Medibots: The world's smallest surgeons

A MAN lies comatose on an operating table. The enormous spider that hangs above him has plunged four appendages into his belly. The spider, made of white steel, probes around inside the man's abdomen then withdraws one of its arms. Held in the machine's claw is a neatly sealed bag containing a scrap of bloody tissue. This is a da Vinci robot. It has allowed a surgeon, sitting at a control desk, to remove the patient's prostate gland in a manner that has several advantages over conventional methods. Yet the future of robotic surgery may lie not only with these hulking beasts but also with devices at the other end of the size spectrum.

The surgeons of tomorrow will include tiny robots that enter our bodies and do their work from the inside, with no need to open patients up or knock them out. While nanobots that swim through the blood are still in the realm of fantasy, several groups are developing devices a few millimetres in size. The first generation of "mini-medibots" may infiltrate our bodies through our ears, eyes and lungs, to deliver drugs, take tissue samples or install medical devices. The engineering challenges are formidable, including developing new methods of propulsion and power supply. Nevertheless, the first prototypes are already being tested in animals and could move into tests on people in the not-too-distant future. "It's not impossible to think of this happening in five years," says Brad Nelson, a roboticist at the Swiss Federal Institute of Technology (EHT) in Zurich. "I'm convinced it's going to get there."

It was the 1970s that saw the arrival of minimally invasive surgery - or keyhole surgery as it is also known. Instead of cutting open the body with large incisions, surgical tools are inserted through holes as small as 1 centimetre in diameter and controlled with external handles. Operations from stomach bypass to gall bladder removal are now done this way, reducing blood loss, pain and recovery time.

Combining keyhole surgery with the da Vinci system means the surgeon no longer handles the instruments directly, but via a computer console. This allows greater precision, as large hand gestures can be scaled down to small instrument movements, and any hand tremor is eliminated. There are over 1000 da Vincis being used in clinics around the world.

Heart crawler

There are several ways that such robotic surgery may be further enhanced. Various articulated, snake-like tools are being developed to access hard-to-reach areas. One such device, the "i-Snake", is controlled by a vision-tracking device worn over the surgeon's eyes (New Scientist, 20 September 2008, p 21). It should be ready for testing on patients within four years, says developer Guang-Zhong Yang, a roboticist at Imperial College London.

With further advances in miniaturisation, the opportunities grow for getting medical devices inside the body in novel ways. One miniature device that is already tried and tested is a camera in a capsule small enough to be swallowed.

In conventional endoscopy, a camera on the end of a flexible tube is inserted either through the mouth or the rectum, but this does not allow it to reach the middle part of the gut. The 25-millimetre-long capsule camera, on the other hand, can observe the entire gut on its journey. More sophisticated versions are being developed that can also release drugs and take samples.

The capsule camera has no need to propel itself because it is pushed along by the normal muscle contractions of the gut. For devices used elsewhere in the body, some of the key challenges are developing new mechanisms for propulsion and power supply on a miniature scale.

One solution is to have wires connecting the robot to a control unit that remains on the outside of the body. This is the case for a robot being developed for heart surgery, called HeartLander.

Operating on the heart has always presented enormous challenges, says Marco Zenati, a heart surgeon at the University of Pittsburgh, Pennsylvania, who is one of the device's inventors. Conventionally the heart is stopped and the patient hooked up to a heart-lung machine. A more recent approach is to perform keyhole surgery on the beating heart, but even so several incisions must be made, and the left lung must be partly deflated to allow access, requiring a general anaesthetic.

The HeartLander robot is designed to be delivered to the heart through a single keyhole incision, from where it can crawl to the right spot. The heart does not have to be stopped, and the left lung need not be deflated, so the patient could be breathing naturally, with just a local anaesthetic. "Coronary surgery can become an outpatient procedure," says Cameron Riviere, the team's roboticist, based at Carnegie Mellon University in Pittsburgh.