Big idea in mini-robotics
Scientists have long sought ways to miniaturize medical devices so they can be permanently implanted in the body. A key stumbling block, however, is finding a way of shrinking the power source for these tiny devices.
Even today’s compact cardiac defibrillators or pacemakers, for example, must be powered by relatively large batteries.
The newly minted machines in Carlo Montemagno’s UCLA lab may overcome this formidable hurdle.
Smaller than a pencil dot, made of silicon and powered by “legs” of living muscle tissue, the devices are a critical first step in the creation of part-human, part-artificial miniature robots. Such machines would be an entirely new class of autonomous devices, ones fueled by glucose, the same energy source as our bodies.
“This is a very important technological advance because it shows that you can fuse a living cell with a synthetic material and make a mechanical device that functions,” says Robert G. Dennis, a biomedical engineer at the University of Michigan in Ann Arbor.
Dennis proved in an earlier study that, under the right conditions, muscle cells automatically transform into functional tissue. UCLA researchers have taken his work further, creating miniature robots powered by heart-muscle tissue. (Unlike other muscle tissue, which must be electrically stimulated, cardiac tissue expands and contracts on its own.)
Ultimately, the technology could be used to power tiny nerve-stimulators that prompt the diaphragm to expand and contract, making it possible for paralyzed patients to breathe without a ventilator. It could also lead to the development of a compact power source for internal sensors, helping physicians diagnose or treat disease. The technology could even drive pacemakers and other implanted devices.
Instead of being driven by micromotors attached to bulky batteries or wires, the resulting devices could be fueled by glucose in the bloodstream. The muscle tissue converts glucose into mechanical energy; the expansion and contraction of the muscle then generates the electrical energy that propels these miniature machines.
“You could make a device smaller than a postage stamp that was fully integrated,” says Montemagno, chairman of the university’s bioengineering department. “You can put it in and forget about it -- no more need to replace batteries, or worry about infections from the external wiring.”
Still, some formidable technical problems need to be solved before these micro-robots will become part of standard medical practice. The tiny implants, which would combine muscle tissue and electronics into a single system, must be made durable, with packaging that protects the electronic parts yet allows them to work inside the body.
Simply creating these first tiny robots was a daunting technological challenge. Researchers had to get the muscle cells to bind to a synthetic material. And once the cells had attached themselves to the material, they had to be able to contract and relax to produce the robot’s crawling motion.
“You can’t grow cells and muscles in thin air,” says Montemagno. “They have to be supported in some way, yet still are free to move.”
Researchers finally hit upon a bit of chemical legerdemain that enabled them to solve these problems. The key was using a special polymer that hardens when heated and liquefies when cooled, says Montemagno.
First they created an arch-shaped mold from silicon and coated it with a layer of this special polymer. Then they painted the underside of the arch with a gold film that sticks to the muscle cells. Finally, the team added cardiac muscle cells from rats to the structure and cooked the whole thing in an incubator.
After three days, the muscle cells had adhered to the silicon and transformed themselves into muscle fibers that grew along the length of the arch. When the structure was removed from the incubator, the polymer cooled, turned into a liquid and was easily washed off.
“This freed up the muscles, which started to move immediately,” says Montemagno.
“Now that we’ve established the basic technology,” he adds, “with enough resources, we could have prototype devices within five years.”
*
Aid in breathing on their own
Miniature robots offer but one potential way to help paralyzed patients breathe without a ventilator. Another option may be an experimental procedure in which electrodes are implanted near the diaphragm.
The electrodes, inserted through three dime-sized incisions, deliver jolts of electricity 12 times a minute to motor points in the body that stimulate the phrenic nerve. Such stimulation prompts the diaphragm to expand and contract.
As a minimally invasive procedure, it is less dangerous than conventional surgery. That type of operation requires opening the chest, which can cause infection. It can also permanently damage the phrenic nerve because implanted electrodes stimulate the nerve directly -- the new technique taps points near the nerve, not right on it.
At a scientific meeting this month, researchers revealed that three of the six people who have undergone the procedure are completely free of the ventilator, and two others are increasing their time off the ventilator. (Actor Christopher Reeve is one who is gradually weaning himself from the assisted-breathing device.) In one patient, the implant system failed to stimulate the diaphragm.
