Folding and assembly of fibroin driven by an AC electric field: effects on film properties

Silk fibroin from Bombyx mori is a high-molecular-weight protein, largely employed in the biomaterials field. Several parameters can affect the folding and assembly of fibroin heavy and light chains. The present work has shown that anisotropic and water-stable films are produced when fibroin solution is cast under an alternating electric field (AC). The treatment can affect the mechanical, thermal and surface properties of fibroin films. These effects have been related to the alignment of molecular dipoles and the formation of oriented supramolecular assemblies. Cell response is affected by this novel processing: MRC5 fibroblasts, cultured on anisotropic fibroin films, preferentially spread parallel to the field direction 6 h after seeding. [Figure: see text].     

Physical properties and structure of silk. II. Dynamic mechanical and dielectric properties of silk fibroin

Dynamic mechanical and dielectric properties of amorphous regenerated films of silk fibroin were studied as a function of temperature. A mechanical loss tangent peak at about 175°C may be due to the segmental motion of the main chains in the amorphous silk fibroin film. The dynamic modulus of the amorphous silk fibroin increased at 185°C due to the crystallization of the silk fibroin. Dielectric loss tangent peaks were observed at about ?40°C and 175°C at 1 kHz. The former is ascribed to the local motion of the amorphous silk fibroin with absorbed water, while the latter seems to originate from the segmental motion of the main chains and the crystallization of silk fibroin.     

丝素蛋白/TiO2复合催化剂的制备及其可见光催化性能

通过溶胶-凝胶法制备了不同掺杂量的丝素蛋白/TiO2复合纳米材料,并研究了其可见光催化活性.用粒度分析、X射线衍射(XRD)、紫外-可见漫反射光谱(UV-Vis-DRS)、平带电位、Zeta-电位、元素分析等方法表征了所制备的催化剂样品.结果显示,在可见光照射下,反应2 h时,丝素蛋白/TiO2-400℃的Cr(VI)光催化还原效率达36%,甲酸降解效率达3.4%;相对纯TiO2,丝素蛋白/TiO2的可见光吸收能力均有提高,以丝素蛋白/TiO2-400℃的增幅最大;相对纯TiO2,丝素蛋白/TiO2的平带电位均有不同程度负移,这意味着光生电子有了更强的还原能力;TiO2-400℃、素蛋白/TiO2-300℃、丝素蛋白/TiO2-400℃、丝素蛋白/TiO2-500℃的Zeta-电位值分别为29、31、36、33 mV,说明丝素蛋白/TiO2-400℃在水中形成的溶胶系统分散程度最高.     

Physical properties and phase separation structure of Antheraea pernyi/Bombyx mori silk fibroin blend films

The physical structure and compatibility of solution-cast Antheraea pernyi/Bombyx mori silk fibroin blend films were stuided by differential scanning calorimetry (DSC), thermomechanical (TMA) and thermogravimetric (TGA) analysis, dynamic viscoelastic measurement, infrared spectroscopy, and x-ray diffractometry. The DSC curves of the blend films showed independent endotherms at 280 and 358°C, corresponding to the thermal decomposition of B. mori and A. pernyi silk fibroins with random coil conformation. The intensity was roughly proportionate to the amount of each component in the blend. The thermal behavior corresponding to the conformational transitions induced by heating on A. pernyi and B. mori silk fibroins overlapped in the temperature range 190–230°C. Thermal expansion and contraction properties, as well as weight retention behavior of the blend films were intermediate between the pure components, as shown by the TMA and TGA curves. The onset temperature of the storage modulus curve decreased markedly, approaching that of B. mori silk fibroin film when the amount of this component in the blend increased. The loss modulus curve of the blend films showed two peaks at ca. 190 and 210°C, the former corresponding to B. mori, and the latter to A. pernyi silk fibroin. Infrared spectra of the blends exhibited absorption bands characteristic of the pure components overlapping in the spectral region 2000–400 cm^?1. The x-ray diffraction peaks at 23 and 21.5°, attributed to the crystalline spacings of A. pernyi and B. mori fibroins, respectively, overlapped in the diffraction curves of the blends, while the peak at 11.4°, of A. pernyi, increased as the content of this fibroin in the blend increased. The degree of crystallinity, calculated from the x-ray diffraction curves, diminished as the amount of B. mori silk fibroin decreased. A low degree of compatibility exists between the two fibroins when they are cast from aqueous solution in the experimental conditions adopted in this work. © 1994 John Wiley & Sons, Inc.     

