If you want to build a fully functional nano-robot, you only need to integrate a series of components such as electronic circuits, sensors and antennas. But if you want it to move, you need flexible materials.

Cornell University's research team has created a micron-sized shape memory driver, which can fold atomic-thick planar materials into solid 3D structures by providing fast oscillating voltage. And once the material is bent, it can keep its shape even if the voltage is removed.

The research results were published in the journal Science Robotics on March 17, entitled "Micro-scale electrically programmable shape memory actuator for low-power micro-robots" and appeared on the cover of the magazine. The main authors of this paper are Liu Qingkun, a postdoctoral researcher, and Wang Wei, a doctoral student.

Shape memory effect refers to the ability of some materials to maintain a temporary specific shape and restore their original shape when they are stimulated by external environment such as temperature, electromagnetic field or light.

The ideal shape memory actuator that can be integrated into a micro intelligent system has many challenges: the material should be able to maintain its shape for a long time, can be electrically driven, and can be bent to a radius of curvature of micron order. In addition, the technology consistent with modern semiconductor manufacturing should be used to realize the integration with existing electronic equipment.

The nano-equipment developed by the team consists of a platinum film with nanometer thickness, and one side of it is covered with a passivation layer. Electrochemical oxidation is carried out by applying DC voltage to the platinum surface, and strain causing bending is generated in the oxide layer. Because the embedded oxygen atoms will gather together to form a potential barrier and prevent them from spreading, the device can maintain its shape even if the voltage is stopped.

By applying a negative voltage to the device, researchers can remove oxygen atoms and quickly reduce platinum to its original state. By changing the pattern of the panel and whether platinum is exposed at the top or bottom, a series of origami structures can be created.

This shape memory driver can not only be folded quickly in 100 ms, but also be folded thousands of times. It can keep its shape for a long time without power supply, which can minimize power consumption and is very beneficial to micro-robots.

The driver also has strong flexibility, and the radius of curvature of the driver can reach below 1 micron. Flexibility is very important for the manufacture of micro-robots, because the size of robots depends on the folding degree of various accessories. The greater the bending degree, the smaller the crease and the smaller the floor space of each machine.

In order to show the research results, the research team of Cornell University also made what may be the world's smallest self-folding origami bird. Prior to this, the smallest walking robot they invented won the Guinness World Record. Now, they hope to set a new record with this self-folding origami bird, which is only 60 microns wide.

Liu Qingkun said: "On such a small scale, it is no longer like traditional mechanical engineering, but a mixed application of chemistry, material science and mechanical engineering. 」

Physics professors Itai Cohen and Paul McEuen, who led the whole project, praised Liu Qingkun's chemical background for bringing extra surprises to the project and providing the electrochemical reaction principle that materials can be folded and kept in shape.

Cohen said: "The most difficult part is to make materials that can respond to CMOS circuits." "This is what Qing Kun did for this shape memory drive. You can drive it with voltage to keep it in a curved shape. 」

At present, the team is trying to integrate its shape memory driver with the circuit to create a walking robot with foldable limbs and a flat robot that moves through waves. These innovations may one day enable the nano-Roomba robot to eliminate bacterial infections in human tissues, and even develop a nano-robot that is ten times smaller than the current surgical equipment.

"We want to have a micro robot with a brain, which means we need components driven by CMOS transistors. 」

Imagine that/kloc-0.00 million assembled micro-robots are released from the wafer, folded into a specific shape, completed their tasks by themselves, or assembled into more complex structures. This is the ultimate vision of the team.

McEwan believes: "The main feature of us as human beings is that we have learned how to build complex machines and systems on a human scale or even larger, but we have not learned how to build machines on a small scale. Learning how to build a machine as small as a cell is a basic development step that human beings can do. 」

So far, the continuous cooperation between McEuen and Cohen has produced many nano-scale machines and components, and each generation is faster, smarter and more elegant than the previous generation.

But an important question is: what principles need to be changed in designing, manufacturing and operating robots of this scale?

"These thin layers are only about 30 atoms thick, while the thickness of paper is 65,438+000,000 atoms. Therefore, it is a great engineering challenge to figure out how to make things with this structure. 」

Dean Culver, the project manager of the Army Research Office of the US Army Combat Command, recognized their work: "Professor Cohen and his team are breaking through the boundary where we can control the speed and accuracy of movement on the micron or even nanometer scale. The scientific progress of this work can not only pave the way for nano-robots, but also realize the interaction with intelligent material design and molecular biology. 」

Paper link: https://robotics.sciencemag.org/content/6/52/eabe6663

Reference content: https://news.cornell.edu/stories/2021/03/self-folding-nanotechnology-creation-world-small list-origami-bird.