A team of engineers and physicians has developed a steerable catheter that for the first time will give neurosurgeons the ability to steer the device in any direction they want while navigating the brain's arteries and blood vessels. The device was inspired by nature, specifically insect legs and flagella – tail-like structures that allow microscopic organisms such as bacteria to swim.
The team from the University of California San Diego describes the breakthrough in the Aug. 18 issue of Science Robotics. The steerable catheter was successfully tested in pigs at the Center for the Future of Surgery at UC San Diego.
A view of the steerable catheter (right) and how it navigates a brain blood vessel (insert on the left).
Approximately one in 50 people in the United States has an unruptured intracranial aneurysm – a thin-walled, blister-like lesion on a cerebral artery that is prone to rupture. Of patients that suffer ruptured aneurysms, more than half die. Half of the survivors experience long-term disabilities.
"As a neurosurgeon, one of the challenges that we have is directing catheters to the delicate, deep recesses of the brain," said Dr. Alexander Khalessi, chair of the Department of Neurological Surgery at UC San Diego Health. "Today's results demonstrate proof of concept for a soft, easily steerable catheter that would significantly improve our ability to treat brain aneurysms and many other neurological conditions, and I look forward to advancing this innovation toward patient care."
Steerable catheters are not available for neurosurgery because of how small the brain's blood vessels are. Specifically, devices need to be less than one millimeter in diameter – that's roughly the diameter of a few human hairs – and about five feet long (160 cm). Industrial fabrication methods struggle at this scale. That’s partially because gravity, electrostatics, and the van der Waals force are all similar at this size. So once you pick something up with tweezers, you cannot drop it. If you coax it from the tweezers, it may leap into the air from opposing forces and disappear, never to be found again.
"Unfortunately, many of the most important blood vessels we need to treat are among the most tortuous and fragile in the body," said James Friend, the paper's corresponding author. "Although robotics is rising to the need in addressing many medical problems, deformable devices at the scales required for these kinds of surgeries simply do not exist." To solve this problem, researchers turned to inspiration both from nature and from soft robotics.
The team had to invent a whole new way of casting silicone in three dimensions that would work at those scales, by depositing concentric layers of silicone on top of one another with different stiffnesses. The result is a silicone rubber catheter with four holes inside its walls, each about one half the diameter of a human hair.
The team also conducted computer simulations to determine the configuration of the catheter; how many holes it should include; where these should be placed; and the amount of hydraulic pressure needed to actuate it. To guide the catheter, the surgeon compresses a handheld controller to pass saline fluid into the tip to steer it. Saline is used to protect the patient; if the device should fail, then saline harmlessly enters the bloodstream. The catheter's steerable tip is visible on X-rays.
"This technology is ideal for situations when I need to make a 180 degree turn from the catheter position in the parent artery, and maintaining position and reducing kick-out is critical," said Dr. David Santiago-Dieppa, neurosurgeon at UC San Diego Health. "This advance may ultimately allow us to treat aneurysms, other brain pathologies and even strokes that we haven't been able to in the past."
The work is poised to make a significant difference in the way aneurysm surgery is conducted, physicians said. "This type of precision can be realized with steerable tools and the successful deployment of these tools should move us forward in permitting improved access, decreased procedural time, better capacity utilization, decreased radiation exposure and other related and expected benefits," said Dr. Alexander Norbash, chair of the Department of Radiology at UC San Diego Health. The next steps include a statistically significant number of animal trials and first in human trial.
MEDICA-tradefair.com; Source: University of California – San Diego