Artificial Silk Research Articles

Spinning Regenerated Silk Fibers with Improved Toughness by Plasticizing with Low Molecular Weight Silk.

Low-molecular weight (LMW) silk was utilized as a LMW silk plasticizer for regenerated silk, generating weak physical crosslinks between high-molecular weight (HMW) silk chains in the amorphous regions of a mixed solution of HMW/LMW silk. The plasticization effect of LMW silk was investigated using mechanical testing, Raman spectroscopy, and wide-angle X-ray scattering (WAXS). Small amounts (10%) of LMW silk resulted in a 19.4% enhancement in fiber extensibility and 37.8% increase in toughness. The addition of the LMW silk facilitated the movement of HMW silk chains during drawing, resulting in an increase in molecular chain orientation when compared with silk spun from 100% HMW silk solution. The best regenerated silk fibers produced in this work had an orientation factor of 0.94 and crystallinity of 47.82%, close to the values of natural degummedBombyx mori silk fiber. The approach and mechanism elucidated here can facilitate artificial silk systems with enhanced properties.

Structural Changes in Spider Dragline Silk after Repeated Supercontraction-Stretching Processes.

Spider dragline silk is well-known for its excellent combination of strength and extensibility as well as another unique property called supercontraction. In our previous work, the changes in conformations of the Nephila edulis spider dragline silk when subjected to different supercontraction processes were extensively investigated. When a native spider dragline silk had free supercontraction, and then restretched to its original length, the content and molecular orientation of different conformations (β-sheet, helix, and random coil) changed but the mechanical properties remained almost the same. Therefore, herein, further supercontraction-stretching treatment was performed up to three cycles, and the corresponding structural changes were investigated. In addition to the synchrotron radiation FTIR (S-FTIR) microspectroscopy employed in our previous study, synchrotron radiation small-angle X-ray scattering (S-SAXS) and atomic force microscopy (AFM) were also used in this work to determine the structural changes of spider dragline silk in different scales. The results show that by repeating the supercontraction-stretching treatment, the β-sheet structure content in spider dragline silk was slightly increased, but its orientation degree remained almost the same. Also, with the increase in cycle of supercontraction-stretching treatments, a 10.5 nm long period perpendicular to the silk fiber axis gradually appeared, endowing the spider dragline silk with periodic structure both along (6.6 nm, already existed in native silk and did not change with the supercontraction-stretching treatment) and perpendicular to the silk fiber axis. After the third supercontraction-stretching cycle, the AFM images displayed a clear 210 nm × 80 nm corn kernel-like structure on the surface of nanofibrils in spider dragline silks, which may be related to the aggregation of 10.5 nm × 6.6 nm periodic structure observed via S-SAXS. Finally, although the structure of spider dragline silk became increasingly regular with the rise in supercontraction-stretching cycles, mechanical properties remained constant after every cycle of the supercontraction-stretching treatment. These findings can aid in further understanding the structural changes that are related to the supercontraction of spider dragline silk and provide useful guidance in fabrication of high-performance regenerated or artificial silk fibers.

The influence of metal ions on native silk rheology

Whilst flow is the basis for silk fibre formation, subtle changes in a silk feedstocks’ chemical environment may serve to increase both energetic efficiency and control hierarchical structure development during spinning. Despite the role of pH being largely understood, the influence of metal ions is not, only being inferred by correlative work and observations. Through a combination of rheology and microscopy, we provide a causative study of how the most abundant metal ions in the silk feedstock, Ca2+ and K+, affect its flow properties and structure. Our results show that Ca2+ ions increase viscosity and prevent molecular alignment and aggregation, providing ideal storage conditions for unspun silk. In contrast, the addition of K+ ions promotes molecular alignment and aggregation and therefore seems to transfer the silk feedstock into a spinning state which confirms recent ‘sticky reptation’ modelling hypotheses. Additionally, we characterised the influence of the ubiquitous kosmotropic agent Li+, used to prepare regenerated silk solutions, and find that it promotes molecular alignment and prevents aggregation which may permit a range of interesting artificial silk processing techniques to be developed. In summary, our results provide a clearer picture of how metal ions co-ordinate, control and thus contribute towards silk protein self-assembly which in turn can inspire structuring approaches in other biopolymer systems.

