The new robot is smaller than a fleas! The assembly technology has won the cover of several top publications


Miniature robot that looks like a crab Courtesy of the interviewee


A “crab” robot smaller than a flea stands on the side of the coin. Courtesy of respondents

Here comes the smallest remote-controlled walking robot in history, only half a millimeter wide and no larger than a flea, which can walk, bend, twist, turn and jump.

These little cuties can perform important tasks in tight spaces. For example, in minimally invasive surgery, they play the role of surgical assistants, because of their very small size, they can easily enter the human body to work – clear blocked arteries, stop bleeding or eliminate malignant tumors.

The creators of this miniature robot are Huang Yonggang and John A. Rogers, who are also named chair professors at Northwestern University, and zhang Yihui, a professor at Tsinghua University’s School of Aeronautics and Astronautics. This research portfolio is luxurious, among which Huang Yonggang is a foreign academician of the Chinese Academy of Sciences, a member of the National Academy of Sciences, the National Academy of Engineering, and the American Academy of Arts and Sciences; john A. Rogers is a member of the American Academy of Sciences. The study was published in the May 25 issue of Science Robotics, a sub-journal of Science.

The movement modes are diverse and the movements are very agile

Nature has inspired mankind infinitely, scientists have invented airplanes through birds, submarines based on the body structure of fish… The study was also inspired by reptiles or insects such as crabs, spiders, inchworms, crickets and beetles.

“We’ve made a lot of different forms of miniature robots, and the one that impresses you the most is the robot that looks like a crab, and they’re really interesting to crawl.” Zhang Yihui, the corresponding author of the paper, introduced it in an interview with China Science News.

The most surprising thing is that these miniature robots are very agile, rapid deformation can reach 10 times per second, and the average speed of walking is half the length of the body per second.

In Huang Yonggang’s view, it is extremely challenging to achieve this on such a small robot.

Therefore, the research team made a lot of considerations in the selection of materials, and finally used a shape memory alloy material, which worked together with silica and a skeleton material to “memorize” the shape and help achieve the purpose of shaping.

Unlike conventional robots, this miniature robot is not driven by complex hardware, hydraulics or electricity. Its strength lies in the elasticity of the body, driven by heat. Zhang Yihui introduced that scanning robots with lasers, because the coefficients of thermal expansion of their assembled materials are different, the thermal mismatch between the materials after heating can drive small robots to continuously change their form, resulting in motion.

“It is precisely because these structures are very small, so the heat propagation occurs in an instant, and its cooling rate is also very fast, and after cooling, the micro-robot will return to its original state.” John A. Rogers explains that’s why they respond quickly.

The laser can not only remotely control the robot to move, the direction of the laser scan also determines the direction of the robot’s walking. For example, if you scan from left to right, the robot will walk from right to left.

Moreover, the movements of each form of robot are also very different. “Through different shape designs, relying on the coordination of legs and the control of deformation, robots can have different movement modes, such as crawling, jumping, turning, walking and other movement modes.” Zhang Yihui said.

Small robots will have a big role. “They can act as surgical assistants in minimally invasive surgery, and because of their very small size, they can easily enter the human body to do their work – clear blocked arteries, stop bleeding or eliminate malignant tumors, and so on.” John A. Rogers said.

N innovations based on a set of methodologies

It is not difficult to make a robot with legs jump and crawl, but it was impossible to carry it out on such a small scale.

The team was able to achieve this based on a microscale three-dimensional structural assembly method. The method was first published in Science in 2015 as a cover paper, with Huang Yonggang, John A. Rogers and Zhang Yihui as corresponding authors.

Once the paper was published, it attracted widespread attention from the academic community, and the results were quickly reported in columns by journals such as Science and Nature, and tracked by professional organizations such as Chemistry Views, IOP Physics World, Nano Today, and also reported by the BBC, Discovery News and other media.

This method became a hit, which is also the first time in the world that controllable mechanical buckling has been introduced into the assembly of complex three-dimensional structures at the microscale, realizing the high-precision assembly from two-dimensional micro-nano films to three-dimensional micro-nano structures.

