The Thermodynamics of Trichocyte Keratins

Abstract

This chapter is an attempt at an excursion into the world of keratins with the help of thermodynamics.After briefly introducing some of the thermodynamic concepts involved in deciphering the behaviour of keratins, we will use them to look into the process of aggregation of keratin molecules into intermediate filaments, and keratin fibres, and then for analysing how keratin materials react to mechanical, thermal and moisture stresses, respectively.In most of the cases entropy appears to be the major driving force of the response occurring in keratins under environmental assault. This fact points to the important role played for keratins by temperature, which, aside from influencing the kinetics of the processes (accelerating or decelerating the rates of the rates), helps increase or decrease the entropic contribution to the Gibbs free energy and, thus, allows thermodynamically the occurrence of the observed behaviour of keratins.

Learning from hair moisture sorption and hysteresis

“…The two transitions are also visible in the mechanical analysis of the fibres under various relative humidities, suggesting that they relate to certain changes in the inner structure of the hair. The first transition, occurring at around 30 %RH (about 7% water content of the fibre) has been considered in this work as being due to the opening of inner structure of the fibre for making room to accommodate more water molecules, while the second transition, occurring between 60and 70 %RH, (about 12% water content) has been assigned, in line with the literature, to the glass transition of amorphous regions of the fibre [23, 24]. Analysis with Harkins–Jura formalism [26] supports the hypothesis that the first transition, occurring at 30–35 %RH (around 7.5% water content of the fibre), reflects the opening of the inner structure.…”

“…The data of Figure 8, acquired by different mechanic measurements (stress–strain and bending respectively) on different keratin fibres (wool and human hair) support this hypothesis well. The transition between 60 and 70 %RH (12% moisture content), noticed by various authors in the literature, is considered to be the glass transition, after which the keratin chains in the matrix relax [23, 24]. The chains can then move with larger amplitudes, creating more free volume into which more water molecules can jump, explaining the upswing of the curve after 60 %RH in Figure 7.…”

Eco-Friendly Processing of Wool and Sustainable Valorization of This Natural Bioresource

“…Interpreting these results, the α-helical structure was proposed to give an account of the secondary structure of the keratin fiber [48]. The organization of the α-helices in keratin intermediate filaments, KIF, which form the macrofibrils, the ordered (crystalline) part of the wool fiber, is driven entropically and follows a lateral and end-to-end association (polymerization) rule, as illustrated in Scheme 1 [49].…”

Processing hair follicles for transmission electron microscopy

“…87,88 Even before keratinization, polymerisation of keratins from dimers to unit-length filaments (the monomer of a KIF) is thought to release water molecules. 89 Because water and its flow is important to hair growth, dehydration-induced morphological degradation 90 is of particular concern for follicles.…”

“…Along the axis of hair growth, there are natural changes in local density within the shaft and surrounding sheaths associated with keratinization via oxidation and cross‐linking of the keratin and cornification resulting in turgor loss 87,88 . Even before keratinization, polymerisation of keratins from dimers to unit‐length filaments (the monomer of a KIF) is thought to release water molecules 89 . Because water and its flow is important to hair growth, dehydration‐induced morphological degradation 90 is of particular concern for follicles.…”