The reptile millirobot changes from caterpillar motion to concertina motion after reprogramming. Credit: City University of Hong Kong

Millirobots that can adapt to unstructured environments, operate in confined spaces, and interact with a diverse range of objects would be desirable for exploration and biomedical applications. However, the development of millirobots has faced difficulty due to their complicated fabrication techniques.

Recently, researchers from the Shenzhen Institutes of Advanced Technology (SIAT) of the Chinese Academy of Sciences, together with the City University of Hong Kong (CityU), have developed an agglutinate, reprogrammable, disintegrable and biocompatible magnetic spray (M-spray) that can easily turn inanimate objects into millirobots.

The research findings have been published in Science Robotics in an article entitled “An agglutinate magnetic spray transforms inanimate objects into millirobots for biomedical applications.”

The magnetic spray (M-spray) is mainly composited from polyvinyl alcohol (PVA), gluten and magnetic particles. The M-skin formed from the M-spray is reprogrammable by adjusting the easy magnetization direction without changing the main structure.

When the covered spray is thoroughly wetted, the spacing between magnetic particles increases due to PVA swelling, and the constraints on magnetic particles from the PVA and gluten are greatly decreased. As a result, the magnetic particles inside the spray can be realigned along the direction of magnetic flux and can overcome constraints when a strong magnetic field is applied.

“The on-demand reprogramming ability endows millirobots with high adaptivity to achieve diverse locomotion. The team demonstrated the reprogramming of a three-section reptile millirobot that could move with 3D caterpillar motion before reprogramming and 2D concertina after reprogramming,” said co-first author Dr. SHANG Wanfeng, associate professor at SIAT.

Agglutinate M-spray converts inanimate objects to millirobots and the M-skin capsule for active delivery in an ex vivo animal model. Credit: SIAT

Moreover, the M-spray can be disintegrated by increasing the kinetic energy of magnetic particles to overcome inner constraints. This is done by applying an oscillating magnetic field in an aqueous environment. This magnetically induced disintegration ensures the constructed millirobot can disintegrate on command.

The research also proved potential applications in the biomedical area, including the navigation ability of an M-spray-covered catheter in the narrow vascular model, the reprogramming of multipoint sampling cotton thread for various sets of steering, and a magnetic spray-covered capsule for active delivery.

A rabbit stomach experiment demonstrated that a constructed capsule millirobot could effectively enhance the retention as well as the concentration of a drug in specific lesions.

“This research offers a general on-demand robot construction method by leveraging the structure and morphology of the targeted objects themselves. With biocompatible components, the side effects from its disintegration are negligible, making it a good candidate for biomedical applications,” said Dr. WU from SIAT.

Read New Magnetic Spray Transforms Objects Into Insect-Scale Robots for Biomedical Applications for more on this development.

Reference: “An agglutinate magnetic spray transforms inanimate objects into millirobots for biomedical applications” by Xiong Yang, Wanfeng Shang, Haojian Lu, Yanting Liu, Liu Yang, Rong Tan, Xinyu Wu and Yajing Shen, 18 November 2020, Science Robotics.DOI: 10.1126/scirobotics.abc8191