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Magnetorheological fluid (MRF) has shown its great potential in the development of large mechanical devices, such as dampers, shock absorbers, rotary brakes, clutches, and prosthetic joints. Recently, more research focus has been invested on using MRF to develop soft, stretchable, and miniaturized devices with variable stiffness for realizing functionalities that cannot be achieved using solid smart materials. Here, based on liquid metal magnetoactive slurries (LMMS), a variable stiffness wire with excellent electrical conductivity is demonstrated. Without exposure to a magnetic field, the LMMS wire has an extremely low stiffness, and can be easily stretched while maintaining an excellent electrical conductivity. When applying a magnetic field, the wire becomes much stiffer and can retain its shape even under a load. The combination of properties of flexibility, high electrical conductivity, and variable stiffness of the wire is harnessed to make a flexible gripper that can grasp objects of various shapes. Moreover, by using gallium instead of its liquid metal alloys, the tunable stiffness range of the LMMS wire is significantly enhanced and can be controlled using both external magnetic fields and temperature-induced phase change. The presented LMMS wire has the potential to be applied in flexible electronics, soft robotics and so on. [ABSTRACT FROM AUTHOR]

The ability to control interfacial tension electrochemically is uniquely available for liquid metals (LMs), in particular gallium‐based LM alloys. This imparts them with excellent locomotion and deformation capabilities and enables diverse applications. However, electrochemical oxidation of LM is a highly dynamic process, which often induces Marangoni instabilities that make it almost impossible to elongate LM and manipulate its morphology directly and precisely on a 2D plane without the assistance of other patterning methods. To overcome these limitations, this study investigates the use of an LM–iron (Fe) particle mixture that is capable of suppressing instabilities during the electrochemical oxidation process, thereby allowing for superelongation of the LM core of the mixture to form a thin wire that is tens of times of its original length. More importantly, the elongated LM core can be manipulated freely on a 2D plane to form complex patterns. Eliminating Marangoni instabilities also allows for the effective spreading and filling of the LM–Fe mixture into molds with complex structures and small features. Harnessing these excellent abilities, a channel‐less patterning method for fabricating elastomeric wearable sensors is demonstrated to detect motions. This study shows the potential for developing functional and flexible structures of LM with superior performance. [ABSTRACT FROM AUTHOR]

Unlike conventional microelectromechanical systems (MEMS), machines based on gallium liquid metal alloys rely on Marangoni flows to induce motion without mechanical moving parts. Despite this advantage, currently developed liquid metal enabled robotic systems still need the locomotion of liquid metal droplets, thereby generating weak actuating forces and limiting their manoeuvrability. Here, a liquid metal engine (LME) is created to work as a jet thruster to continuously power a robot boat without the need of locomotion. In addition, the engine is electrically driven by surface tension without any mechanical moving parts. The structural design and the parameters of operation of the LME are investigated and optimized. Finally, the manipulation of the LME using a motor control unit is demonstrated for driving an untethered robot boat to realize complex locomotion with the precise control over the direction and speed. Thus, this LME could offer new opportunities for developing high‐performance liquid metal machines to power robotic systems. [ABSTRACT FROM AUTHOR]

Gallium-based liquid metal alloys have been attracting attention from both industry and academia as soft, deformable, reconfigurable and multifunctional materials in microfluidic, electronic and electromagnetic devices. Although various technologies have been explored to control the morphology of liquid metals, there is still a lack of methods that can achieve precise morphological control over a free-standing liquid metal droplet without the use of mechanical confinement. Electrochemical manipulation can be relatively easy to apply to liquid metals, but there is a need for techniques that can enable automatic and precise control. Here, we investigate the use of an electrochemical technique combined with a feedback control system to automatically and precisely control the morphology of a free-standing liquid metal droplet in a sodium hydroxide solution. We establish a proof-of-concept platform controlled by a microcontroller to demonstrate the reconfiguration of a liquid metal droplet to desired patterns. We expect that this method will be further developed to realize future reconfigurable liquid metal-enabled soft robots. [ABSTRACT FROM AUTHOR]

