Abstract
Sculpting and stopping multilayered co-flowing streams is challenging due to inhomogeneous pressure distribution within a fluidic circuit composed of multiple interconnected microchannels having variable flow resistances. Here, we have investigated three different flow control methods to effectively stop a multilayered flow inside a 3D-printed microfluidic channel by bringing the average flow velocity from >100 mm s-1 to below a critical velocity of 200 µm s-1 within a certain delay time tD of ∼2s. Firstly, we 3D printed a sequence of three concentric nozzles (∼75 µm) embedded serially inside the microchannel (∼200 µm) using a two-photon polymerization (2PP) method. Secondly, we used the 2PP-based 3D printed device to produce a structured coaxial flow of four streams with individual layer thicknesses of O(10 µm) within the outlet section of the microchannel. Thirdly, we removed the pressure gradient across the fluidic circuit, from > 2 bar to ∼0 bar, to stop the multilayered flow and measured tD to assess the performance of the three stop flow methods. During the stop-flow phase, an inhomogeneous pressure gradient across different inlets resulted in a backflow to inlet channels with lower pressures. In the three stop-flow methods investigated, we systemically managed the fluidic capacitance to minimize a dimensionless backflow index (BFI) value from ∼0.3 (worst case) to ∼0.03 (best case) for a total flow rate ranging from 16.8 µl min-1 to 168 µl min-1. Finally, we have recommended the best stop-flow conditions, which resulted in a minimal delay time of tD ∼ 2s and a BFI < 0.05.
Competing Interest Statement
The authors have declared no competing interest.
