Fibroin Fibers Research Articles

Structural stability of biofilms produced from silkworm cocoon fibers

Biofilms were obtained from cocoons of the silkworm, Bombyx mori, involving the removal of sericin, extraction and solubilization of fibroin fibers, dialysis of fibroin dispersions and preparation of biofilms by the casting process. Biofilm transparency was verified by UV?Vis spectroscopy and thermal stability by thermogravimetric/differential scanning calorimetry (TG/DSC). Soon after preparation, the solidification of the fibroin solution prepared from the cocoons and extracted by the Ajisawa method was monitored until the biofilm stabilized, using attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) as a function of time. The results showed that there was a change in the conformation from the silk I structure (?-helix) to silk II (?-sheet). In order to improve the characterization of the biofilms obtained by the Ajisawa method and LiBr solubilization of fibroin fibers, Raman spectroscopy was used to verify the stabilization of the different possible molecular conformations for the fibers in these materials, by comparison with the cocoon spectra and those of the solid (freeze-dried precipitated by dialysis for 72 h. By comparing the Raman spectra of the biofilms in terms of the intensities of the broadened band characteristic of amide I, it was possible to assess the conformational changes in both materials based on the possible transitions between ?-sheet conformations and flexible ?-helix and ?-turn structures. The results showed a dispersion of these conformations in the biofilms generated and in the solid freeze-dried hydrogel spectrum, and the ?-sheet conformation was found to be predominant. The TG and DSC curves showed that the materials with higher ?-sheet content exhibited higher thermal stability. Thus, the data obtained further elucidated the properties of these materials that are widely used in various processes.

Silk fibroin-decorated with tunable Au/Ag nanodendrites: A plastic near-infrared SERS substrate with periodic microstructures for ultra-sensitive monitoring of lactic acid in human sweat

The flexible and plastic near-infrared surface-enhanced Raman spectroscopy (NIR-SERS) substrate, with efficient tunable surface microstructures for probe molecular detection on irregular targets, has great potential for ultra-sensitive monitoring in real-world scenarios. Herein, we propose an interesting 785 nm laser-excited plastic SERS substrate based on the silk fibroin fibers (SFF) decorated with multiple-branched Au/Ag nanodendrites (NDs). Compared with the original smooth flexible substrate, the further constructed plastic SFF-Au/Ag NDs with concave pyramid surface microstructures provides a relatively higher NIR-SERS activity at bottom of the inward concave region. Moreover, the enhanced NIR-SERS activity is also highly related to the content of Au/Ag NDs in the hybrid flexible substrate. The maximal NIR-SERS signal intensity can be realized at the content of 0.15 wt% Au/Ag NDs in the SFF-Au/Ag NDs, which is about 8-fold enhancement compared to that obtained at the content of 0.01 wt%. Then, the molecular detection limits of crystal violet (CV) and 4-mercaptobenzoic acid (4-MBA) are calculated about 10−15 and 10−13 M, respectively, reaching the ultra-sensitive requirements of NIR-SERS trace detection. Moreover, the substrate can detect lactic acid (LA) molecules with a concentration as low as 10−9 M, and can effectively reflect slight LA fluctuation in human sweat, providing a basis for the realization of ultra-sensitive NIR-SERS health monitoring.

Activation of extracellular electron network in non-electroactive bacteria by Bombyx mori silk

Extracellular electron transfer material (EETM) has increasingly attracted attentions for the enhancing effect on multiple microbial reactions. Especially, EETM is known to be essential to activate the energy network in non-electroactive bacteria. It is motivated to find out an EETM which is natural-based, environmentally friendly, and easily produced at large-scale. In this study, Bombyx mori silk is found, for the first time, to function as an EETM by using an EETM-dependent pentachlorophenol (PCP) dechlorinating anaerobic microbial culture. Subsequently, by dividing fibroin fiber into different soluble/insoluble fractions and correlating their EET functions with their structural properties based on various spectroscopic analyses, the β-sheet configuration is suggested as an essential structure supporting the EET function of silk materials. The analyses also suggested the involvement of sulfur-containing amino acids in this function. The EET function is not degraded by boiling or acid/alkaline treatments and the material can be utilized multiple times, although it is susceptible to UV irradiation. Bombyx mori silk also enhance other microbial reactions, including Fe(III)OOH reduction, CO2 reduction to acetate, and nitrogen fixation. This discovery provides a basis for developing biotechnology for environmental remediation, global warming reduction, and biofertilizer production using Bombyx mori silk and its wastes.

