Characterising the effect of geometry on a microchamber for producing controlled concentration gradients

•A 2D concentration gradient within a microfluidics device has been characterised.•The effects of geometry on time to steady-state have been determined.•The effects of geometry on concentration profile and symmetry have been determined.•An important recommendation – entrance width to the chamber should be below 80 μm.

A microfluidic diffusion chamber with 3 inlets and a circular central chamber allows a 2D concentration gradient to develop. This diffusion chamber has been characterised numerically for the effect geometry has on equilibrium time, the concentration profile and the flow profile within the central chamber. As the Einstein–Smoluchowski relation predicts, the time to reach steady state is proportional to the square of the radius of the chamber but features within the chamber are qualitatively insensitive to the size of the chamber within the range of 100–1000 μm. Inlet width had a much more significant effect on the qualitative behaviour within the chamber, affecting the symmetry of the concentration profile. It is recommended that inlet widths are less than 80 μm to preserve symmetry. In this paper, the effect of geometry on both transient and steady-state behaviour has been explored, providing a basis and criteria for designing chambers for a wide range of applications, including studying the effect of concentration gradients on cell mobility or a rapid assay for biofilm development in a range of concentrations.

Graphical abstractGeometry affects flow and concentration profiles, shown above, and the time to reach steady state. Inlet width has a critical length, above which asymmetries arise.Figure optionsDownload full-size imageDownload high-quality image (204 K)Download as PowerPoint slide