Mini/Micro/Nano Scale Liquid Metal Motors

Electronic skin based on natural biodegradable polymers for human motion monitoring

The wearability of the flexible electronic skin (e-skin) allows it to attach to the skin for human motion monitoring, which is essential for studying human motion and especially for assessing how well patients are recovering from rehabilitation therapy. However, the use of non-degradable synthetic materials in e-skin may raise skin safety concerns. Natural biodegradable polymers with advantages such as biodegradability, biocompatibility, sustainability, natural abundance, and low cost have the potential to be alternative materials for constructing flexible e-skin and applying them to human motion monitoring. This review summarizes the applications of natural biodegradable polymers in e-skin for human motion monitoring over the past three years, focusing on the discussion of cellulose, chitosan, silk fibroin, gelatin, and sodium alginate. Finally, we summarize the opportunities and challenges of e-skin based on natural biodegradable polymers. It is hoped that this review will provide insights for the future development of flexible e-skin in the field of human motion monitoring.

Gallium-based liquid metals as smart responsive materials: Morphological forms and stimuli characterization

Gallium-based liquid metals (GaLMs) have garnered monumental attention from the scientific community due to their diverse actuation characteristics. These metals possess remarkable characteristics, including high surface tension, excellent electrical and thermal conductivity, phase transformation behaviour, minimal viscosity and vapour pressure, lack of toxicity, and biocompatibility. In addition, GaLMs have melting points that are either lower or near room temperature, making them incredibly beneficial when compared to solid metals since they can be easily deformed. Thus, there has been significant progress in developing multifunctional devices using GaLMs, including bio-devices, flexible and self-healing circuits, and actuators. Despite numerous reports on these liquid metals (LMs), there is an urgent need for consolidated and coherent literature regarding their actuation principles linked to the targeted application. This will ensure that the reader gets the flavour of physics behind the actuation mechanism and how it can be utilized in diverse fields. Moreover, the actuation mechanism has been scattered in the literature, and thus, the primary motive of this review is to provide a one-stop solution for the actuation mechanism and the associated dynamics while directing the readers to specialized literature. Thus, addressing this issue, we thoroughly examine and present a detailed account of the actuation mechanisms of GaLMs while highlighting the science behind them. We also discuss the various morphologies of GaLMs and their crucial physical characteristics which decide their targeted application. Furthermore, we also delve into commonly held beliefs about GaLMs in the literature, such as their toxicity and antibacterial properties, to offer readers a more accurate understanding. Finally, we have explored several key unanswered aspects of the LM that should be explored in future research. The core strength of this review lies in its simplistic approach in offering a starting point for researchers venturing this innovative field, while we make use of existing literature to develop a comprehensive understanding.

Liquid Metal as Energy Conversion Sensitizers: Materials and Applications

Energy can exist in nature in a wide range of forms. Energy conversion refers to the process in which energy is converted from one form to another, and this process will be greatly enhanced by energy conversion sensitizers. Recently, an emerging class of new materials, namely liquid metals (LMs), shows excellent prospects as highly versatile materials. Notably, in terms of energy delivery and conversion, LMs functional materials are chemical responsive, heat-responsive, photo-responsive, magnetic-responsive, microwave-responsive, and medical imaging responsive. All these intrinsic virtues enabled promising applications in energy conversion, which means LMs can act as energy sensitizers for enhancing energy conversion and transport. Herein, first the unique properties of the light, heat, magnetic and microwave converting capacity of gallium-based LMs materials are summarized. Then platforms and applications of LM-based energy conversion sensitizers are highlighted. Finally, some of the potential applications and opportunities of LMs are prospected as energy conversion sensitizers in the future, as well as unresolved challenges. Collectively, it is believed that this review provides a clear perspective for LMs mediated energy conversion, and this topic will help deepen knowledge of the physical chemistry properties of LMs functional materials.

Smart Eutectic Gallium-Indium: From Properties to Applications

Eutectic gallium-indium (EGaIn), a liquid metal with a melting point close to or below room temperature, has attracted extensive attention in recent years due to its excellent properties such as fluidity, high conductivity, thermal conductivity, stretchability, self-healing capability, biocompatibility, and recyclability. These features of EGaIn can be adjusted by changing the experimental condition, and various composite materials with extended properties can be further obtained by mixing EGaIn with other materials. In this review, not only the are unique properties of EGaIn introduced, but also the working principles for the EGaIn-based devices are illustrated and the developments of EGaIn-related techniques are summarized. The applications of EGaIn in various fields, such as flexible electronics (sensors, antennas, electronic circuits), molecular electronics (molecular memory, opto-electronic switches, or reconfigurable junctions), energy catalysis (heat management, motors, generators, batteries), biomedical science (drug delivery, tumor therapy, bioimaging and neural interfaces) are reviewed. Finally, a critical discussion of the main challenges for the development of EGaIn-based techniques are discussed, and the potential applications in new fields are prospected.