Tongland works in Galloway and the women engineers

In 1916, a factory was established by William Beardmore and Thomas Pullinger at Tongland in south-west Scotland that was for much of the time that it was in operation staffed by women. Initially manufacturing aero engines, the women were being trained for a career in engineering, not simply as war workers. This continued post-war with manufacture of tractor engines and then Galloway motor cars. The factory was innovative for the time, being powered by a small hydroelectric scheme and built on the same principle as the Albert Kahn designed factories used by Henry Ford. By the late 1920s the building was being used for artificial silk production (Rayon) and staffed by less skilled women. The factory was used by the RAF during WWII and is still extant today. Although some articles have been written about aspects of this industrial site, this article covers the complete history from construction to the present day.

Low-loss light-guiding, strong silk generated by a bioinspired microfluidic chip

The necessity of optical waveguides with low-loss light guiding of biomedical devices is driving increasing demands for development of biocompatible photonic components. Spider silks have extraordinary mechanical properties; thus, the design of high-performance artificial silk fibers as optical waveguides for low-loss light guiding has been one of the focuses of researches in the field of biomimetic fibers. In this study, regenerated silk fibroin (RSF)/cellulose nanofibers (CNF) hybrid fibers were wet-spun through a microfluidic channel that mimics the shape of spider’s major ampullate gland. The generated RSF/CNF fibers with high crystallinity, high mesophase content and small crystallite size, thus showed a low light loss of 1.0 dB/cm, which was much lower than that of degummed-silk and most commercial waveguides. Additionally, the fibers had high sound velocity and was knittable. The break strength of the RSF/CNF fiber containing 5 wt% CNF was as high as 710 ± 33 MPa, which was significantly higher than that of silkworm silk fiber. The developed optical waveguides had high performance, biocompatibility, biodegradability, flexibility, and toughness, thus may be suitably applied in biological media, biophotonics and brain-machine interfaces.

Properties of Biomimetic Artificial Spider Silk Fibers Tuned by PostSpin Bath Incubation.

Efficient production of artificial spider silk fibers with properties that match its natural counterpart has still not been achieved. Recently, a biomimetic process for spinning recombinant spider silk proteins (spidroins) was presented, in which important molecular mechanisms involved in native spider silk spinning were recapitulated. However, drawbacks of these fibers included inferior mechanical properties and problems with low resistance to aqueous environments. In this work, we show that ≥5 h incubation of the fibers, in a collection bath of 500 mM NaAc and 200 mM NaCl, at pH 5 results in fibers that do not dissolve in water or phosphate buffered saline, which implies that the fibers can be used for applications that involve wet/humid conditions. Furthermore, incubation in the collection bath improved the strain at break and was associated with increased β-sheet content, but did not affect the fiber morphology. In summary, we present a simple way to improve artificial spider silk fiber strain at break and resistance to aqueous solvents.

Structure-Function Relationship of Artificial Spider Silk Fibers Produced by Straining Flow Spinning.

The production of large quantities of artificial spider silk fibers that match the mechanical properties of the native material has turned out to be challenging. Recent advancements in the field make biomimetic spinning approaches an attractive way forward since they allow the spider silk proteins to assemble into the secondary, tertiary, and quaternary structures that are characteristic of the native silk fiber. Straining flow spinning (SFS) is a newly developed and versatile method that allows production under a wide range of processing conditions. Here, we use a recombinant spider silk protein that shows unprecedented water solubility and that is capable of native-like assembly, and we spin it into fibers by the SFS technique. We show that fibers may be spun using different hydrodynamical and chemical conditions and conclude that these spinning conditions affect fiber mechanics. In particular, it was found that the addition of acetonitrile and polyethylene glycol to the collection bath results in fibers with increased β-sheet content and improved mechanical properties.

Engineered a novel pH-sensitive short major ampullate spidroin

The pH diversification has been proved as an important factor affecting the self-assembly of spidroin. Herein, we constructed a novel spider silk protein (NT-MaSp1s-CT) with the pH-dependent secondary structures, containing pH-sensitive N-terminal, C-terminal domains and a repeated core region with merely 191 amino acids. Then pH sensitivity of NT-MaSp1s-CT was detected at different pH conditions and NT-MaSp1s-CT displayed pH-dependent conformational transitions consistent with rational designed objective. Besides, the micelles theory was employed to inquiry the assembly mechanism of NT-MaSp1s-CT in high concentration spinning dope. As expected, NT-MaSp1s-CT protein can be spun into continuous and uniform fibers with the pH ranging from 2 to 11, which is the largest pH boundary for artificial spider silk formation, simplifying the assembly conditions and paving a broad path for spinning process. Moreover, the hemolysis and cytotoxicity of NT-MaSp1s-CT fibers were also determined and the novel fibers exhibit excellent biocompatibility, providing wider potential applications in the biomedical and pharmaceutical fields.

