Formation of silk fibroin nanoparticles in water-miscible organic solvent and their characterization |
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Authors: | Yu-Qing Zhang Wei-De Shen Ru-Li Xiang Lan-Jian Zhuge Wei-Jian Gao Wen-Bao Wang |
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Institution: | (1) Silk Biotechnol. Lab., School of Life Science, Soochow University, 702-303 Room, No. 1 Hengyi Road, Dushuhu Higher Education Town, Suzhou, 215123, P.R. China;(2) Analytical Center, Soochow University, 304-4115 Room, No.1 Hengyi Road, Dushuhu Higher Education Town, Suzhou, 215123, P.R. China |
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Abstract: | When Silk fibre derived from Bombyx mori, a native biopolymer, was dissolved in highly concentrated neutral salts such as CaCl2, the regenerated liquid silk, a gradually degraded peptide mixture of silk fibroin, could be obtained. The silk fibroin nanoparticles
were prepared rapidly from the liquid silk by using water-miscible protonic and polar aprotonic organic solvents. The nanoparticles
are insoluble but well dispersed and stable in aqueous solution and are globular particles with a range of 35–125 nm in diameter
by means of TEM, SEM, AFM and laser sizer. Over one half of the ɛ-amino groups exist around the protein nanoparticles by using
a trinitrobenzenesulfonic acid (TNBS) method. Raman spectra shows the tyrosine residues on the surface of the globules are
more exposed than those on native silk fibers. The crystalline polymorph and conformation transition of the silk nanoparticles
from random-coil and α-helix form (Silk I) into anti-parallel β-sheet form (Silk II) are investigated in detail by using infrared,
fluorescence and Raman spectroscopy, DSC, 13C CP-MAS NMR and electron diffraction. X-ray diffraction of the silk nanoparticles shows that the nanoparticles crystallinity
is about four fifths of the native fiber. Our results indicate that the degraded peptide chains of the regenerated silk is
gathered homogeneously or heterogeneously to form a looser globular structure in aqueous solution. When introduced into excessive
organic solvent, the looser globules of the liquid silk are rapidly dispersed and simultaneously dehydrated internally and
externally, resulting in the further chain–chain contact, arrangement of those hydrophobic domains inside the globules and
final formation of crystalline silk nanoparticles with β-sheet configuration. The morphology and size of the nanoparticles
are relative to the kinds, properties and even molecular structures of organic solvents, and more significantly to the looser
globular substructure of the degraded silk fibroin in aqueous solution. It is possible that the silk protein nanoparticles
are potentially useful in biomaterials such as cosmetics, anti-UV skincare products, industrial materials and surface improving
materials, especially in enzyme/drug delivery system as vehicle. |
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Keywords: | silk fibroin nanoparticles organic solvents biomaterials drug delivery colloids |
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