Bioinspired Silk Fiber Spinning System via Automated Track-Drawing.

Regenerated silk fibroin (SF) fiber is a multifaceted protein matrix suitable for engineering a wide variety of biological materials. Numerous artificial spinning systems have been developed to mimic the molecular structure and hierarchical properties found in native silks. Here, we show a bioinspired technique that can readily form nanofibers and induce both orientation and structure formation of crystalline β-sheet assemblies seen in natural silk. In this study, electrospun postdrawn SF nanofibers were fabricated using an automated track-drawing (TD) approach for the continuous production of highly aligned protein nanofibers. This one-step postdrawing process simulates the dominant pulling force seen in natural spinning. The mechanical performance of the postdrawn SF nanofibers with a draw ratio of 2 (DR2) via TD exhibited a 115% increase in Young's modulus and an 80% increase in ultimate tensile strength, compared with the undrawn SF fibers after water treatment. It was also determined that the intermolecular β-sheet content in DR2 nanofibers increased by 75%. This contribution led to higher glass-transition and degradation temperatures. These biomimetic fibers with structural hierarchy and mechanical properties may be used to build high-performance load-bearing and directionally propagating structures relevant in biomaterial and sustainable material applications.

Controllable release of vascular endothelial growth factor (VEGF) by wheel spinning alginate/silk fibroin fibers for wound healing

The acute wound healing process requires a quick and short-stage vascular endothelial growth factor (VEGF) supply, especially, in the early-stage of injury. To date, research has rarely met the demand for controlled VEGF quick release. Herein, a novel wheel spinning technique was introduced to fabricate alginate (Alg)/silk fibroin (SF) composite fiber for loading VEGF and achieving controllable release. In turn, it was demonstrated that the parameter of wheel spinning and Alg/SF material morphological combination significantly influence VEGF release behavior and fiber degradation speed, which could be controlled by adjusting spinning solution concentration and modifying SF morphology. The loading concentration and SF structural features interacted with each other to affect the VEGF release behavior, indicating that growth factors such as VEGF could be released in a controllable fashion. It could therefore be developed as a novel approach to control the wound healing process.

Silk fibroin fibers decorated with urchin-like Au/Ag nanoalloys: a flexible hygroscopic SERS sensor for monitoring of folic acid in human sweat.

Surface-enhanced Raman scattering (SERS) spectroscopy has become a powerful and sensitive analytical tool for the detection and assessment of chemical/biological molecules in special scenarios. Herein we propose a flexible hygroscopic SERS biocompatible sensor based on the silk fibroin fibers (SFF) decorated with urchin-like Au/Ag nanoalloys (NAs). The hybrid SFF-Au/Ag NAs with a stronger absorbance capacity (500∼1100 nm) and excellent hygroscopicity provide a remarkable higher near-infrared (NIR)-SERS activity than that of bare urchin-like Au/Ag NAs. The interesting NIR-SERS sensor enables the limit of detection (LOD) of folic acid (FA) to be achieved at nanomolar (nM, 10-9 M) level, facilitating the ultrasensitive monitoring of FA in human sweat and offering reliable real-time personal health management in the near future.

Experimental determination of the frictional characteristics of fabrics made of natural silk

Natural silk fabric is directly derived from insect produced cocoons containing large volumes of fibroin protein. The fibroin fibres secreted by the two silk glands of Bombyx mori are smooth and soft and form the structural center of silk. Sericin is a coating with an amorphous structure that bonds the two strands. It is the component hardening the raw thread. The fabric as we know it with low mass per unit area. The level of friction of textile materials depends on a number of test factors - normal load, contact surface area, friction speed, as well as the nature of the textile surface and the direction of friction - warp - warp, warp – weft. In this study, four types of fabric made of 100% natural silk have been examined. They all have different characteristics for mass per unit area, weave, density and linear density of the warp and weft threads. The study makes use of appliance tribometer MXD -02, from Labthink, China to determine the values of static and dynamic friction coefficients. Friction is conducted in different directions and under different pressure. This experimental study has clearly showed that silk fabrics with higher surface mass - display friction coefficient values (at rest and in sliding) greater than 1. Friction index and friction coefficient are influenced by the test direction where friction index in warp direction of one fabric with parallel arrangement of the threads is higher compared to threads in weft direction of another fabric.

