Ultrasound and magnetism allow drug delivery nanobeads to travel upstream

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Although various groups are already working on nanoparticles that could be used for the directed delivery of drugs through the bloodstream, most of these particles are designed to “go with the flow.” Now, however, Swiss researchers have created some that can actually travel upstream.

Developed at the ETH Zurich research institute, the new nanoparticles are actually tiny magnetic beads made of iron oxide associated with a polymer. They could also be loaded with pharmaceuticals that needed to be delivered to a specific place in the body. Each bead is only 3 microns wide.

In laboratory tests, the beads were placed in a liquid that flowed through a glass tube with an inside diameter of 150 to 300 micrometers, roughly the width of a blood vessel. When subjected to an externally applied magnetic field, the beads clustered into a “swarm” about 15 to 40 microns in width.

Then, directed pulses of ultrasound were used to move this swarm against a wall of the tube. Passing thereafter to a turning magnetic field, the scientists were able to push the swarm along the tube, in the opposite direction to that of the liquid flow.

A diagram showing how a swarm of nanobeads (red) is able to move upstream by moving towards the wall of the tube

Ahmed et al. Nature Machine Intelligence 2021

Putting the swarm against the wall of the tube helped, as the friction between the liquid and the glass made the current weaker there. Canoeists paddling upstream on rivers use a similar trick, in that they stay close to the shore where the water moves more slowly.

Scientists now plan to see how the technology works in real animal blood vessels. It is hoped that the beads could eventually be used not only for targeted drug delivery, but also in microsurgical procedures such as unblocking blocked blood vessels.

“As ultrasonic waves and magnetic fields penetrate body tissues, our method is ideal for controlling micro-vehicles inside the body,” says Professor Daniel Ahmed, who is leading the project with Professor Bradley Nelson.

The magnetic beads can be seen in action upstream, in the video below.

A research article was recently published in the journal Nature Machine Intelligence.

Source: ETH Zurich

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