Regenerated Silk Fibroin Aqueous Solution Research Articles

Gelation mechanism of regenerated silk fibroin aqueous solution during storage

Gelation mechanism of regenerated silk fibroin aqueous solution during storage

A facile fabrication of silk/MoS2 hybrids for Photothermal therapy

Photothermal therapy, due to its safety and effectiveness, has attracted tremendous interest in the area of cancer treatment in recent few decades. The emerging of two-dimensional transition metal dichalcogenides has provided this promising therapy with a novel genus of nanomaterials. Herein, we present a facile one-step way to prepare a hybrid of regenerated silk fibroin (RSF) and molybdenum disulfide (MoS2) nanosheets simply by directly adding MoS2 dispersion into RSF aqueous solution to induce the self-assembly of silk protein on the surface of MoS2 flakes. The produced RSF/MoS2 hybrids demonstrate better photothermal performance and less cytotoxicity than the pristine MoS2. In the meantime, the RSF/MoS2 hybrids show a good photothermal stability. Finally and importantly, the RSF/MoS2 hybrids display a satisfying photothermal capability on ablating HeLa cells in vitro, which imply that such a protein/inorganic hybrid material holds a great promise as a photothermal agent in future cancer treatment.

Biocompatible silk fibroin scaffold prepared by reactive inkjet printing

It has recently been shown that regenerated silk fibroin (RSF) aqueous solution can be printed using an inkjet printer. In this communication, we demonstrate an alternative reactive inkjet printing method that provides control over RSF crystallinity through β-sheet concentration. A biocompatible film has successfully been produced through the alternate printing of RSF aqueous solution and methanol using reactive inkjet printing. Control over the formation of the β-sheet structure was achieved by printing different ratios of RSF to methanol and was confirmed using Fourier Transform Infra Red spectroscopy. The biocompatibility of the printed silk scaffold was demonstrated by the growth of fibroblast cells upon its surface.

Hybrid Silk Fibers Dry-Spun from Regenerated Silk Fibroin/Graphene Oxide Aqueous Solutions.

Regenerated silk fibroin (RSF)/graphene oxide (GO) hybrid silk fibers were dry-spun from a mixed dope of GO suspension and RSF aqueous solution. It was observed that the presence of GO greatly affect the viscosity of RSF solution. The RSF/GO hybrid fibers showed from FTIR result lower β-sheet content compared to that of pure RSF fibers. The result of synchrotron radiation wide-angle X-ray diffraction showed that the addition of GO confined the crystallization of silk fibroin (SF) leading to the decrease of crystallinity, smaller crystallite size, and new formation of interphase zones in the artificial silks. Synchrotron radiation small-angle X-ray scattering also proved that GO sheets in the hybrid silks and blended solutions were coated with a certain thickness of interphase zones due to the complex interaction between the two components. A low addition of GO, together with the mesophase zones formed between GO and RSF, enhanced the mechanical properties of hybrid fibers. The highest breaking stress of the hybrid fibers reached 435.5 ± 71.6 MPa, 23% improvement in comparison to that of degummed silk and 72% larger than that of pure RSF silk fiber. The hybrid RSF/GO materials with good biocompatibility and enhanced mechanical properties may have potential applications in tissue engineering, bioelectronic devices, or energy storage.

Influence factors analysis on the formation of silk I structure

Regenerated silk fibroin aqueous solution was used to study the crystalline structure of Bombyx mori silk fibroin in vitro. By controlling environmental conditions and concentration of silk fibroin solution, it provided a means for the direct preparing silk I structure and understanding the details of silk fibroin molecules interactions in formation process. In this study, silk fibroin molecules were assembled to form random coil at low concentration of solution and then, as the concentration increases, were converted to silk I at 55% relative humidity (RH). At the same time, the structure of silk fibroin forming below 45°C was mostly in silk I. A partial ternary phase diagram of temperature–humidity–concentration was constructed based on the results. The results showed silk I structure could be controlled by adjusting the external environmental conditions. The enhanced control over silk I structure, as embodied in phase diagram, could potentially be utilized to understand the molecular chain conformation of silk I in further research work.

