Randomized trial examines molecular transitions in hair fibres during strain, highlighting humidity's role.
Hair is primarily composed of proteins notably keratin and keratin associated proteins (KAPs), forming a complex composite material with important structural functions in nature. Its mechanical behaviour is intricate and includes conformational changes, notably the transition of keratin from α-helix to β-sheet structures. However, the precise conditions under which this transition occurs during stress-strain experiments and the influence of humidity on this process remain unresolved. In this study we use two structurally sensitive methods, Raman spectroscopy and wide-angle X-ray scattering (WAXS), to study the changes in situ as a function of strain under controlled conditions of humidity. The results are analysed by two-dimensional correlation methods, two-dimensional correlation spectroscopy (2D-COS) and perturbation correlation moving window two-dimensional correlation spectroscopy (PCMW2D), which clearly relate molecular changes to the strain. The results show for the first time for both methods, that two main α-helix to β-sheet transitions are generally observed, and that these shifts in position with changing humidity. Also, these transitions go via a disordered state. It is concluded that water modifies the matrix of the hair, which then determines at what strain the intermediate filaments unfold. These results are discussed in terms of the present proposed models of hair mechanical behaviour.
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Pudney et al. (2026) studied this question.