Magnetic threads slide through blood vessels to reach clots in the brain

Wires coated with magnetic materials and hydrogel can be guided through arteries by magnetic fields

Original source: Physics World

A team of researchers from Massachusetts Institute of Technology has designed a new surgical tool that is manoeuvrable through some of the narrowest twisting networks of blood vessels to help treat stroke and aneurysm. Using hydrogels and magnetic materials, they have created a magnetically steerable guidewire that can slide easily through blood vessels to reach blood clots in the brain (Science Robotics 10.1126/scirobotics.aax7329).

It is vital to treat stroke as quickly as possible to prevent potentially lethal damage – outcomes are better for patients who are treated within the first hour after the stroke, known as the “Golden Hour”. One method used to reduce clots is an endovascular procedure in which a guidewire inserted in a leg or groin is manipulated through the body to the blood vessel in the brain where the blockage is located.

Endovascular surgery is technically difficult, and the procedure requires a specially trained surgeon. A traditional guidewire can also be tricky to manoeuvre through tight spots and can create friction and further damage vessels.

To address the difficulties of control and friction, the team combined their knowledge of hydrogels and magnetic materials to design the new guidewire to be externally steerable and less damaging to blood vessels.

Down to the wire

The wire core is made from nitinol, a nickel titanium alloy. It is bendy and springy – allowing for more flexibility within the complex maze of brain blood vessels. The researchers coated the core with a paste containing magnetic particles to make it steerable. This allows the wire to be operated remotely.

The team also coated the wire in a hydrogel, to make it pass through blood vessels more easily. Hydrogels are formed from biocompatible polymers that can hold a large amount of water and are particularly smooth. Coating the wire with the hydrogel reduced friction on the walls of the blood vessel, making it easy to manipulate, even in tight spots.

To test the wire, the researchers passed it through a life-sized silicone replica of blood vessels in the brain. They filled the replica with a blood-like fluid and, using a large magnet, successfully manipulated the wire through the complex model.

The guidewire can also be functionalized to deliver clot-reducing drugs or break up blockages using lasers. For the latter, the team was able to replace the nitinol core of their previous model with an optical fibre designed to transmit laser light. They could then remotely activate the laser once it reached the blockage.

Looking to the future

This system was operated by manually moving the magnets to better control its location whilst being able to see the wire. However, in the future, the team hopes to manipulate the magnets with a more precise control system whilst visualizing the wire with a fluoroscope to replicate surgical conditions.

“Existing platforms could apply magnetic field and perform 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,” lead author Yoonho Kim says. “In the next step, our hope is to leverage existing technologies to test our robotic thread in vivo.”