Fibroin nanofibers production by electrospinning method.

Silk fibroin, which has many characteristic properties such as low inflammation reaction, biodegradation, suppleness, good antithrombogenic details, biocompatibility and high tensile strength is a very good candidate for biomedical applications. Electrospinning procures high surface area, porous, nanofiber dimension fiber generation, which is a plain method. An experimental study was carried out to produce nanofiber structure from silk fibroin by electrospinning and the electrospinning parameters for the spinning of uniform, continuous and silk fibroin fibers were optimized. As a result, the effect of variables of concentration, distance and applied voltage on the strength, thickness, surface structure, fiber diameter of nanomaterial was investigated. Then, in vitro cell viability of the silk fibroin mat was analyzed. It was seen that the strength, mat thickness, and fiber diameter increased with solution concentration rise. It was found that the values of the fiber diameter and tensile strength decreased with increasing distance. It was determined that the effect of distance varies depending on the concentration in the mat thicknesses. The tensile strength was affected inversely proportional the applied voltage rises and distance. It was found that the fiber diameter values decreased together with increasing applied voltage. At cell viability of silk fibroin mat was occurred high cell viability after 24 h, but it was obtained low cell viability at the 48th h.

Conductive polypyrrole-encapsulated silk fibroin fibers for cardiac tissue engineering

Polypyrrole (PPy) has been utilized in smart scaffolds to improve the functionality of the engineered cardiac tissue. Compared to the commonly used aqueous coating, here, PPy was blended into silk fibroin (SF) solution to electrospin conductive PPy-encapsulated SF nanofibers. Combinations of various SF concentrations (5%, 7%, and 12%) and different PPy-to-SF ratios (15:85, 30:70, and 40:60) were compared. PPy reduced the fiber diameter (0.431 ± 0.060 μm), better-mimicking the myocardium fibrils. Conductive mats with 7% SF showed the closest mechanical properties (1.437 ± 0.044 MPa) to the native myocardium; meanwhile, a PPy-to-SF ratio of 15:85 exhibited sufficient electrical conductivity for cardiomyocytes (CMs). In vitro studies using three different types of CM demonstrated that the hybrid mats support CM contraction. Primary neonatal rat CMs on the mat with a PPy-to-SF ratio of 15:85 were elongated and orientated anisotropically with locally organized sarcomeric striations. By contrast, human-induced pluripotent stem cell derived-CMs on the mat with a PPy-to-SF ratio of 30:70 exhibited the strongest contractions. Contraction synchrony was further improved by external stimulation. Taken together, these findings indicated the great potential of the PPy-encapsulated SF electrospun mat for cardiac tissue engineering.

Structural investigations of polyurethane and silk‐polyurethane composite fiber studied by 13C solid‐state NMR spectroscopy

AbstractBombyx mori silk fibroin (SF) fibers possess excellent mechanical properties together with biocompatibility and have attracted great attention in applications including biomaterials. The SF‐polyurethane (PU) composite materials are expected to improve the mechanical properties and expand the application of SF. In this article, PU consisting of isophorone diisocyanate (IPDI) and poly (butylene adipate) is synthesized and characterized using 13C solid‐state NMR spectroscopy. Then, the regenerated SF‐PU (95: 5 wt%) fiber is prepared, which results in a 11.7% increase in tensile strength and 81% increase in elongation‐at‐break compared with those of SF fiber. The reason for the increase is due to the increase of random coil conformation in SF observed by 13C solid‐state NMR and the presence of IPDI in the PU. Thus, it can be emphasized that this PU is very effective in changing the conformation of SF fiber by increasing random coil fraction and improve the mechanical properties.

