Small molecule gradient generator for microfluidic viscous shear-free cell culture

Abstract

We present a microfluidic device for generating steep gradient interfaces of small molecules by confronting two flows with different chemical concentrations. We separate a gradient generation channel and a cell culture channel by a polyester membrane so that viscous shear stress from the bottom channel flow does not interfere with cells attached on the top of the membrane. We use rhodamine-B (400 Da) and BCECF AM (686 Da, pH-sensitive cell-permeable dye) to characterize the steepness of the diffusional interface. We demonstrate ∼50 μm wide steps narrower than 5 cell diameters for < 1kDa molecules and ∼140 μm steps for pH gradients across HeLa cell culture with no convective shear applied to the cells.