To date, photothermal sensitizers include organic and inorganic nanomaterials for biomedical applications. However, the impediments of low biodegradability and potential toxicity hinder their further applications in clinics. Liquid metal nanospheres show superior photothermal effects under near-infrared laser irradiation, in addition, a transformation in shape can be triggered, which also promotes biodegradability that helps to avoid potential systemic toxicity. Here, we fabricated tunable liquid metal nanoparticles having sphere-shaped to rod-shaped characteristics, resulting in good biocompatibility, favorable photothermal conversion efficiency, and targeting capability to tumors. The synthesis strategy is easy to achieve through one-step sonication. We systematically evaluated the photothermal properties of these liquid metal nanoparticles as well as their destructive effects on tumors in a quantitative way both in vitro and in vivo under laser exposure. Results have shown for the first time in mice that gallium nanorods, regulated and controlled through the production of GaO(OH), displayed outstanding photothermal conversion efficiency and exhibited distinct temperature elevation compared to gallium nanospheres and gallium-indium alloy nanorods. These shape transformable and biocompatible gallium nanorods establish the basis for the future laser ablation of tumors to achieve enhanced therapeutic outcomes. This shape tunability of a smart nano-liquid metal directly contributes to enhanced photothermal therapy in mice and opens new opportunities for potential applications with tumor therapy and imaging.

Sensors are core elements to directly obtain information from surrounding objects for further detecting, judging and controlling purposes. With the rapid development of soft electronics, flexible sensors have made considerable progress, and can better fit the objects to detect and, thus respond to changes more sensitively. Recently, as a newly emerging electronic ink, liquid metal is being increasingly investigated to realize various electronic elements, especially soft ones. Compared to conventional soft sensors, the introduction of liquid metal shows rather unique advantages. Due to excellent flexibility and conductivity, liquid-metal soft sensors present high enhancement in sensitivity and precision, thus producing many profound applications. So far, a series of flexible and wearable sensors based on liquid metal have been designed and tested. Their applications have also witnessed a growing exploration in biomedical areas, including health-monitoring, electronic skin, wearable devices and intelligent robots etc. This article presents a systematic review of the typical progress of liquid metal-enabled soft sensors, including material innovations, fabrication strategies, fundamental principles, representative application examples, and so on. The perspectives of liquid-metal soft sensors is finally interpreted to conclude the future challenges and opportunities.

Liquid materials with the ability to transit between conductor and insulator are of great scientific and practical significance. However, achieving the conduction of a liquid metal droplet network is still a challenge. To solve these problems, a generalized method is proposed to fabricate temperature tunable liquid conductor–insulator transition composites, which is achieved firstly via freezing and thawing liquid metal droplets dispersed in dimethicone. Such composites also impart conductivity to the dispersed liquid metal droplet network. To illustrate the typical application of the thus realized materials, a visualized circuit is constructed based on the relationship between the color and the conduction. In addition, reconfigurable and repairable circuits are fabricated depending on the inherent liquid properties of these materials. Furthermore, this universal mechanism has been revealed via the abnormal volume expansion ratio of the liquid metal droplets during the phase change. By calculating the volume change ratio of all metals, we speculate and confirm that gallium-based alloys and bismuth-based alloys can be used to prepare such conductive transition materials. Accordingly, we identify more eligible materials with suitable phase transition points, which significantly extends the transition temperature from insulator to conductor. The liquid material preparation strategy proposed here provides a novel paradigm for achieving the conductor–insulator transition at a wide temperature range and offers promising potential for future applications.

Phase change materials that can absorb or release large amounts of heat during phase transition, play a critical role in many important processes, including heat dissipation, thermal energy storage, and solar energy utilization. In general, phase change materials are usually encapsulated in passive modules to provide assurance for energy management. The shape and mechanical changes of these materials are greatly ignored. An emerging class of phase change materials, liquid metals (LMs) have attracted significant interest beyond thermal management, including in transformable robots, flexible electronics, soft actuators, and biomedicine. Interestingly, the melting point of LM is highly tunable around body temperature, allowing it to experience considerable stiffness change when interacting with human organisms during solid–liquid change, which brings about novel phenomena, applied technologies, and therapeutic methods, such as mechanical destruction of tumors, neural electrode implantation technique, and embolization therapy. This review focuses on the technology, regulation, and application of the phase change process along with diverse changes of LM to facilitate emerging biomedical applications based on the influences of mechanical stiffness change and versatile regulation strategies. Typical applications will also be categorized and summarized. Lastly, the advantages and challenges of using the unique and reversible process for biomedicine will be discussed.