Mussel-Inspired Multifunctional Integrated Liquid Metal-Based Magnetic Suspensions with Rheological, Magnetic, Electrical, and Thermal Reinforcement

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.

Magnetically Responsive Gallium-Based Liquid Metal: Preparation, Property and Application

Magnetically responsive soft smart materials have garnered significant academic attention due to their flexibility, remote controllability, and reconfigurability. However, traditional soft materials used in the construction of these magnetically responsive systems typically exhibit low density and poor thermal and electrical conductivities. These limitations result in suboptimal performance in applications such as medical radiography, high-performance electronic devices, and thermal management. To address these challenges, magnetically responsive gallium-based liquid metals have emerged as promising alternatives. In this review, we summarize the methodologies for achieving magnetically responsive liquid metals, including the integration of magnetic agents into the liquid metal matrix and the utilization of induced Lorentz forces. We then provide a comprehensive discussion of the key physicochemical properties of these materials and the factors influencing them. Additionally, we explore the advanced and potential applications of magnetically responsive liquid metals. Finally, we discuss the current challenges in this field and present an outlook on future developments and research directions.

LM-Gel Plasticine Based on Binary Cooperative with Kneadable Shaping and Conductivity

Liquid metal (LM)-based polymers have received growing interest for wearable health monitoring, electronic skins, and soft robotics. However, fabricating multifunctional LM-based polymers, in particular, featuring a convenient shaping ability while offering excellent deformability and conductivity remains a challenge. To overcome this obstacle, here, we propose a strategy to prepare LM-Gel "plasticine" (LGP) with great deformability, which is composed of a PVA (poly(vinyl alcohol)) soft network and an LM conductive phase. LGP can be easily constructed into different shapes such as plasticine and can be applied to different conditions (such as building a 3D circuit, circuit repair, and switch). Meanwhile, LGP has great conductivity (2.3 × 104 S/m) after surface annealing. Besides, LGP has a good electric heating performance, which shows the potential for application in wearable heating devices. Thus, this approach not only provides a way to prepare LM-polymer plasticine but also provides a novel perspective toward extending the applied range of LM-polymer composites.

Principles and methods of liquid metal actuators

As a promising material, liquid metals (LMs) have gained considerable interest in the field of soft robotics due to their ability to move as designed routines or change their shape dramatically under external stimuli. Inspired by the science fiction film Terminator, tremendous efforts have been devoted to liquid robots with high compliance and intelligence. How to manipulate LM droplets is crucial to achieving this goal. Accordingly, this review is dedicated to presenting the principles driving LMs and summarizing the potential methods to develop LM actuators of high maneuverability. Moreover, the recent progress of LM robots based on these methods is overviewed. The challenges and prospects of implementing autonomous robots have been proposed.

Stretchable surface electromyography electrode array patch for tendon location and muscle injury prevention

Surface electromyography (sEMG) can provide multiplexed information about muscle performance. If current sEMG electrodes are stretchable, arrayed, and able to be used multiple times, they would offer adequate high-quality data for continuous monitoring. The lack of these properties delays the widespread use of sEMG in clinics and in everyday life. Here, we address these constraints by design of an adhesive dry electrode using tannic acid, polyvinyl alcohol, and PEDOT:PSS (TPP). The TPP electrode offers superior stretchability (~200%) and adhesiveness (0.58 N/cm) compared to current electrodes, ensuring stable and long-term contact with the skin for recording (>20 dB; >5 days). In addition, we developed a metal-polymer electrode array patch (MEAP) comprising liquid metal (LM) circuits and TPP electrodes. The MEAP demonstrated better conformability than commercial arrays, resulting in higher signal-to-noise ratio and more stable recordings during muscle movements. Manufactured using scalable screen-printing, these MEAPs feature a completely stretchable material and array architecture, enabling real-time monitoring of muscle stress, fatigue, and tendon displacement. Their potential to reduce muscle and tendon injuries and enhance performance in daily exercise and professional sports holds great promise.

Reactive wetting enabled anchoring of non-wettable iron oxide in liquid metal for miniature soft robot

Magnetic liquid metal (LM) soft robots attract considerable attentions because of distinctive immiscibility, deformability and maneuverability. However, conventional LM composites relying on alloying between LM and metallic magnetic powders suffer from diminished magnetism over time and potential safety risk upon leakage of metallic components. Herein, we report a strategy to composite inert and biocompatible iron oxide (Fe3O4) magnetic nanoparticles into eutectic gallium indium LM via reactive wetting mechanism. To address the intrinsic interfacial non-wettability between Fe3O4 and LM, a silver intermediate layer was introduced to fuse with indium component into AgxIny intermetallic compounds, facilitating the anchoring of Fe3O4 nanoparticles inside LM with improved magnetic stability. Subsequently, a miniature soft robot was constructed to perform various controllable deformation and locomotion behaviors under actuation of external magnetic field. Finally, practical feasibility of applying LM soft robot in an ex vivo porcine stomach was validated under in-situ monitoring by endoscope and X-ray imaging.

