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Small snake robots used for surgery have captured the imaginations of some of the world’s top innovators. Howie Choset, associate professor of Robotics at Carnegie Mellon University is no exception. His involvement with the technology began in the 1990s and this year will see his team conducting their first human clinical trials using a snake robot.

A successful outcome could mean an explosion in the number of minimally invasive cardiac procedures when these devices reach the market in three years time.

Choset discusses the journey from concept to surgical arena for his breakthrough cardiac snake – CardioARM. Choset’s team, at Cardiorobotics Inc, has been developing the CardioARM (Articulated Robotic MedProbe) for several years. The device is a teleoperated probe with a non-linear lumen comprised of a series of highly flexible links, capable of assuming the shape of its surroundings or being reshaped according to need.

The probe remembers previous configurations as it moves through a three-dimensional volume, thereby reducing the risk of damaging surrounding tissue when retracting. The links can be made of almost any material and can also be disposable. But what makes the CardioARM vastly different from other minimally invasive cardiac surgery methods is it requires only a single entry point, whereas other surgical systems such as da Vinci can require as many as five or six.

The beginning

“The idea is, if you can make a robot device small enough to enter through the solar plexus, make a 2cm turn one way and then a 2cm turn another way and position this device behind the heart, you can then deliver a whole host of therapies and diagnostics which otherwise would have required that you crack the chest,” explains Choset. “So that idea/concept/wish to have a small snake robot isn’t new and one I personally have been thinking about since I went to graduate school at CalTech.”

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The idea for a small surgical snake robot initially came to Choset from his graduate school advisor Joel Burdick, who teamed up with two graduate students, Greg Chirikjian and Andrew Brett Slatkin in an attempt to flesh out the concept. The team was trying to develop a surgical robot for minimally invasive surgery on the intestines using a technology they termed “hyper-redundant robotics”, meaning the machines have many different degrees of freedom – similar to a snake.

Some years later, Marco Zenati, who is now a cardiac surgeon at the University of Pittsburgh, gave a talk at Carnegie Mellon. He pretty much described a need for a small snake robot. He and Choset got together along with a third colleague, Alon Wolf, now a professor at the Technion in Israel, and the three started surveying the field.

New discoveries

“At this point, my group had already built a few snake robots largely geared towards urban search and rescue, and one we built to do in-situ repairs on naval vessels,” says Choset. “You want those robots to be as small as possible. They were only 45mm in diameter, which was the best we could do at the time. It was in between writing the second and third grant that we worked out how to build the small snake robot.

“In fact, it is wonderful. I pretty much sat down and said “I’m going to figure this out right now”. Twenty minutes later, the idea came to me. That never happens. I normally have other people around me, distracting me. It may be the most profound thing I’ve ever figured out.”

“The CardioARM uses four cables to “marionette the device”, which the surgeon controls through a computer and joystick.”

What made this revelation a breakthrough is that most people who try to make a small surgical snake robot try to develop new kinds of actuator technology, such as electric motors. The muscles in your arms are actuators and people have even developed microelectromechanical systems (MEMS) technology with this in mind.

“Up until this point there were two types of small snake robots,” explains Choset. “One group were made from novel actuators, which is great work. But these devices are not ready for primetime, so those robots don’t work yet.

“The others are made out of actuators that I call “imaginary actuators” because they don’t exist,” he continues. “People say to make a small snake robot just use small motors and of course that”‘ not realistic. As to the other people who are funded to build small snake robots like iSnake in England, we have no idea how they are actuating that robot. Perhaps their application is different and only limited to the luminal spaces whereas we are moving our robot around in the three-dimensional intracavity spaces.

Regardless, some people think those are just the details, shrink things down. But that is the critical part, trying to make things small, strong and manoeuvrable, which is what we figured out that day.”

Pulling strings

The CardioARM uses four cables to “marionette the device”, which the surgeon controls through a computer and joystick. “We shape the device however we want with these four cables and at the same time we have a feeder mechanism that pushes the snake into the body,” explains Choset. “The combination of pushing and getting the shape allows us to access the desired area.”

