DNA topology dictates emergent bulk elasticity and hindered macromolecular diffusion in DNA-dextran composites

Polymer architecture plays critical roles in both bulk rheological properties and microscale macromolecular dynamics in entangled polymer solutions and composites. Ring polymers, in particular, have been the topic of much debate due to the inability of the celebrated reptation model to capture their observed dynamics. Macrorheology and differential dynamic microscopy (DDM) are powerful methods to determine entangled polymer dynamics across scales; yet, they typically require different samples under different conditions, preventing direct coupling of bulk rheological properties to the underlying macromolecular dynamics. Here, we perform macrorheology on composites of highly overlapping DNA and dextran polymers, focusing on the role of DNA topology (rings versus linear chains) as well as the relative volume fractions of DNA and dextran. On the same samples under the same conditions, we perform DDM and single-molecule tracking on embedded fluorescent-labeled DNA molecules immediately before and after bulk measurements. We show DNA-dextran composites exhibit unexpected nonmonotonic dependences of bulk viscoelasticity and molecular-level transport properties on the fraction of DNA comprising the composites, with characteristics that are strongly dependent on the DNA topology. We rationalize our results as arising from stretching and bundling of linear DNA versus compaction, swelling, and threading of rings driven by dextran-mediated depletion interactions. (C) 2022 The Society of Rheology.

Automated summary

Polymer architecture plays a critical role in both bulk rheological properties and microscale macromolecular dynamics in entangled polymer solutions and composites. This study investigates the influence of DNA topology (rings versus linear chains) and the relative volume fractions of DNA and dextran on the viscoelasticity and molecular-level transport properties of DNA-dextran composites. The results show nonmonotonic dependences on the fraction of DNA comprising the composites, with characteristics strongly dependent on the DNA topology.