Development of non-linear gradient microfluidic devices*

Mechanical stress introduced by the flow in microfluidic chambers induces shear stress thus impacting the live cells migration patterns. Our last-year work showed that constructing a flowless linear gradient requires two mirrored gradient chambers. In this work we present microfluidic devices that generates non-linear chemical gradients. By splitting and recombining the input flows through a combination of bifurcated (mixers and splitters) and trifurcated (splitters) channels one can generate a chemical gradient across a microfluidics chamber. As the input chemicals flowing downstream mix, a linear gradient can only achieve relative lateral gradients either from 0% to 50% or from 50% to 100%. However, we demonstrate that these mirrored gradient can be non-linear in order to accommodate a steeper flowless gradient. By introducing bias when recombining the flows in the mixers one can generate non-linear gradients. Different bias between mixers input channels can accommodate steeper lateral gradients from 100% to: (a) 37% for a 2:1 bias, (b) 30% for a 3:1 bias, (c) 27% for a 4:1 bias and (d) 24% for a 5:1 bias. This type of separated, flowless gradient offers new opportunities to study the migration of live cells free of physical flow.