Morphology of regenerated silk fibroin: Effects of freezing temperature, alcohol addition, and molecular weight

Abstract

Regenerated silk fibroin (RSF) was prepared by dissolving in a CaCl 2 / ethanol/H 2 O solvent system, freezing, and lyophilization. The effect of freezing temperature, alcohol addition, and molecular weight on the morphological and conformational changes were investigated through scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, and differential scanning calorimetry analysis. However, the addition of a small amount of methanol induced the morphological change of RSF to a fine-particle aggregate, which resulted from the formation of a ␤-sheet crystalline structure. The lower the freezing temperature was, the more the formation of aggregates was favored, and the finer powder aggregates were formed. As the amount of added hydrophilic alcohol such as methanol and ethanol increased in the silk fibroin solution, a spherical powder form was changed to fine aggregates with the enhancement of thermal stability and crystallinity. On the other hand, RSFs prepared with a hydrophobic alcohol such as 1-butanol or 1-octanol showed a lump-like or sheet-like shape of morphology without any changes in conformational transition. It is concluded that the molecular weight of the silk fibroin and the type and amount of alcohol were determining factors in the morphological features of RSF, especially the size and shape of fibroin particles. A uniform ultrafine powder of RSF with a spherical form (ϳ 1 m) can be obtained when the molecular weight and the alcohol addition to the silk fibroin solution are controlled.

Effect of polyaspartic acid on hydroxyapatite deposition in silk fibroin blend films

“…In order to expand its application in biomaterials, the water-insoluble SF films were also prepared by inducing the structure transition from unstable silk I to silk II. The transition was commonly studied through treatment of aqueous ethanol solution [13,14]. At the same time, biodegradable polymers such as chitosan [15], cellulose [16] and sodium alginate [17] have been widely used in the conformation transition of SF.…”

Tetracycline-incorporated Silk Fibroin Films

“…Silk fibroin treated with moderated condition salt condition can form film in standard condition. The phase of silk fibroin solution is varied with an additive, for instance, silk fibroin solution is coagulated by addition of alcohol (Nam and Park, 2001). In this experiment, silk fibroin films were successfully fabricated from tetracycline dissolved silk fibroin solution.…”

Silk fibroin microparticles as carriers for delivery of human recombinant BMPs. Physical characterization and drug release

“…Silk fibroin has been investigated as a carrier for BMPs in several contributions by Kaplan and colleagues, in form of membranes for healing cranial defects in mice (Karageorgiou et al, 2004), electrospun nanofibers (Li et al, 2006), and scaffolds used for critical size defects in rats (Kirker-Head et al, 2007) and mice (Karageorgiou et al, 2006). Fibroin has been recently described to produce microparticles when precipitated with ethanol at specific fibroin concentrations and freeze temperature (Nam and Park, 2001;Cao et al, 2007;Zhang et al, 2007). Ethanol causes a shift in the random coil structure of fibroin to an insoluble beta-sheet configuration (Nam and Park, 2001).…”

“…Fibroin has been recently described to produce microparticles when precipitated with ethanol at specific fibroin concentrations and freeze temperature (Nam and Park, 2001;Cao et al, 2007;Zhang et al, 2007). Ethanol causes a shift in the random coil structure of fibroin to an insoluble beta-sheet configuration (Nam and Park, 2001). The addition of ethanol to the fibroin solution causes it to either precipitate to form a gel that can be used as a scaffold for tissue engineering (Nazarov et al, 2004;Tamada, 2005) or to form a gel consisting of micrometric particles (Nam and Park, 2001;Zhang et al, 2007).…”

“…Ethanol causes a shift in the random coil structure of fibroin to an insoluble beta-sheet configuration (Nam and Park, 2001). The addition of ethanol to the fibroin solution causes it to either precipitate to form a gel that can be used as a scaffold for tissue engineering (Nazarov et al, 2004;Tamada, 2005) or to form a gel consisting of micrometric particles (Nam and Park, 2001;Zhang et al, 2007). If these variables are controlled, a control of particle size is possible and could be adapted to specific clinical applications.…”