Capsule Crawler Opens New Surgical Vistas

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Mark Rentschler is developing a device that could open the door to advanced robotic surgiccal procedures within the abdominal cavity.
Mark Rentschler is developing a device that could open the door to advanced robotic surgiccal procedures within the abdominal cavity.

The introduction of the “pill camera”—a tiny capsule containing a video-recording device that can be used to image the gastrointestinal tract—ushered in a new era in medical diagnostic procedures.

Now, assistant professor of mechanical engineering Mark Rentschler is taking the concept to the next level by trying to give the capsule greater mobility and open the door to advanced, robotic surgical procedures. His approach begins with adding treads (think snow tires) and remote control capabilities so that the device can maneuver around the various tissues and organs within the abdominal cavity and tract.

“Mobile devices that have wheels are generally less complex and more robust than those with legs,” he says. “There are fundamental reasons we drive wheeled cars instead of vehicles with legs.”

Early in his mechanical engineering education, Rentschler completed a summer exchange program in automotive engineering in Belfort, France, which may have provided the germ of the idea. He subsequently adapted his focus to autonomous underwater vehicles as a graduate student at MIT, and then to biomedical devices while working on his PhD at the University of Nebraska.

The constant throughout these experiences was a focus on design and control of dynamic systems. Although the applications are diverse, many of the design principles remain the same.

The pill camera, also known as capsule endoscopy, was developed about five years ago as an easy and inexpensive way for a doctor to find polyps or diagnose other abnormalities in the digestive system. The capsule, which includes a camera, batteries, and transmitter, glides smoothly through the digestive system after it is swallowed, and then is naturally excreted after completing its work.

But such devices are severely limited in what they can do, Rentschler points out. Driven purely by peristalsis, they can’t turn or reverse direction, look behind obstructions, or pause to perform any operations. In addition, it is very difficult to correlate images with actual location within the tract if an image shows something of interest.

So Rentschler’s research group, which includes a full range of BS, MS, and PhD students, is studying everything from tread design and performance to characterization and modeling of tissue mechanics. Their goal is to create the optimal design for a robotic surgery assist device known as a Capsule Crawler.

Rentschler says that in-vivo robotic devices, or those that are fully contained within the body, could enable the exploration and biopsy of tissue using tools that are much more flexible and provide better visual feedback to the surgeon than laparoscopic systems—and with no incisions or resulting trauma to the patient.

A CU-Boulder faculty member since fall 2008, Rentschler already has three patents and was named CU-Boulder’s 2009 New Inventor of the Year. He has a secondary appointment in the Department of Surgery at the CU School of Medicine and teaches courses in medical device design and advanced product design.

He successfully demonstrated the use of surgical crawler prototypes during pig surgeries at the Nebraska Medical Center, where he held a post-doctoral position before coming to Colorado. Not only was the surgeon able to move the tethered crawler around the abdominal cavity as desired, but in one test, the surgeon even performed a simple gall bladder removal using only visual feedback from the onboard crawler camera system.

Rentschler subsequently helped create a wireless version of the device, although he says it was bigger than the tethered crawler due to the batteries required, and raised a concern that it could possibly be difficult to recover in some surgeries without a tether.

Wanting to expand on his early successes, Rentschler says his goal within the next 20 years is to design surgical robotic tools that can be used to perform human surgeries through any natural orifice of the body. That would open the door to lung surgery using a robotic device inserted through the mouth and trachea, for example, without any external incision required.

He currently has several medical device projects under way, including an improved laparoscopy tool that provides better imaging capabilities at a lower cost and also integrates a viewing screen that will be easier for doctors to use. Laparoscopy, which is minimally invasive surgery in the abdominal cavity, is typically performed with the surgeon having to look away from the patient to view what is happening on a separate video screen.

Rentschler has regular collaborations with clinical faculty such as Dr. Jonathan Schoen, who specializes in advanced minimally invasive surgeries.

“We have a good working relationship. We bounce ideas off of each other and it’s good for the research,” says Schoen, adding that he has worked with the CU engineering faculty and students on new tools and equipment at various times during his six years on the Medical School faculty.

The ultimate goal of creating a radio frequency-controlled, micro-robotic device that doesn’t require the insertion of instruments through the abdominal wall is particularly innovative and challenging, Schoen says. “If we can do procedures without the need for general anesthetic, tethering, or sedation, that would be a big step in patient care advancement.”


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