Aspects of the Morphology of the Silk ofBombyx Mori

Silk-based biomaterials in biomedical textiles and fiber-based implants

Biomedical textiles and fiber-based implants (BTFIs) have been in routine clinical use to facilitate healing for nearly five decades. Amongst the variety of biomaterials used, silk-based biomaterials (SBBs) have been widely used clinically viz. sutures for centuries and are being increasingly recognized as a prospective material for biomedical textiles. The ease of processing, controllable degradability, remarkable mechanical properties and biocompatibility have prompted the use of SBBs for various BTFIs for extracorporeal implants, soft tissue repair, healthcare/hygiene products and related needs. The present Review focuses on BTFIs from the perspective of types and physical and biological properties, and this discussion is followed with an examination of the advantages and limitations of BTFIs from SBBs. The Review covers progress in surface coatings, physical and chemical modifications of SBBs for BTFIs and identifies future needs and opportunities for the further development for BTFIs using SBBs.

Review structure of silk by raman spectromicroscopy: from the spinning glands to the fibers

Raman spectroscopy has long been proved to be a useful tool to study the conformation of protein-based materials such as silk. Thanks to recent developments, linearly polarized Raman spectromicroscopy has appeared very efficient to characterize the molecular structure of native single silk fibers and spinning dopes because it can provide information relative to the protein secondary structure, molecular orientation, and amino acid composition. This review will describe recent advances in the study of the structure of silk by Raman spectromicroscopy. A particular emphasis is put on the spider dragline and silkworm cocoon threads, other fibers spun by orb-weaving spiders, the spinning dope contained in their silk glands and the effect of mechanical deformation. Taken together, the results of the literature show that Raman spectromicroscopy is particularly efficient to investigate all aspects of silk structure and production. The data provided can lead to a better understanding of the structure of the silk dope, transformations occurring during the spinning process, and structure and mechanical properties of native fibers.

Correlation of the β-sheet crystal size in silk fibers with the protein amino acid sequence

Low voltage transmission electron microscopy (LVTEM) and wide angle X-ray scattering (WAXS) are used to independently determine the size of the β-sheet crystalline regions in Bombyx mori silk fibers. The peak in the size distributions of the major and minor axes of the anisotropic crystallites measured from the LVTEM images compare well with the average sizes as determined by Scherrer analysis of the X-ray fiber diagrams. These values are then discussed in the context of the B. mori fibroin heavy chain amino acid sequence, and the underlying mechanism for the organism's control on fiber crystallite size, and therefore mechanical properties, is proposed.

pH induced changes in the rheology of silk fibroin solution from the middle division of Bombyx mori silkworm

The rheological properties of fibroin silk solutions extracted from the middle division of Bombyx mori silkworms were examined. Acidification of the solutions with acetic acid vapor gelled the material, a process which at short time scales could be reversed by exposure to ammonia vapor. The solution could also be converted to sol from the gel state by the addition of EDTA. The possible mechanisms for gel formation in fibroin solutions is discussed as are the implications for the process of spinning silk fibers.

Short and long range order of the morphology of silk from Latrodectus hesperus (Black Widow) as characterized by atomic force microscopy

The surfaces of both stretched and unstretched silk threads from the cobweb weaver, Latrodectus hesperus (Black Widow) have been examined by atomic force microscopy (AFM). AFM images of cobweb scaffolding threads show both unordered and highly ordered regions. Two types of fibers within the threads were observed: thicker (approximately 300 nm in diameter) fibers oriented parallel to the thread axis and thinner (10-100 nm) fibrils oriented across the thread axis. While regions which lacked parallel fibers or fibrils were observed on threads at all strain values, the probability of observing fibers and/or fibrils increased with strain. High-resolution AFM images show that with increasing strain, both mean fiber and fibril diameters decrease and that fibrils align themselves more closely with the thread axis. The observation of fibers and fibrils within the cobweb threads has implications for current models of the secondary and tertiary structure and organization of spider silk.