Dubbed the Intelligent Pill or iPill, the new drug-delivery system packs a micropump and sensors that monitor the body's temperature and pH balance into one pill. If the body's temperature and pH reach certain levels, the iPill responds by pumping out more or less of its drug payload. It could be used to treat many ailments like AIDS or diabetes. [...]
The iPill's electronic gadgetry, 400 square micrometers in size, fills a space smaller than the area of 10 blood cells. It is encapsulated in a penny-size plastic casing that is resistant to stomach acids. Keeping the iPill small does, however, mean the device can only store one milliliter of drugs in its internal reservoir. But that should be enough for many drugs. [...]
Badawy's prototype iPill has an ARM VII microprocessor, and silicon-oxide sensors. The sensors feed information about the patient's body to the iPill's chip, which in turn controls the micropumps that squeeze out a drug dose. "When an electrical voltage is applied to the smart material of the pumps, the pumps expand and force the drug down a channel and out of the pill," Badawy said.
The system is powered by supercapacitors -- layers of metal that store up to four hours of power. Once the device does its work, it goes out the way of all solid human waste products, usually within one to three days. [...] "We are looking at ways to prolong the working time, and this is one of our biggest problems. We are looking for an alternative power source so it will last for 12 hours or one day," Badawy said.
"It's the smallest synthetic motor that's ever been made," said Alex Zettl, professor of physics at UC Berkeley and faculty scientist at Lawrence Berkeley National Laboratory. "Nature is still a little bit ahead of us - there are biological motors that are equal or slightly smaller in size - but we are catching up." [...]
Because the rotor can be positioned at any angle, the motor could be used in optical circuits to redirect light, a process called optical switching. The rotor could be rapidly flipped back and forth to create a microwave oscillator, or the spinning rotor could be used to mix liquids in microfluidic devices.
The motor is about 500 nanometers across, 300 times smaller than the diameter of a human hair. While the part that rotates, the rotor, is between 100 and 300 nanometers long, the carbon nanotube shaft to which it is attached is only a few atoms across, perhaps 5-10 nanometers thick. [...]
The team's scanning electron microscope (SEM) can take pictures every 33 milliseconds and no faster, so they can't tell whether the rotor spins or flips faster than 30 times per second. "We assume you could go much, much faster than that, probably to microwave frequencies [a billion cycles per second]," Zettl said. "There's no way we can detect that right now, but in principle the motor should be able to run that fast." [...]
Interestingly, the rotor does not continue spinning for long once the electricity is turned off. It is so small that it has little inertia, so any tiny electric charges remaining on the device after it's turned off tend to stop the rotor immediately. "The nanoworld is weird - different things dominate," Zettl said. "Gravity plays no role whatsoever and inertial effects are basically nonexistent because things are just so small, so that little things like residual electric fields can play a dominant role. It's counter intuitive."