Preparation of silk fibroin and graphene composite membrane and its response driving performance test

With the development of materials, intelligent materials have the functions of sensing, controlling and driving objects, self-adaptive repair and so on, so they have been widely used. Silk fibroin fiber is a kind of natural protein, which is formed by silk degumming, insoluble in water, and can be decomposed gradually in alkaline solution without irritation and side effects, so it has a good prospect of biological application. The silk fibroin film was mixed with graphene composites, and the intelligent materials for functional response were prepared by means of the excellent optical and thermal properties of graphene. The biaxially oriented polypropylene film (BOPP) / silk fibroin bilayer composite film was prepared by the simple composite method, which showed good thermal response bending deformation properties. The graphene solution was dripped on one side of the fibroin film by a dripping method. After low-temperature drying, the final BOPP/SF/RGO/PEDOT:PSS composite film was prepared by adding a layer of poly (3meme 4-ethylenedioxythiophene / polystyrene sulfonate) (PEDOT:PSS). The flexible film driver was prepared, which can respond to multiple stimuli under light, heat and humidity.

Preparation and Biocompatibility Characterization of Silk Fibroin 3D Scaffolds

In this paper, three different mass fractions of sodium carbonate were used for degumming to obtain different degrees of damaged silk fibroin fibers, which were then treated with formic acid to shrink and bond them into 3D scaffolds. The structure and performance of silk fibroin fibers and silk fibroin 3D scaffolds were characterized by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, a differential thermal scanner, a universal materials testing machine, and laser confocal microscopy, and the degradation performance was tested by protease degradation. The results showed that an excessive mass fraction of sodium carbonate would cause partial hydrolysis of fibroin fibers, decrease the mechanical properties of fibroin fiber, increase the surface roughness of fibroin fibers, and make mouse embryonic fibroblasts easier to adhere and grow. Silk fibroin fibers were slightly dissolved, shrunk, and dispersed in formic acid. The mass fraction of sodium carbonate can adjust the enzymatic degradation rate of the silk fibroin 3D scaffolds. With the extension of the degradation time, minerals will be deposited on the surface of the scaffolds. The results show that the silk fibroin 3D scaffolds have biocompatibility, mechanical properties, and degradability, which provides a good material for a barrier biofilm in the future.

Extraction of silk fibroin and glycidyl methacrylate grafting on silk fibroin optimization of SF-g-GMA for meniscus tissue engineering

In this work, silk fibroin (SF) fibers were dissolved in calcium chloride (CaCl2) solution. Effects of CaCl2 concentration (40, 50 and 60%wt) and ratio between silk fibroin and CaCl2 (1:5, 1:10, 1:15, 1:20 and 1:25 wt/wt) on silk fibroin solubility were studied. Dialysis method was used to remove salt and purify the dissolved silk fibroin. Effect of dialysis time on the efficiency of removing salt was studied. Glycidyl methacrylate was grafted onto SF by the trans-esterification reaction. The grafting reaction was confirmed by FTIR.

Silk granular hydrogels self-reinforced with regenerated silk fibroin fibers.

Granular hydrogels with high stability, strength, and toughness are laborious to develop. Post-curing is often employed to bind microgels chemically and enhance mechanical properties. Here a unique strategy was investigated to maintain microgels together with a novel self-reinforced silk granular hydrogel composed of 10 wt% 20 kDa poly(ethylene glycol) dimethacrylate microgels and regenerated silk fibroin fibers. The principle is to use the swelling of microgels to concentrate the surrounding solution and regenerate silk fibroin in situ. Self-reinforcement is subsequently one of the added functions. We showed that silk fibroin in most compositions was homogeneously distributed and had successfully regenerated in situ around microgels, holding them together in a network-like structure. FTIR analysis revealed the presence of amorphous and crystalline silk fibroin, where 50% of the secondary structures could be assigned to strong β-sheets. Swelling ratios, i.e. 10-45 vol%, increased proportionally with the microgel content, suggesting that mainly microgels governed swelling. In contrast, the elastic modulus, i.e. 58-296 kPa, increased almost linearly with silk fibroin content. Moreover, we showed that the precursor could be injected and cast into a given shape. Viscous precursors of various compositions were also placed side by side to create mechanical gradients. Finally, it was demonstrated that silk granular hydrogel could successfully be synthesized with other microgels like gelatin methacryloyl. Silk granular hydrogels represent, therefore, a novel class of self-reinforced hydrogel structures with tunable swelling and elastic properties.

