Regenerated Silk Fibroin Fibers Research Articles

Heat-Insulated Regenerated Fibers with UV Resistance: Silk Fibroin/Al2O3 Nanoparticles.

The various wastes generated by silkworm silk textiles that are no longer in use are increasing, which is causing considerable waste and contamination. This issue has attracted widespread attention in countries that use a lot of silk. Therefore, enhancing the mechanical properties of regenerated silk fibroin (RSF) and enriching the function of silk are important directions to expand the comprehensive utilization of silk products. In this paper, the preparation of RSF/Al2O3 nanoparticles (NPs) hybrid fiber with different Al2O3 NPs contents by wet spinning and its novel performance are reported. It was found that the RSF/Al2O3 NPs hybrid fiber was a multifunctional fiber material with thermal insulation and UV resistance. Natural light tests showed that the temperature rise rate of RSF/Al2O3 NPs hybrid fibers was slower than that of RSF fibers, and the average temperature rose from 29.1 °C to about 35.4 °C in 15 min, while RSF fibers could rise to about 40.1 °C. UV absorption tests showed that the hybrid fiber was resistant to UV radiation. Furthermore, the addition of Al2O3 NPs may improve the mechanical properties of the hybrid fibers. This was because the blending of Al2O3 NPs promoted the self-assembly of β-sheets in the RSF reaction mixture in a dose-dependent manner, which was manifested as the RSF/Al2O3 NPs hybrid fibers had more β-sheets, crystallinity, and a smaller crystal size. In addition, RSF/Al2O3 NPs hybrid fibers had good biocompatibility and durability in micro-alkaline sweat environments. The above performance makes the RSF/Al2O3 NPs hybrid fibers promising candidates for application in heat-insulating and UV-resistant fabrics as well as military clothing.

Dynamic Adaptive Wrinkle‐Structured Silk Fibroin/MXene Composite Fibers for Switchable Electromagnetic Interference Shielding

AbstractFlexible and dynamic adaptive conductive composite fibers are demanded for functional fabrics and wearable devices, yet the weak interfaces often impair the critical performances for complicated application scenarios. Here, a general and scalable strategy is proposed to construct robust and reversible wrinkle structures on regenerated silk fibroin (RSF) fiber with 2D nanomaterials (i.e., MXene, graphene) by wet‐spinning technique. The dynamic conformation transition of silk fibroin and the core‐shell modulus mismatching together are responsible for the formation of wrinkled structures. Then, it effectively optimizes the interfaces between the assembled nanomaterials and fiber substrate, which significantly reinforce the fibers, complete conductive pathways, and endow exceptional robustness and durability. The MXene‐based fiber shows a high conductivity of ≈1125 S cm−1, far superior tensile strength of 214.3 ± 6.8 MPa and toughness of 15.2 ± 1.5 MJ m−3 as compared to RSF fiber. More interestingly, the transformable wrinkled structure further modulates surface behaviors and properties of the fibers, such as the switchable shielding performances from “off‐state” to “on‐state” induced by humidity. Additionally, the integration of mechanical flexibility and outstanding capacitance (≈829 F cm−3) further expects the great promise of MXene‐based fibers for self‐powered wearable electronics, and intelligent fabrics.

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.

Pulling and analyzing silk fibers from aqueous solution using a robotic device

Spiders, silkworms, and many other animals can spin silk with exceptional properties. However, artificially spun fibers often fall short of their natural counterparts partly due sub-optimal production methods. A variety of methods, such as wet-, dry-, and biomimetic spinning have been used. The methods are based on extrusion, whereas natural spinning also involves pulling. Another shortcoming is that there is a lack feedback control during extension. Here we demonstrate a robotic fiber pulling device that enables controlled pulling of silk fibers and in situ measurement of extensional forces during the pulling and tensile testing of the pulled fibers. The pulling device was used to study two types of silk—one recombinant spider silk (a structural variant of ADF3) and one regenerated silk fibroin. Also, dextran—a branched polysaccharide—was used as a reference material for the procedure due to its straightforward preparation and storage. No post-treatments were applied. The pulled regenerated silk fibroin fibers achieved high tensile strength in comparison to similar extrusion-based methods. The mechanical properties of the recombinant spider silk fibers seemed to be affected by the liquid-liquid phase separation of the silk proteins.

