The new magnetic spray transforms objects into millirobots for biomedical applications

Researchers from a joint research project led by a scientist from City University of Hong Kong (CityU) have developed an easy way to create millirobots by coating objects with a glue-like magnetic spray. Pushed by the magnetic field, coated objects can crawl, walk or roll on surfaces. Because the magnetic coating is biocompatible and can be disintegrated into powders when needed, this technology demonstrates the potential for biomedical applications, including catheter navigation and drug delivery.

The research team is led by Dr. Shen Yajing, Associate Professor of the Department of Biomedical Engineering (BME) at CityU in collaboration with the Shenzhen Institutes of Advanced Technology (SIAT), Chinese Academy of Sciences (CAS). The research results were published in the scientific journal Robotic science, entitled “An agglutinated magnetic spray transforms inanimate objects into millirobots for biomedical applications”.

Transforming objects into millirobots with a “magnetic coating”

Scientists have developed millirobots or insect-scale robots that can adapt to different environments for exploration and biomedical applications.

Dr. Shen’s research team devised a simple approach to building millirobots by coating objects with a glue-like composite magnetic spray called M-spray. “Our idea is that by wearing this magnetic coating, we can transform any object into a robot and control its locomotion. The M-spray we developed can attach itself to the targeted object and activate it when guided by a magnetic field,” he explained. dr. Shen.

Composed of polyvinyl alcohol (PVA), gluten and iron particles, M-spray can adhere to the rough and smooth surfaces of 1-D, 2-D or 3-D objects instantly, stably and firmly. The film that has formed on the surface is about 0.1-0.25mm thick, thin enough to preserve the original size, shape and structure of the objects.

After coating the object with M-spray, the researchers magnetized it with single or multiple directions of magnetization, which could control how the object moved from a magnetic field. Then they applied heat to the object until the coating solidified.

In this way, when guided by a magnetic field, objects can be transformed into millirobots with different modes of locomotion, such as crawling, flipping, walking and rolling on various surfaces including glass, leather, wood and sand. The team demonstrated this by converting cotton thread (1-D), origami (flat 2-D flatbed), polydimethylsiloxane film (curved / soft 2-D surface) and plastic tube (round 3-D object) into a soft reptile robot, multi-foot robot, walking robot and rolling robot respectively.

Reprogramming on request to change the mode of locomotion

The team can reprogram the mode of locomotion of the millirobot upon request. Mr. Yang Xiong, the co-first author of this article, explained that conventionally, the initial structure of the robot is usually fixed once built, thereby limiting its versatility in motion. However, by fully wetting the solidified M-spray coating to make it sticky like glue and then applying a strong magnetic field, it is possible to change the direction of distribution and alignment of the magnetic particles (axis of easy magnetization) of the M-spray coating.

Their experiments showed that the same millirobot can switch between a different mode of locomotion, such as from a faster 3-D caterpillar movement in a spacious environment to a slower 2-D accordion movement to pass through a confined space. .

Navigation skills and disintegrating properties

This reprogrammable activation function is also useful for navigating to targets. To explore the potential in biomedical applications, the team conducted experiments with a catheter, which is widely used for insertion into the body to treat disease or perform surgical procedures. They showed that the M-spray coated catheter can perform tight or smooth bends. And the impact of blood / liquid flow on the range of motion and stability of the M-spray coated catheter was limited.

By reprogramming the M-spray coating of different sections of a cotton thread according to the delivery activity and the environment, they further demonstrated that it is possible to achieve quick steering and smoothly pass through a narrow and uneven structure. Dr. Shen pointed out that from a clinical application standpoint, this can prevent unexpected immersion into the throat wall during insertion.

“Activity-based reprogramming offers promising potential for catheter manipulation in the esophagus, vessel and urethra complex where navigation is always required,” he said.

Another important feature of this technology is that the M-spray coating can be disintegrated into powder on demand by manipulating a magnetic field. “All the raw materials in M-spray, namely PVA, gluten and iron particles, are biocompatible. The disintegrated coating could be absorbed or excreted by the human body,” said Dr. Shen, pointing out the side effect of the disintegration of M-spray is negligible.

Successful drug delivery in the rabbit’s stomach

To further test the feasibility and effectiveness of the M-spray-enabled millirobot for drug delivery, the team conducted in vivo tests with rabbits and M-spray-coated capsules. During the delivery process, the rabbits were anesthetized and the location of the capsule in the stomach was monitored by radiological imaging. When the capsule reached the targeted region, the researchers disintegrated the coating by applying an oscillating magnetic field. “The controllable disintegration property of M-spray allows the drug to be released in a targeted location rather than dispersing in the organ,” added Dr. Shen.

Although the M-spray coating will begin to disintegrate in about eight minutes in a highly acidic environment (pH level 1), the team showed that an additional layer of PVA on the surface of the M-spray coating could prolong it to about 15 minutes. And if you replace the iron particles with nickel particles, the coating could remain stable in a highly acidic environment even after 30 minutes.

“The results of our experiment indicated that several millirobots could be built with the M-spray adapting to various environments, surface conditions and obstacles. We hope that this construction strategy will contribute to the development and application of millirobots in different fields, such as active transport, mobile sensors and devices, especially for activities in confined spaces, “said Dr. Shen.

Provided by the City University of Hong Kong