Controlled microscale diffusion gradients in quiescent extracellular fluid.

Microchannels offer a means of establishing concentration gradients of soluble factors over micron length scales representative of those in tissues. Here, we report the development of a microfluidic channel system wherein a hydrogel has been patterned to generate temporally and spatially stable concentration gradients of multiple solutes in quiescent extracellular fluid. The fluorophore Alexa Fluor 488 and a fluorescent glucose analog are used as probes to illustrate the generation of stable, reproducible, and linear probe concentration gradients. A method is described for estimating the diffusivity and hydrogel permeability of a solute from in situ imaging data. Concentration gradients are also generated in the presence of a mouse insulinoma cell line to demonstrate the compatibility of the system with living cells. The net transport and metabolism rate of the glucose analog is found to be heterogeneous and independent of the applied extracellular gradient. This system may be suitable for the study of cell response to various extracellular gradients of soluble factors.