Two non-centrosymmetric cubic seleno-germanates related to CsCl-type structure: Synthesis, structure, magnetic and optical properties

Two related non-centrosymmetric, cubic, quaternary chalcogenides, containing europium have been synthesized employing the molten flux method and by the reaction of europium halides with the ternary seleno-germanate, Na₆Ge₂Se₆. The reactions of Eu, Ge and Se were accomplished in a molten Na₂Se₂ flux at 800 °C for 150 h in an evacuated fused silica ampoule and yielded Na₂EuGeSe₄ (I). Similarly, Na_0.75Eu_1.625GeSe₄ (II), could be synthesized at slightly lower temperature (750 °C) with a different starting ratio of Eu, Ge, Se and Na₂Se₂. A reaction between EuCl₃ and Na₆Ge₂Se₆ in 1:2 ratio at 650 °C for 96 h in an evacuated fused silica ampoule yielded Na₂EuGeSe₄ (I), while the reaction between EuI₂ and Na₆Ge₂Se₆ in 1:1 ratio under similar conditions yielded Na_0.75Eu_1.625GeSe₄ (II). Crystal data for these compounds are as follows: I, cubic, space group I4¯3m (no. 217), a=7.3466(3), Z=2; II, cubic, space group I4¯3d (no. 220), a=14.7065(8), Z=16. The crystal structures of I and II are closely related and can be compared to a CsCl-type and its ordered superstructure, respectively. These compounds are semiconductors with optical band gaps around 2 eV. The temperature dependence of the magnetic susceptibility indicated that both compounds are paramagnetic with μ_eff.=7.6 and 7.73 μ_B, for I and II, respectively, close to the theoretical value of 7.94 μ_B for Eu²⁺. Raman spectroscopic characterization of the compounds is also reported.     

Separation of thorium from aqueous solution using silk fibroin

In this study we investigate the basic features of thorium adsorption from aqueous systems by silk fibroin. Our previous study showed that this biopolymer has high efficiency for U(VI) adsorption. It is well-known that thorium, which is a tetravalent metal, is a more reactive element than uranium. Thorium(IV) adsorption proves to be very rapid and dependent on pH, temperature, retention time, concentration of ion, amount of fibroin, volume of solution and volume-to-mass ratio.     

Influence of an iodine treatment on the structure and physical properties of Bombyx mori silk fibroin fiber

Silk fibroin (SF) fiber from the Bombyx mori silkworm was treated with a 1.23 N iodine/potassium iodide (I₂–KI) aqueous solution, and the structure and physical properties were investigated to elucidate the effects of the iodine treatment. The SF fiber absorbed polyiodide ions such as I and I by immersion in the I₂–KI solution, and the weight gain of the SF fiber increased with the treatment time; it became saturated at about 20 wt % after 40 h. The results of the weight gain, Fourier transform infrared spectroscopy, and X‐ray diffraction measurements suggested that polyiodide ions mainly entered the amorphous region. Moreover, a new sharp reflection in the meridional direction, corresponding to a period of 7.0 Å, was observed and indicated the possibility of the formation of a mesophase structure of β‐conformation chains. Dynamic viscoelastic measurements showed that the molecular motion of the crystalline regions at about 220 °C was enhanced and shifted to lower temperature by the introduction of polyiodide ions. This indicated that the iodine component weakened the hydrogen bonding between the SF molecules forming the β‐sheet structure and caused molecular motion of the crystal to occur more easily with heating. With heating above 270 °C, the iodine component introduced intermolecular crosslinking to SF, and the melt flow of the sample was inhibited. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3418–3426, 2006     

Excited state properties of sizable molecules in solution: from structure to reactivity

We review some recent advances in quantum mechanical methods devised specifically for the study of excited electronic state of large size molecules in solution. The adopted theoretical/computational framework is rooted in the density functional theory (DFT) and its time-dependent extension (TD-DFT) for the characterization of ground and excited states, in the polarizable continuum model (PCM) for the treatment of bulk solvent effects, and in time-dependent quantum mechanical methods for chemical dynamics. Selected applications to the simulation of absorption spectra, to the interpretation of time-resolved experiments, and to the computation of dissociative electron transfer rates are presented and discussed.     

Study on porous silk fibroin materials: 3. Influence of repeated freeze–thawing on the structure and properties of porous silk fibroin materials

The influence of repeated freeze–thawing on pore structural characteristics and physical properties of porous silk fibroin materials prepared by freeze drying were studied. It showed that when quick‐frozen silk fibroin solution was repeatedly thawed and frozen before being vacuum dried, thus pore size of prepared porous silk fibroin materials increased from 67 µm to about 120 µm, and pore density decreased from 80 per square millimeter to about 28 per square millimeter; at the same time compression ratio and moisture permeability increased from 22.7% and 230 g/m² hr to about 33.7% and 308 g/m² hr, respectively, tensile strength and dissolvability in hot water decreased from 20.2 N/cm² and 42.7% to about 12.5 N/cm² and 26.1%, respectively. Both the times of repeated thawing and the thawing temperature had a certain influence on the above‐mentioned pore characteristic parameters and physical properties. Copyright © 2001 John Wiley & Sons, Ltd.     

