The structure of the “amorphous” matrix of keratins

•Transient electro-thermal technique measured structure in amorphous phase of hair.•Results indicate considerable ordering of material within this phase.•Phonon/spin diffusion and TEM suggest that this arises from grains within matrix.•The size and fine-scale details of the nano-grains have yet to be established.•Measurements indicate the importance of external and physiological factors. Various keratin fibers, particularly human hairs, were investigated by transmission electron microscopy, TEM, solid-state 1H NMR and Transient Electro-Thermal Technique, TET. The results converge to suggest that the matrix of keratin fiber cortex, far from being amorphous, has a well-defined nano-scale grainy structure, the size of these grains being around 2–4nm. The size of the grains appears to strongly depend on the chemical treatment of the fiber, on the temperature and on the relative humidity of the environment, as well as on the physiological factors at the level of fiber production in follicle. By suggesting an organization at the nano-scale of the protein chains in these grains, likely to be Keratin Associated Proteins, the results challenge the view of matrix as a homogeneous glassy material. Moreover, they indicate the potential of further investigating the purpose of this structure that appears to reflect not only chemical treatments of keratins but also biological processes at the level of the follicle.