(435i) Microfluidic Hydrogel Structures for Controlled Concentration Gradients and Fast Solution Switching

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 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.