Recent progress in liquid metal printing and its applications

This paper focuses on the latest research printing technology and broad application for flexible liquid metal (LM) materials. Through the newest template printing method, centrifugal force assisted method, pen lithography technology, and laser method, the precision of liquid metal printing on the devices was improved to 10 nm. The development of novel liquid metal inks, such as PVA-LM ink and ethanol/PDMS/LM double emulsion ink, have further enhanced the recovery, rapid printing, high conductivity, and strain resistance. At the same time, liquid metals also show promise in the application of biochemical sensors, photocatalysts, composite materials, driving machines, and electrode materials. Liquid metals have been applied to biomedical, pressure/gas, and electrochemical sensors. The sensitivity, biostability, and electrochemical performance of these LM sensors were improved rapidly. They could continue to be used in healthy respiratory, heartbeat monitoring, and dopamine detection. Meanwhile, the applications of liquid metal droplets in catalytic-assisted MoS2 deposition, catalytic growth of two-dimensional (2D) lamellar, catalytic free radical polymerization, catalytic hydrogen absorption/dehydrogenation, photo/electrocatalysis, and other fields were also summarized. Through improving liquid metal composites, magnetic, thermal, electrical, and tensile enhancement alloys, and shape memory alloys with excellent properties could also be prepared. Finally, the applications of liquid metal in micro-motors, intelligent robot feet, nanorobots, self-actuation, and electrode materials were also summarized. This paper comprehensively summarizes the practical application of liquid metals in different fields, which helps understand LMs development trends, and lays a foundation for subsequent research.

A liquid metal-polydopamine composite for cell culture and electro-stimulation

Gallium (Ga) is a low melting point metal in the liquid state in the biological environment which presents a unique combination of fluidity, softness, and metallic electrical and thermal properties. In this work, liquid Ga is proposed as a biocompatible electrode material for cell culture by electro-stimulation since the cytotoxicity of Ga is generally considered low and some Ga compounds have been reported to exhibit anti-bacterial and anti-inflammatory activities. Complementarily, polydopamine (PDA) was coated on liquid Ga to increase the attachment capability of cells on the liquid Ga electrode and provide enhanced biocompatibility. The liquid Ga layer could be readily painted at room temperature on a solid inert substrate, followed by the formation of a nanoscale PDA coating layer resulting in a conformable and biocompatible composite electrode. The PDA layer was shown to coordinate with Ga³⁺, which is sourced from liquid Ga, providing electrical conductivity in the cell culture medium. The PDA-Ga³⁺ composite acted as a conductive substrate for advanced electro-stimulation for cell culture methods of representative animal fibroblasts. The cell proliferation was observed to increase by ∼143% as compared to a standard glass coverslip at a low potential of 0.1 V of direct coupling stimulation. This novel PDA-Ga³⁺ composite has potential applications in cell culture and regenerative medicine.

Recent Advances in Thermal Interface Materials for Thermal Management of High-Power Electronics

With the increased level of integration and miniaturization of modern electronics, high-power density electronics require efficient heat dissipation per unit area. To improve the heat dissipation capability of high-power electronic systems, advanced thermal interface materials (TIMs) with high thermal conductivity and low interfacial thermal resistance are urgently needed in the structural design of advanced electronics. Metal-, carbon- and polymer-based TIMs can reach high thermal conductivity and are promising for heat dissipation in high-power electronics. This review article introduces the heat dissipation models, classification, performances and fabrication methods of advanced TIMs, and provides a summary of the recent research status and developing trends of micro- and nanoscale TIMs used for heat dissipation in high-power electronics.

Liquid Metal Composites with Enhanced Thermal Conductivity and Stability Using Molecular Thermal Linker

Gallium-based liquid metal (LM) composite with metallic fillers is an emerging class of thermal interface materials (TIMs), which are widely applied in electronics and power systems to improve their performance. In situ alloying between gallium and many metallic fillers like copper and silver, however, leads to a deteriorated composite stability. This paper presents an interfacial engineering approach using 3-chloropropyltriethoxysilane (CPTES) to serve as effective thermal linkers and diffusion barriers at the copper-gallium oxide interfaces in the LM matrix, achieving an enhancement in both thermal conductivity and stability of the composite. By mixing LM with copper particles modified by CPTES, a thermal conductivity (κ) as high as 65.9 W m^-1 K^-1 is achieved. In addition, κ can be tuned by altering the terminal groups of silane molecules, demonstrating the flexibility of this approach. The potential use of such composite as a TIM is also shown in the heat dissipation of a computer central processing unit. While most studies on LM-based composites enhance the material performance via direct mixing of various fillers, this work provides a different approach to fabricate high-performance LM-based composites and may further advance their applications in various areas including thermal management systems, flexible electronics, consumer electronics, and biomedical systems.