From the Labs: Nanotechnology

Muscle-Powered Devices
Novel machines could improve drug testing and lead to new kinds of robots

SOURCE: “Muscular Thin Films for Building Actuators and Powering Devices”
George M. Whitesides, Kevin Kit Parker, et al.
Science 317: 1366-1370

RESULTS: Researchers at Harvard University have made several small mechanical devices powered by heart muscle harvested from rats. The creations include pumps, a device that “walks,” and one that swims.

WHY IT MATTERS: The scientists made the machines to study the behavior of muscles and to provide a platform for testing heart drugs. (The devices provide an easy way to monitor the effect of drugs on heart tissue.) Eventually, they could be used in new types of robots that can change shape, grip objects, and propel themselves.

METHODS: The researchers used a fabrication method called spin coating to make ultrathin elastic films; then they applied patterns of proteins to the films. Finally, they added heart-muscle cells; guided by the protein patterns, the cells organized themselves into working muscle tissue. To make the various devices, the researchers cut the muscular thin films into specific shapes (such as a triangle that resembled a fish’s tail) and changed the alignment of the cells. The devices, which must remain in a solution that keeps the muscles alive, can be controlled by electronic signals sent through the solution.

NEXT STEPS: The researchers are working to create devices that use human muscle tissue, perhaps grown from stem cells; such devices could be used in drug testing or to patch damaged heart muscle. So far, the muscle tissue survives for only a few weeks. For robotics applications, the scientists may combine heart muscle with other types of cells to increase longevity.

SOURCE: “Electrically Excited Infrared Emission from InN Nanowire Transistors”
Jia Chen et al.
Nano Letters 7: 2276-2280

RESULTS: IBM researchers have demonstrated a new technique for converting electricity into infrared light in indium nitride nanowires. Previously, getting a nanowire to emit light required injecting it with both electrons and “holes”–a physicist’s shorthand for the absence of an electron. (An electron that leaps to fill a hole may leave another hole behind it; in this sense, the hole can be seen as moving.) Since the new technique requires only the injection of electrons, it is simpler and potentially more efficient.

WHY IT MATTERS: Light-emitting nanowires could be integrated into the microchips used in telecommunications. They could also be used for optical communication between devices on computer chips, which could significantly improve processing speed. Infrared light, which has previously been difficult to produce in nanowires, is ideal for use in silicon-based chips, the industry standard. What’s more, the electron-only injection method yields light emitters that are brighter and more efficient than other nanowire devices.

METHODS: The researchers grew indium nitride nanowires by combining indium and indium oxide with ammonia at 700 ºC. The nanowires, which were suspended in rubbing alcohol, were then dispersed over a silicon wafer patterned with electrodes. The wires bridged the electrodes, forming transistorlike devices. A current delivered by the electrodes caused the nanowires to emit light.

NEXT STEPS: Using these light-emitting nanowires in microchips will require methods for arranging nanowires into complex circuits at high speeds.