A surgical robot that can change its shape to skirt safely around vital organs and navigate inside arteries could one day spare cardiac patients the risks of open heart surgery.

The instruments currently used in keyhole surgery are either stiff and needle-like, so they can only be maneuvred in straight lines, or flexible and unable to transmit any force to the tissue.

"Catheters are great, but they are like floppy noodles," says Pierre Dupont, a biomedical engineer at Boston University. "They follow curvature and contours, but you have limited control at the tip -- you can't pull and push on tissue."

Now, Dupont and his team have come up with a way to combine the steerability of a flexible catheter with the stiffness of a needle. Called a concentric tube robot, the technology relies on a series of telescoping curved tubes. As each tube extends and twists from the preceding one, the robot is able to form a multitude of serpentine shapes, allowing it to easily navigate inside an artery while also being stiff enough to transmit force from the surgeon's hand to the area of interest.

The robot could greatly extend the range of procedures that can be carried out via minimally invasive surgery, Dupont told the International Conference on Robotics and Automation in Anchorage, Alaska, in May. For example, it could be used to perform some cardiac operations that currently require open heart surgery, with the robot reaching the heart via the veins in the neck.

The concentric tube robot comprises three gently curved nickel alloy tubes, each a couple of millimeters wide. Surgeons identify the path they wish to navigate in advance, then choose the combination of pre-curved tubes that would enable the robot to adopt the shapes needed to follow that route.

Using electric motors, each tube can rotate independently, and is able to telescope into and out of the other tubes. The surgeon uses a joystick to control the device, aided by software that helps plan the route and steer the robot.

At its tip, the robot has a high degree of three-dimensional dexterity, and can be fitted with a number of cutting, gripping and cauterizing tools to be used during surgery.

The robot has been tested in heart surgery on pigs.

"We successfully used the robot to plug holes in the heart," says Dupont, who's now developing the robot at Boston Children's Hospital, Boston, Mass.

The team came up with the idea when trying to develop a surgical tool that could gently grasp a fetus's limb to turn it in the right direction for in-utero surgery.

"There's a great need for higher surgical dexterity and these nested tubes seem quite an advance," says Brian Davies, of the medical mechatronics lab at Imperial College London. But he warns that verifying the robot's software is safe -- and not prone to lethal, jerky hiccups -- will be a major challenge.

 

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