Fibres

Fibrous proteins (keratin, elastin, collagen, fibroin ...) make up to one third of the proteins of mammals and birds. They are structural proteins with a protective and/or mechanical function. Silk appears to be the ‘simplest’ model because it mainly consists of two small amino acids residues (alanine and glycine). Some silks have comparable or superior mechanical properties compared to those of synthetic fibres and could be used in technical applications (e.g. biomedical) if the variability of their properties can be controlled. This work focuses on the structure of silks from: Bombyx mori (domestic silkworm) degummed or not, Nephila madagascariensis (wild spider, no sericin coating), GM Bombyx mori (including a gene of Nephila) a recombinant spider silk 4RepCT (Escherichia Coli). Silk is analyzed by Raman spectroscopy (and FTIR), uni-axial tensile testing, and also by the coupling of these methods. The analysis of the low wavenumbers region in Raman spectroscopy allowed the characterization of ordered regions of 2-3 microns separated by about 60 microns. This is the first evidence of the heterogeneous structure of silk. Coupling with the uni-axial tensile test shows that these ordered regions are stressed under macroscopic deformation, suggesting silk organization according to Prevorsek’s model, i.e. that the same macromolecular chain belongs to both amorphous and ordered regions. The statistical study of the mechanical properties of silkworm and spider silks shows great dispersion, but a good stability over time (decades). Genetic modification does not improve the fibres mechanical properties but a slight decrease in their variability. Various strategies have been investigated to control the variability: bacterial production, solubilization of silk and films regeneration. The role of water in silk biosynthesis, as well as the effect of various parameters (filtration, pH, drying ...) during the preparation of the films were studied. It was confirmed that the presence of protein aggregates promotes the organization in film and two types of films were prepared. The most amorphous ones have the most interesting mechanical properties, though only a few percent of those from the starting fibres. The fabrication of regenerated silk matrix composites reinforced by silk fibres increases the strength and strain to failure. These initial results are encouraging for the development of silk fibres/regenerated silk matrix composite materials.