Influence of shear on the structures and properties of regenerated silk fibroin aqueous solutions

Regenerated silk fibroin molecules in aqueous solutions gradually form rod-like liquid crystal structures after being applied sufficient shear rate and shear time.

Role of Ca2+ on structures and properties of regenerated silk fibroin aqueous solutions and fibres

It has been known that the concentration of Ca2+ gradually increased along the silk gland of silkworm and it played an important role in the spinning process of silk fibre in vivo. In this work, Raman spectrometer, synchrotron radiation wide angle X-ray diffraction facility and material testing instrument were used to investigate the effect of Ca2+ on the structures and properties of regenerated silk fibroin (RSF) in its aqueous solutions and dry spun fibres. It was found that as the concentration of Ca2+ increased in the RSF aqueous solutions and fibres, the conformational transition to β-sheet was promoted, and the resultant post-treated RSF fibre showed higher crystallinity, higher crystalline orientation as well as better mechanical properties. Therefore, it could be concluded that the addition of Ca2+ had improved the structures of RSF aqueous solutions and the resultant fibres, and it might be a feasible approach to obtaining high performance RSF fibres.

Effects of environment parameters on sol-gel transition and dry-spinnability of regenerated silk fibroin aqueous solution

Protein concentration, pH, the types and concentrations of metallic ions, and extensional flow are thought to be important environment parameters affecting the natural spinning process. In this study, we investigate the effects of the types and concentrations of metallic ions (Ca2+, Mg2+, and K+ ions), pH, and silk fibroin concentration on the sol-gel transition and the rheological behavior of a regenerated silk fibroin (RSF) aqueous solution. The results show that with an increase in the silk fibroin concentration, the weak acidic RSF aqueous solutions containing Mg2+ or Ca2+ ions undergo a phase transition to a weak gel state. Moreover, the rheological characterization of RSF aqueous solutions shows a dramatic change, and their apparent viscosities increase by almost three orders of magnitude and approach the apparent viscosity of the native dope in the silkworm gland. By using conventional pressure equipment, we investigate the dry-spinnability of weak gels. Further, we observe that the as-spun fibers exhibit a smooth surface and have inferior mechanical properties. The structure of the as-spun fibers is predominantly in a random coil or Silk I conformation.

A simple process for dry spinning of regenerated silk fibroin aqueous solution

Abstract

Fabrication of an alternative regenerated silk fibroin nanofiber and carbonated hydroxyapatite multilayered composite via layer-by-layer

A novel multilayered composite consisting of regenerated silk fibroin (RSF) nanofiber and carbonated hydroxyapatite (CHA) was fabricated with the combination of electrospinning of RSF aqueous solution and soaking in CaCl2 and Na2HPO4 solutions alternately. The chemical composition and morphologies of RSF/CHA composite were characterized by FT-IR, XRD, TGA, EDX, and SEM. The results showed that such an organic/inorganic composite had an alternate layered structure, while the CHA mineral partly penetrated into the porous RSF mats, which was similar to the structure of natural nacre. By tuning the CHA deposition procedure and RSF electrospinning condition independently, the thickness of each layer of CHA and RSF, as well as the layer numbers of composite, could be easily regulated. For example, the average thickness of CHA layers with 5 and 10 mineralization cycles were 1.63 and 3.19 μm, while 9.03 and 30.12 μm of porous RSF nanofiber layers could be formed with 7 and 24 h electrospinning process, respectively. Thus, it may provide an efficient and general approach to produce a series of inorganic/organic multilayered biomaterials for biomedical engineering.

