June 7, 2012
For cardiac patients, repair of defects often requires open-heart surgery and temporary paralysis of the organ. But a set of robotic tools developed by researchers at Boston Children’s Hospital could eventually enable surgeons to operate on the heart through small incisions while the heart continues to beat.
The use of small incisions and the insertion of robotic tools are increasingly common in many types of surgery. Such so-called minimally invasive surgery offers quicker recovery times than conventional surgery and reduced risk of infection, because the cuts in the body are much smaller. In the case of minimally invasive cardiac surgery, robotic tools have had to be delivered by catheters—smooth, flexible tubes that can carry, for example, an artery-opening stent. But because they are flexible, catheters can deliver only small amounts of force and can be difficult to position precisely.
The team at Boston Children’s Hospital instead uses curved-metal-tube robots to create a stiffer tool delivery platform inside the heart. “With standard open-heart procedures, we can pull tissue from one area to another. We can’t do that with a catheter. These robotic devices can exert some force, so they are able to do much of what a surgeon does, except they are navigating through the blood vessels,” says Pedro del Nido, a pediatric cardiac surgeon involved in the project.
The devices reach the heart through an incision in the neck that leads to the jugular vein. From there, long, narrow concentric tubes carry the surgical devices through the large blood vessels to the heart.
One of the team’s tools can close holes in the heart. Surgeons typically close such holes with a suture in a procedure that requires open-heart surgery and stopping the heart. The team at Children’s, led by bioengineer Pierre Dupont, and its collaborators at Microfabrica have developed a metallic suture-like device that can be deployed by the concentric-tube robot. Key to developing the millimeter-scale device was a specialized manufacturing process to make the tiny gears, chains, and pulleys needed. The suture-like device pierces the heart tissue on each side of the hole and extends wings that grab onto each piece of tissue. Then a ratcheting mechanism brings the two pieces together, immediately sealing the hole. Now in close contact, the pieces of tissue likely fuse together and around the metallic implant.
The Dupont group is one of a few research teams trying to bring a rich set of tools to tucked-away places in the body without the need for large openings. “With these devices, we are trying to get best of both worlds”—that is, a minimally invasive procedure that can make use of all skills of a surgeon, says Howie Choset, an engineer at Carnegie Mellon University who is developing his own surgical robotic devices. “When you open up the heart, there are all sorts of things you can do—we want to acquire those capabilities without making a big incision.”
The team at Children’s has tested the closure device in live pigs, and surgeons were able to repair holes in an actively pumping heart. One of the challenges of operating through small incisions is that the surgeon cannot directly see where the device is positioned. So the team uses a combination of real-time x-rays and ultrasound to navigate the robot inside the heart and to monitor device deployment.
Irregular tissue growth inside the heart can hamper the function of the organ, so the team and its collaborators have also developed a rotating cutting device for the tip of the concentric-tube robot. The device integrates irrigation and suction of liquids, processes important when operating on a functioning heart.
“Inside the beating heart, if you cut any piece of tissue free, you don’t want it to escape because it could shoot off and plug an artery, perhaps cause a stroke,” says Dupont. The device sucks in debris while it cuts away tissue. Another challenge in a blood-filled heart is clotting, a natural reaction to foreign material. So the device irrigates the tissue debris with a clot-preventing saline solution to prevent clogging in the robot.
So far, the cutting device has been tested only in pig hearts on a lab bench. But the group has plans to test it in live pigs soon.