The Bridged μ-lane Microfluidic System Fabrication

The bridged μ-Lane device consists of two layers of silicon polymer poly-dimethylsiloxane (PDMS): a closed microchannel (0.1 μL volume, 95-μm-hydraulic diameter: 90 μm-depth, 100 μm-width; 1.3 cm-length), a source reservoir (SRR) and a sink reservoir (SKR) (9 μl volume each) on the bottom layer, and a source chamber (SRC) and sink chamber (SKC) (170 μl volume each) connected by an open, hemispherical bridge channel (2-mm-depth; 9-mm-length) on the top layer (Fig. 5a). The device is fabricated using elastomeric molding of PDMS and bonding of PDMS to PDMS and PDMS to glass. The SRC and SKC in the top layer are fluidically connected to the SRR and SKR in the bottom layer, and the bridge channel connects the SRC to the SKC in order to balance their solution volumes (Fig. 5b). The complete bridged μ-Lane system is thus composed of the upper user interface layer with an open bridge channel that connects the SRC and SKC chambers, as well as a bottom layer closed microchannel that connects the SRR and SKR reservoirs⁹⁵. The double-layered PDMS is then bonded to chemically cleaned (Nanostrip, Freemont, CA) glass slides using ozone gas exposure. Cells are incubated along the microchannel and the cell culture media is manually loaded until it has filled the SRR, microchannel, SKR, SKC, and bridge channel. The engineering design of the bridged μ-lane uses the large chamber/reservoir, reservoir/microchannel and chamber/microchannel volume ratios to facilitate sample loading via conventional pipette to maintain constant reagent concentration and gradual fluidic transport into the microchannel over appropriate experimental timescales. The bridged channel eliminates hydrostatic pressure differences between the SRC and SKC so that only density differences between SRC and SKC reagent concentrations exist and drive convective minuscule bulk velocity flow through the microchannel in the bottom layer, while minimizing time required to attain a steady-state gradient of the ligand^95,96. The test chemical solution is micropipette loaded into the SRC until the sample makes contact with the solution within the bridge channel to initiate system operation.