Active nematics director and flow field data

<p>We conduct our experiments on the microtubule-kinesin active nematic system pioneered in Sanchez et al. 2012. The long rod-like MTs are bundled together via depletion interactions and are driven out of equilibrium by the action of kinesin-streptavidin motor protein complexes, which are units that induce relative motion utilizing ATP<br> as the energy source. Depletion forces also aid in driving the MT bundles to form bundles to the oil-water<br> fluid interface, where they execute self-sustained bending and buckling instabilities. The system is extensile,<br> which means that active stresses cause the MT bundles to extend in length and contract in width.</p> <p>&nbsp;</p> <p>To investigate the dynamics of defects in 2D flat space, we prepare the active nematic in a flow-cell setup<br> where the entire pool of ingredients is confined in a 2D sealed cell roughly 10 cm2 in area and 100 &mu;m in<br> thickness. The lower surface of the cell is subjected to hydrophobic treatment (using Aquapel) and the<br> upper surface to hydrophilic treatment (using polyacrylamide coating) to enhance wetting by the respective<br> fluid phases. A fluorinated oil (HFE-7500 with surfactant E2K0660) forms the oil-phase, and the active MT<br> suspension forms the water-phase. We obtained purified tubulin monomers and kinesin&ndash;streptavidin motor<br> protein complexes from the Dogic Group at Brandeis University. The polymerization of tubulin to<br> MTs is performed in our lab before mixing with other biomaterials as per the protocols described in previous<br> works. The final active mix has 20% MTs by volume aided with 144&mu;M ATP. The entire flow<br> cell is sealed by epoxy resin and centrifuged at 1000 RPM to accelerate the depletion mechanism to the<br> interface.</p> <p><br> We use confocal fluorescence microscopy for visualization. The MTs are labeled with AlexaFlour 647 dye<br> and illuminated at 633 nm; the excitation and emission peaks are at 651 nm and 667 nm, respectively. After<br> sample preparation and centrifugation, we wait for 15-20 minutes to allow for uniform depletion, and then<br> image at a constant framerate till the activity ceases. Typically, the MTs stay active for 6+ hours. Imaging<br> is done using 10&times; and 20&times; objectives to focus on regions with area on the order of mm2, away from the<br> edges of the flow cell. The imaging process results in a time series of 8-bit grayscale images, which are stored<br> as the raw data.</p> <p>&nbsp;</p> <p>For more information, see &quot;Physically-informed data-driven modeling of active nematics&quot; by Golden et al.</p>