A new type of micromotor has been developed. Directed by magnets and powered by ultrasound, these micromotors are capable of traveling across microscopic particles and cells in very crowded areas without causing any damage.

These microswimmers provide a new way to manipulate single particles with precise control and in three dimensions, without having to do special sample preparation, labeling, surface modification, said Joseph Wang, a professor of nanoengineering at University of California San Diego (USCD), in a UCSD press release.

Wang, Thomas Mallouk, a professor of chemistry at the University of Pennsylvania, and Wei Wang, professor of materials science and engineering at Harbin Institute of Technology, are credited as senior authors of a paper detailing the development of these micromotors. The study was published on Oct. 25 in Science Advances.

Researchers tested the technology by moving HeLa cells the oldest and most commonly used cell line for scientific research and silica particles in aqueous media with micromotors. They accomplished this task without damaging nearby particles and cells. In one test, the researchers were able to create letters by pushing particles with the micromotors. In another, they exerted control over the micromotors, making them climb up microscopic blocks and stairs. This test demonstrated that they were capable of navigating over three-dimensional objects.

The micromotors are essentially gold-coated hollow polymer structures that are shaped like a half capsule. Within the body of the micromotor is a tiny magnetic nickel nanoparticle, allowing them to be steered with magnets. The inside surface is treated so it can repel water, so when the micromotor is submerged in water, an air bubble is trapped inside the device. This trapped bubble is integral to the functioning of the micromotor, as it allows the micromotor to respond to ultrasound. Upon receiving ultrasound waves, the trapped bubble begins to oscillate, forming forces that give it an initial push to movement. By applying an external magnetic field, it can move continuously, while altering the direction of the field allows researchers to control the speed and trajectory of the micromotors.

We have a lot of control over the motion, unlike a chemically fueled micromotor that relies on random motion to reach its target, said Fernando Soto, a nanoengineering Ph.D. student studying at UC San Diego. Also, ultrasound and magnets are biocompatible, making this micromotor system attractive for use in biological applications.

The authors plan on making improvements to the micromotors in the coming years. For example, they want to make them more biocompatible using biodegradable polymers and a magnetic material that is less toxic, such as iron oxide. Thanks to this technology, the researchers have opened new possibilities for nanomedicine, tissue engineering, targeted drug delivery, regenerative medicine, and other applications in the field of biochemistry.

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Micromotors move single cells using magnets and ultrasound - CMU The Tartan Online