Gallium‐based room temperature liquid metal alloys have recently been explored to be an emerging functional material. They have attracted particular attentions in a variety of applications due to their unique properties. Many of the applications are based on the precise control over the motion of liquid metal, and yet, the fact that currently lacking the advanced and reliable controlling methods greatly hinders the potential of liquid metal to be applied in a wider range of fields. In this study, an innovative approach is developed to obtain functional liquid metal (FLM) by modifying it with copper–iron magnetic nanoparticles (Cu–Fe NPs). The magnetic modification process enables the Cu–Fe NPs to be suspended within the liquid metal and form the FLM. The FLM exhibits similar appearance, actuating behaviors, and deformability in alkaline solutions to those of pure liquid metal alloys. Meanwhile, the magnetic modification enables the precise and rapid manipulation of the liquid metal using a magnetic field. Most importantly, for the first time, the precise control and climbing locomotion of the FLM is demonstrated with the interworking of both electric and magnetic fields simultaneously. The remarkable features of the FLM may represent vast potentials toward the development of future intelligent soft robots. An innovative electrochemistry‐assisted method for obtaining functional liquid metal (FLM) by modifying Galinstan with copper–iron magnetic nanoparticles is proposed. The FLM exhibits similar appearance, fluidity, and deformability as liquid metal without modification. Most importantly, the magnetic modification allows the precise control and climbing locomotion of the FLM with the interworking of both electric and magnetic fields simultaneously. [ABSTRACT FROM AUTHOR]

Functional liquid metal nanoparticles (NPs), produced from eutectic alloys of gallium, promise new horizons in the fields of sensors, microfluidics, flexible electronics, catalysis, and biomedicine. Here, the development of a vapor cavity generating ultrasonic platform for nebulizing liquid metal within aqueous media for the one‐step production of stable and functional liquid metal NPs is shown. The size distribution of the NPs is fully characterized and it is demonstrated that various macro and small molecules can also be grafted onto these liquid metal NPs during the liquid‐based nebulization process. The cytotoxicity of the NPs grafted with different molecules is further explored. Moreover, it is shown that it is possible to control the thickness of the oxide layer on the produced NPs using electrochemistry that can be embedded within the platform. It is envisaged that this platform can be adapted as a cost‐effective and versatile device for the rapid production of functional liquid metal NPs for future liquid metal‐based optical, electronic, catalytic, and biomedical applications. An ultrasonic platform for nebulizing liquid metal within aqueous media is developed to achieve one‐step production of stable and functional liquid metal nanoparticles grafted with different molecules. This platform is able to control the thickness of the oxide layer on the produced nanoparticles using embedded electrochemical components. The demonstrated technique may enable future liquid metal‐based electronic, catalytic, and biomedical applications. [ABSTRACT FROM AUTHOR]

Gallium (Ga) and Ga-based liquid metal (LM) alloys offer low toxicity, excellent electrical and thermal conductivities, and fluidity at or near room temperature. Ga-based LM particles (LMPs) synthesized from these LMs exhibit both fluidic and metallic properties and are suitable for versatile functionalization in therapeutics. Functionalized Ga-based LMPs can be actuated using physical or chemical stimuli for drug delivery, cancer treatment, bioimaging, and biosensing. However, many of the fundamentals of their unique characteristics for therapeutics remain underexplored. We present the most recent advances in Ga-based LMPs in therapeutics based on the underlying mechanisms of their design and implementation. We also highlight some future biotechnological opportunities for Ga-based LMPs based on their extraordinary advantages. The surface tension of gallium (Ga)-based liquid metals (LMs) can be broken using mechanical and chemical means, and smaller Ga-based LM particles (LMPs) can be constructed. Ga-based LMPs offer both fluidic and metallic cores and peculiar interfacial properties, which differ fundamentally from the properties of solid metal particles. Ga-based LMPs hold great potential for therapeutics. Functionalized Ga-based LMPs can be designed and activated for drug delivery, cancer treatment, bioimaging, and biosensing on stimulation by light, electromagnetic fields, mechanical means, or chemical reactions. Fundamental understanding of the effects of Ga-based LMPs' surface oxides, their interactions with cells and their organelles, and their specific alloy composition with other elements should be further explored to expand the horizons of therapeutics using LMPs. [ABSTRACT FROM AUTHOR]