Bioengineers have eagerly explored tiny mechanisms that move microscopic or nanoscopic amounts of fluid. Already used in ink-jet printers, microfluidic devices hold out the promise of efficient and rapid medical assays requiring only minuscule sample volumes for results. Potential applications include lab-on-a-chip devices for on-site chemical analyses, engineered vital organs, and in vivo pharmacies that secrete drugs when needed. In terms of implants, one of the main problems is power. Microfluidics typically rely on large external gear and electricity supplies to run actuators that drive fluids through microchannels. Now a group of researchers has innovated a concept that instead relies on an old-fashioned kind of engine--a living heart.

The team, based in Japan, has transformed cultured rat heart muscle cells into a spherical, pulsating micropump five millimeters in diameter that requires no external power, wires or stimuli. The simple device consists of a hollow, flexible silicone sphere with tubes 400 microns wide at opposite sides--in structure, it resembles an earthworm's one-chamber heart. Rat heart muscle cells (cardiomyocytes) surround the sphere, and when they pulsate in sync, they drive fluid through the tubes and the sphere. Cell nutrients in the surrounding medium power the cells.