Best stroke: Microswimmers that can deliver drugs around the body

Picture an artificial cell: a self-propelling mixture of chemicals, somewhere between a thousandth and a tenth of a millimetre in size, able to travel around the body delivering medicines.

This could become a reality with microswimmers – micrometre-sized blobs of liquid that can move independently, thanks to either chemical or physical mechanisms. There are plenty of naturally occurring microswimmers, but researchers have begun to tune artificial ones to do more interesting jobs.

Artificial microswimmers can be very simple – last year, a group of researchers published a method for microswimmers you could make at home (provided you have a pipette and a microscope). But more complex “microrobots” have even more potential.

Last month, for instance, researchers at the Max Planck Institute for Intelligent Systems, Germany, announced they’d developed light-powered microswimmers that can move through biological fluids.

The researchers’ microswimmers are made from a porous substance called poly(heptazine imide) carbon nitride. This material comprises organic (carbon-containing) molecules linked together in a flat sheet, making it a “two-dimensional” polymer.

The microswimmers can be propelled forwards by light, and can also be triggered to release chemicals they’re holding – making them prime targets for drug delivery.

Light-powered microswimmers aren’t an entirely new concept, though it had previously been tricky to make them work in biological environments.

“The use of light as the energy source of propulsion is very convenient when doing experiments in a petri dish or for applications directly under the skin,” says co-author Filip Podjaski.

“There is just one problem: even tiny concentrations of salts prohibit light-controlled motion. Salts are found in all biological liquids – in blood, cellular fluids, digestive fluids etc.”

But these microswimmers can move in even the most saline liquids. Podjaski says this is because of the porous nature of the material, as well as its light sensitivity.

“In addition, in this material, light favours the mobility of ions, making the particle even faster,” he says.

Currently, the microswimmers can release drugs in very acidic environments, but the researchers are still looking for other release mechanisms they can use. Artificial microswimmers are a long way from drug delivery or use in humans, but they’ve got plenty of exciting potential.

“We hope to inspire many smart minds to find even better ways for controlling microrobots and designing a responsive function to the benefit of our society,” says co-author Metin Sitti.

The findings were published in Science Robotics.

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