Researchers are using the popular children's LEGO pieces to re-create - on a much larger scale - the microscopic activity taking place inside microfluidic arrays, commonly called lab-on-a-chip devices. The observations could offer clues on how to improve the design and fabrication of lab-on-a-chip technology.

"Microfluidic arrays are like miniature chemical plants," said Joelle Frechette, an assistant professor of chemical and biomolecular engineering at Johns Hopkins and one of the leaders of the project. "One of the key components of these devices is the ability to separate one type of constituent from another. We investigated a microfluidic separation method that we suspected would remain the same when you scale it up from micrometers or nanometers to something as large as the size of billiard balls."

Dr. Frechette and her collaborator, German Drazer, went on to design an array using cylindrical LEGO pegs stacked two high and arranged in rows and columns on a LEGO board - creating a lattice of obstacles. They attached the board to a Plexiglass sheet and pressed it up against one wall of a Plexiglass tank filled with glycerol. Stainless steel and plastic balls of varying sizes were manually released from the top of the array - with a camera tracking and timing their paths to the bottom of the lattice. The board was then rotated to increase the angle between gravity, and the columns of the array (known as the forcing angle).

Through numerous trials the research team began to notice a pattern - the larger particles did not move through the array in a random manner, as the smaller balls usually did. Instead their paths turned out to be predictable - with precision, said Dr. Drazer.

"Our experiment shows that if you know one single parameter—a measure of the asymmetry in the motion of a particle around a single obstacle—you can predict the path that particles will follow in a microfluidic array at any forcing angle, simply by doing geometry." Drazer said.

The fact that the balls moved in the same direction inside the array for different forcing angles is referred to as phase locking. If the array were to be scaled down to micro- or nanosize, the researchers said they would expect these phenomena to still be present and even increase depending on the factors such as the unavoidable irregularities of particle size or surface roughness.

"There are forces present between a particle and an obstacle when they get really close to each other which are present whether the system is at the micro- or nanoscale or as large as the LEGO board," Frechette said. "In this separation method, the periodic arrangement of the obstacles allows the small effect of these forces to accumulate, and amplify, which we suspect is the mechanism for particle separation."

This principle could be applied to the design of micro- or nanofluidic arrays, she added, so that they could be fabricated to "sort particles that had a different roughness, different charge or different size. They should follow a different path in an array and could be collected separately."

Phase locking is likely to become less important, Drazer cautioned, as the number of particles in solution becomes more concentrated. "Next," he said, "we have to look at how concentrated your suspension can be before this principle is destroyed by particle-particle interactions."

Source: http://releases.jhu.edu/2009/08/25/legos-help-researchers-learn-what-hap...