The smallest version of CardioARM measures 300mm in length and is 10mm in diameter. The ultimate goal for Choset and his team is a robot snake that can be used by non-surgeons through small incisions.

Cardiorobotics has already completed 14 successful live pig operations as well as two cadaver operations. The company expects to perform the first human operation by the end of 2009. Barring any unforeseen problems during surgical trials, the CardioARM should reach the market in the next three years.

The key features of CardioARM are:

  • Single-port access for deep anatomical procedures
  • Small diameter and radius of curvature
  • Unlimited degrees of freedom
  • Steerable, self-supported, non-linear therapeutic path
  • Steerable, self-supported, non-linear visualisation path
  • Teleoperated, with “joystick” and “pause” button
  • Memory – device remembers its configuration
  • Non-linear lumen
  • MR-compatible
  • Disposable.

Choset is quick to point out that none of this would have been possible within a university setting. Thanks to the advice of his long-time friend, Bill Thomasmyeyer, president of the National Center for Defense Robotics in Pittsburgh’s Tehnology Collaborative, Choset and his team took the technology from the classroom to the boardroom.

“There is no way, as a professor being supported by government grant dollars, that I could have arrived at this so quickly,” explains Choset. “To have this kind of result and success is mind boggling.” The move opened up new channels of funding for the project, such as the Pittsburgh Life Science Greenhouse (PLSG). One of their advisors, Jim Jordan, saw great potential for the technology and gave the team a small grant which was used to hire an engineer. Jordan helped crystallise what the market could potentially look like, helped with strategy and eventually introduced the team to its first real CEO. Without him, there would not have been a company.

“The ultimate goal for Choset and his team is a robot snake that can be used by non-surgeons through small incisions.”

“One of our founders is a cardiac surgeon but, just because he is, it doesn’t necessarily mean the target application of what the company is looking at will be limited to cardiac,” adds Choset. “It just so happens that, based on market need or interest, a lot of the applications for this technology are cardiac.

“One particular application we are looking at is ablation therapy. Currently, your chest has to be cracked open in order to do this. Though there are endo-luminal approaches, they aren’t perfect. You can have collateral damage to the oesophagus, and a small chance that a fatal clot could form. With our device, you can perform an ablation in a completely minimally invasive way, through the subxiphoid process.”

Though the initial outlay in terms of cost will undoubtedly be higher at the beginning, Choset and his team believe the longer-term healthcare expenditure will be significantly reduced through shorter hospital stays, reduced incidence of infection, faster recovery time and reduced post-operative pain.

What next?

At present, the CardioARM utilises a direct visualisation system that relies on the surgeon’s in-depth knowledge of anatomical structures in order to pinpoint the device’s location within the body. “We have a fibre optic that passes through the body of the snake,” says Choset. “We are starting to work with another company called Bluebelt Technologies. They are developing ultrasound visual capabilities that will allow us to look at 3D rendered images with the snake, where we can see what it sees and have additional visualisation that way.

“This visualisation is just one small thing,” he explains. “I’m working with another colleague Baranco Jaramaz. We’re trying to get a more refined image which will work for a NOTES (Natural Orifice Transluminal Endoscopic Surgery) application. So we can enter the mouth, poke a hole in the stomach, go through the stomach, go to the pancreas – remove part of the pancreas and come back out without visible scars. I believe in England last year there were four appendectomies done with a NOTES approach. But they used a floppy endoscope, whereas our robot will be able to access more places.

Choset also sees some use for removing the lymph nodes in the throat. There is one procedure the team is looking at, for the treatment of hyperhidrosis (excessive sweating). “I bet you that as soon as we do one procedure, in two years you and I will be talking about the ten procedures that other people thought of that make a lot more sense than what I’m telling you now,” he concludes. The future seems bright for such an innovative technology.