Structure/property relationships in alpha-keratin materials

Alpha-keratinous materials are biological composites, which exhibit a complex morphological fine structure. The various levels of this composite structure and the related structural models are discussed. Namely, in the context of the mechanical as well as thermal analysis the structure is suitably simplified as a two-phase, filament/matrix composite, with a 25-30% fraction of α-helical proteins in filamentous, intermediate filaments (IF). As a consequence of the multi-level complexity of their structure, the materials show a wide variety of structure/property relationships, of which a selected group is considered, which can be investigated by thermal methods and, namely, by Differential Scanning Calorimetry (DSC). The following primary topics will be covered: ► Viscoelastic, reversible transitions in keratins • β- and α- (glass) transition and their dependence on water content ► The irreversible denaturation transition in α-keratins • its dependence on water content; • kinetical aspects of the α → random → β-transition ► Multimodality of the denaturation transition, which relates to material inhomogeneities on the cell level.