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Robotic Device Navigates Brain Blood Vessels

Robotic wire

Robotic wire, in black, navigating through simulated brain blood vessels (Massachusetts Institute of Technology)

29 Aug. 2019. Engineers and materials scientists designed a robotic device thin and flexible enough to thread through blood vessels in a model brain under remote control. A team from Massachusetts Institute of Technology describes the device in yesterday’s issue of the journal Science Robotics (paid subscription required).

Researchers from the lab of Xuanhe Zhao, professor of mechanical engineering at MIT, are seeking better therapeutic tools for disorders affecting the brain, such as stroke or aneurysms where quick treatment can prevent a patient’s disability or death. Stroke occurs when blood flow to the brain is interrupted, cutting the oxygen needed by brain cells to function. The vast majority (85%) of strokes are caused by blood clots, while many other strokes are caused by blood vessel leakage in the brain. Nearly 800,000 people in the U.S. have a stroke each year, with paralysis and weakness in the limbs among the results.

“If acute stroke can be treated within the first 90 minutes or so, patients’ survival rates could increase significantly,” says Zhao in an MIT statement. “If we could design a device to reverse blood vessel blockage within this ‘golden hour,’ we could potentially avoid permanent brain damage.”

Zhao’s lab studies soft robotics, particularly materials and mechanics at the interface between humans and machines. To clear blood clots from the brain today, surgeons use a a thin wire inserted through a vein, carefully navigated into and through the brain to deliver drugs with a catheter or physically break up the clot. Current robots designed for treating brain disorders, say the authors, can get no smaller than millimeter or centimeter scale, because of limits to miniaturization. And these devices encounter damaging friction when inside blood vessels.

The team led by graduate student Yoonho Kim designed an ultra-thin  — less than a millimeter in diameter — wire-like device known as a continuum robot to enter and navigate through complex and sensitive blood vessels in the brain. The wire is made of a nickel-titanium alloy, flexible enough to bend and hold its shape, yet can return to its original form as well. The wire is also covered with a magnetic ink for navigation. A hydrogel lubricant, made with a water-based polymer that does not affect magnetic properties, then coats the wire, which the authors report reduces friction to less than one-tenth, allowing it to slip through tight spaces without injuring blood vessels.

The researchers constructed a life-size silicone model of a brain’s blood vessel system to test the robotic device. The team used computed tomography or CT scans to design the brain model. The researchers filled the vessels with a liquid similar in viscosity to human blood, and added simulated clots and aneurysms, or bulges in blood vessels that can cause a stroke if they burst. The researchers demonstrated the device, navigating through the array of thin complex blood vessels guided by a remote-controlled magnet. This brief (40 second) video shows some of that demonstration.

In another demonstration, the team incorporated an optical fiber with the guide wire, and kept the diameter of the device to about half a millimeter. The researchers report the device can be guided remotely by a magnet and activate a laser at a designated location, adding other therapeutic applications.

Kim and Zhao are inventors on a provisional patent — indicating an intent to file a patent — for the technology.

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