Tensile properties of synthetic pyriform spider silk fibers depend on the number of repetitive units as well as the presence of N- and C-terminal domains

Spiders can spin seven different types of silk, some of which are well characterized, but studies on natural and synthetic pyriform silks are few. In this study, recombinant spidroins composed of one to three pyriform repeat units from Araneus ventricosus, in some cases flanked with non-repetitive N- and C-terminal domains (NT and CT), were produced and spun into continuous silk fibers using a wet-spinning process in organic solvents. All the fibers showed high and similar tensile strain (60–80%), but the Young's modulus, stress and toughness of fibers increased with increasing number of repeat units and in the presence of NT and CT as well. Systematic studies of the secondary structure contents of the different spinning dopes and spun fibers revealed no major differences between the different types of recombinant spidroins. This suggests that optimal tensile properties of artificial spider silks require the presence of several repetitive units as well as terminal domains and that secondary structure content of silk dope and fibers have limited correlation with mechanical behaviors.

Towards engineering and production of artificial spider silk using tools of synthetic biology.

Spider silk is one of the strongest biomaterials available in nature. Its mechanical properties make it a good candidate for applications in various fields ranging from protective armour to bandages for wound dressing to coatings for medical implants. Spider silk is formed by an intricate arrangement of spidroins, which are extremely large proteins containing long stretches of repeating segments rich in alanine and glycine. A large amount of research has been directed towards harnessing the spectacular potential of spider silks and using them for different applications. The interdisciplinary approach of synthetic biology is an ideal tool to study these spider silk proteins and work towards the engineering and production of synthetic spider silk. This review aims to highlight the recent progress that has been made in the study of spider silk proteins using different branches of synthetic biology. Here, the authors discuss the different computational approaches, directed evolution techniques and various expression platforms that have been tested for the successful production of spider silk. Future challenges facing the field and possible solutions offered by synthetic biology are also discussed.

Evaluation of the potential of chimeric spidroins/poly(L-lactic-co-ε-caprolactone) (PLCL) nanofibrous scaffolds for tissue engineering.

In this study, a novel type of chimeric spider silk proteins (spidroins) NTW1-4CT was blended with poly(L-lactic-co-ε-caprolactone) (PLCL) to obtain nanofibrous scaffolds via electrospinning. Spidroins are composed of a N-terminal module (NT) from major ampullate spidroins, a C-terminal module (CT) from minor ampullate spidroins and 1-4 repeat modules (W) from aciniform spidroins. Physical characteristics and structures of NTW1-4CT/PLCL (25/75, w/w) blend scaffolds were carried out by scanning electron microscope (SEM), water contact angles measurements, Fourier transform infrared (FTIR) spectroscopy and tensile mechanical tests. Results showed that blending with spidroins decreased diameters of nanofibers and increased porosity and wettability of scaffolds. Additionally, chimeric spidroins undergone a similar structural transition in electrospinning process as with the formation process of native and artificial spider silks from other spidroins. With amounts of W modules increasing, the tensile strength and elongation of blend scaffolds were also increased. Particularly, NTW4CT/PLCL (25/75) scaffolds revealed much higher breaking stress than pure PLCL scaffolds. In vitro experiments, human umbilical vein endothelial cells (HUVEC) cultured on NTW4CT/PLCL (25/75) scaffolds displayed significantly higher activity of proliferation and adhesion than on pure PLCL scaffolds. All results suggested that chimeric spidroins/PLCL, especially NTW4CT/PLCL (25/75) blend nanofibrous scaffolds had promising potential for vascular tissue engineering.

Dyeability and antioxidant activity of artificial silk with Equisetum arvense L. extract

PurposeEquisetum arvense L. (Equisetum) is a weed that is very difficult to remove because of its deep roots. The purpose of this paper is to examine the dyeability and antioxidant activity of Equisetum extracted from hot water.Design/methodology/approachDry Equisetum was extracted at 100°C for 2 h, and its dyeability according to time, temperature and repetition cycle, and the mordant effect by skim milk powder were confirmed. The color change according to the K/S, fastness to rubbing, light, sweat and washing, UV protection rate and antioxidant activity were evaluated.FindingsUV‒Vis spectroscopy showed that the Equisetum extract contained a flavonoid compound. The addition of Equisetum to artificial silk produced the greatest color difference when dyed at 60°C for 1 h, and the K/S value increased slightly after the pre-mordant treatment. In the fastness test, light and washing had no significant effect, but the fastness to rubbing was very good at Grades 4 and 5, and there was also a considerable improvement in the UV protection rate. The antioxidant activity of the extract was confirmed by an analysis of the radical scavenging ability through the DPPH (1,1-diphenyl 2-picryl-hydrazyl) and ABTS ([2,2’- azino-bis (3-ethylbenzothialzoline-6-sulfonic acid) diammonium salt]) tests.Originality/valueThese results revealed a new natural antioxidant-containing dyestuff, weed grass, which is easy to obtain, easy to use as a dyeing material and has excellent antioxidant activity in an extracted dye solution and dyeing fabric.

