters or thermoelectric generators, which released heat (36-36.9 °C/1-1.5 V) into the environment. Then, these multifunctional LM fibers were applied as high-performance strain sensors and bending sensors. These flexible LM conductive fibers could be successfully utilized in intelligent wearable fabrics and were expected to be widely utilized in artificial muscle and sensor fields.

Laser-Engraved Liquid Metal Circuit for Wearable Electronics

Conventional patterning methods for producing liquid metal (LM) electronic circuits, such as the template method, use chemical etching, which requires long cycle times, high costs, and multiple-step operations. In this study, a novel and reliable laser engraving micro-fabrication technology was introduced, which was used to fabricate personalized patterns of LM electronic circuits. First, by digitizing the pattern, a laser printing technology was used to burn a polyethylene (PE) film, where a polydimethylsiloxane (PDMS) or paper substrate was used to produce grooves. Then, the grooves were filled with LM and the PE film was removed; finally, the metal was packaged with PDMS film. The experimental results showed that the prepared LM could fabricate precise patterned electronic circuits, such as golden serpentine curves and Peano curves. The minimum width and height of the LM circuit were 253 μm and 200 μm, respectively, whereas the printed LM circuit on paper reached a minimum height of 26 μm. This LM flexible circuit could also be adapted to various sensor devices and was successfully applied to heart rate detection. Laser engraving micro-processing technologies could be used to customize various high-resolution LM circuit patterns in a short time, and have broad prospects in the manufacture of flexible electronic equipment.

Supported Cu/W/Mo/Ni—Liquid Metal Catalyst with Core-Shell Structure for Photocatalytic Degradation

Room-temperature liquid metal is a very ideal material for the design of catalytic materials. At low temperatures, the liquid metal enters the liquid state. It provides an opportunity to utilize the liquid phase in the catalysis, which is far superior to the traditional solid-phase catalyst. Aiming at the low performance and narrow application scope of the existing single-phase liquid metal catalyst, this paper proposed a type of liquid metal/metal oxide core-shell composite multi-metal catalyst. The Ga2O3 core-shell heterostructure was formed by chemical modification of liquid metals with different nano metals Cu/W/Mo/Ni, and it was applied to photocatalytic degrading organic contaminated raw liquor. The effects of different metal species on the rate of catalytic degradation were explored. The selectivity and stability of the LM/MO core-shell composite catalytic material were clarified, and it was found that the Ni-LM catalyst could degrade methylene blue and Congo red by 92% and 79%, respectively. The catalytic mechanism and charge transfer mechanism were revealed by combining the optical band gap value. Finally, we provided a theoretical basis for the further development of liquid metal photocatalytic materials in the field of new energy environments.