Unique Stretching Dynamics of Single Ring Polymers in 3-Dimensional Flows

Ring polymers are a unique class of macromolecules that lack free ends and exhibit unique flow properties due to their closed chain topology. Despite recent progress, we lack a complete understanding of the nonequilibrium behavior of ring polymers in flow. Prior work in single polymer dynamics has nearly exclusively focused on studying polymer motion in two-dimensional (2D) flows generated in planar microfluidic geometries. In this work, we report the direct observation of ring DNA dynamics in 3D flow fields using single molecule techniques. We study the transient and steady-state stretching dynamics of single DNA ring polymers in both uniaxial and biaxial extensional flows using a 3D-printed microfluidic device coupled with simultaneous dual orthogonal-plane imaging and fluorescence microscopy. Our results show clear differences in the conformational stretching dynamics and coil-stretch transition of ring polymers in 3D extensional flows relative to planar extensional flow. In all cases, results for ring polymer dynamics in 3D flows are directly compared to linear chain counterparts. Overall, our results provide a new understanding of the nonequilibrium dynamics of ring polymers in 3D flows.