A theoretical study on the capillary rise of non-Newtonian power-law fluids

The phenomena of capillary rise with the effect of displaced fluids are ubiquitous in both science and engineering, and the mathematical models and their analytical solutions of this problem have also received increasing attention. In this paper, a theoretical study on the rising dynamics of non-Newtonian power-law fluids in a capillary is performed, and the classical Lucas–Washburn equation is generalized to a nonlinear second-order differential equation in which the effects of the power-law index and displaced fluids are included. We analyze the imbibition behaviors of power-law fluids under the influence of displaced fluids in details, and also present some analytical solutions of different special cases and different time stages. The results show that for different special cases, it takes shorter time for shear thickening fluid to reach the equilibrium height. For different time stages, however, the rising phenomena of power-law fluids are more complex, and the average time for the shear-thinning fluid to reach the equilibrium height is longer compared to shear-thickening fluid, but an opposite phenomenon is observed for the case of μ1,0/μ2,0=100 (here μ1,0/μ2,0 is the viscosity ratio of two power-law fluids) in viscous time stage. In inertial time stages, the density ratio of the absorbed fluid to the displaced fluid also has a significant effect on the rising dynamics of imbibing fluid. Furthermore, the effect of dynamic contact angle is also included in the governing equation and analytical solutions. Through a comparison between the theoretical results and experimental data, a good agreement is observed. These results can be used as a priori for liquid absorption in industrial applications, including oil recovery, fuel cells and water collection of artificial silk.

Новые перспективные материалы на основе рекомбинантного и регенерированного шелка для медицины и конструкционных тканей

Одним из наиболее прочных природных материалов является паутина. Прочность ее нитей может достигать 1.3–1.5 ГПа, что сопоставимо с прочностью стали. Энергия ее разрушения достигает огромных значений 194–283 МДж/м3 , поэтому текстиль на основе паучьих нитей может найти применение в изготовлении композиционных элементов для летательных аппаратов и автомобилей. Волокна паука обладают высокой биосовместимостью, поддерживают жизнеспособность клеток и обладают антибактериальными свойствами и не вызывают иммунного ответа. Таким образом, они могут быть использованы для изготовления трехмерных пористых клеточных каркасов для целей тканевой инженерии. К несомненным достоинствам волокон паука относится то, что они не плавятся. Поэтому текстильные изделия из паучьего шелка можно использовать для изготовления армейской экипировки. К сожалению, производить паучий шелк с помощью массового разведения пауков невозможно. В связи с этим ведется разработка его синтетических аналогов с помощью технологии рекомбинантной ДНК. С целью создания отечественной технологии изготовления искусственного шелкового волокна и медицинских материалов в данном обзоре приводятся основные работы в области исследования реологических свойств растворов спидроина (основной материал паутины) и фиброина шелка, показывающие, как структурные превращения спидроина, индуцированные изменением pH, содержанием соли и напряжением сдвига, определяют его способность к самоорганизации в водных растворах. Приводится анализ важнейших работ в области мокрого, сухо-мокрого формования и электроформования волокон, а также сравнение механических свойств волокон рекомбинантного спидроина с соответствующими показателями природных волокон паука. Значительные успехи, достигнутые в последнее время в этой области, позволяют перейти к созданию волокнистых материалов нового поколения.

Peeling and Mesoscale Dissociation of Silk Fibers for Hybridization of Electrothermic Fibrous Composites

Natural silk cocoons have fibrillary structure at several levels of length scales, which offered mechanical properties superior to many artificial silk materials. Despite the fact that many solvent...

Artificial spider silk from ion-doped and twisted core-sheath hydrogel fibres

Spider silks show unique combinations of strength, toughness, extensibility, and energy absorption. To date, it has been difficult to obtain spider silk-like mechanical properties using non-protein approaches. Here, we report on an artificial spider silk produced by the water-evaporation-induced self-assembly of hydrogel fibre made from polyacrylic acid and silica nanoparticles. The artificial spider silk consists of hierarchical core-sheath structured hydrogel fibres, which are reinforced by ion doping and twist insertion. The fibre exhibits a tensile strength of 895 MPa and a stretchability of 44.3%, achieving mechanical properties comparable to spider silk. The material also presents a high toughness of 370 MJ m−3 and a damping capacity of 95%. The hydrogel fibre shows only ~1/9 of the impact force of cotton yarn with negligible rebound when used for impact reduction applications. This work opens an avenue towards the fabrication of artificial spider silk with applications in kinetic energy buffering and shock-absorbing.

