Tiny robotic tools powered by magnetic fields could enable minimally invasive brain surgery

Professor Eric Diller is from the University of Toronto Faculty of Applied Science & Engineering

He said: “In the past couple of decades, there has been this huge explosion of robotic tools that enable minimally invasive surgery, which can improve recovery times and outcomes for patients,” says

“We can now replicate the wrist and hand movements of a surgeon on a centimetre scale, and these tools are widely used in surgeries that take place in the torso. But when it comes to neurosurgery, we are working with an even more restrictive space.”

Current robotic surgical tools are typically driven by cables connected to electric motors, in much the same way that human fingers are manipulated by tendons in the hand that are connected to muscles in the wrist.

But Diller said that at smaller length scales, the cable-based approach starts to break down.

He added: “The smaller you get, the harder you have to pull on the cables.

“And at a certain point, you start to get problems with friction that lead to less reliable operation.”

Diller and his collaborators have been working for several years on an alternative approach.

Instead of cables and pulleys, their robotic tools contain magnetically active materials that respond to external electromagnetic fields controlled by the surgical team.

The system consists of two parts. The first is the tiny tools themselves: a gripper, a scalpel and a set of forceps.

The second part is what the team calls a coil table, which is a surgical table with several electromagnetic coils embedded inside.

In this design, the patient would be positioned with their head on top of the embedded coils, and the robotic tools would be inserted into the brain by means of a small incision.

By altering the amount of electricity flowing into the coils, the team can manipulate the magnetic fields, causing the tools to grip, pull or cut tissue as desired.

To test the tools, Diller and his team partnered with physicians and researchers at SickKids, including Doctors James Drake and Thomas Looi. Together, they designed and built a phantom brain — a life-sized model made of silicone rubber that simulates the geometry of a real brain.

The team then used small pieces of tofu and bits of raspberries to simulate the mechanical properties of the brain tissue they would need to work with.

Changyan He is a former postdoctoral fellow co-supervised by both Drake and Diller, now an assistant professor at the University of Newcastle in New South Wales, Australia.

He said: “The tofu is best for simulating cuts with the scalpel, because it has a consistency very similar to that of the corpus collosum, which is the part of the brain we were targeting,” says

“The raspberries were used for the gripping tasks, to see if we could remove them in the way that a surgeon would remove diseased tissue.”

The performance of these magnetically-actuated tools was compared with that of standard tools handled by trained physicians.

In the paper, the team reports that the cuts made with the magnetic scalpel were consistent and narrow, with an average width of 0.3 to 0.4 millimetres.

That was even more precise than those from the traditional hand tools, which ranged from 0.6 to 2.1 millimetres.

As for the grippers, they were able to successfully pick up the target 76 per cent of the time.

The team also tested the operation of the tools in animal models, where they found that they performed similarly well.

He said: “I think we were all a bit surprised at just how well they performed.

“Our previous work was in very controlled environments, so we thought it might take a year or more of experimentation to get them to the point where they were comparable to human-operated tools.”

Despite the team’s success so far, Diller cautioned that it may still be a long time before these tools see the inside of an operating room.

Image: University of Toronto / Tyler Irving