A soft magnetic-guided robot, which strangely looks like a worm that can move through narrow and sinuous blood vessels (like those of the cerebrovascular system), has been developed by American researchers.
This creation by mechanical engineer Xuanhe Zhao and his colleagues at the Massachusetts Institute of Technology (MIT) may one day, coupled with current endovascular technologies, allow doctors to quickly treat blockages and lesions, such as those that occur during aneurysms and strokes (stroke).
- Stroke causes a sudden loss of brain function caused by interruption of blood flow to the brain (ischemic stroke) or rupture of cerebral blood vessels (hemorrhagic stroke).
- You should know that about 1.9 million brain cells die every minute after a stroke.
- It is therefore a medical emergency.
- If acute stroke is treated in the first 90 minutes, the survival rate of patients increases dramatically.
- Thus, every minute of hesitation can affect the movement, motor coordination, vision and memory of the person.
- Approximately 850,000 Americans live with the consequences of a stroke.
A solution to blood clots
Today, 80% of Americans survive their stroke, but more than half still have a long-term disability.
If we could develop a technique that can quickly restore blood flow within one hour after blocking a blood vessel, we could potentially avoid permanent brain damage. It’s our hope! explains Xuanhe Zhao.
To remove blood clots as quickly as possible in the brain of a patient, surgeons often perform a vascular endoscopy, a minimally invasive surgical procedure during which a thin wire is inserted into an artery, a blood vessel of the brain, legs or wool.
During this procedure, the doctor uses the technique of fluoroscopy, which consists of injecting into the blood a product that is revealed by the X-ray beams. It allows to visualize the blood vessels and allows a surgeon to weave a wire to the damaged brain vessel.
A catheter may then be placed along the wire to deliver drugs or clot retrieval devices to the affected area.
This procedure is very physically demanding for surgeons, who are also repeatedly exposed to fluoroscopy radiation.
The yarns used in such procedures must be handled manually and are generally made from a core of metal alloys coated with a polymer. The latter can potentially generate friction and damage the vessels, especially in hard-to-reach places.
The potential treatment
The MIT team realized that advances in their laboratory could help improve the endovascular procedure, both in the design of the guide wire and in terms of physicians’ exposure to radiation.
So she combined her work on hydrogels (biocompatible materials made mostly of water) and on magnetic activation to produce a robotic wire coated with hydrogel. She has shown that this wire is thin enough to be magnetically guided through a life-size silicone replica of the blood vessels of the brain.
The core of the robotic wire is made of a nickel-titanium alloy, or nitinol , a material that is both flexible and elastic. The yarn is coated with a rubbery paste containing magnetic particles.
Then, a hydrogel is applied to encompass the wire and the magnetic coating. This skin does not affect the reactivity of the magnetic particles and provides the wire with a smooth, frictionless and biocompatible surface.
Remote controlled and adjustable
The researchers showed activation and precision of the robot wire using a magnet. They managed to direct the robot wire through several scenarios that recall the introduction of a thread into the hole of a needle.
In addition, the authors of this work published in the journal Science Robotics (New Window) also tested the thread in a silicone replica of the major blood vessels of the brain. They even recreated clots and aneurysms, modeled after the CT scans of a real patient.
The silicone vessels were filled with a liquid simulating the viscosity of the blood.
One of the challenges of surgery was to navigate the complicated blood vessels of the brain, which have very small diameters, that commercial catheters can not reach.
Kyujin Cho, Professor of Mechanical Engineering at Seoul National University
This technique has the potential to overcome this hurdle and allow surgery in the brain without open surgery , says Dr. Kyujin Cho, who was not involved in this study.
The wire, which works at the submillimeter scale, can also be used to deliver drugs to prevent clot formation or to break blockages with laser light.
To demonstrate this ability, the researchers even replaced the nucleus with nitinol of the wire by an optical fiber that they could direct to activate a laser once a target reached.
The technique is safe for surgeons because they do not have to physically push the wire through the blood vessels. Doctors would not need to be in the immediate vicinity of a patient and would not be exposed to radiation.
The next step
The robot has not been tested on real human brains. It has been tested on tissue samples and will soon be on animal brains.
Tests must also be performed to establish the mechanical life of the robot and the biocompatibility of its components with the human body. Researchers do not see this as a potential problem, since the hydrogel is water-based and has already been shown to be non-toxic.
One thing is certain: the research team hopes to test their robotic yarn in vivo with existing technologies.
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