The structure–property relationships of artificial silk fabricated by dry-spinning process

Regenerated silk fibroin (RSF) fibers were dry-spun from RSF aqueous solution and then post-treated in ethanol aqueous solution. In order to prepare artificial silk which are tougher and stronger than their natural counterpart, the structure–property relationships of the RSF fibers and natural silkworm silks were investigated by using synchrotron radiation X-ray microdiffraction technology, birefringence measurements and Raman spectroscopy. The as-spun RSF fibers with poor mechanical properties exhibited a strong diffraction peak of the [021] lattice plane and a weak diffraction peak of the [020]/[200] lattice plane. However, both the natural silk and the post-treated RSF fibers with exceptional mechanical properties showed weak diffraction peaks of the [021] lattice plane and strong diffraction peaks of the [020]/[200] lattice plane. Nevertheless, the two crystalline peaks are attributed to the silk II structure of silk fibroin. By deconvoluting the one-dimensional wide-angle X-ray microdiffraction pattern, the crystallinity and the degree of crystalline orientation were obtained. The as-spun fibers showed low crystallinity and low crystalline orientation, but the microstructure of the RSF fibers could be improved greatly and even become similar to that of degummed cocoon silk by post-treatment. When the as-spun RSF fibers were first drawn 3 to 4 times with a draw rate of 0.9 mm s−1 in ethanol aqueous solution and then immersed in the same solution for another hour, the breaking strain and breaking energy of the post-treated fibers were significantly greater than those of degummed cocoon silk.

A bio-inspired microfluidic concentrator for regenerated silk fibroin solution

In this article, microfluidic channels (500μm in width, 65–85μm in depth) in micro-chips were fabricated in poly-(dimethylsiloxane) (PDMS) on a mold of SU-8 photoresist based on photolithography process. By biomimicking the silk glands and the spinning duct of silkworms, the chips were designed and used for the concentration of regenerated silk fibroin (RSF) aqueous solution. The microfluidic devices based on regenerated cellulose membrane involve a flow of RSF aqueous solution on a donor side and a flow of polyethyleneglycol (PEG) aqueous solution on an acceptor side. The enrichment factor was characterized by varying the flow rates of the RSF solution and the PEG solution, and the concentrations of PEG and RSF solutions at inlets. The results showed that the enrichment efficiency varied as the flow factors changed. The RSF concentration of the solution was enriched up to 31.2wt% from 12wt% by using the microfluidic chip. The experiments facilitated the enrichment of RSF solution in a microfluidic channel as silkworm did. It might be further applied for the microfluidic spinning of RSF fiber.

Effect of Concentration on Structure and Properties of Concentrated Regenerated Silk Fibroin Solution

The thermal properties and rheological behavior of concentrated regenerated silk fibroin aqueous solution from 15% to 37% was investigated by differential scanning calorimetry (DSC) and rheometer. Also the conformation of solutions was characterized by Raman spectra. It was discovered that the major endothermic peak in the DSC curves shifted toward the lower temperature region with increasing the concentration. This behavior suggests increasing the concentration can accelerate conformational transition of silk fibroin from random coil and α-helix to β-sheet structure. In addition, it was found that the viscosity of solution increased with increasing concentration in favor of spinning.

Bio-inspired capillary dry spinning of regenerated silk fibroin aqueous solution

To biomimic the spinning process of silkworm or spider, a capillary spinning equipment was applied to spin regenerated silk fibroin (RSF) fibers from RSF aqueous solutions in air. This equipment exhibits a wide processing window for various RSF aqueous solutions. The effects of pH, metal ions, RSF concentration and spinning parameters on the spinnability of the spinning dope and the mechanical properties of the obtained fibers were investigated. As a result, spinning dopes with a pH from 5.2 to 6.9 have good spinnability, especially for the dope with a pH of 6.0 and a Ca 2+ concentration of 0.3 M. The RSF concentration of this dope ranges from 44% to 48%. Under optimized conditions of our dry spinning experiments (L/D, 133; take-up speed, 30 mm/s), the obtained as-spun fiber has a breaking strength of 46 MPa, which can be improved up to 359 MPa after a preliminary post-drawing in 80 vol.% ethanol aqueous solution.

