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Micro-robot holds promise for new surgical technique

A few years from now, patients with polyps or other ailments of the large intestine may be operated on by tiny robots controlled by surgeons who never touch the patient directly, using a technology being developed by MIT students.

James McLurkin, a senior in electrical engineering with a minor in mechanical engineering, has been working on micro-robots that are capable of several simple tasks and responses. The first relatively simple micro-robot was developed in 1987 in the Artificial Intelligence Lab by Professor Rodney Brooks, professor of electrical engineering and associate director of the lab; former research staff member Anita Flynn, now a graduate student and Mr. McLurkin's UROP advisor; Dave Barrett, now a graduate student in the Department of Ocean Engineering, and former graduate student Sandy Wells.

Mr. McLurkin's invention, which he has dubbed Cleo, has sensors to detect ambient light, infrared light and tilt, plus a battery recharge sensor and a pair of tiny antennae in front to detect obstacles. There is also a claw that allows the micro-robot to grasp and carry objects. The robot can be operated by a person with a joystick through a director control, but it also functions independently when untethered.

Measuring about an inch and a half on a side, the device is small enough to move through an adult's colon, but it isn't close to being ready for practical use. The main problem is not in the micro-robot's size or mechanical abilities, but in its inability to function in the hostile environment of the human body. The large intestine, Mr. McLurkin pointed out, is wet, slippery and lacks firm surfaces, and it is also three-dimensional with several bends, so moving around in a way that is both reliable and non-harmful to the patient presents significant engineering problems.

One possibility being worked on by Dean Franck and Art Shectman (both juniors in mechanical engineering and UROPs with Ms. Flynn) is to somehow seal the micro-robot inside a rubber-like membrane turned inside-out on itself like a rolled-up sock, "but to make a mechanical version of this is hard, to say the least," Mr. McLurkin noted. An early prototype in the AI Lab consists of a cylinder with three sets of treads spaced evenly around the circumference, so the robot no longer has a top or bottom.

If the problems can be overcome, surgeons could some day have a tool for repairing problems in the colon without the need for cutting a patient open or using an endoscope. The robot would be inserted into a patient's rectum and make its way to the problem area, guided by a surgeon who could see what the robot sees through a tiny camera whose images are transmitted back to the outside world through a cable. The same cable would provide light, power and air, and it would transmit the surgeon's directions-he or she could steer the device, enlarge the operating field by pumping in air to distend the colon, operate a small device for removing a polyp, and suction away surgical debris.

Surgeons can already operate remotely in this fashion by using an endoscope, or flexible tube. However, doctors are interested in micro-robots because they are more maneuverable than an endoscope and hence more comfortable for the patient. Also, if even smaller models could be built, they could gain access to places such as the small intestine that endoscopes can't go, Ms. Flynn said.

A simpler micro-robot called Goliath that Mr. McLurkin made about two years ago sparked interest from surgeons, and the ongoing work (which he will continue next year while he finishes his course work and thesis) is now funded by a grant from the Advanced Research Products Agency. When Ms. Flynn was invited to explain the micro-robot work at a conference, "the surgeons just went crazy," she said. "They're very enamored of technology because it's changed surgery so much in the past few years."

The largest single part in Cleo is the N-cell battery on top. A series of colored lights informs the human operator of what the robot is sensing (e.g., light, an obstacle or a tilted surface). Other parts include 12 miniature circuit boards built by Mr. McLurkin, a Motorola microprocessor, the sensors and various other parts borrowed from everyday objects.

For example, he and Ms. Flynn obtained the three motors (one for each tread and one for the claw) at no charge from a company with a stockpile of malfunctioning beepers of the type that vibrate rather than emit sound. Each original motor, about the size of two pencil erasers, had a small weight encircling only half of the drive shaft, so when the shaft spun, the entire device vibrated like an unbalanced washing machine. Once that weight is removed, the motor is an efficient drive device for micro-robots.

Many of the little wheels, cogs, treads and other parts came from cannibalized toys such as a motorized car. "It's one of the few things that's built with mechanical parts of the size we need," Mr. McLurkin said. "There isn't a micro-part catalog out there." Consequently, he pores over numerous electronic trade journals in search of components and tracking down unlikely sources like the beeper company. "I spend a lot of time on the phone," he said.

Ms. Flynn is researching a smaller type of motor called a piezoelectric ultrasonic motor, in which a piezoceramic material bends when an electric current is applied to it. She has built a test model eight millimeters in diameter using bulk piezoelectric materials and test structures just two millimeters in diameter using thin-film piezoelectrics on silicon. Piezoelectric sensor technology is already used in the devices that cause supermarket doors to swing open when pressure is applied to a floor mat, and the larger-scale piezoelectric ultrasonic motors themselves are commercially available in Japan, although they are much too big to use in a micro-robot, she added.

If the motors and other components can be made small enough, a "micro-robot on a chip" could be built inexpensively in one integrated process rather than assembling and wiring together disparate parts, Ms. Flynn explained. "You'd sort of print robots," she said.

Loading the micro-robot with instructions on how to react to various stimuli brings Mr. McLurkin's computer programming skills into play. The microprocessor has two kilobytes of EEPROM (electronic erasable programmable read-only memory) and receives data from a Macintosh through a small serial port. The limited storage space presents an obstacle to endowing the micro-robot with more sophisticated abilities; nonetheless, "you can get complex-looking behaviors out of relatively simple programs," he noted.

In his thesis work, Mr. McLurkin hopes to build many copies of Cleo or its successor and have them work in concert like ants, a species that holds a special interest for him.

The micro-robot served as a concrete example of how undergraduates' basic research can yield projects that may one day prove extremely practical. Several Washington officials were impressed by a tabletop demonstration he gave during a recent student trip to showcase and defend UROP, which is threatened by cutbacks because of changes in government accounting rules. (See MIT Tech Talk, May 11, 1994.) Without further funding, the micro-robot will probably remain just a novelty, he noted. "It's cute, but it's not anywhere near the point where you'd want it do anything real."

A version of this article appeared in the May 18, 1994 issue of MIT Tech Talk (Volume 38, Number 33).

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