Researchers at the National Institute of Standards and Technology (NIST) have created a new microfluidic device out of ordinary, inexpensive components. Led by engineer Javier Atencia, the “diffusion-based gradient generator” basically turns a glass slide, plastic sheets and double-sided tape into a tool to rapidly assess how changing concentrations of specific chemicals affect living cells.
The method offers a simple and inexpensive way to expose an array of cultured cells to a chemical gradient—a solution where the chemical concentration changes gradually and predictably across the array. Using such a gradient is a rapid, high-throughput way to evaluate the effect on cell growth or toxicity.
The gradient is created by diffusion, which is the gentle movement of matter from one point to another by random molecular motion. Conventional microfluidic systems usually mix fluids by pumping them in a circular motion or by twisting and folding them together. The advantage of diffusion over conventional systems is a great reduction in the risk of cells being swept away or damaged by shearing forces in the test fluid. (Source: NIST Tech Beat)
The gradient generator is built in layers, with each section precisely positioned with an alignment tab. The base is a glass slide, upon which is attached a strip of double-sided tape cut to have a row of four micrometer-sized channels. On top of this is a polystyrene strip cut to have two lines each of four tiny circular “wells” where each pair lines up with the ends of the channel below it. The next layer is another strip of double-sided tape, this time with a Y-shaped canal cut into it to serve as the flow path for the chemical gradient. Finally, a Mylar strip cut to have an identical Y-canal serves as the cover.
Once the test cells are added, the hinged cover is lowered and affixed, sealing the gradient generator. Magnetic connectors are used to accomplish fluid flow in and out of the system. Kept at constant pressure, this flow assures a steady-state stream through the device and creates a diffusion gradient in each buried channel. Cells in the channels are simultaneously exposed to a range of chemical concentrations from high to low.
For more information access: J. Atencia, et al. A robust diffusion-based gradient generator for dynamic cell assays. Lab on a Chip, Vol. 12, Pages 309-315 (2012). DOI: 10.1039/C1LC20829B
Image courtesy of Cooksey/NIST