Ring DNA confers enhanced bulk elasticity and restricted macromolecular diffusion in DNA-dextran blends

TL;DR

This study investigates how DNA topology (ring vs. linear) influences the bulk elasticity and microscopic diffusion in DNA-dextran blends, revealing topology-dependent non-monotonic behaviors through combined rheology and microscopy.

Contribution

It provides the first direct coupling of bulk rheological measurements with microscopic dynamics in DNA composites, highlighting the impact of DNA topology on material properties.

Findings

Ring DNA causes enhanced bulk elasticity.

DNA topology significantly affects macromolecular diffusion.

Non-monotonic dependence of properties on DNA fraction was observed.

Abstract

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 non-monotonic 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.