Researchers in Switzerland have created miniature robots power by ultrasound that can travel in a swarm against the flow in the bloodstream.
The team at ETH Zurich used magnetic beads made of iron oxide and a polymer with a diameter of 3 micrometres as the microvehicles. A magnetic field induces these particles to cluster into a swarm with a diameter of between 15 and 40 micrometres.
The team headed by Daniel Ahmed and Bradley Nelson, professors at the Department of Mechanical and Process Engineering of ETH Zurich studied the behaviour of this swarm in a thin glass tube with liquid flowing through it. The glass tubes had a diameter of 150 to 300 micrometres, a similar size to the blood vessels in a tumour.
To propel the microswarm against the flow in the tube, the ETH researchers used the same approach as a canoeist on a river. Hugging the side of the vessel means the current is slower than in the middle of the river.
Using ultrasound at a specific frequency, the scientists first guided the cluster of microbeads close to the wall of the tube. Then the researchers switched to a rotating magnetic field to propel the swarm against the flow.
The next step is to explore how the microvehicles respond in the blood vessels of animals. “As both ultrasound waves and magnetic fields penetrate body tissue, our method is ideal for controlling microvehicles inside the body,” said Professor Ahmed.
This technique could be used for microsurgery, such as unclogging blocked blood vessels, or to deliver cancer drugs to tumours via the blood vessels and release them directly into the tumour tissue. Lastly, another area of application is transferring drugs from blood vessels into the tissues of the brain.
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