| The sensing of chemical gradients plays an important role in the guidance of cells for tissue development, migration of cells in the immune system, and human disease. We have developed a microfluidic transwell insert for generating concentration gradients in a user-friendly and modular format that is compatible with conventional cell cultures. The device is simply inserted into a standard 6-well plate were it hangs self-supported at a distance of 250 microm above the cell culture surface. The core aspect of our design is the delivery of small microflows through a track-etched membrane into the cell culture well. The microfluidic transwell can deliver quantifiable, large-area gradients to a large number of cells or tissue explants with extremely low fluid shear stress. Finite-element modeling was used to describe porous membrane flow and molecular transport for predicting gradients generated by the device. Transwell microfluidic gradients were applied to a large population of neutrophil-like cells to demonstrate the direct observation of chemotaxis. Additionally, the modular design and low fluid shear stress made it possible to apply gradients to sensitive neuronal explant cultures. With a simplified interfacing scheme and well-defined, quantifiable gradients, the microfluidic transwell device has potential for broad applications to gradient sensing biology. |
