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Stanford Report, October 1, 2003

Miniscule mechanical hand designed to reach for unique medical touch A multidisplinary effort leads to technical innovation


Tethered to the outside world by a thin wire, a tiny machine creeps through blood vessels, searching out deadly plaques and obliterating them with a zap of a laser. While it may sound like the stuff of science fiction, it isn’t. Stanford researchers are creating a micro-device that physicians could guide through the body to help diagnose and treat clogged arteries and other diseases. While a laser will come later, for now David Liang, MD, PhD, is focusing on a tiny eye that could give physicians an unprecedented view into blood vessels.

Currently, physicians can treat patients with coronary disease with bypass surgery or angioplasty to allow blood to flow freely through the veins. Both procedures have drawbacks: surgery is invasive and vessels can close back up after being opened with balloons or stents in angioplasty. In addition, doctors often have difficulties simply locating the blockages.

Fluoroscopy, in which images are taken of vessels highlighted by a dye injected into the patient, can solve that problem, but if an artery is blocked, the dye can’t flow and doctors are unable to visualize the other side. Existing miniaturized ultrasounds can cruise through vessels, but their design prohibits cameras from facing straight ahead so they send back images of only the vessel’s side walls.

"We can see where we’ve been, but we can’t see where we want to go," said Liang. "It’s like blacking out the windshield of your car and navigating through side and rear windows."

To solve this problem, Liang, an assistant professor of cardiovascular medicine, and Bob Hu, MD, an assistant professor of cardiovascular medicine, experimented with mirrors, laser pointers and spare rotating parts, but they couldn’t get their desired field of vision. They then approached Fritz Prinz, PhD, professor in the mechanical engineering department, who gladly accepted the challenge. "If you think it is virtually impossible, it’s just the right thing for us," said Prinz. His lab had to consider the size of the device, the materials used, how long it should last and how to power it. They began by simply asking if designs or materials were feasible, and ultimately went through 15 to 20 different versions. "Iteration is everything," Prinz said. "The second time around you’re a lot smarter than the first."

The prototype device is made of nitronol, a superelastic metal often used in nanotechnology, extremely small-scale design of products 100 times smaller than the diameter of a human hair. Nitronol’s superelastic properties allow it to bend without snapping so it can return to its original form. The engineers found a way to collect images in front of the device by mounting an ultrasound camera on a nitronol coil that can sweep back and forth.

Nitronol can also act as its own motor. When heated, a wire made out of the metal changes state and then returns to its original form when cooled. Physicians could therefore send electric current through the wire to make it contract and relax like a muscle, piloting the device through blood vessels.

The first version of the mini-machine, which is less than 1.5 mm long and can take 20 pictures a second, is being prepared for testing in animal models. The team plans to add more components to the basic motor and ultrasound camera: a laser could clean out arterial debris, perhaps someday replacing the old and fallible balloon and stent angioplasty techniques; "fingers" could enable surgeons to perform microsurgeries in blood vessels and other hard-to-reach places, such as the base of the brain.

"What I would love to see is a hand the size of a grain of rice," said Liang. "The trend is to do surgery through smaller and smaller holes, but the tools we use now are relatively crude, and basically all we do is put them on a long stick. We’re limited in terms of what we can access." The current surgical technology is lacking a way for surgeons to feel their way around the insides of the body without opening it up. The new device "puts the ultrasound at the tips of their fingers," said Liang, so doctors can see and feel through the vessels.

Many times physicians wait until it’s absolutely necessary to do surgeries, since more invasive procedures carry greater risks. With this device, Liang hopes medical problems can be corrected sooner. "I used to be very idealistic about basic science, and learning things for the sake of knowledge," said Liang. "But now as I’m older, I think that if I can do something just to help somebody, that would be enough."

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