Fabrication and electroosmotic flow analysis of freely-suspended, 3D microchannels

Suspended microchannels suitable for electroosmotic flow were fabricated by coating and dissolving sacrificial polymer fibers created by a new technique which involves using a pressurized syringe loaded with solution to directly deposit filaments of solution on the substrate in a "connect-the-dots" style. Additionally, because both the stylus and syringe were controlled with an ultra-high precision instrument, the fibers, and subsequent microchannels, can be precisely positioned in three dimensions. The diameters of the fibers were controlled, within the range of 400 nm to 100 μm, by varying the concentration of the PMMA solution or the fiber length. It was discovered that increasing either of these variables led to an increase in fiber diameter. The fibers were coated with a hydrophilic layer of glass followed by a structurally-supportive layer of poly(para-xylylene) (Parylene), then dissolved to produce hollow microchannels with diameters ranging from 4 to 100 μm. Electric potentials were applied across buffer solution-filled microchannels suspended between two electrodes to induce electroosmotic flow. A particle imaging velocimetry (PIV) system was employed to visualize and measure flow under potentials ranging from -100 to 100 V.