Nanomechanics of single keratin fibres: A Raman study of the alpha helix -> beta sheet transition and water effect

TL;DR

This study uses micro-Raman spectroscopy to investigate nano-structural changes in keratin fibers, such as alpha helix to beta sheet transition and water effects, during mechanical strain in different humidity conditions.

Contribution

It provides a quantitative analysis of keratin conformational changes and chain dynamics during strain, integrating Raman spectroscopy with mechanical analysis for the first time.

Findings

Water facilitates chain sliding and reduces bond energy in keratin.

Raman spectral analysis reveals alpha helix to beta sheet transition during strain.

Nano-mechanical and micro-mechanical analyses are consistent with structural models.

Abstract

The use of micro-Raman spectroscopy, through chemical bond nano-scale probes, allows the changes in conformations (alpha helix -> beta sheet), chain orientation, disconnection of disulfide bonds (-20%) and the increase of intra and inter-chain distances during the strain to be distinguished. The combination of micro-Raman spectroscopy and a allows a quantitative measure of the extension of chemical bonds in the peptidic chain during loading. The nano-structural transformations of keratin during the strain of human hair in a dry environment (40-60 % relative humidity) and saturated with water have been studied. The water permits the sliding of the chains and decreases the bond energy hair. Spectral analyses and 2D correlation are two coherent and independent methods to follow change the Raman probes which are sensitive to structural . The between nano-mechanical (Raman) and micro-mechanical (strain/stress) analyses confirms the validity of the experimental results, tools and principles used, as well as the agreement with the structural model of keratin fibres described by Chapman & Hearle.