D-band strain underestimates fibril strain for twisted collagen fibrils at low strains

TL;DR

This study reveals that D-band strain measurements significantly underestimate actual fibril strain in twisted collagen fibrils at low strains, highlighting limitations in current tissue-level strain assessment methods.

Contribution

The paper introduces an elastomeric collagen fibril model incorporating molecular tilt to evaluate the accuracy of D-band strain as a proxy for fibril strain.

Findings

D-band strain underestimates fibril strain in strongly twisted fibrils

Underestimation is significant at low strains

Model accounts for molecular tilt coupling

Abstract

Collagen fibrils are the main structural component of load-bearing tissues such as tendons, ligaments, skin, the cornea of the eye, and the heart. The D-band of collagen fibrils is an axial periodic density modulation that can be easily characterized by tissue-level X-ray scattering. During mechanical testing, D-band strain is often used as a proxy for fibril strain. However, this approach ignores the coupling between strain and molecular tilt. We examine the validity of this approximation using an elastomeric collagen fibril model that includes both the D-band and a molecular tilt field. In the low strain regime, we show that the D-band strain substantially underestimates fibril strain for strongly twisted collagen fibrils -- such as fibrils from skin or corneal tissue.