The Size Effect of Silver Nanoparticles on Reinforcing the Mechanical Properties of Regenerated Fibers

Regenerated silk fibroin (RSF), made from discarded silk cocoons, can be processed into regenerated silk fibers by a simple, inexpensive, and environmentally friendly wet-spinning process. However, the breaking strength and toughness of most RSF fibers are lower than those of natural silk. In this study, Ag nanoparticles (NPs) of different sizes were introduced into RSF to form RSF/AgNPs hybrid fibers by wet spinning. The effects of AgNPs of different sizes on the mechanical properties and structure of the hybrid fibers were investigated. The results demonstrated that the mechanical properties of hybrid fibers were significantly improved, especially the breaking strain, after the addition of four different sizes of AgNPs. With the reduction in AgNPs size (2-60 nm), the breaking strength and breaking strain of hybrid fibers tended to increase. The results showed that the hybrid fibers containing 2 nm AgNPs were remarkable, with excellent mechanical properties and toughness, and the breaking strain reached 138.27%, which was far greater than blank RSF fibers (15.02%) and even natural silk (about 21%). The S-FTIR and WAXD showed that, compared with the larger AgNPs, the smaller AgNPs contributed more to the formation of silk fibroin β-sheet and crystallinity, and reduced the β-crystallite size. This study is helpful to understand the relationship between the size of nanoparticles and the mechanical properties of hybrid fibers.

Axonal Guidance Using Biofunctionalized Straining Flow Spinning Regenerated Silk Fibroin Fibers as Scaffold

After an injury, the limited regenerative capacity of the central nervous system makes the reconnection and functional recovery of the affected nervous tissue almost impossible. To address this problem, biomaterials appear as a promising option for the design of scaffolds that promote and guide this regenerative process. Based on previous seminal works on the ability of regenerated silk fibroin fibers spun through the straining flow spinning (SFS) technique, this study is intended to show that the usage of functionalized SFS fibers allows an enhancement of the guidance ability of the material when compared with the control (nonfunctionalized) fibers. It is shown that the axons of the neurons not only tend to follow the path marked by the fibers, in contrast to the isotropic growth observed on conventional culture plates, but also that this guidance can be further modulated through the biofunctionalization of the material with adhesion peptides. Establishing the guidance ability of these fibers opens the possibility of their use as implants for spinal cord injuries, so that they may represent the core of a therapy that would allow the reconnection of the injured ends of the spinal cord.

Novel Dry Spinning Process of Natural Macromolecules for Sustainable Fiber Material -1- Proof of the Concept Using Silk Fibroin.

Researchers around the world are developing technologies to minimize carbon dioxide emissions or carbon neutrality in various fields. In this study, the dry spinning of regenerated silk fibroin (RSF) was achieved as a proof of concept for a process using ionic liquids as dissolution aids and plasticizers in developing natural polymeric materials. A dry spinning equipment system combining a stainless-steel syringe and a brushless motor was built to generate fiber compacts from a dope of silk fibroin obtained by degumming silkworm silk cocoons and ionic liquid 1-hexyl-3-methyl-imidazolium chloride ([HMIM][Cl]) according to a general method. The maximum stress and maximum elongation of the RSF fibers were 159.9 MPa and 31.5%, respectively. RSF fibers containing ionic liquids have a homogeneous internal structure according to morphological investigations. Elemental analysis of fiber cross sections revealed the homogeneous distribution of nonvolatile ionic liquid [HMIM][Cl] in RSF fibers. Furthermore, the removal of ionic liquids from RSF fibers through impregnation washing with organic solvents was verified to enhance industrial applications. Tensile testing showed that the fiber strength could be maintained even after removing the ionic liquid. Thermogravimetric analysis results show that the organic solvent 1,1,1,3,3,3-hexafluoro-2-propanol is chemically coordinated to silk fibroin and, as a natural polymer, can withstand heat up to 250 °C.

