Magnetically Powered Shape‐Transformable Liquid Metal Micromotors

Abstract

The creation of micromotors that can convert stored energy to autonomous movement would be of great value in various applications, ranging from chemical sensing to precision water-quality screening and from cleaning clogged arteries to repairing microscopic cracks. Many of micromotors, based on different propulsion mechanisms (e.g., magnetic fields, ultrasound filed, chemical fuels, light, and bubble propulsion), [1][2][3][4][5][6][7][8][9] have been designed and fabricated over the past decade. Generally, they are built of rigid materials [10] to maintain a good maneuverability, but often with limited body compliance and adaptability in confined spaces. [11][12][13] In contrast to the hard Shape-transformable liquid metal (LM) micromachines have attracted the attention of the scientific community over the past 5 years, but the inconvenience of transfer routes and the use of corrosive fuels have limited their potential applications. In this work, a shape-transformable LM micromotor that is fabricated by a simple, versatile ice-assisted transfer printing method is demonstrated, in which an ice layer is employed as a "sacrificial" substrate that can enable the direct transfer of LM micromotors to arbitrary target substrates conveniently. The resulting LM microswimmers display efficient propulsion of over 60 µm s −1 (≈3 bodylength s −1 ) under elliptically polarized magnetic fields, comparable to that of the common magnetic micro/ nanomotors with rigid bodies. Moreover, these LM micromotors can undergo dramatic morphological transformation in an aqueous environment under the irradiation of an alternating magnetic field. The ability to transform the shape and efficiently propel LM microswimmers holds great promise for chemical sensing, controlled cargo transport, materials science, and even artificial intelligence in ways that are not possible with rigid-bodies microrobots.bodied, nature has created a wide range of biological motors with deformable bodies at small scales. They often have strong ability to actively adapt to their environment, thus can perform various demanding tasks in complex environments. Inspired by nature, researchers have begun to explore the design and control shape-transformable micromotors composed of compliant materials [14,15] (e.g., hydrogels, [16] granular media, [17] lowmelting point alloys, [18,19] and electroactive polymers [14] ) to ensure maneuverability, adaptability and agility in practical applications. Liquid metals (LMs) are typical examples of highly extensible and adaptable compliant materials, [20,21] such as Gallium and gallium-containing alloys (e.g., eutectic gallium-indium (EGaIn): 75% gallium and 25% indium; Galinstan: 68.5% gallium, 21.5% indium, and 10% tin). One of the most striking features of these gallium-based liquid metals is the nearly instant formation of a passivating oxide layer on their surface in the present of oxygen. This oxide layer (mainly composed of Ga 2 O 3 ) mechanically stabilizes the liquid metals into nonequilibrium shapes [22] and can be removed ...

Mini/Micro/Nano Scale Liquid Metal Motors

“…LMMMs are generally in the shape of spheres [45], rods [46], and rice ( Figure 2A) [47], which is determined by fabrication methods and parameters [46,48]. There are three common methods to prepare MCLMTs: Sonication [25], transfer printing [49], and pressurefilter-template [9] methods. The former one can produce LMMMs in the sphere, rod, and rice shape by varying parameters.…”

“…By contrast, spheres can be hardly propelled by these two fields, because the symmetry lengths of diameters cannot produce enough pressure difference. For MCLMTs motivated by magnetic fields, special designs such as helical tails and dumbbell-like shapes are required [49]. Besides, the function of LMNPs can also be influenced by their shape.…”

“…In contrast, a smaller magnetic field created by a neodymium magnet fails to induce this shape transformation. When the heat is insufficient to promote the oxidation and the drag force is too weak to change the surface area, another type of shape transforms of LM nanomaterial will be triggered [49]. With an alternating magnetic field (AMF) irradiation, the EGaIn MNMTs underwent a morphological transformation from a bowling-pin-like shape to a sphere in an aqueous environment ( Figure 4D).…”

Micro/nanoscale magnetic robots for biomedical applications

“…They are often used to actuate helical robots, one of the most widely used designs of microrobots or nanorobots whose actuation is achieved by the induction of rolling, corkscrew, and spin-top motions [ [42] , [43] , [44] ]. It has been found in the literature that the magnetic particle aggregates and some other interesting structures can be manipulated by rotating magnetic fields as well [ [45] , [46] , [47] , [48] , [49] , [50] ].…”

Self‐Propelled Micro/Nanomotors for Tumor Targeting Delivery and Therapy

“…Another interesting research about magnetic micromotors was reported by Liu et al recently. [58] In this study, they presented a design and fabrication of shape-transformable liquid metal micromotors using The magnetic field acting on the micromotor could make the motor wobbles rapidly, which immediately broke the symmetry of pressure distribution in fluid and then led to the motion of micromotors. Furthermore, due to the oxide layer of EGaIn was broken by local heat during the conversion from magnetic energy, the liquid metal micromotors could undergo a morphological transformation.…”