Turning white blood cells into medicinal microrobots with light

Medicinal microrobots are currently being developed to allow doctors to better treat and prevent diseases.

But most of these are made with synthetic materials that have been shown to trigger immune responses in small animals, causing them to be cleared from the body before they can do their job.

Now, scientists have reported for the first time their success using cells already present in the body – white blood cells called neutrophils – as natural, biocompatible microrobots in living fish.

The team used lasers to precisely control the neutrophils, or “neutrobots”, to perform multiple tasks – showing they could someday deliver drugs to precise locations in the body.

In a new study published in ACS Central Science, the authors write that the neutrobots “could hold great promise for the active execution of complex medical tasks in vivo, with great potential utility in the treatment of inflammatory diseases”.

Instead of requiring injections or the consumption of capsules to get the microrobot inside an animal or person, they propose using cells already present in the body as a less invasive alternative that wouldn’t set off the immune system.

“Unlike traditional medical microdevices, this neutrophil microcraft is free from artificial microstructures and invasive implantation processes, thus avoiding complicated preparation technology and tissue damage,” the authors say.

Neutrophils already naturally pick up nanoparticles and dead red blood cells, and can migrate through blood vessels into adjacent tissues, so they are good candidates for becoming microrobots.

It’s already been shown that neutrophils can be guided and moved around by lasers in lab dishes, but the researchers wanted to demonstrate whether this approach would work inside living animals.

A neutrophil microrobot engulfing a nanoparticle
A laser precisely guided a “neutrobot” toward a nanoparticle (at left), which was picked up and transported away (right). Credit: adapted from ACS Central Science 2022, DOI 10.1021acscentsci.2c00468

The researchers – from the Institute of Nanophotonics in Jinan University, China – manipulated and manoeuvred neutrophils in zebrafish tails, using focused laser beams as remote optical tweezers.

They found that the neutrobots could be moved up to 1.3 micrometres per second, which is three times faster than a neutrophil naturally moves.

Even further, the team was able to use the optical tweezers to control the functions that neutrophils perform as part of the immune system. A neutrobot was moved through a blood vessel wall into the surrounding tissue, another picked up and transported a plastic nanoparticle (showing its potential for carrying medicine), and when a neutrobot was pushed toward red blood cell debris, it engulfed the pieces.

Because they successfully controlled neutrobots in vivo (inside a living thing), the researchers say this study advances the possibilities for targeted drug delivery and precise treatment of diseases.

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