Fabrication Of Monodispersed Silk Fibroin Nanoparticles And Their Ordered Self-assembly

As a natural protein, silk fibroin is extracted from silkworm silk. For its superiormechanical properties, excellent biocompatibility and biodegradability, it has been notonly widely employed in traditional fabric and clothing area, but also has great potentialapplications in cosmetics, biomedicine, materials and other fields. In recent years,aggregate-state nanoparticles prepared by silk fibroin in nanometer scale have receivedthe extensive attention, which is mostly in biomedicines, such as enzymeimmobilization, drug and gene delivery, etc. However, there’s little publication inself-assembly fabricating the silk fibroin nanoparticles to colloidal crystal.To study the effect of molecular weight and structure of silk fibroin, severaldifferent solvent systems were used to dissolve Bombyx mori silk fibroin in this thesis.The silk fibroin nanoparticles were prepared by salting out silk fibroin solution withpotassium phosphate. The effect on properties of silk fibroin nanoparticles wasdetermined by changing the ionic strength, pH of potassium phosphate solution and theconcentration of silk fibroin solution. The colloidal crystals were fabricated byself-assembly of gravity deposition and electric-field inducement.The result has been exhibited as follows. When the degummed silk was dissolvedby LiBr-H₂O or CaCl₂-CH₃CH₂OH-H₂O under60℃for1h, the silk fibroin had highmolecular weight and wide molecular weight distribution, which was attributed to thelow decomposition degree. While it was dissolved by either the same systems under90℃for6h, relatively low molecular weight was obtained due to severely broken up ofthe polypeptides chains. Moreover, LiBr-H₂O had better dissolving capacity thanCaCl₂-CH₃CH₂OH-H₂O in the same condition. Different solvent method had little effecton the secondary structure of silk fibroin, the structure of silk fibroin was mainlyrandom coil conformation.silk fibroin nanoparticles with good morphology were prepared by silk fibroindissolved by LiBr-H₂O under90℃for6h.The nanoparticles with spherical structured and good dispersion were formed when the ionic strength and the pH were above0.6Mand6, respectively. The salting out efficiency improved with the increasing ionicstrength and pH of potassium phosphate solution. when the concentration of silk fibroinwas0.25mg/mL²0mg/mL,the average diameter of the particle was544nm³.36μm,the mono-dispersity was0.072⁰.273. The low concentration of silk fibroin wouldcause the narrow particle size distribution, aggregation and non-dispersity. Thedispersity of the particles improve with the increasing concentration of silk fibroin, butthe particle sizes increased and the particle size distribution became wider. Researchshowed that when the concentration was2mg/mL¹0mg/mL, the silk fibroinnanoparticles had regular spherical shape, smooth surface, good monodispersity withoutobvious aggregation. It is demonstrated from the FTIR results that the random coilconformation of silk fibroin was transformed to β-sheet structure by salting out. Thecolloidal crystal was firstly attempted to be fabricated by self-assembly of silk fibroinnanoparticles. However, the colloidal crystal were failed to form a large area orderedstructure. This study will need further investigations.