Physical and chemical properties of tussah silk fibroin films

Physical and chemical structure, as well as thermal behavior of solution-cast regenerated films, prepared from tussah (Antheraea pernyi) silk fibroin, were compared with those of solution-cast native films, in order to ascertain whether treatment (degumming, dissolution) used for preparation affected their properties. Regenerated fibroin films exhibited a higher thermal stability than native ones, as shown by differential scanning calorimetry, thermomechanical analysis, and dynamic mechanical behavior. Glass transition temperature and other relevant thermal transitions of the regenerated silk specimen shifted to higher temperatures compared with those of native specimen. Molecular conformation and crystalline structure did not show significant differences between the two kinds of silk films. Amino acid composition and molecular weight, however, distribution changed markedly after dissolving tussah silk fibroin fiber in concentrated LiSCN in polypeptide size was the main features for the regenerated silk fibroin. © 1994 John Wiley & Sons, Inc.     

Physical properties and structure of silk. V. Thermal behavior of silk fibroin in the random-coil conformation

The thermal behavior of films of amorphous silk fibroin in the random-coil conformation has been investigated in the temperature range 25–220°C by differential scanning calorimetry (DSC), thermal expansion, dynamic mechanical measurements, x-ray diffraction, and infrared spectroscopy. As the temperature is raised, water is lost up to about 100°C. Intramolecular and intermolecular hydrogen bonds are broken between 150 and 180°C. The glass transition is observed at 173°C by DSC. The random-coil→β-form transition accompanied by reformation of hydrogen bonds takes place above 180°C. Thermally induced crystallization to the β-form crystals starts at about 190°C.     

Microrheological studies of regenerated silk fibroin solution by video microscopy

We have carried out studies on the rheological properties of regenerated silk fibroin (RSF) solution using video microscopy. The degummed silk from the Bombyx mori silkworm was used to prepare RSF solution by dissolving it in calcium nitrate tetrahydrate‐methanol solvent. Measurements were carried out by tracking the position of an embedded micron‐sized polystyrene bead within the RSF solution through video imaging. The time dependent mean squared displacement (MSD) of the bead in solution and hence the complex shear modulus of this solution was calculated from the bead's position information. We present here the results of rheological measurements of the silk polymer network in solution over a frequency range, whose upper limit is the frame capture rate of our camera at full resolution. By examining the distribution of MSD of beads at different locations within the sample volume, we demonstrate that this probe technique enables us to detect local inhomogeneities at nanometre length scales, not detectable either by a rheometer or from diffusing wave spectroscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2555–2562, 2007     

Cationic assembly of metal complex aggregates: structural diversity,solution stability,and magnetic properties

The tetradentate imino-carboxylate ligand [L](2)(-) chelates the equatorial sites of Ni(II) to give the complex [Ni(L)(MeOH)(2)] in which a Ni(II) center is bound in an octahedral coordination environment with MeOH ligands occupying the axial sites. Lanthanide (Ln) and Group II metal ions (M) template the aggregation of six [Ni(L)] fragments into the octahedral cage aggregates (M[Ni(L)](6))(x)(+) (1: M = Sr(II); x = 2,2: M = Ba(II); x = 2, 3: M = La(III); x = 3, 4: M = Ce(III); x = 3, 5: M = Pr(III); x = 3, and 6: M = Nd(III); x = 3). In the presence of Group I cations, however, aggregates composed of the alkali metal-oxide cations template various cage compounds. Thus, Na(+) forms the trigonal bipyramidal [Na(5)O](3+) core within a tricapped trigonal prismatic [Ni(L)](9) aggregate to give ((Na(5)O) subset [Ni(L)](9)(MeOH)(3))(BF(4))(2).OH.CH(3)OH, 7. Li(+) and Na(+) together form a mixed Li(+)/Na(+) core comprising distorted trigonal bipyramidal [Na(3)Li(2)O](3+) within an approximately anti-square prismatic [Ni(L)](8) cage in ((Na(3)Li(2)O) subset [Ni(L)](8)(CH(3)OH)(1.3)(BF(4))(0.7))(BF(4))(2.3).(CH(3)OH)(2.75).(C(4)H(10)O)(0.5), 8, while in the presence of Li(+), a tetrahedral [Li(4)O](2+) core within a hexanuclear open cage [Ni(L)](6) in ((Li(4)O) subset [Ni(L)](6)(CH(3)OH)(3))2ClO(4).1.85CH(3)OH, 9, is produced. In the presence of H(2)O, the Cs(+) cation induces the aggregation of the [Ni(L)(H(2)O)(2)] monomer to give the cluster Cs(2)[Ni(L)(H(2)O)(2)](6).2I.4CH(3)OH.5.25H(2)O, 10. Analysis by electronic spectroscopy and mass spectrometry indicates that in solution the trend in stability follows the order 1-6 > 7 > 8 approximately 9. Magnetic susceptibility data indicate that there is net antiferromagnetic exchange between magnetic centers within the cages.     

