Generating Microgradients

Photograph showing a microfluidic device we used for generating gradients of a green and red dyes in solution. The three incoming channels (top part of the photograph) were connected to syringes via tubing (not visible). After combining the streams into a single, wide channel (bottom of the photograph) a gradient was formed across the channel, perpendicular to the direction of flow.

Using laminar flow in microfluidic systems, we have been able to generate complex gradients. The gradient generators are designed and fabricated using soft lithography. The basic principle of operation involves splitting and recombining streams of liquid in microchannels; diffusion within these channels accomplishes mixing. The design of the channel system controls the structure of the gradient produced. These gradients will be useful in a range of applications in cell biology, especially in experiments that ask what the cell senses in its environment.