Silk fibers degradation

On the other hand, organic silk itself is the subject of Chapter 25 by Hersh, Tucker, and Becker. A number of historical silk fibers were examined in order to understand the chemistry of the degradation process. The roles of photochemical processes as well as heat are discussed. The chemical processes of aging are complex and slow. Either historical samples must be... 

Figure 2). Silk fibers swell 192 in cross-sectional area, whereas linen swells 472 (6). Fiber swelling is limited by the interchain forces holding the polymers together in the crystalline areas only when these forces are broken in degradation processes can the fiber swell more. Water is attracted by the peptide bonds of silk and by the cellulosic hydroxyls of linen. The first monolayer of water adsorbed by each polymer molecule is directly adsorbed and thus is tightly held in association with the polymer chain. Subsequent layers of water molecules are indirectly attached and thus are loosely held in association with other water molecules. 

Effect of Fiber Degradation on the Corrosion Solution. Hydrolysis and oxidation of protein and cellulose have been described in the literature primarily with the focus on degradation in industrial processing conditions. In alkaline conditions, amino acids are released from silk in a chain unzipping mechanism in acidic conditions, the scissions are random (8,9). As the polymer deteriorates, free carboxyl and amine end groups are formed. Tyrosine oxidizes to a quinone this reaction gives aged silk its yellow coloration. Amorphous areas of the fiber are attacked first. 

The thermal degradation of silk was studied by Kurup-pillai, Hersh, and Tucker ( Historic Textile and Paper Materials, ACS Advances in Chemistry Series, No. 212, 1986) by measuring the tensile strength of silk fibers at various times of exposure to elevated temperature. The loss of tensile strength follows first-order kinetics,... 

Similarly, protein fibers such as silk are degradable to mixtures of amino acids, but a direct synthesis of silk has not yet been accomplished. Another polymer for which there is no current synthetic method is cellulose, which is composed of -1,4-linked o-glucopyranose units ... 

A model for the process of silk pseudomorph formation on bronze is proposed, including solution of copper ions, transport inside the swollen silk, reaction with available anions, and deposition of the resulting products. The maintenance of the outer physical structure of the fiber is attributed to the network of the polymer chains of silk and the maintenance of some structural integrity during degradation. The presence of green and black pseudomorphs of equal size in the same location on the halberd led to a discussion of the possibility of difierential replacement of dyed silk fibers and undyed silk fibers. 

Natural silk contains two groups of proteins, fibroin and sericin [60] produced by certain insect larvae to form cocoons. Due to their specific molecular structure, silk fibers have significant durability, biocompatibility, degradability, and strength compared to otha- biomaterials [61], Fibrous silk was shown to have more stability compared to globular proteins due to its considerable numbo of hydrogen bonds, hydrophobicity, and crystalhne structure. It is insoluble in the majority of solvents like dilute acid, alkali, and water [62],... 

There is a lot of ambiguity as to whether silk is resorbable or not US Pharmacopeia classifies silk as non-degradable material. This is because the US Pharmacopeia defines absorbable material as one that loses most of its tensile strength in vivo within 60 days post-implantation. However, the literature shows that silk undergoes proteolytic degradation over a longer period of time, which is 1-2 years. Studies have indicated that silk fibers lose most of their tensile strength within the first year in vivo and resorb completely within 2 years of implantation [30, 35]. 

Notice that silk fibroin dissolved from Bombyx mori silk fibers can be reformulated into silk fibroin films by casting solutions of silk proteins onto a substrate and allowing the evaporation of the solvent. As-cast films made from aqueous solutions of silk fibroin are mechanically weak and typically unstractured or a-heUx-rich [5, 42]. In tissue engineering studies, in order to modulate the mechanical properties and the rate/extent of degradation, the crystalline state (/3-sheet content) and morphology need to be controlled [8]. 

Polyamide fibers are most frequently used in mixtures with natural fibers. Natural fibers contain specific microflora on the surface and inside. Therefore, capron fibers mixed with cotton, wool or linen are affected by their microflora. It is found [43-45] that capron fiber degradation by microorganisms obtained from wool is characterized as deep fiber decay microorganisms extracted from natural silk cause streakiness of capron fibers microorganisms extracted from cotton cause fading and decomposition microorganisms extracted from linen cause fading, streakiness and decomposition. 

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