Over the past few decades, there has been a significant surge in the development of robotic tools designed to facilitate minimally invasive surgeries, improving recovery times and patient outcomes. These advancements now allow surgeons to replicate hand and wrist movements at a centimeter scale, with these tools commonly used in surgeries involving the torso. However, neurosurgery presents a more challenging environment due to the smaller and more confined space within the brain. Traditional robotic surgical tools, which are usually powered by cables connected to electric motors, are limited in such tight spaces. These tools function similarly to the way human fingers are moved by tendons connected to wrist muscles. But at smaller length scales, the cable-based approach becomes problematic, as friction from the cables affects performance, reducing the reliability of the operation. To address this issue, a team of engineers has developed a set of tiny robotic instruments capable of enabling 'keyhole surgery' in the brain.

The team at the University of Toronto Engineering (Toronto, ON, Canada), along with collaborators, has developed a set of robotic tools just 3 millimeters in diameter to grip, pull, and cut tissue. These miniature tools are powered by external magnetic fields rather than motors, allowing for their tiny size and precise function. For several years, the research team has been working on an alternative to the conventional cable-driven system used in existing robotic surgical tools. Instead of relying on cables and pulleys, their tools incorporate magnetically active materials that respond to electromagnetic fields controlled externally by the surgical team. The system consists of two key components. The first is the robotic tools themselves: a gripper, a scalpel, and a set of forceps. The second component is a specially designed surgical table, referred to as a coil table, embedded with multiple electromagnetic coils. In this design, the patient’s head is positioned over these coils, and the robotic tools are inserted into the brain through a small incision. By adjusting the current flowing through the coils, the team can manipulate the magnetic fields, enabling the tools to grip, pull, or cut tissue as needed. To test the functionality of these tools, the team worked with physicians and researchers to create a life-sized phantom brain made from silicone rubber, simulating the geometry of a real brain.

To simulate brain tissue properties, the team used small pieces of tofu and raspberries. Tofu was chosen because it mimics the texture of the corpus callosum, the part of the brain targeted for cuts with the scalpel. Raspberries, on the other hand, were used to test the grippers’ ability to remove tissue, replicating how a surgeon would extract diseased tissue. The performance of these magnetically-controlled tools was compared with standard tools operated by trained physicians. The findings, published in Science Robotics, revealed that the magnetic scalpel produced consistently narrow and precise cuts, with an average width of 0.3 to 0.4 millimeters. This level of precision surpassed that of traditional hand tools, which produced cuts ranging from 0.6 to 2.1 millimeters. The grippers successfully picked up the target tissue 76% of the time. Additionally, when tested on animal models, the tools performed similarly well. Despite the progress, the researchers note that it may still be some time before these tools are used in actual surgeries. Nonetheless, they are optimistic about the potential of this technology and its ability to revolutionize brain surgery.

“The technology development timeline for medical devices — especially surgical robots — can be years to decades. There’s a lot we still need to figure out. We want to make sure we can fit our field generation system comfortably into the operating room, and make it compatible with imaging systems like fluoroscopy, which makes use of X-rays,” said Professor Eric Diller (MIE). “It’s a radically different approach to how to how to make and drive these kinds of tools, but it’s also one that can lead to capabilities that are far beyond what we can do today.” 

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