Microfluidic Hydrogel Structures for Controlled Concentration Gradients and Fast Solution Switching

J.S. Paustian, R. Nery Azevedo, T.M. Squires
University of California, Santa Barbara, US

Keywords: hydrogels, polymer networks

Summary:

Hydrogels are aqueous polymer networks that are solid under stress, but are permeable to water and solutes. We present a simple microfluidic technique to synthesize in-channel hydrogel structures with precise, high resolution microscale geometries. We create create hydrogel membrane walls, with feature sizes under 10 microns, that remain sturdy under high shear from adjacent flows and withstand pressure gradients. At the same time, the hydrogel membranes allow solute, solvent, and electric fields to pass from one channel to another, without passing an appreciable fluid flow, thus enabling chemical conditions on one side of the membrane to be changed without mixing, stirring, or diluting. These patterned, permeable membranes allow us to set up defined concentration or pH gradients, rapidly modify solute composition in a microchamber, or pass electric currents between channels in specified regions. Microscale dynamics, transport, and transient rheology can be probed in intriguing new ways. We provide several examples of the novel experiments enabled by these micropatterned hydrogels.