'Microfluidic palette' may paint clearer picture of biological...( The masterpieces that spring from th...)

The masterpieces that spring from the talents of Rembrandt, Van Gogh and other artists often begin with the creation of a gradient of colors on a palette. In a similar manner, researchers at the National Institute of Standards and Technology (NIST) have created an innovative device called the "microfluidic palette" to produce multiple, steady-state chemical gradientsgradual changes in concentration across an areain a miniature chamber about the diameter of a pinhead. The tool can be used to study the complex biological mechanisms in cells responsible for cancer metastasis, wound healing, biofilm formation and other fluid-related processes.

The advantage of the NIST system, as described in a new paper,* is that the gradients are generated by diffusionthe gentle movement of matter from one point to another by random molecular motion. Microfluidic systems usually mix fluids more actively, by pumps and the circulation of currents. Diffusion gradients allow cells being studied to remain in the microchamber without the chance of their being swept away. Diffusion also permits chemical molecules to move in and out of the cells naturally and eliminates the risk of shear stresses, commonly produced by currents, which could cause the cells to rupture or behave abnormally.

The NIST microfluidic palette manages this with a clever plumbing trick. The key element of the palette is the microchamber, a small disk-shaped area only 1.5 millimeters (0.06 inch) across etched into the center of a glass wafer. Tiny holes at its circumferencethree in the prototype, but it could be moreallow various mixtures to flow into the chamber. Beneath the chamber, each access port connects to the long tail of a Y-shaped channel etched into a second layer. These channels deliver test chemicals to the chamber. Fluid flow in and out of the short arms of each Y at constant pressure assures a constant stream of fresh chemicals. Because the pressure in the chamber is balanced b
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