Prevention of intestinal adhesion and regeneration of abdominal wall tissue with meshes containing an electrostatically spun acellular dermal matrix (ADM)/silk fibroin (SF) fiber composite polypropylene mesh

The repair of abdominal wall defects often requires the use of polypropylene (PP) as the main material. After a PP mesh is implanted in the body, contact with the intestine can cause adhesions between the intestine and the mesh, leading to serious complications such as intestinal fistula. In this study, we used electrostatic spinning technology to coat one side of PP meshes with an electrostatically spun isolating layer of acellular dermal matrix (ADM)/silk fibroin (SF) hybrid material. These meshes were used to repair abdominal wall defects in model rats and were compared with polycaprolactone (PCL) composite polypropylene meshes and PP meshes. The results showed that the adhesion score and area of ADM/SF-PP meshes were smaller than those of PCL-PP and PP meshes. Immunohistochemical assessment revealed that the ADM/SF meshes could effectively reduce the inflammatory response at the contact surface between the meshes and abdominal organs. The tissues regenerated on the abdominal side were rich in new blood vessels. Furthermore, the ADM/SF meshes could effectively reduce the expression levels of the inflammation-related factors IL-6 and TNF-α. The expression levels of tissue regeneration-related factors, such as VEGF and PAX-7, were also higher after ADM/SF-PP mesh-mediated repair than after PCL-PP mesh and PP mesh repair. Thus, ADM/SF-PP meshes can effectively reduce the inflammatory response at the contact surface between the meshes and abdominal organs and quickly promote regeneration of abdominal surface tissue to prevent and reduce abdominal adhesion and support restoration of the abdominal wall.

Silk as templates for hydroxyapatite biomineralization: A comparative study of Bombyx mori and Antheraea pernyi silkworm silks

Silk is extensively investigated in bone tissue engineering due to its extraordinary mechanical properties and ability to regulate biomineralization. Protein templates regulate biomineralization process through chemical interaction with ions. However, the effect of structural differences in silk fibroin on biomineralization has not been studied in detail. In this study, Antheraea pernyi silk fibroin (ASF) and Bombyx mori silk fibroin (BSF) fibers were used as templates to study the effect of silk species on biomineralization. The results showed that silk fibroin could induce the formation of calcium-deficient hydroxyapatite in simulated body fluid (SBF), and the SBF treatment resulted in the formation of silk I crystals. Compared with BSF, ASF exhibited a higher ability to induce mineralization, which may depend on the differences in hydrophilic amorphous fractions between ASF and BSF. The amorphous fractions of ASF contain more acidic amino acids, which can provide more nucleation sites in the initial stage of mineralization, resulting in faster mineralization process and more mineral deposits. This study decodes the key role of silk fibroin fractions on biomineralization, and provides deeper insights for the study of silk fibroin as biomineralization template and bone repair materials.

Diclofenac Embedded in Silk Fibroin Fibers as a Drug Delivery System.

Silk fibroin is a biocompatible, non-toxic, mechanically robust protein, and it is commonly used and studied as a material for biomedical applications. Silk fibroin also gained particular interest as a drug carrier vehicle, and numerous silk formats have been investigated for this purpose. Herein, we have prepared electrospun nanofibers from pure silk fibroin and blended silk fibroin/casein, followed by the incorporation of an anti-inflammatory drug, diclofenac. Casein serves as an excipient in pharmaceutical products and has a positive effect on the gradual release of drugs. The characteristics of the investigated composites were estimated by scanning electron microscope, transmission electron microscope, thermogravimetric analysis, and a lifetime of diclofenac by electron paramagnetic resonance analysis. The cumulative release in vitro of diclofenac sodium salt, together with the antiproliferative effect of diclofenac sodium salt-loaded silk nanofibers against the growth of two cancer cell lines, are presented and discussed.

