Physical entanglements mediate coherent motion of the active topological glass confined within a spherical cavity

TL;DR

This study investigates how activity-induced topological constraints in confined active polymer rings lead to coherent motion and microphase separation, providing insights into chromatin organization at small scales.

Contribution

It introduces a model of active topological glass with activity-enhanced entanglements, revealing their role in coherent motion and microphase separation within confined polymers.

Findings

Active constraints generate coherent motion in the system.

Microphase separation occurs between active and passive segments.

Tank-treading enhances phase separation when relaxation is suppressed.

Abstract

Motivated by chromosomes enclosed in nucleus and the recently discovered active topological glass, we study a spherically confined melt of long nonconcatenated active polymer rings. Without activity, the rings exhibit the same average large-scale conformational properties as chromatin fiber. Upon activating consecutive monomer segments on the rings, the system arrives at a glassy steady state due to activity-enhanced topological constraints. The latter generate coherent motions of the system, however the resulting large-scale structures are inconsistent with the fractal globule model. We observe microphase separation between active and passive segments without systematic trends in the positioning of active domains within the confining sphere. We find that tank-treading of active segments along the ring contour enhances active-passive phase separation in the state of active topological glass when both diffusional and conformational relaxation of the rings are significantly suppressed. Finally, although the present model of partly-active rings is not compatible with the large-scale chromatin organization, our results suggest that the activity-enhanced entanglements that result in facilitated intra- and inter-chromosomal contacts might be relevant for chromatin structure at smaller scales.