Recent Progress of Applying Mesoscopic Functionalization Engineering Principles to Spin Advanced Regenerated Silk Fibroin Fibers

Recent Progress of Applying Mesoscopic Functionalization Engineering Principles to Spin Advanced Regenerated Silk Fibroin Fibers

Polydopamine-Induced Multilevel Engineering of Regenerated Silk Fibroin Fiber for Photothermal Conversion.

Solid photothermal materials with favorable biocompatibility and modifiable mechanical properties demonstrate obvious superiority and growing demand. In this work, polydopamine (PDA) induced functionalization of regenerated silk fibroin (RSF) fibers has satisfactory photothermal conversion ability and flexibility. Based on multilevel engineering, RSF solution containing PDA nanoparticles is wet spun to PDA-incorporating RSF (PDA@RSF) fibers, and then the fibers are coated with PDA via oxidative self-polymerization of dopamine to form PDA@RSF-PDA (PRP) fibers. During the wet spinning process, PDA is to adjust the mechanical properties of RSF by affecting its hierarchical structure. Meanwhile, coated PDA gives the PRP fibers extensive absorption of near-infrared light and sunlight, which is further fabricated into PRP fibrous membranes. The temperature of PRP fibrous membranes can be adjusted and increases to about 50°C within 360 s under 808nm laser irradiation with a power density of 0.6Wcm-2 , and PRP fibrous membranes exhibit effective photothermal cytotoxicity both in vitro and in vivo. Under the simulated sunlight, the temperature of PRP fiber increases to more than 200°C from room temperature and the material can generate 4.5V voltage when assembled with a differential thermal battery, which means that the material also has the potential for flexible wearable electronic devices.

Reduced graphene oxide/titanium dioxide hybrid nanofiller-reinforced electrospun silk fibroin scaffolds for tissue engineering

Reduced graphene oxide/titanium dioxide (RGO@TiO2) hybrid nanoparticle was synthesized and used as a filler to study the synergistic effects on electrospun regenerated silk fibroin (RSF) mats. The incorporation of the hybrid filler increased the average diameter of RSF fibers, but decreased the content of β-sheet conformation. The breaking strength of RSF/RGO@TiO2 composite mat increased by 220%. Moreover, the composite mat supported the growth and expansion of cells and had a good antibacterial property. This study may provide a new development perspective of multifunctional nanocomposite based on RGO@TiO2 hybrid filler.

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.

Artificial ligament made from silk protein/Laponite hybrid fibers

With developments in tissue engineering, artificial ligaments are expected to be future materials for anterior cruciate ligament (ACL) reconstruction. However, poor healing of the intraosseous part after ACL reconstruction significantly hinders their applications in this field. In this study, a bioactive clay Laponite (LAP) was introduced into the regenerated silk fibroin (RSF) spinning dope to produce functional RSF/LAP hybrid fibers by wet-spinning. These RSF/LAP hybrid fibers were then woven into artificial ligament for ACL reconstruction. The structure and mechanical properties of RSF/LAP hybrid fibers were extensively studied by different means. Results confirmed the presence of LAP in RSF fibers and revealed that the addition of LAP slightly deteriorated the comprehensive mechanical properties of RSF fibers. However, they were still much tougher (with higher breaking energy) than those of degummed natural silkworm silk that was earlier used for making artificial ligament. The artificial ligament woven from RSF/LAP hybrid fibers showed better cytocompatibility and osteogenic differentiation with mouse pre-osteoblasts in vitro than those made from degummed natural silkworm silks and pure RSF fibers. Furthermore, in vivo study in a rat ACL reconstruction model demonstrated that the presence of LAP in the artificial ligament could significantly enhance the graft osseointegration process and also improve the corresponding biomechanical properties of the artificial ligament. Based upon these results, the RSF/LAP hybrid fibers, which can be mass produced by wet-spinning process, are believed to have a great potential for use as artificial ligament materials for ACL reconstruction. Statement of SignificanceIn this study, we successfully introduced Laponite (LAP), a kind of clay that has the function of osteogenic induction, into regenerated silk fibroin (RSF) fibers, which was prepared by a mature wet-spinning method developed in our lab. We believe that through artificial spinning, additional functional components can be added into RSF fibers, which one can hardly achieve with natural silks. We showed that the artificial ligament woven from RSF/LAP hybrid fibers had better cytocompatibility and osteogenic differentiation for mouse pre-osteoblasts in vitro, and significantly enhanced the graft osseointegration process and improved the corresponding biomechanical properties in a rat ACL reconstruction model in vivo, compared to those artificial ligaments made from degummed natural silkworm silks and pure RSF fibers.