Silk fibroin microfibers and chitosan modified poly (glycerol sebacate) composite scaffolds for skin tissue engineering

Porous mSF/PGS and CS/PGS composite scaffolds were prepared by the combination of poly(glycerol sebacate) (PGS) with silk fibroin microfibers (mSF) and chitosan (CS) as modifiers through particulate leaching and freeze-drying techniques. Both mSF/PGS and CS/PGS scaffolds show highly interconnected and open porous structures, and the crosslink density and water absorption of PGS were obviously enhanced by the modifiers. Moreover, the silk fibroin microfiber and chitosan can slow down and control the degradation rate of PGS. The biocompatibility of these porous PGS based composite scaffolds for skin tissue engineering was evaluated by cell culture experiments, and the results indicate of the good attachment, proliferation and deep penetration of cells into these composite scaffolds.     

Surface properties of silk fibroin films and their interaction with fibroblasts

There is a growing interest in the use of silk as a biomaterial for tissue engineering. Silk threads from Bombyx mori have a fibrous core of fibroin, the protein responsible for biocompatibility and bioactivity, which is surrounded by a family of "gummy" proteins, called sericins, which are almost completely removed during silk degumming. Three different methanol treatments on regenerated fibroin films were used to convert viscous solutions of Silk I to an insoluble crystalline form (Silk II), in an attempt to devise new processing protocols for the creation of a cell guiding fibroin surface. Human fibroblasts (MRC5 line) were used as probes of the cell-biomaterial interaction in the early stages of the process (1 h, 3 h, 6 h and 4 d after seeding). The effect of each treatment on cell adhesion, spreading and distribution was monitored by scanning electron microscopy (SEM) and was correlated to superficial properties (like roughness and crystallinity) and fibroin conformation by means of atomic force microscopy (AFM), used in both topographical and acoustic mode, and attenuated total internal reflection infrared spectroscopy (FTIR-ATR). It was found that traditional methanol treatments where fibroin films were soaked in methanol solution produced roughness patterns that affected only the very early stages of fibroblast adhesion (until 3 h from seeding), while the new treatment proposed could really dialogue with the cells. Its non-homogeneous surface can explain the existence of cells spreading in specific directions and the presence of cell repellent areas even 4 d after seeding.     

Structural characterization and mechanical properties of electrospun silk fibroin nanofiber mats

The regenerated silk fibroin dissolved in formic acid was electrospun into nanofiber mats. Structural characteristics of the spun as received and methanol and ethanol treated fibers were examined using the Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. Mechanical properties and air permeability of the electrospun mats were also studied. IR spectroscopy and X-ray diffractometry showed random coil conformation and amorphous structure for as-spun fibers while typical FTIR spectra and X-ray diffractograms of β-sheet crystalline structure were recorded for the methanol and ethanol treated fibers. The mechanical properties of the mats were found to be dependent on fiber diameter. The mats containing fibers with smaller diameter had higher tensile strength but lower breaking strain. Methanol and ethanol treatment enhanced tensile strengths of the mats at the expenses of their breaking strain. Air permeability and pore size of the mats are strongly associated with diameter of the electrospun fibers.     

Synthesis, structure and solution properties of the novel polyampholytes based on cellulose

A novel cellulose-based polyampholyte derivative, carboxylethyl quaternized cellulose (CEQC), was homogeneously synthesized by introducing positively charged quaternary ammonium groups and negatively charged carboxyl groups to the backbone of cellulose. The structure and dilute solution properties of CEQCs were characterized with elemental analysis, FTIR, NMR, viscometer, light scattering and zeta-potential measurement. The nitrogen content and total degree of substituent of acylamino and carboxyl groups increased with an increase of the molar ratio of acrylamide to the anhydroglucose unit of quaternized cellulose (QC). The salt-resistance of CEQC was improved remarkably by introducing opposite charged carboxyl to the QC chains. The intrinsic viscosity of the prepared polyampholytes was found to be very sensitive to the pH of the solutions. CEQC-1, the sample with relative low content of carboxyl groups, behaved as a classical cationic polyelectrolyte. However, CEQC-2 and CEQC-3, the samples with higher content of carboxyl groups, displayed typical polyampholyte behavior, and the isoelectric points (IEP) were determined to be 5.0 and 3.8 respectively. This work provided a facile method for the synthesis of novel cellulose-based polyampholytes with different IEP.