Mapping deformation dynamics to composition of topologically-active DNA blends.

Area of Science:

• Polymer physics
• Rheology
• Biophysics

Background:

• The influence of polymer topology (circular vs. linear) on blend rheology and dynamics is a long-standing research question.
• Linear polymers typically exhibit larger coils and more entanglements than circular polymers.
• Threading of circular polymers by linear chains can introduce constraints, altering blend mobility and rheological properties.

Purpose of the Study:

• To experimentally map the stress response and deformation dynamics of DNA blends across a wide range of topological compositions.
• To investigate the role of supercoiling in the behavior of circular-linear polymer blends.
• To understand the interplay between polymer topology, entanglement, and threading propensity.

Main Methods:

• Utilized in situ enzymatic topological conversion to create DNA blends with over 70 fractions of linear, ring, and supercoiled molecules.
• Employed optical tweezers integrating differential dynamic microscopy (OpTiDDM) to precisely measure strain-induced deformation dynamics.
• Quantified strain-coupling through superdiffusive dynamics aligned with applied strain.

Main Results:

• Strain-coupling is maximized in blends with comparable fractions of ring and linear polymers, specifically when supercoiling is absent.
• Increasing the fraction of supercoiled molecules significantly reduces strain-coupling.
• Converting ring polymers to linear chains results in a more moderate reduction in strain-coupling compared to supercoiling.

Conclusions:

• The observed strain-coupling is a direct result of the balance between polymer overlap and threading probability, which is influenced by topological composition.
• Optimal strain-coupling occurs in blends with a high proportion of circular polymers and a low proportion of supercoiled molecules.
• Enzymatic topological conversion and advanced microscopy techniques enable high-resolution mapping of polymer blend dynamics.