Aqueous-based electrospun P(NIPAAm-co-AAc)/RSF medicated fibrous mats for dual temperature- and pH-responsive drug controlled release.

This paper presents a green method for fabricating dual temperature- and pH-responsive electrospun fibrous mats from an aqueous-based blend poly(N-isopropylacrylamide-co-acrylic acid) (P(NIPAAm-co-AAc)) and regenerated silk fibroin (RSF) by employing electrospinning technique. P(NIPAAm-co-AAc) was synthesized by free radical solution polymerization and its low critical solution temperature (LCST) was in the physiological range (38.8 °C). The P(NIPAAm-co-AAc)/RSF fibers were prepared by electrospinning technology in the presence of the crosslinking agents (EDC·HCl and NHS) with water as solvent. After in situ crosslinking and water-annealing process, the water-stable composite fibrous mats were obtained. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were used to analyze the crosslinking process. Temperature and pH dual stimuli-responsive swelling-shrinking behavior of the fibrous mats were observed when the temperature was below and above the LCST of the copolymer at different pHs. In addition, rhodamine B-loaded the fibrous mats also showed dual temperature and pH controlled release behavior, demonstrating the potential use of the fibrous mats for “smart” controlled drug delivery applications.

A Novel Facile and Green Synthesis Protocol to Prepare High Strength Regenerated Silk Fibroin/SiO2 Composite Fiber

In this work, regenerated silk fibroin (RSF) and silicon dioxide (SiO2) composite fiber was successfully extruded by wet spinning method. The effect of SiO2 addition on structure of the composite fiber at microscopic level is studied, which subsequently correlated to the mechanical performance. The best concentration ratio for composite fiber is identified by screening SiO2 concentration from 0.025 w/w% to 0.5 w/w%. The experimental results revealed that the SiO2 at a low concentration of 0.1 w/w% was well distributed. The breaking stress, breaking strain and Young’s modulus at 0.1 w/w% SiO2 addition of the RSF fibers increased considerably compared to the neat RSF fibers from 243±3 to 458±21 MPa, 51±4 % to 54±7 % and 6.34±0.55 to 11.69±1.12 GPa, respectively. To the best of our knowledge, this is the first report for RSF/SiO2 composite fiber. We believed the insight provided in this report which looks into the structural evolution should be beneficial to the future design and building of other advanced functional fibers.

Recycling of waste silk fibers towards silk fibroin fibers with different structures through wet spinning technique

This study aims at dealing with a sustainable strategy and cleaner production through recycling of waste silk fibers towards regenerated silk fibroin fibers (RSFFs) with particular and interesting morphologies such as lumen-containing RSFF. This was implemented via wet-spinning of undialyzed solution using two coagulation baths. RSFF structure controlling process was accomplished through adjusting the production parameters. RSFFs with both irregular and circular cross-sections were produced. Coagulation at 23 and 35 °C led to RSFFs with bean- or U-shaped cross-sections. Isolated pores were observed within the cross-section of RSFF coagulated at 35 °C. Further increasing the coagulation bath temperature to 55 °C resulted in lumen-containing RSFF. The RSFFs showed increased wicking properties according to the order of: circular cross-section< bean-shaped cross-section< U-shaped cross-section< lumen-containing cross-section. The messy mass composed of β-cyclodextrin-containing RSFFs showed not only biocompatibility without toxicity, but also significantly enhanced cell proliferation and directed cell growth and adhesion.