Phase-Transitional Bismuth-Based Metals enable Rapid Embolotherapy, Hyperthermia, and Biomedical Imaging

Embolization has been an important minimally invasive therapy for occlusion of malfunctioned vasculature and tumor treatment via target delivering embolic agents. The limitation of conventional embolic agents, such as fabrication process, precipitation time, invisibility, and lack of integrated functions often leads to insufficient embolization efficacy. To overcome these drawbacks, a multifunctional bismuth (Bi)-based liquid embolic agent for simultaneous realization of embolotherapy, thermotherapy, as well as high-contrast biomedical imaging is proposed. Benefitting from the suitable melting point, flexible nature, metallic merit, and easygoing operation via injection, the versatile embolic agent can achieve rapid liquid-solid phase transition, magnetic hyperthermia, and multimodal imaging capability. The Bi-based materials are demonstrated with excellent arteriovenous embolization efficiency and favorable biocompatibility according to in vivo investigations. Introduction of the liquid embolic agent to tumor arteries achieves evident tumor regression and rather clear imaging under computed tomography (CT), magnetic resonance imaging (MRI), and thermographs for consistently tracking the implants over the biological body. Further, the combined therapy coupled with thermotherapy exhibits improved therapeutic efficiency with formation of necrosis and total tumor eradiation at day 15 after the treatment. The present innovative embolic agent and the surgical principle provide a promising modality for embolization and potential theranostic platform of tumors.

Responsive Liquid Metal Droplets: From Bulk to Nano

Droplets exist widely in nature and play an extremely important role in a broad variety of industrial processes. Typical droplets, including water and oil droplets, have received extensive attention and research, however their single properties still cannot meet diverse needs. Fortunately, liquid metal droplets emerging in recent years possess outstanding properties, including large surface tension, excellent electrical and thermal conductivity, convenient chemical processing, easy transition between liquid and solid phase state, and large-scale deformability, etc. More interestingly, liquid metal droplets with unique features can respond to external factors, including the electronic field, magnetic field, acoustic field, chemical field, temperature, and light, exhibiting extraordinary intelligent response characteristics. Their development over the past decade has brought substantial breakthroughs and progress. To better promote the advancement of this field, the present article is devoted to systematically summarizing and analyzing the recent fundamental progress of responsive liquid metal droplets, not only involving droplet characteristics and preparation methods, but also focusing on their diverse response behaviors and mechanisms. On this basis, the challenges and prospects related to the following development of liquid metal droplets are also proposed. In the future, responsive liquid metal droplets with a rapid development trend are expected to play a key role in soft robots, biomedicine, smart matter, and a variety of other fields.

Alkaline-Driven Liquid Metal Janus Micromotor with a Coating Material-Dependent Propulsion Mechanism

Micro/nanomotors have achieved huge progress in driving power divergence and accurate maneuver manipulations in the last two decades. However, there are still several obstacles to the potential biomedical applications, with respect to their biotoxicity and biocompatibility. Gallium- and indium-based liquid metal (LM) alloys are outstanding candidates for solving these issues due to their good biocompatibility and low biotoxicity. Hereby, we fabricate LM Janus micromotors (LMJMs) through ultrasonically dispersing GaInSn LM into microparticles and sputtering different materials as demanded to tune their moving performance. These LMJMs can move in alkaline solution due to the reaction between Ga and NaOH. There are two driving mechanisms when sputtering materials are metallic or nonmetallic. One is self-electrophoresis when sputtering materials are metallic, and the other one is self-diffusiophoresis when sputtering materials are nonmetallic. Our LMJMs can flip between those two modes by varying the deposited materials. The self-electrophoresis-driven LMJMs' moving speed is much faster than the self-diffusiophoresis-driven LMJMs' speed. The reason is that the former occurs galvanic corrosion reaction, while the latter is correlated to chemical corrosion reaction. The switching of the driving mechanism of the LMJMs can be used to fit into different biochemical application scenarios.