MIT engineers have developed robotic thread (in black) that can be steered magnetically and is small enough to work through narrow spaces such as the vasculature of the human brain. The researchers envision the technology may be used in the future to clear blockages in patients with stroke and aneurysms. Source: MITEngineers at the Massachusetts Institute of Technology (MIT) have created a thread-like, magnetically steerable robot that is capable of navigating through narrow, winding environments like the brain.

The team combined their knowledge of hydrogels, which are biocompatible materials composed mainly of water, and 3D-printed magnetically actuated material. They proceeded to develop a magnetically steerable, hydrogel-coated robotic thread that is thin enough to magnetically navigate through a silicone replica of the brain.

Composed of nickel-titanium alloy (nitinol), which is a “bendy” and “springy” material that returns to its original shape when bent, the robotic thread was coated in a rubbery paste or ink with magnetic particles embedded throughout. The team then used a previously developed chemical process to both coat and bond the magnetic material with hydrogel, offering the wire a smooth and frictionless biocompatible surface without affecting the responsiveness of the embedded magnetic particles.

Using a large magnet, the team steered the thread through various circuitous pathways detailed in the silicone replica of the brain’s blood vessels, encountering clots and aneurysms modeled after those found in the CT scans of actual patients. The silicone vessel also contained a blood-like liquid to mimic real-life conditions within brain blood vessels.

Eventually, the team of engineers hopes to pair the robotic thread with common endovascular technologies to enable surgeons to remotely steer the robot through a patient’s brain vessels for the purpose of rapidly treating blockages or lesions similar to those that occur along with strokes and aneurysms.

"Stroke is the number five cause of death and a leading cause of disability in the United States. If acute stroke can be treated within the first 90 minutes or so, patients' survival rates could increase significantly," said Xuanhe Zhao, associate professor of mechanical engineering and of civil and environmental engineering at MIT. "If we could design a device to reverse blood vessel blockage within this 'golden hour,' we could potentially avoid permanent brain damage. That's our hope."

Clearing blood clots in the brain is generally a matter of performing endovascular procedures, which are minimally invasive surgeries wherein a surgeon inserts thin wires through a patient’s main artery located typically in the groin or the leg. A fluoroscope simultaneously guides the surgeon, imaging the blood vessels with x-rays while the surgeon manually rotates the wire into damaged brain cells. Surgeons then thread a catheter along the wire to deliver drugs to or retrieve blood clots from the affected areas — a physically taxing procedure that also exposes the surgeon to repeated radiation from the fluoroscopy.

Additionally, the medical guidewires for such procedures are passive and generally require manual manipulation. They are also generally composed of core metallic alloys and coated in polymer, which, according to researchers, could possibly produce friction, and consequently damage the vessel linings in the event that the wire becomes stuck or lodged in a tight space.

As such, the team believes the robotic thread could potentially improve endovascular procedures and reduce surgeons' exposure to the associated radiation by enabling the surgeon to operate the magnet and thus the thread remotely.

"Existing platforms could apply magnetic field and do the fluoroscopy procedure at the same time to the patient, and the doctor could be in the other room, or even in a different city, controlling the magnetic field with a joystick," said lead author Yoonho Kim, a graduate student in MIT's Department of Mechanical Engineering. "Our hope is to leverage existing technologies to test our robotic thread in vivo in the next step."

Researchers detail their soft robotic design in the journal Science Robotics.