Flow focusing through gels as a tool to generate 3D concentration profiles in hydrogel-filled microfluidic chips.

Laminar flow patterning is an iconic microfluidic technology used to deliver chemicals to specific regions on a two-dimensional surface with high spatial fidelity. Here we present a novel extension of this technology using Darcy flow within a three-dimensional (3D) hydrogel. Our test device is a simple 3-inlet microfluidic channel, totally filled with collagen, a cured biological hydrogel, where the concentration profiles of solutes are manipulated via the inlet pressures. This method allows solutes to be delivered with 50 micron accuracy within the gel, as we evidence by controlling concentration profiles of 40 kDa and 1 kDa fluorescent polysaccharide dyes. Furthermore, we design and test a 3D-printed version of our device with an extra two inlets for control of the vertical position of the concentration profile, demonstrating that this method is easily extensible to control of the concentration profile in 3D.