The medical field will require smaller and more complex microrobots to better target drug delivery, assist in fertilization, and conduct biopsies. The nanobots, however, are difficult to make and require a precise, labor-intensive manufacturing process.

In addition to a steady hand, a microrobot maker has traditionally needed needle-nosed tweezers, a microscope, and at least eight hours.

With the help of magnets and a 3D printer, University of Toronto engineers want to speed up the process – to 20 minutes.

Each microrobot is the size of a pin head, and built by carefully arranging microscopic sections of magnetic needles atop a flat, flexible material. Once deployed, the researchers apply magnetic fields to induce the microrobots to squirm through fluid channels, or close their tiny mechanical 'jaws' to take a tissue sample.

"If we were taking samples in the urinary tract or within fluid cavities of the brain, we envision that an optimized technique would be instrumental in scaling down surgical robotic tools," said the lab’s lead researcher Professor Eric Diller.

To demonstrate their new technique, the researchers devised more than 20 different robotic shapes, which were then programmed into a 3D printer. The printer built the microrobot as designed, orienting the magnetically patterned particles as part of the process.

"Previously, we would prepare one shape and manually design it, spend weeks planning it, before we could fabricate it. And that's just one shape," said Diller. "Then when we build it, we would inevitably discover specific quirks – for example, we might have to tweak it to be a little bigger or thinner to make it work."

Cutting out those early steps, Diller and his team have developed a simplified, just-click-print approach that allows the consideration of a variety of designs.

In an interview with Tech Briefs, Diller explains how the automated assembly process will open the door for even smaller, even more complex microrobots.

Tech Briefs: What inspired this idea?

Prof. Eric Diller: Our previous work focused on manual assembly of microrobots using tweezers under a microscope. We took inspiration from 3D printers which can pattern any shape automatically in a precise and fast way. Our challenge was to adapt the operation of a 3D printer to simultaneously print and program the magnetization profile within the microrobot.

Tech Briefs: Are you truly able to program the shapes and click print? How simple is the method?

Diller: We design the microrobot shape using computer modelling software, which we then send to our new magnetic printing machine. This machine then forms the shapes of the microrobot similar to how a 3D printer works, but while also programming a magnetic pattern into the microrobot. Just like a 3D printer, our machine prints thin layers one at a time.

Tech Briefs: What kinds of shapes are possible?

Diller: Any thin shapes are possible, and in our recent paper we show 14 different flat shapes such as multi-arm grippers, 8-legged crawling robots, and folding rings. Because the technology is easy and quick to use, we can iterate on our design, tweaking the size and shape to refine the performance of the microrobot.

Tianqi Xu holds up a 3D printed magnetized medical robot
Tianqi Xu holds up a microrobot that was fabricated using their automated system. (Image Credit: Liz Do, U of T Engineering)

Tech Briefs: What are the most challenging aspects of manual assembly of microrobots?

Diller: Manually assembling microrobots requires fine dexterity, a steady hand, and lots of time. Just assembling the many blocks of a microrobot using tweezers and glue required many hours. Each block must be custom made itself, which involved many precision steps over several days. There were many chances for errors, the minimum size was limited to building blocks 1/2-mm in size, and the slow [pace] impeded the design process.

Tech Briefs: What are the most exciting applications to you with these kinds of self-assembled robots?

Diller: We plan to adapt the gripping microrobots shown in our recent work to take biopsy samples inside the human body. We are also modifying the design into swallow-able capsules for collecting samples inside the stomach and small intestine, and to use as surgical tools.

A gif of the University of Toronto microrobot which has a gripping jaw and can carry cargo.
A microrobot with gripping-jaw, cargo-carrying capabilities. (Gif Credit: Tianqi Xu)

Tech Briefs: What’s next regarding this work?

Diller: We're working to upgrade our printing machine to make fully 3D shapes rather than the mostly flat designs we've shown here. This will allow us to develop more complex microrobots with richer functions. We are also exploring different magnetic materials to use in our microrobots for biomedical applications because the rare-earth magnets used here are not biocompatible. Finally, we are working on the use of medical imaging, such as ultrasound, to observe the motion of microrobots inside the body. This will allow us to track and operate the microrobots when we can't see them directly.

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