Artificial spinning of natural silk threads

Silk producing arthropods spin solid fibres from an aqueous protein feedstock apparently relying on the complex structure of the silk protein and its controlled aggregation by shear forces, alongside biochemical changes. This flow-induced phase-transition of the stored native silk molecules is irreversible, environmentally sound and remarkably energy efficient. The process seemingly relies on a self-assembling, fibrillation process. Here we test this hypothesis by biomimetically spinning a native-based silk feedstock, extracted by custom processes, into silk fibres that equal their natural models’ mechanical properties. Importantly, these filaments, which featured cross-section morphologies ranged from large crescent-like to small ribbon-like shapes, also had the slender cross-sectional areas of native fibres and their hierarchical nanofibrillar structures. The modulation of the post-draw conditions directly affected mechanical properties, correlated with the extent of fibre crystallinity, i.e. degree of molecular order. We believe our study contributes significantly to the understanding and development of artificial silks by demonstrating successful biomimetic spinning relies on appropriately designed feedstock properties. In addition, our study provides inspiration for low-energy routes to novel synthetic polymers.

Aggregation State of Residual α-Helices and Their Influence on Physical Properties of S. c. ricini Native Fiber.

Formation of the α-helical conformation in the poly-l-alanine (PA) sequence regions, subsequent structural transition to β-sheet during natural spinning, and presence of residual α-helices in Samia cynthia ricini (S. c. ricini) native silk fiber have been experimentally proven. However, the aggregation state of the residual α-helices, and their influence on the mechanical deformation behavior in native fiber remain unclear. Here we show that the α-helices form an ordered aggregation state with a hexagonal packing in the aqueous solution, some of which remain during natural spinning. X-ray scattering and differential scanning calorimetry (DSC) analyses revealed occurrence of a structural transition of the residual α-helices to the β-sheet structure, accompanied by disappearance of the plateau region in the force-strain curve, due to heat-treatment at ~220 °C. On the basis of X-ray scattering before and after tensile stretching of S. c. ricini native silk, a direct connection between the plateau region and the α-helix to β-sheet structural transition was confirmed. Our findings demonstrate the importance of the PA sequence regions in fiber structure formation and their influence on the tensile deformation behavior of S. c. ricini silk, features believed to be essentially similar in other saturniid silks. We strongly believe the residual ordered α-helices to be strategically and systematically designed by S. c. ricini silkworms to impart flexibility in native silk fiber. We anticipate that these knowledge forms a basis for fruitful strategies in the design and development of amino acid sequences for artificial silks with desired mechanical properties.

Strong Silk Fibers Containing Cellulose Nanofibers Generated by a Bioinspired Microfluidic Chip

As spider silks have extraordinary mechanical properties, the design of high-performance artificial silk fibers has been one of the focuses in the field of biomimetic fibers. Cellulose nanofibers (...

Advanced Recombinant and Regenerated Silk Materials for Medicine and Tissue Engineering

A spiderweb is one of the strongest natural materials. The strength of its filaments can reach 1.3–1.5 GPa, which is comparable to the strength of steel. Its toughness reaches enormous values of 194–283 MJ/m3; therefore, textiles based on spider yarns may be promising in the production of composite materials for aircraft and automobiles. Spiderweb fibers have high biocompatibility and antibacterial properties, support cell viability, and do not cause an immune response. Thus, they can be used for manufacturing three-dimensional porous cell scaffolds for tissue engineering purposes. The undoubted advantages of spiderweb fibers include the fact that they do not melt. Therefore, textile products made of spider silk can be used for the production of military equipment. Unfortunately, mass production of spider silk using breeding of spiders is not possible. In this regard, development of synthetic analogues using recombinant DNA technology is of current interest. In order to create the technology for manufacturing artificial silk fiber and medical materials, this review presents the main findings in studying the rheological properties of solutions of spidroin (the main web material) and silk fibroin. These findings demonstrated how structural transformations of spidroin are induced by a change in the pH, salt content, and shear stress, and determine its ability for self-organization in aqueous solutions. An analysis of the most important studies of wet, dry–wet spinning, and electrospinning of fibers is presented, as is a comparison of the mechanical properties of the fibers of recombinant spidroin and natural spider fibers. Significant recent successes in this area allow us to advance toward the creation of a new generation of fibrous materials.