# Thermal Fracture Kinetics of Heterogeneous Semiflexible Polymers

## TL;DR

This paper models how thermal fluctuations cause fracture in heterogeneous semiflexible polymers, revealing that mechanical heterogeneity increases fragmentation rates, especially when chain end movement is constrained, with implications for cytoskeletal filament disassembly.

## Contribution

It introduces a continuum wormlike chain model that accounts for heterogeneity and predicts enhanced thermal fragmentation in semiflexible polymers, particularly in biological contexts.

## Key findings

- Heterogeneity in filament stiffness increases fracture rate.
- Constraints on chain end movement amplify thermal fragmentation.
- Model explains actin filament severing at softening boundaries.

## Abstract

The fracture and severing of polymer chains plays a critical role in the failure of fibrous materials and the regulated turnover of intracellular filaments. Using continuum wormlike chain models, we investigate the fracture of semiflexible polymers via thermal bending fluctuations, focusing on the role of filament flexibility and dynamics. Our results highlight a previously unappreciated consequence of mechanical heterogeneity in the filament, which enhances the rate of thermal fragmentation particularly in cases where constraints hinder the movement of the chain ends. Although generally applicable to semiflexible chains with regions of different bending stiffness, the model is motivated by a specific biophysical system: the enhanced severing of actin filaments at the boundary between stiff bare regions and mechanically softened regions that are coated with cofilin regulatory proteins. The results presented here point to a potential mechanism for disassembly of filament networks in general and cytoskeletal actin networks in particular by the introduction of locally softened chain regions, as occurs with cofilin binding.