A Comparative Study of Solutions of Silk Fibroin in 1-Butyl-3-methylimidazolium Chloride and Acetate (original) (raw)

Swelling and dissolution of silk fibroin (Bombyx mori) in N-methyl morpholine N-oxide

International Journal of Biological Macromolecules, 1999

Bombyx mori silk fibers were dissolved in N-methyl morpholine N-oxide (MMNO), an organic cyclic amine oxide used for the solvent spinning of regenerated cellulosic fibers. The commercial MMNO monohydrate used in this study as a solvent for silk is a hygroscopic compound crystalline at room temperature, which becomes an active solvent after melting at 76°C. The degree of hydration of MMNO was checked by DSC measurements. The solvation power of MMNO towards silk fibroin drastically decreased at a water content ]20-21% w/w. Dissolution of silk required both thermal and mechanical energy. The optimum temperature was 100°C. At lower temperatures dissolution proceeded very slowly. At higher temperatures, rapid depolymerization of silk fibroin occurred. The value of the Flory-Huggins interaction parameter for the MMNO -H 2 O -silk fibroin system was − 8.5, suggesting that dissolution is a thermodynamically favored process. The extent of degradation of silk fibroin was assessed by measuring the intrinsic viscosity and determining the amino acid composition of silk after regeneration with an aqueous methanol solution, which was effective in removing the solvent and coagulating silk. Regenerated silk fibroin membranes were characterized by infrared spectroscopy, differential scanning calorimetry and scanning electron microscopy. The prevailing molecular conformation of silk fibroin chains was the b-sheet structure, as shown by the intense amide I-III bands at 1704, 1627, 1515, 1260, and 1230 cm − 1 . The value of the I 1260 /I 1230 intensity ratio (crystallinity index) was 0.68, comparable to that of the fibers. The DSC thermogram was characteristic of a silk fibroin material with unoriented b-sheet crystalline structure, with an intense decomposition endotherm at 294°C. The SEM examination of fractured surfaces showed the presence of a dense microstructure with a very fine texture formed by densely packed roundish particles of about 100 -200 nm diameter.

Interfacial Rheology of Natural Silk Fibroin at Air/Water and Oil/Water Interfaces

Langmuir, 2011

Silk produced by the domesticated silkworm, Bombyx mori, has attracted recent attention because of its excellent mechanical properties, outstanding biocompatibility, low biodegradability, and minimal inflammatory reaction. These properties have led to the exploration of its use in biotechnological and biomedical applications, such as controlled drug release and tissue engineering scaffolds. 1,2 Silk, as it is emitted from the glands of the silkworm, consists of a fibroin core (75 wt %) surrounded by gelatin-like sericin proteins (25 wt %), with the former constituent being a fibrous, structural protein with high crystallinity. As a result, fibers formed from this material display highly oriented crystalline alignment along the fiber axis. 3À5 The sericin protein, with a large fraction of water-soluble serine and other hydrophilic amino acids, serves as a binder and aids silk fiber spinning by the animal. The sericin can be easily removed from cocoons to eliminate its adverse effects in medical applications. The core protein of silk, silk fibroin (SF), is composed of highly repetitive amino acid sequences with alternating hydrophobic and hydrophilic blocks along the molecular chains and can be regarded as nature's counterpart of a synthetic, multiblock polyelectrolyte. This multiblock structure allows the protein to self-assemble into micelles and form gels in concentrated solution. 6,7 The relatively hydrophobic silk fibroin molecules consist of heavy and light chains of approximately 360 and 25 kDa in M w , respectively, connected by disulfide linkages. 8 The polypeptide chain is a known polymorph and can achieve at least three secondary conformations, two of which are stable and one of which is metastable. The two most commonly known conformations are called silk I and silk II, which exist as dimorphs of the fibroin from Bombyx mori. Silk I is a structure residing in 51 solution in the glands of the silk worm before the spinning 52 process. 9,10 Silk II gives rise to the crystalline structure of fibroin 53 in native silk fiber, with antiparallel β sheets crystallized in 54 hydrophobic regions and more or less random conformations 55 existing in hydrophilic regions. 11 It is the unique coexistence of 56 both crystallized hydrophobic pleated β sheets and amorphous 57 hydrophilic regions in the fibroin structure that gives silk extra-58 ordinary mechanical properties with both high tensile strength 59 and exceptional toughness. Silk III, reported by Valluzzi and 60 Gido, 12À14 is a crystalline structure formed at the interface of air 61 and water. The formation of different secondary structures in 62 fibroin depends on the charge density, pH, and salinity of its 63 aqueous solvent and its processing conditions. 64 Silk fibroin possesses regions of different hydrophobicity 65 when it folds into the appropriate secondary or higher-order 66 structures. The coexistence of distinct hydrophobic and hydro-67 philic regions endows the silk fibroin molecules with amphiphilic 68 character and surface activity, allowing silk fibroin to reside at 69 fluid interfaces and form stable viscoelastic films at the surface of 70 an aqueous medium and either air or oil. If this occurs, then the 71 silk fibroin can be used as an emulsifier to form stable emulsions 72 by creating viscoelastic shells on the surfaces of dispersed drops. 73 Similarly, this mechanism can be used to stabilize foams effec-74 tively. These shells resist droplet or bubble deformation and 75 prevent droplet and bubble coalescence and macroscopic phase 76 separation. The purpose of this article is to report on the ability of

Investigation of Rheological Properties and Conformation of Silk Fibroin in the Solution of AmimCl

Biomacromolecules, 2012

The conformation and eventual morphology of silk fibroin (SF) chains are crucial for the mechanical properties of SF materials, and are strongly related to the solvation step as a key stage in their processing conditions. In this work, a novel SF/AmimCl (1-allyl-3-methylimidazolium chloride) solution with unique properties is reported and compared with conventional regenerated SF aqueous solutions, based on an investigation of its rheological properties. The steady shearing behavior suggested that AmimCl is a good solvent for SF molecules, and shear thinning of semidiluted SF/AmimCl solution at high shear rates showed behavior similar to that in native spinning, which is due to the rearrangement and orientation of SF molecular chains. Fitting of experimental dynamic viscoelastic data to the Rouse model provided an effective method to estimate the molecular weight of SF. We believe that this work not only provides a better understanding of the relationship between properties of silk protein and aggregation states of their molecular chains, but also provides tools to fabricate high-performance SF-based materials.

Preparation and application of porous silk fibroin materials

Journal of Applied Polymer Science, 1994

This article deals with the preparation and morphological characterization of porous materials obtained by freezing and lyophilizing silk fibroin solutions. When an aqueous silk solution is frozen at different temperatures (-18, -45, and -8O"C), the average pore size decreases with lowering of the freezing temperature. Silk fibroin aggregates obtained in these conditions exhibit a sheetlike structure. By lowering the pH from neutrality to 4.01 and 2.65, the morphology of the solid phase changes from a sheet to a fiber structure. The average pore size is smaller a t pH 4.01 than is the former value corresponding to the isoelectric point of silk fibroin. The addition of different amounts of methanol to the silk solution results in a sharp fall of the average pore size and hardens the material, as a consequence of the high packing density of the fibroin molecules. Silk fibroin aggregates prepared in these conditions exhibit a typical fibrous structure. A drug-delivery system was prepared by incorporating acetylsalicyclic acid into a porous silk fibroin carrier, and the kinetics of the drug release was studied.