The principle doesn’t sound complicated. “Unlike traditional operations, we do not directly make three-dimensional forms, but first make some two-dimensional structures, that is, flat film patterns, and then apply some mechanical loads to it, so that it cleverly becomes the target three-dimensional structure.” Zhang Yihui introduced, just like folding three-dimensional Christmas cards, after opening, the three-dimensional structure will bounce up.

In this process, there is also an important role, that is, an assembly platform made of very soft elastic polymers (such as silicone, rubber, etc.). This material is highly stretchable and can be pulled to a large size, making it easy to compress the flat film pattern on top.

Zhang Yihui said that the three materials mentioned earlier to make miniature robots are on such an assembly platform, through the action of compression force, from two-dimensional structure to three-dimensional structure, and under the blessing of the special “memory” ability of the material itself, it is successfully solidified. “Only complex three-dimensional structures can make complex movements, like the ‘crab’ robot we developed.”

In view of its contribution to the field of three-dimensional microstructure assembly, in 2017, Nature Reviews Materials invited this international research team to write a review paper on the three-dimensional microstructure forming method, introducing this set of mechanical assembly methods and allowing the scientific community to better understand the application scope, latest progress and development trends of these methods.

The method is suitable for a wide range of material types, such as semiconductor silicon, metal, ceramics, polymers, plastics and other material types, and is suitable for the assembly of materials at various feature scales, such as from nanometers to decimeters, making it easy to create small structural shapes.

“That said, with this manufacturing method, we can develop walking robots of all shapes and sizes, which is an interesting whim.” Zhang Yihui said.

Interest dictates, and keeps exploring

“Embarking on the road of scientific research is entirely due to interest.” Zhang Yihui has always held a respectful and rigorous attitude towards scientific research, he wants to carry out some useful research in combination with the needs of the country and society, and hopes to use his disciplinary background knowledge to solve some technical difficulties and key scientific problems.

Born in Nanling County, Wuhu City, Anhui Province, he graduated from Nanjing University of Aeronautics and Astronautics with a bachelor’s degree, and obtained his master’s and doctoral degrees from the Department of Engineering Mechanics of the School of Aeronautics and Astronautics of Tsinghua University, mainly studying the deformation and failure behavior of advanced materials and structures during this period.

In 2011, Zhang Yihui came to Northwestern University in the United States as a postdoctoral fellow and a research assistant professor. During this period, Huang Yonggang had a great influence on Zhang Yihui. “I was very fortunate to be able to enter Mr. Huang Yonggang’s research group to study. Mr. Huang is one of the pioneers of inorganic flexible electronic technology. Zhang Yihui said.

His hard work and outstanding talent are appreciated by his mentors. Under the guidance of Huang Yonggang, he gradually became involved in flexible electronic technology, burst out some inspiration, and collaborated with John A. Rogers’s research group to develop buckling mechanics-guided microscale three-dimensional structure assembly technology.

In addition to the micro-robots in this paper, the research team has also expanded this set of assembly technology for the development of new micro-devices such as reconfigurable three-dimensional microelectronic devices, low-frequency vibration energy harvesters, and bionic microelectronic aircraft, and the relevant series of achievements have been published as cover articles in top journals.

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Representative cover article published by the research team in the direction of 3D microstructure assembly. Courtesy of respondents

For example, a winged microchip, published on the cover of nature last September, is the smallest artificial flight structure ever developed by the team. As professor V.V. Tsukruk of Georgia Institute of Technology in the United States commented, the assembly technology has important application prospects in biomedical devices, microelectronics and other fields.

“I am honored to do research with top scientists. Because of the long-term cooperation, we have a tacit understanding, follow them to learn, and I have accumulated a lot of valuable experience. Zhang Yihui said.

At present, this micro-robot research is still in the exploration stage, and the next step is that the research team will do some work to make them interact better with people, integrate intelligence, and give robots more intelligence. (Source: China Science Daily Zhang Qingdan)

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