The new magnetic spray turns objects into insect-scale robots for biomedical applications

After the re-programming of the reptile millirobot changes from the caterpillar movement to the concert movement. Credit: Hong Kong City University

An easy way to make millirobots by covering objects with a magnetic spray of glue was developed in a joint study led by a scientist at Hong Kong City University (CityU). Driven by magnetic fields, they can explore covered objects, walk or walk on different surfaces. Because magnetic coating is bio-compatible and can be broken down into dust when necessary, this technology demonstrates the potential for biomedical applications, including catheter navigation and medications.

It is led by Dr. Shen Yajing, an associate professor in the CityU Department of Biomedical Engineering (BME), in collaboration with the Shenzhen Institute of Advanced Technology (SIAT), the Chinese Academy of Sciences (CAS). The research findings were published in the scientific journal Science Robotics, “an agglutinated magnetic spray converts inanimate objects into milirobots for biomedical applications.”


An easy way to make millirobots by covering objects with a magnetic spray was developed in a joint study led by a CityU scientist. Because magnetic coating is bio-compatible and can be broken down into dust when necessary, this technology demonstrates the potential for biomedical applications. Credit: Hong Kong City University

Converting objects into millirobots with a “magnetic layer”

Scientists have been exploring and developing milirobots or insect-scale robots that can be adapted to different environments for biomedical applications.

Dr. Shen’s research team made a simple approach by covering objects to build millirobots with a magnetic glue-like spray called M-spray. “Our idea is that by placing this ‘magnetic layer’ we can turn any object into a robot and control its locomotion. The M-spray we have developed can be glued to the target object and ‘activated’ by a magnetic field,” Shen explained. doctors.

Dr. Shen and the CityU team

Dr. Shen (middle) and the CityU team. Credit: Hong Kong City University

Composed of polyvinyl alcohol (PVA), gluten, and iron particles, M-spray can be attached to rough, smooth, stable, and solid surfaces on an object (1D), two (2D), or three-dimensional (3D) surfaces. The film he created on the surface is about 0.1 to 0.25 mm thick, thin enough to preserve the original size, shape, and structure of the objects.

After covering the object with M-spray, the researchers magnetized it in single or multiple magnetization directions to control how the object moved through a magnetic field. The heat was then applied to the object until the coating solidified.

In this way, driven by a magnetic field, objects can become milomobots with different modes of locomotion, such as crawling, flipping, walking, and rolling, glass, leather, wood sand, and different surfaces. The group demonstrated this feature by turning cotton thread (1D), origami (2D flat plane), polydimethylsiloxane (PDMS) film (2D curved / soft surface) and plastic tube (3D round object) into soft reptile robots, multi-foot robots. roaming robot and rolling robot respectively.

On-demand reprogramming to change the mode of locomotion

What makes this approach unique is that the group can request that the milirobot’s mode of locomotion be reprogrammed.

Mr. Yang Xiong, the first author of this article, explains that conventionally, the initial structure of the robot is usually fixed after it is built, and thus limits its versatility in movement. However, to make the solidified M-spray coating completely wet with adhesive like glue and then applying a strong magnetic field, the direction of distribution and alignment of the magnetic particles of the M spray spray coating can be changed.

On-Demand Millirobot reprogramming

After the re-programming of the reptile millirobot changes from the caterpillar movement to the concert movement. Credit: Hong Kong City University

Their experiments showed that the same milirobot could switch between different modes of locomotion, such as from a faster movement of a wide-angle 3D caterpillar to a slower motion of a 2D concertina, passing through a narrow gap.

Ability to navigate and unstructured property

This reprogrammable operation helps you navigate in the direction of your goals. To study the potential in biomedical applications, the team conducted experiments with a catheter, which is widely used to treat diseases of insertion into the body or to perform surgical procedures. They demonstrated that M-spray-coated catheters could make sharp or smooth turns. The effect of blood / fluid flow on the ability to move and stabilize in the M-coated catheter was limited.

By reprogramming the M-spray coating of different sections of a cotton thread, based on the distribution task and the environment, they also showed that it could achieve fast driving and could pass through an irregular and narrow structure. Dr. Shen pointed out that from a clinical application point of view, this can prevent accidental penetration into the wall of the throat when inserted. “Task-based reprogramming offers a promising ability to manipulate catheters where navigation in the esophagus, vessel, and urethra complex is always necessary,” he said.

Another important feature of this technology is that the M-spray coating can be dissolved in powder on request by manipulating a magnetic field. “All M-spray raw materials, namely PVA, gluten and iron particles, are biocompatible. Dissolved coating can be absorbed or expelled by the human body, ”Dr. Shen said, emphasizing the side effect of the decay of the M spray.

Providing a successful medicine in the rabbit stomach

To verify the viability and effectiveness of the M-spray-enabled millirobot medication, the team conducted in vivo tests with rabbits and an M-spray-coated capsule. During the birth, the rabbits were anesthetized, and the position of the capsule in the abdomen was monitored by radiological imaging. When it reached the target region of the capsule, the researchers dismantled the coating by applying an oscillating magnetic field. “The disintegrating properties of the M-spray allow it to be released at the site of the drug rather than scattering it in the organ,” Dr Shen added.

Although the M-spray coating began to dissolve in about eight minutes at a very acidic (pH level 1) level, the team showed that an additional layer of PVA on the surface of the M-spray coating could last about 15 minutes. And by replacing iron particles with nickel particles, the coatings could remain stable even after 30 minutes in a highly acidic environment.

“The results of our experiment indicate that different millirobots could be built with M-spray to adapt to different environments, surfaces and obstacles. , ”Dr. Shen said.

Reference: November 18, 2020, Science Robotics.
DOI: 10.1126 / scirobotics.abc8191

Dr. Shen of CityU and Dr. Wu Xinyu of SIAT CAS are the authors of the article. The first authors are Mr. Yang Xiong, a PhD student at BMU in CityU, and Dr. Shang Wanfeng from SIAT CAS. Other co-authors include Dr. Lu Haojian, Dr. Liu Yanting, Mr. Yang Liu, and Ms. Tan Rong, new graduates and PhD students in the Dr. Shen team.

The research was supported by the National Science Foundation of China and the Research Grants Council of Hong Kong.

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