High synergetic transition metal phosphides@ nitrogen doped porous carbon nanosheets hybrids derived from silk fibroin and phytic acid self-assembly for ultra-high performance lithium storage
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Continuous Wet Spinning of Regenerated Silk Fibers from Spinning Dopes Containing 4% Fibroin Protein
The wet spinning of fibers from regenerated silk fibroin has long been a research goal. Due to the degradation of the molecular structure of the fibroin protein during the preparation of the regenerated silk fibroin solution, fibroin concentrations with at least 10% protein content are required to achieve sufficient viscosity for wet spinning. In this study, a spinning dope formulation of regenerated silk fibroin is presented that shows a rheological behavior similar to that of native silk fibroin isolated from the glands of B. mori silkworm larvae. In addition, we present a wet-spinning process that enables, for the first time, the continuous wet spinning of regenerated silk fibroin with only 4% fibroin protein content into an endless fiber. Furthermore, the tensile strength of these wet-spun regenerated silk fibroin fibers per percentage of fibroin is higher than that of all continuous spinning approaches applied to regenerated and native silk fibroin published so far.
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Regenerated silk fibroin materials show properties dependent on the methods used to process them. The molecular structures of B. mori silk fibroin both in solution and in solid states were studied and compared using X-ray diffraction, FTIR, and (13)C NMR spectroscopy. Some portion of fibroin protein molecules dissolved in formic acid already have a beta-sheet structure, whereas those dissolved in TFA have some helical conformation. Moreover, fibroin molecules were spontaneously assembled into an ordered structure as the acidic solvents were removed from the fibroin-acidic solvent systems. This may be responsible for the improved physical properties of regenerated fibroin materials from acidic solvents. Regenerated fibroin materials have shown poor mechanical properties and brittleness compared to their original form. These problems were technically solved by improving the fiber forming process according to a method reported here. The regenerated fibroin fibers showed much better mechanical properties compared to the native silk fiber and their physical and chemical properties were characterized by X-ray diffraction, solid state (13)C NMR spectroscopy, SinTech tensile testing, and SEM.
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Various methods have been studied to make a regenerated silk fibroin solution. However, most of them take too much time and effort to liquefy. Here, we report that a regenerated silk fibroin solution could be prepared within seconds through acid proteolysis for the first time. The solubilized fibroin could be applied to advanced tissue engineering. Our method shortened the production time to one day (more than 10 times) compared to the general fibroin solution preparation method. It was confirmed that the initial protein affinity nearly doubled from 0.028 to 0.076 μg·mm-2 in FF(ac) compared to FF(aq). A fibroin nanofiber layer having a volumetric hierarchical structure was prepared by electrospinning an acid-proteolyzed fibroin solution, followed by gas foaming. In vitro results of cell adhesion and proliferation capacity of the gas-foamed scaffold were not significantly different compared to the two-dimensional (2D) fibroin nanofiber membrane, overcoming the limitations of volumetric nanofiber scaffolds. We are confident that our research will greatly contribute to the development of regenerative engineering using other proteins.
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Medical sheets are useful in surgically repair vascular disease. To avoid long-term side effects, they are to be replaced with regenerated tissue after implantation. Silk fibroin is a fibrous protein secreted by silkworm. The advantage of silk fibroin is its biocompatibility and has been used as regenerative artificial materials. The problem of its biodegradability is that the effect is time consuming. In this study, SVVYGLR peptide was used to expect promoting cell migration and accelerating the biodegradation of silk fibroin. Silk fibroin and polyurethane-based medical sheets with or without SVVYGLR peptide were implanted in rat abdominal aorta (silk fibroin/polyurethane/SVVYGLR peptide versus silk fibroin/polyurethane). The result of histological evaluation indicated that the new cell layer created under both sheets was composed of endothelial cells, smooth muscle, and fibroin in both sheets and similar to a native vessel. Both sheets did not show any excessive inflammation or calcification, and moderate biodegradability was observed. The decrease of silk fibroin indicated the biodegradability of all sheets. Silk fibroin/polyurethane/SVVYGLR peptide had many small vessels in the regenerated tissue than silk fibroin/polyurethane. This appearance indicated that SVVYGLR peptide promoted the angiogenesis in the regenerative tissue. This study suggested that SVVYGLR peptide could give the angiogenic-promoting activity to silk fibroin-based vascular repairing sheet.
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A novel prosthesis using silk fibroin with blending heparin and sulfonated silk fibroin was studied. Anticoagulation activities of heparin/silk fibroin and sulfonated silk fibroin/silk fibroin vascular and mechanical property results showed that heparin/silk fibroin and sulfonated silk fibroin/silk fibroin vascular could meet the requirement of small caliber grafts. This study indicated that silk fibroin could be used for developing tissue engineering biological vascular grafts that could use for human coronary or low extremity artery bypasses.
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Films from silk fibroin protein are one of the most promising biomaterials because of their exquisite balance between mechanical properties and biocompatibility. Numerous schemes have been proposed for processing fibroin film, utilizing liquid silk fibroin (LSF) or regenerated silk fibroin (RSF). The films cast from LSF or RSF in the solution state are water-soluble, and therefore require postproduction treatment inducing β-sheet formation, to render them insoluble in water. Many kinds of postproduction treatments, using alcohol–water solution, water vapor, or controlled temperature, have been developed. However, the tuning and reproducibility of such treatments are quite sensitive and frequently render the fibroin films less flexible or even brittle because of the formation of an over content of β-sheet. To overcome this, we developed a novel scheme for fibroin processing using silk-gland fibroin (SGF). The essence of this scheme is to create a softly solidified fibroin-gel state of the silk glands with an imperfect β-sheet structure, by treating them with an ethanol/water mixture. Such a fibroin gel was found to dissolve in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The SGF film cast from the HFIP solution shows a flexible and water-insoluble nature with high reproducibility. In addition to this improvement, the SGF film produced by this method contains a significantly low level of residual HFIP molecules compared to the traditional RSF films prepared from an HFIP solution. The mechanism underlying these advantageous characteristics was investigated from the structural viewpoint, by using techniques such as 13C solid-state NMR, differential scanning calorimetry, and wide-angle X-ray diffraction.
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Fibroin gene expression in the posterior silk gland of normal strain (J-131/J-131), Nd strain (Nd(2)/Nd(2)) and their hybrid (J-131/Nd(2)) silkworms was compared on the levels of fibroin and fibroin mRNA production. The syntheses of both fibroin and fibroin mRNA in the Nd(2) and the hybrid silkworms were greatly reduced when compared with those of the normal silkworm. This result indicates that the Nd(2) gene represses dominantly fibroin gene expression, presumably at the level of transcription of fibroin gene. Estimation of gene products (fibroin and fibroin mRNA) from two fibroin alleles, Fnor and SNd, of the hybrid silkworm, J-131/Nd(2), demonstrates that the expression of the fibroin allele SNd derived from Nd(2) mutant strain is more severely repressed than that of the fibroin allele Fnor derived from J-131 strain.
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Regenerated silk fibroin fibers show properties dependent on the molecular weight of fibroin. The cocoon-degumming approaches had great impact on the degradation of silk fibroin. The effect of degumming pH value to electrospining of fibroin was studied in this paper. The viscosity and molecular weight of regenerated silk fibroin were studied using rheometer and gel electrophoresis. The results showed that the weaker the alkalinity of degumming reagent, there was the milder the effect on silk fibroin molecular. The fibroin fibers can be prepared by electrospining with low concentration of regenerated silk fibroin solution.
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