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在最新出版的《半导体学报》2019年第12期上，吉林大学张永来教授介绍了激光加工石墨烯柔性机器人的研究进展。分析了石墨烯作为柔性机器人主体材料的独特优势，如机械强度高、导电/导热性好、生物兼容性好、柔性、透明等。激光加工技术作为一种超精细、非接触、无掩膜的程序化加工方式，在石墨烯器件制备和集成方面体现出高效率、灵活图案化、精确物性调控等优点。
经过多年研究积累，研究者们已经实现利用各种激光调节石墨烯材料的物性和形貌，并通过复合或者杂化的方式对其改性，还发现了石墨烯材料的敏感特性，可以对多种环境信号产生应变，实现刺激响应驱动等功能。利用激光制备石墨烯机器人可以巧妙的解决目前柔性机器人所面临的运动方式简单、功能单一等问题。目前，人们已经可以利用激光加工技术制备出多重响应、功能丰富、高度集成的石墨烯柔性传感器与执行器，为研究开发灵活、可靠的石墨烯MEMS技术和柔性机器人提供了重要支撑。
Soft robots are a kind of intelligent systems, which can achieve predetermined functions independently through its own deformation or under environmental stimuli. Unlike traditional robots based on rigid materials, soft robots exhibit distinct advantages such as non-invasive, highly integrated and holistic functionalized properties. Actuators based on soft materials have been widely investigated and introduced into robotic systems. However, at present, most soft robots can only realize simple and basic deformation, such as bending, rotating, vibration, and reconfiguration performances. In this regard, robots that possess multi-functionality and permit flexible manipulation are highly desired, especially for their potential applications in artificial intelligence. To bridge this gap, novel materials and effective fabrication technologies are thus becoming increasingly important.
As a well-known flexible 2D material, graphene has been successfully prepared by mechanical exfoliation in 2004. Afterwards, enormous works emerge extensively. Considerable studies have been focused on the controllable preparation of graphene and graphene-related materials, morphologies of which can be well tuned from micro to macro structures, such as quantum dots, nanosheets, nanoribbons, nanomeshes in microscopic and various macro-structures (fiber, ribbon, film, paper, foam)[1]. Graphene has many unique properties, i.e. excellent electrical/thermal conductivity, high optical transparency, and high mechanical strength. All of these physical properties can be further adjusted through doping, hybridizing and mixing with other chemical components, making graphene a superior material for robot design. For example, taking advantage of the good conductivity of graphene, electric-driven actuators with large deflection (> 1.0 cm-1) under low input voltage (≤ 5 V) were achieved[2]. Utilizing the good photothermal effect of graphene, Ying et al. successfully designed an optical-driven rolling and folding system[3]. Graphene oxide (GO), as one of the important graphene derivatives, features unique water adsorption property. Large amounts of oxygen-containing functional groups within GO layers make it possible to develop humidity-driven soft robots[4]. Actuations triggered by other stimulation signals, such as magnetism and pH, can be realized by hybridizing/mixing graphene with corresponding functional materials. Nowadays, research on the topic of soft robots based on graphene is still in its infancy. Graphene soft robots for commercialization and functionalized usage are still challenging.
After the rapid progress of laser fabrication technique these years, laser fabrication becomes more developed and powerful. Especially, in the case of processing graphene-related materials, no matter the surface/interface properties or the physical/chemical properties of graphene can be well controlled. Problems with respect to the modification, patterning, structuring and integration in manufacturing graphene-based soft robots can be overcome with the help of laser fabrication. According to different working principles, laser fabrication strategies can be divided into different categories, such as laser direct writing, two-beam laser interference, laser lithography, and spatial light modulation processing[5]. Choosing reasonable methods may provide more possibilities for broad applications of robots. For example, complex 3D structures are directly constructed by using a laser direct writing process. Taking advantages of the high precision and three-dimensional processing ability of femtosecond laser fabrication, Qu et al. demonstrated the local reduction of non-planar GO fiber (Figs. 1(a) and 1(b)) and produced a moisture responsive fiber robot[6]. Mask-free patterning capability is quite helpful to fabricate various predesigned 2D/3D structures. Following the deformation of materials, laser fabrication also enables 4D printing, making robots reconfigurable to adapt to the environment. For instance, a vivid spider robot that integrated a variety of light active actuators was produced by using a simple laser-scribing method (Figs. 1(c) and 1(d))[7]. In this process, GO was converted into reduced GO (RGO) with greatly improved photothermal conversion efficiencies. Laser with high energy density is used for cutting, welding or ablation process, thereby kirigami/origami robots are made, making soft robots easy-to-reach in daily life.
Figure 1. (a) Laser reduction of GO fiber. (b) Various predesigned GO actuators. (c) Graphene spider robot made by one-step laser scribing method. (d) The walking spider robot.
In summary, soft robots are still at an early stage and have a long way to go. Laser fabrication of graphene materials reveals great potential for developing graphene-based soft robotics. Graphene with tunable thermal/electronic conductivities, hierarchical structures and controllable surface morphologies has been successfully realized via laser processing. Various graphene actuators have been made in response to different stimuli such as humidity, light, heat and electricity, which will benefit robots with more functionality. We deem that graphene-based soft robots that can be applied in a wide range of scientific and industrial fields will be highly anticipated in the near future.
References
[1] Cheng H, Huang Y, Shi G, et al. Graphene-based functional architectures: sheets regulation and macrostructure construction toward actuators and power generators. Acc Chem Res, 2017, 50(7), 1663
[2] Chen L, Weng M, Zhou Z, et al. Large-deformation curling actuators based on carbon nanotube composite: advanced-structure design and biomimetic application. ACS Nano, 2015, 9(12), 12189
[3] Hu Y, Wu G, Lan T, et al. A graphene-based bimorph structure for design of high performance photoactuators. Adv Mater, 2015, 27(47), 7867
[4] Dong Y, Wang J, Guo X, et al. Multi-stimuli-responsive programmable biomimetic actuator. Nat Commun, 2019, 10(1), 4087
[5] You R, Liu Y Q, Hao Y L, et al. Laser fabrication of graphene-based flexible electronics. Adv Mater, 2019, 1901981
[6] Cheng H, Liu J, Zhao Y, et al. Graphene fibers with predetermined deformation as moisture-triggered actuators and robots. Angew Chem Int Ed, 2013, 52(40), 10482
[7] Han B, Zhang Y L, Zhu L, et al. Plasmonic-assisted graphene oxide artificial muscles. Adv Mater, 2019, 31(5), 1806386
1981年出生，博士，吉林大学电子科学与工程学院，教授，博士生导师，2015年国家优秀青年基金获得者。 长期从事超快激光微纳加工及非硅MEMS器件研究，发表SCI论文120余篇。
点击阅读张永来教授文章：
Laser fabrication of graphene-based soft robots
Bing Han and Yong-Lai Zhang
J. Semicond. 2019, 40(12), 120401
doi: 10.1088/1674-4926/40/12/120401
“深紫外发光材料与器件”专题 《半导体学报》组织了一期“深紫外发光材料与器件”专题。该专题包括6篇综述文章和9篇研究论文，已于2019年第12期正式出版并可在线阅读，欢迎关注。 专刊详情请见：半导体学报2019年第12期——深紫外发光材料与器件专题
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