Posttreatment of the dry-spun fibers obtained from regenerated silk fibroin aqueous solution in ethanol aqueous solution

Abstract

Studies on the post-treatment of the dry-spun fibers from regenerated silk fibroin solution: Post-treatment agent and method

By mimicking the spinning process of silkworm, regenerated silk fibroin (RSF) biofibers were dry-spun from RSF aqueous solutions and then post-treated. The effects of post-treatment agents on the conformation, surface morphology, orientation and mechanical properties of the fibers were studied. Compared to inorganic salt system, alcohol/water system obviously induced the fibroin conformation transition from random coil/α-helix to β-sheet. In addition, the post-drawing process induced the orientation of the β-sheet crystallites, which contributed to the improved breaking stress of the fiber. When the fiber was drawn two times in 80vol.% ethanol aqueous solution, and then immersed in the solution for 1h, the breaking stress and the elongation at break of the fiber were increased to 199MPa and 55%, respectively.

Electrospinning and rheology of regenerated Bombyx mori silk fibroin aqueous solutions: The effects of pH and concentration

In this study, we prepared regenerated silk fibroin (RSF) aqueous solution to approach the environmental condition in the gland of silkworm, Bombyx mori. Then electrospinning technique was used to prepare the silk fibers. The results showed that pH and concentration had a remarkable influence on the properties of RSF aqueous solutions. With the increase in concentration and the decrease in pH, the rheological behavior of RSF aqueous solutions exhibited a transition from Newtonion fluid to non-Newtonion fluid. At the same time, lowering the pH could induce gel formation and decrease the electrospinnable concentration of RSF aqueous solutions. With the decrease in pH and concentration, the morphology of the electrospun silk fibers changed from belt-like shape to uniform cylinder. The conformation of the electrospun silk fibers was characterized by RS, WAXD and DSC. It was found that electrospun fibers were predominantly random coil/silk I conformation.

Investigation of Structural Transition of Regenerated Silk Fibroin Aqueous Solution by Rheo-NMR Spectroscopy

In this study we applied Rheo-NMR to investigate the structural change of Bombyx mori silk fibroin in aqueous solution under shear. Monitoring the time dependence of 1H solution NMR spectra of silk fibroin subjected to constant shear strain, signal intensities of random coil decreased suddenly during shear while peaks from beta-sheet structure did not arise in the solution spectra. After these experiments, an aggregate of silk was found in the Couette flow cell and its secondary structure was determined as beta-sheet by 13C solid-state NMR. In conclusion the moderate shear applied here triggered the change in the secondary structure.

Morphology and structure of electrospun mats from regenerated silk fibroin aqueous solutions with adjusting pH

In this paper, regenerated silk fibroin (SF) aqueous solutions were adjusted to a pH of 6.9 by mimicing the condition in the posterior division of silkworm's gland and rheological behavior of solutions was investigated. The electrospinning technique was used to prepare fibers, and non-woven mats of regenerated B. mori silk fibroin were successfully obtained. The effects of electrospinning parameters on the morphology and diameter of regenerated silk fibers were investigated by orthogonal design. Statistical analysis showed that voltage, the concentration of regenerated SF solutions and the distance between tip and collection plate were the most dominant parameters to fiber morphology, diameter and diameter distribution, respectively. An optimal electrospinning condition was obtained in producing uniform cylindrical fibers with an average diameter of 1300 nm. It was as follows: the concentration 30%, voltage 40 kV, distance 20 cm. The structure of electrospun mats was characterized by Raman spectroscopy (RS), wide-angle X-ray diffraction (WAXD) and modulated differential scanning calorimetry (MDSC). It was found that electrospun mats were predominantly random coil/silk I structure, and the transition to silk II (β-sheet) rich structure should be further explored.

EFFECT OF STORAGE TIME AND CONCENTRATION ON STRUCTURE OF REGENERATED SILK FIBROIN SOLUTION

Concentrated regenerated silk fibroin (RSF) aqueous solutions with concentration close to that of the native silk fibroin (15.5%, 25.5% and 31%) were prepared. The effect of storage time and concentration on the conformational transition of the concentrated RSF aqueous solution was studied by Raman spectroscopy and circular dichroism (CD) spectroscopy. At the same time, the conformational change of RSF aqueous solution in flowing state was also investigated. It was found that the conformation of silk fibroin was changed gradually from random coil/α-helix to β-sheet structure during the storage. And the conformational transformation was accelerated with the increasing of the RSF aqueous solution concentration. When the solution was in flowing state, the conformational transformation was also accelerated.