Lamellar Structure in Alanine-Glycine Copolypeptides Studied by Solid-State NMR Spectroscopy: A Model for the Crystalline Domain of Bombyx mori Silk Fibroin in Silk II Form.

Bombyx mori silk fibroin (SF) fibers with excellent mechanical properties have attracted widespread attention as new biomaterials. However, the structural details are still not conclusive. Here, we propose a lamellar structure for the crystalline domain of the SF fiber based on structural analyses of the Ala Cβ peaks in the 13C cross-polarization/magic angle spinning NMR spectra of (Ala-Gly)m (m = 9, 12, 15, and 25) and 13C selectively labeled (Ala-Gly)15 model peptides. Namely, three Ala Cβ peaks with relative intensities of 1:2:1 obtained by deconvolution were assigned to two kinds of β-sheet and a β-turn, which are interpreted as a lamellar structure formed by repetitive folding using β-turns every eighth amino acid, for which the basic structure is (Ala-Gly)4 in an antipolar arrangement. The dynamics and intermolecular arrangement were further studied using 13C solid-state spin-lattice relaxation time observations and the rotational echo double resonance experiments, respectively.

On the Secondary Structure of Silk Fibroin Nanoparticles Obtained Using Ionic Liquids: An Infrared Spectroscopy Study.

Silk fibroin from Bombyx mori caterpillar is an outstanding biocompatible polymer for the production of biomaterials. Its impressive combination of strength, flexibility, and degradability are related to the protein’s secondary structure, which may be altered during the manufacture of the biomaterial. The present study looks at the silk fibroin secondary structure during nanoparticle production using ionic liquids and high-power ultrasound using novel infrared spectroscopic approaches. The infrared spectrum of silk fibroin fibers shows that they are composed of 58% β-sheet, 9% turns, and 33% irregular and/or turn-like structures. When fibroin was dissolved in ionic liquids, its amide I band resembled that of soluble silk and no β-sheet absorption was detected. Silk fibroin nanoparticles regenerated from the ionic liquid solution exhibited an amide I band that resembled that of the silk fibers but had a reduced β-sheet content and a corresponding higher content of turns, suggesting an incomplete turn-to-sheet transition during the regeneration process. Both the analysis of the experimental infrared spectrum and spectrum calculations suggest a particular type of β-sheet structure that was involved in this deficiency, whereas the two other types of β-sheet structure found in silk fibroin fibers were readily formed.

Greener degumming production of layered sericin peptides from a silkworm cocoon and their physicochemical characteristics and bioactivities in vitro

The greener degumming method not only affects evidently the mechanical properties and uses of silk fibroin fiber, but also involves in some interesting issues including the recovery and utilization of sericin in a large number of alkaline degumming waste solutions. To this day, it remains one of the key issues deeply trouble us for the silk processing industry. Here, we systematically reported that three kinds of greener degumming methods could extract the outer-layered (OLS), inner-layered (ILS) and whole (WS) sericin peptides, respectively. Among them, the degumming method by using calcium hydroxide (CH) had an obvious advantage that the whole sericin (WS) could be fully recycled by neutralizing with sulfuric or phosphoric acid. The results show that the degumming ratios of OLS, ILS and WS were 11.4%, 16.65% and 28.61%, respectively. Three sericin peptides had evident differences from physicochemical properties and bioactivities in vitro. OLS obtained from boiling water had the highest in molecular weight (≥30 kDa), and both its antioxidation and antibacterial activities were higher than those of ILS extracted under 120 °C water for 2 h. ILS contains more β-sheet structures and its thermal decomposition temperature is approximately 14 °C higher than that of OLS. Almost the same as or higher than glycerin, the hygroscopic capacity of OLS in 160 h and the moisturizing properties of WS in 100 h reach about 32% and 50%, respectively. Furthermore, the WS had the lowest in molecular weight and stronger tyrosinase inhibitory activity and all samples had α-glucosidase inhibitory activity. Therefore, these cleaner production methods for silk degumming can result in three sericin peptides, of which OLS and ILS have potential applications and developmental value in the fields of medical biomaterials, and WS is preferable to biopharmaceuticals, cosmetics, and advanced health foods.