Silk Fibroin Nanofibers

Fibroin is an insoluble protein present in silk created by silkworms and spiders. Its primary structure mainly consists of the recurrent amino acid sequence of glycine-serine-glycine-alanine-glycine-alanine (5). 

As stated above, silk fibroin is a natural polymer and has thus established a good reputation for bone tissue engineering applications due to its many unique properties, including exceptional 

Electrospinning is a technique used for the production of polymer nanofiber meshes. The use of biodegradable and biocompatible pol miers to produce nanofibers that closely mimic the extracellular matrix of different tissues has opened a wide range of possibilities for the application of electrospinning in tissue engineering (8). Functional materials formed by the electrospinning technology are of interest for many bioactive applications. The issues of this topic have been reviewed (9). 

Electrospun silk fibroin scaffolds exhibit a large surface area, high porosity, and interconnection for cell adhesion and proliferation. They may replace collagen for many tissue engineering applications (10). 

Despite such advantages, electrospun silk fibroin scaffolds are still limited as bone tissue replacement due to their low mechanical strengths. The enhancement of the mechanical strength has been demonstrated by incorporating inorganic ceramics into pol5miers. 

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Jeong, L., Lee, K.Y., Liu, J.W., and Park, W.H. "Time-resolved structural investigation of regenerated silk fibroin nanofibers treated with solvent vapor". Int. ]. Biol. Macromol. 38(2), 140-144 (2006). 

Min BM et al (2006) Regenerated silk fibroin nanofibers water vapor-induced structural changes and their effects on the behavior of normal human cells. Macromol Biosci 6(4) 285-292... 

Min, B.M., et al., 2004. Electrospinning of silk fibroin nanofibers and its effect on the adhesion and spreading of normal human keratinocytes and fibroblasts in vitro. Biomaterials 25 (7-8), 1289-1297. 

Park WH, Jeong L, Yoo DI, Hudson S (2004) Effect of chitosan on morphology and conformation of electrospun silk fibroin nanofibers. Polymers 45 7151-7157 Patnaik PR (2006) Dispersion optimization to enhance PHB production in fed-batch cultures of Ralstonia eutropha. Bioresour Technol 97 1994-2001 Patra SN, Bhattacharyya D, Ray S, Easteal AJ (2009) Electrospun poly(lactic add) based conducting nanofibrous networks. lOP Conference Series Mater Sci Eng doi 10.1088/1757-899X/4/l/012020 Peh KSH, Sodhi NS, de Jong J, Sekercioglu CH, Yap CAM, Lim SLH (2006) Conservation value of degraded habitats for forest birds in southern Peninsular Malaysia. Divers Distrib 12 572-581... 

Figure 7.7 SEM image of silk fibroin nanofibers spun from 12% formic acid illustrating the small fiber diameters obtained. Reproduced with permission from Min et al. (2004b). Copyright 2004. Elsevier.

Figure 7.8 Fiber diameter distribution of electrospun silk fibroin nanofiber from SEM image anaiysis. A 19.5% solution of silk in formic acid was used in eiectrospinning. Fiber anaiysis was based on SEM images of the mat. Reproduced with permission from Sukigara (2003). Copyright 2003. Elsevier.

However, electrospinning of a mixture of silk fibroin and inorganic ceramics, such as hydroxyapatite, is still a challenging task. The mechanical properties of electrospun silk fibroin scaffolds can be enhanced by uniformly dispersing hydroxyapatite nanoparticles within silk fibroin nanofibers. Hydroxyapatite nanoparticles were modified by y-glycidox q3ropyltrimethoxysilane for uniform dispersion and enhanced interfacial bonding between hydroxyapatite and silk fibroin fibers. 

The mechanical moduli and dependency on the content of the hydroxyapatite nanoparticles could be analyzed using three point bending with a tipless atomic force microscopy cantilever (12). An increase of the hydroxyapatite content up to 20% increased the mechanical properties of the composite scaffolds. But a further increase above 20% disrupted the polymer chain networks within silk fibroin nanofibers and weakened the mechanical strength (10). 

Nanofibers canbe electrospun fromboth synthetic and natural polymers. Figures 7.2 and 7.3 show SEM images of electrospun polyaciylonitiile and silk fibroin nanofibers, respectively. 

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