"Keep cool to reduce friction" might be the advice given designers of nanoscale machinery by researchers who have just completed a study of factors influencing the formation of "water bridges" – capillary connections that can glue surfaces together, giving rise to friction forces.

When surfaces touch in a humid environment, moisture forms water bridges, or capillaries, between them. On familiar size scales, this process – known as nucleation – helps hold sand castles and wet concrete together, and is critical to the formation of clouds. But sometimes these structures can be less helpful, causing friction sufficient to slow or even stop nanoscale machinery – or in food processing, creating large clusters of sugar, salt, baby cereals or coffee.

By studying the frictional forces acting on an atomic force microscope (AFM) tip drawn across a glass surface, researchers at the Georgia Institute of Technology have demonstrated for the first time that the formation of these capillaries is thermally activated. Their study suggests that it may be possible to reduce the adhesion between surfaces by reducing temperatures and putting nanoscale surfaces into motion before the water bridges have time to form.

Tiny. Cheap. No moving parts. Aerosol cans and UAVs may never be the same.

It sounds implausible, if not impossible: a pump the size of an Altoid that can replace the pressure tanks, seals, valves, fittings, exposed wicks, airflow pathways, and other complex mechanical parts of every small combustion device. Think camp stoves, lanterns - any portable fuel-burning equipment used for cooking, lighting, or heating. And the potential of this remarkable invention, called a capillary pump, goes far beyond redesigned camping gear to small generators, fuel cells, even unmanned aerial vehicles.

Vapore, the company behind the pump, has already sold more than a dozen $5,000 evaluation kits to several national labs, military contractors, and manufacturers. "The other day, I got a call from a Fortune 500 company that sells air fresheners and insecticides," says Vapore CEO Rob Lerner. "They're considering the pump as a way to eliminate disposable aerosol cans."

A fluidic rectifier is a special kind of device in which the flow in one direction does not experience the same resistance as the flow in the opposite direction. Acting in a similar way to a diode in an electronic circuit, a rectifier that can control the flow of fluids through microscopic channels would open up the possibility of developing more complex integrated microfluidic circuits for biotechnology applications.

An array of magnetic traps designed for manipulating individual biomolecules and measuring the ultrasmall forces that affect their behavior has been demonstrated by scientists at the National Institute of Standards and Technology (NIST).

Described in a recent issue of Applied Physics Letters, the chip-scale, microfluidic device works in conjunction with a magnetic force microscope. It's intended to serve as magnetic "tweezers" that can stretch, twist and uncoil individual biomolecules such as strands of DNA.

California Institute of Technology researchers have designed a microfluidic rectifier that is simply a channel whose shape makes flow resistance different for fluids flowing in opposite directions.

This makes it act like a diode, which allows electricity to flow in only one direction, or a mechanical check valve, which blocks fluids from reversing direction.

Flow in the reverse direction faces more than twice the resistance of forward flow.

The microfluidic rectifier could be used in integrated microfluidic circuits, which use control fluids to operate pumps and valves that move samples and reagents in biochips.

Researchers who are developing biochips are taking two distinct approaches in devising ways to shunt tiny amounts of liquids around. One focuses on finding ways to form microscopic channels and tiny mechanical pumps. The other is aimed at using electricity to maneuver tiny droplets on surfaces.

Researchers from the University of Texas M.D. Anderson Cancer Center have advanced the second approach with a programmable biochip that uses an array of electrodes to place water droplets on a surface, insert substances into the droplets, and move and merge the droplets. The device contains no moving parts.

In an upcoming issue of PRL, researchers describe how they split tiny droplets of water into even smaller droplets of precisely reproducible size, using a method so simple it almost qualifies as child's play. They sent flows of droplets in single file through micrometer-scale networks of channels containing T-shaped connections. The technique might be used in future devices that automate biochemical reactions with the fluidic equivalent of computer chips.

Researchers at Purdue University in the US have developed a new method to quickly and inexpensively create microfluidic chips, analytic devices with potential applications in food safety, biosecurity, clinical diagnostics, pharmaceuticals and other industries.