Dissipation and recovery in collagen fibrils under cyclic loading: a molecular dynamics study

TL;DR

This study uses molecular dynamics simulations to explore how collagen fibrils dissipate energy and recover under cyclic loading, highlighting the role of cross-linking in these processes.

Contribution

It introduces a modified molecular dynamics model that incorporates cross-link reformation, enabling simulation of recovery phenomena in collagen fibrils.

Findings

Model replicates experimental hysteresis and residual strain behavior.

Cross-linking degree significantly affects mechanical response.

Simulated cycle number to steady state matches experimental data.

Abstract

The hysteretic behavior exhibited by collagen fibrils, when subjected to cyclic loading, is known to result in both dissipation as well as accumulation of residual strain. On subsequent relaxation, partial recovery has also been reported. Cross-links have been considered to play a key role in overall mechanical properties. Here, we modify an existing coarse grained molecular dynamics model for collagen fibril with initially cross-linked collagen molecules, which is known to reproduce the response to uniaxial strain, by incorporating reformation of cross-links to allow for possible recovery of the fibril. Using molecular dynamics simulations, we show that our model successfully replicates the key features observed in experimental data, including the movement of hysteresis loops, the time evolution of residual strains and energy dissipation, as well as the recovery observed during relaxation. We also show that the characteristic cycle number, describing the approach towards steady state, has a value similar to that in experiments. We also emphasize the vital role of the degree of cross-linking on the key features of the macroscopic response to cyclic loading.