This sticky spray can create biomedical robots on demand

In robotics, tiny bots are all the rage. They could also be the future of medicine.

A team of roboticists from China has developed a spray that can transform inanimate objects, like a strip of paper, into a fully articulating robotic drone controlled by a simple magnet.

This Frankenstein monster-esque creation may sound menacing or like something from an old Batman & Robin comic, but it has the potential to completely change how drugs are delivered in the human body.

Over the last decade, a slew of innovations in biomimicry and material design have brought roboticists' dream of sending tiny, insect-sized robots into human bodies close to reality. But there are still fundamental limitations holding this technology back. And one of them is manufacturing.

"[A]t least two key challenges must be taken into consideration: unmodifiable structure after fabrication and target size increment," the authors of this study write.

Simply: You need to be able to keep the robots supple enough to change shape and scale on demand.

While scientists have created armies of tiny bots before, the authors of this new study argue that these robots still suffer from limited deformability — they can stretch, compress, or roll, but they cannot change their overall shape. In the body, that limitation may present unforeseen problems, like navigating a stomach ulcer blocking a clear path through the body.

So rather than designing a super-specialized fleet of tiny bots that could only complete one job at a time, the authors of this study took a different approach. They designed a magnetic spray to transform scraps of paper into shapeshifting bots on demand.

"Under the actuation of magnetic field, the constructed millirobots are able to demonstrate a range of locomotive abilities: crawling, walking, and rolling," report the authors.

The study's findings were published Wednesday in the journal Science Robotics.

How does it work — In their spray, dubbed "M-Spray" scientists combined a mix of iron particles, gluten, and a kind of 3D printing material called polyvinyl alcohol. When first sprayed on an object, M-Spray is sticky enough to seep into a surface's nooks and crannies, creating a thorough coating. After application, the thin film becomes rigid and tightly bonded to its host material.

Like a puppeteer pulling strings, the scientists can then control these mini bots using a simple magnet. In videos of their trials, the robots hobble, slither, or scurry across tables with spider-like ease.

For more granular movements, researchers also designed a stencil-like application method that allowed them to spray only certain quadrants of a material. This tactic created more appendages to control, and resulted in more advanced looking motion.

Incredibly, these bots can stretch out to 1000 times their own volume and bear the brunt of 100 times their own weight.

The real deal — The researchers tested the bots in two different, life-like trials. In the first trial, they wanted to see how well a worm-shaped bot could squirm through a model catheter. In the second trial, the researchers guided a pellet-shaped bot filled with faux, microbead "drugs" to the stomach of a live rabbit.

The bots were both able to perform smooth, precise movements in the cramped environment of the catheter, while also deftly maneuvering specific targets en route to the rabbit's stomach.

Because this coating is easily disintegrated with acid or magnetic oscillation, it poses no risk to living hosts, the researchers say.

Takeaways — In the future, the researchers plan to test their design with new materials, as well as on different applications. This is just one of many approaches to the problem of quickly and effectively targeting drug delivery in the body, but they hope their design can make a lasting impact.

"Our approach offers a general on-demand robot construction method by leveraging the structure and morphology of the targeted objects themselves and may find a wide range of applications in biomedical engineering," the researchers write.

Abstract: Millirobots that can adapt to unstructured environments, operate in confined spaces, and interact with a diverse range of objects would be desirable for exploration and biomedical applications. The continued development of millirobots, however, requires simple and scalable fabrication techniques. Here, we propose a minimalist approach to construct millirobots by coating inanimate objects with a composited agglutinate magnetic spray. Our approach enables a variety of one-dimensional (1D), 2D, or 3D objects to be covered with a thin magnetically drivable film (~100 to 250 micrometers in thickness). The film is thin enough to preserve the original size, morphology, and structure of the objects while providing actuation of up to hundreds of times its own weight. Under the actuation of a magnetic field, our millirobots are able to demonstrate a range of locomotive abilities: crawling, walking, and rolling. Moreover, we can reprogram and disintegrate the magnetic film on our millirobots on demand. We leverage these abilities to demonstrate biomedical applications, including catheter navigation and drug delivery.