Effect of Water on the Structure and Dynamics of Regenerated [3-13C] Ser, [3-13C] , and [3-13C] Ala-Bombyx mori Silk Fibroin Studied with 13C Solid-State Nuclear Magnetic Resonance.

The effects of water on the structure and dynamics of natural and regenerated silk fibroin (SF) samples were studied using 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. We prepared different types of SF materials, sponges, and fibers with different preparation methods and compared their NMR spectra in the dry and hydrated states. Three kinds of 13C NMR techniques, r-INEPT, CP/MAS, and DD/MAS, coupled with 13C isotope labeling of Ser, Tyr, and Ala residues were used. In the hydrated sponges, several conformations, that is, Silk I* and two kinds of β-sheets, A and B, random coil, and highly mobile hydrated random coil were observed, and the fractions were determined. The fractions were remarkably different among the three sponges but with only small differences among the regenerated and native fibers. The increase in the fraction of β-sheet B might be one of the structural factors for preparing stronger regenerated SF fiber.

Microfluidic Dry-spinning and Characterization of Regenerated Silk Fibroin Fibers.

The protocol demonstrates a method for mimicking the spinning process of silkworm. In the native spinning process, the contracting spinning duct enables the silk proteins to be compact and ordered by shearing and elongation forces. Here, a biomimetic microfluidic channel was designed to mimic the specific geometry of the spinning duct of the silkworm. Regenerated silk fibroin (RSF) spinning doped with high concentration, was extruded through the microchannel to dry-spin fibers at ambient temperature and pressure. In the post-treated process, the as-spun fibers were drawn and stored in ethanol aqueous solution. Synchrotron radiation wide-angle X-ray diffraction (SR-WAXD) technology was used to investigate the microstructure of single RSF fibers, which were fixed to a sample holder with the RSF fiber axis normal to the microbeam of the X-ray. The crystallinity, crystallite size, and crystalline orientation of the fiber were calculated from the WAXD data. The diffraction arcs near the equator of the two-dimensional WAXD pattern indicate that the post-treated RSF fiber has a high orientation degree.

Microfluidic Dry-spinning and Characterization of Regenerated Silk Fibroin Fibers

Microfluidic Dry-spinning and Characterization of Regenerated Silk Fibroin Fibers

Insights into Silk Formation Process: Correlation of Mechanical Properties and Structural Evolution during Artificial Spinning of Silk Fibers.

The extraordinary comprehensive mechanical properties of animal silk (especially spider and silkworm silk) have led to extensive research on the underlying mechanisms involved. Herein, we selected various regenerated silk fibroin (RSF) fibers by choosing different postdraw conditions in a wet-spinning process developed in this laboratory to study their structure-property relationship. We use synchrotron radiation infrared and X-ray diffraction techniques to monitor the structural differences in these RSF fibers and correlate them with their mechanical properties. The results show that with the increase of post draw-down ratio, the β-sheet content, crystallinity, and molecular orientation in these RSF fibers increase while the crystalline size decreases. The relationship between structural changes and the draw-down ratio reflects the corresponding variation in mechanical properties, namely, an increase in breaking stress with a decline in breaking strain in relation to increases in draw-down ratio. Therefore, these results provide solid and direct evidence on the evolution of structure during the artificial spinning process and on how structure determines the final mechanical performance of silk fibers. We believe this study provides a good background on the relationship between microscopic structure and macroscopic properties in polymer science and may prove useful in the production of high performance materials, not only for silk fibers but also for other natural and synthetic polymeric materials.

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.