Silk biocomposites

Sericin is recovered during the various stages of producing raw silk. Sericin is oxidation-, bacterial-, and UV-resistant, and it absorbs and releases moisture rapidly. Sericin can be cross-linked, copolymerized, and blended with other macromolecular materials, especially artificial polymers. The materials modified with sericin and sericin composites are useful as degradable biomaterials, biomedical materials, polymers, functional membranes, fibers, and fabrics [26]. 

Progress made in electrospinning in the past decade has allowed for the production of fibers in nanoscale diameters from various polymers. Tissue engineering has benefited a lot from this process and quite often silk protein is used to produce nanofiber scaffolds for ceU cultures. Human bone marrow stromal cells were found to proHferate in vitro very well on mats made from poly(ethylene oxide) (PEO) and B. mori silk aqueous solution electrospun nanofibers [27]. A very interesting work by 

Kaplan et al. [28], combined bone morphogenetic proteins and HAp nanoparticles in the mixtures for electrospinning composite silk nanofibers. They have shown that this combination resulted in the highest calcium deposition in nanofibrous electrospun scaffolds for mesenchymal stem cell cultures. 

Properly engineered silk scaffolds have been successfully apphed in wound healing and in tissue engineering/regeneration of bone, cartilage, tendon, and ligament tissues as shown in Table 14.2 [24]. 

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Natural fibers are basically derived from three natural resources, which are plants, animals, and minerals. Fibers from plants can be obtained from leaf (sisal fibers), bast (nettle fibers), seed (cotton), fruit (coconut) and wood (hard and softwood). Silk, wool and feathers are examples of animal fibers. Natural fibers from plants are widely used in fabrication of biocomposites for various applications [5]. 

It was found by Cho s research group [24] that the thermal expansion of neat poly(butylene succinate) dramatically reduced by reinforcing it with chopped silk fibers, which are animal-based natural fibers, without any surface treatment or modification, indicating much improved dimensional stability of silk/PBS biocomposites, as seen in Figure 4.19. The linear coefficients of thermal expansion (GTE) were 294 x 10 for neat PBS and 10 x 10 to 52 x 10 °G for silk/PBS biocomposites, depending on the fiber content incorporated. This result implied that such a reduction of the GTE may be further performed by enhancing the fiber-matrix adhesion through optional surface modification of raw silk fibers. 

Figure 4.19 Thermal expansion behavior of PBS and silk/PBS biocomposites with various silk fiber contents as a function of temperature, measured using thermomechanical analysis (TMA). (After S.M. Lee et al. [24].)...

Lee, S.M., Han, S.O., Cho, D., Park, W.H., and Lee, S.G. (2005) Influence of chopped fiber length on the mechanical and thermal properties of silk fiber-reinforced poly(butylene succinate) biocomposites. Polym. Polym. Compos., 13, 479-488. 

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