Natural Silk Research Articles

Dynamic dual-crosslinking antibacterial hydrogel with enhanced bio-adhesion and self-healing activities for rapid hemostasis in vitro and in vivo

Bio-adhesives based on natural polymer silk fibroin (SF) are high-profiled in the development of rapid hemostatic agents because of their good biocompatibility and biodegradability. However, the lack of bioactivity, mechanical and bio-adhesion performance, restrict their use in the biomedical field. Herein, based on the dynamic dual-crosslinking mechanism, we fabricated a silk microfibers (SMFs)-based multifunctional hemostatic hydrogel by incorporating tannic acid-coated SMF (TA@SMF) motifs into the network of poly(vinyl alcohol)-borax (PB) hydrogel. The cohesion-enhancing strategy, along with dynamic borate-diol bonds and hydrogen bonds, synergically provide the hydrogel with enhanced bio-adhesion and self-healing properties. TA@SMF/PB gel has an elongation at break of more than 600% and adheres to pig skin even after 24 h immersion in water. In vitro experiments have shown good antibacterial, antioxidant, biocompatibility, and hemostatic properties of the TA@SMF/PB gel. In vivo degradation and mouse liver hemostatic test further verified its biosafety and rapid hemostasis performance. The hemostatic time of 42.0 ± 4.9 s in TA@SMF-0.5 was significantly shorter than that in other experimental groups. This study is the original report for functionalizing SMFs with TA as a hemostasis material, which affords a versatile SMF-based toolkit that provides promising candidate materials for rapid hemostatic and infectious wound healing.

Silk fibroin‐based conductive and antibacterial hydrogels with a dual network for flexible sensors

AbstractThe flexible wearable hydrogel strain sensors for human motion monitoring have attracted broad attention. However, developing a high‐strength hydrogel strain sensor remains challenging and achieves synergistic characteristics such as biocompatibility, antibacterial activity, and conductivity. This work proposes a two‐step UV polymerization method for the preparation of (hydrolyzed silk fibroin (HSF)/polyacrylamide (PAM)/polyacrylic acid (PAA)/poly sulfobetaine methacrylate (PSBMA) composite hydrogels. The monomers AM and AA undergo self‐polymerization and copolymerization. Meanwhile, SF is cross‐linked with them via multiple hydrogen bonds to form the first network. After the second UV initiation, SBMA polymerizes to create the second network. The HSF8%/PAM/PAA/PSBMA2%possesses superior tensile strength (1.49 ± 0.07 MPa) and compressive modulus (21.47 ± 1.07 MPa at 99% strain). The SBMA (4 wt%) endows hydrogels with antibacterial activity (98.53% ± 4.93%). The H+ionized by PAA and the ion channels constructed by SBMA (4 wt%) provide hydrogel with ionic conductivity (0.950 S m−1). The hydrogel could be used as a flexible strain sensor to monitor human joint activity. The natural silk fibroin allows the hydrogel to retain degradability. Therefore, the SF‐based conductive hydrogel shows the potential application in flexible strain sensors.

Special fog harvesting mode on bioinspired hydrophilic dual-thread spider silk fiber

Normal bioinspired spider silk fibers (BSSFs) show effective fog collection abilities but are weak in the rapid transport of captured droplets, which could potentially hinder the further improvement of fog harvesting efficiency. Factually, previous works have shown that the main axis of natural spider silk consists of two separate, parallel threads, similar to the microchannel structure of Sarracenia trichome. This structural feature may be an important factor contributing to the highly efficient fog harvesting ability of spider silks. However, to the best of our knowledge, previous studies on BSSFs have ignored this feature. In this work, inspired by spider silk and Sarracenia trichome, a novel bioinspired hydrophilic dual-thread spider silk fiber (HDSSF) is obtained via a simple dipping coating method to introduce capillary force. On the HDSSF, compared to previous works, a totally different fog harvesting mode was observed, i.e., captured droplets could be rapidly transported to spindle knots under the effect of capillary force and internal Laplace pressure difference via the connectivity of liquid film and no obvious droplets could be observed on the threads. The experimental observations and underlying mechanism analyses have verified that this special fog harvesting mode allows rapid transport and directional collection of droplets to accelerate the surface reconstruction rate, coupled with the high droplet capture ability of fiber, resulting in a significant improvement of fog harvesting efficiency (9.03 g cm−2·h−1, a 590% increase compared with normal BSSF). Such HDSSF is potentially applicable in high-efficiency fog harvesting systems, droplet transport devices and other engineering applications related to fog harvesting.

Wet spinning is employed to produce spider silk with high elasticity

Spider silk exhibits exceptional strength and elasticity in its natural form. Over the course of several decades, researchers have been working on artificially spinning recombinant spider silk proteins (spidroin) in order to replicate the remarkable mechanical properties of natural spider silk. In this study, we utilized the wet spinning method to investigate the relationship between the concentration of the coagulation bath and fiber performance. We discovered that the concentration of methanol plays a crucial role in determining the continuity, diameter, and mechanical properties of the fibers. Lower concentrations of methanol favor the production of continuous, thinner fibers with higher strain. Additionally, secondary stretching during the spinning process contributes to the production of silk fibers with stable mechanical properties and thermal stability. By employing different concentrations of methanol and applying additional stretching, we successfully produced silk fibers with a high strain of 2.1652 ± 0.3871 mm/mm. Furthermore, these wet-spun fibers demonstrated the ability to promote the growth of Schwann cells, indicating their potential application in the field of biomedical engineering. Hence, the exceptional mechanical properties and the ability to promote cellular growth make the obtained spider silk fibers highly promising for various biomedical applications.

Effect of Sericin Content on the Structural Characteristics and Properties of New Silk Nonwoven Fabrics.

Recently, natural silk nonwoven fabrics have attracted attention in biomedical and cosmetic applications because of their excellent biocompatibility, mechanical properties, and easy preparation. Herein, silk nonwoven fabrics were prepared by carding silk filaments to improve their productivity, and the effect of sericin content on the structure and properties of silk nonwoven fabrics was investigated. Owing to the binding effect of sericin in silk, a natural silk nonwoven fabric was successfully prepared through carding, wetting, and hot press treatments. Sericin content affected the structural characteristics and properties of the silk nonwoven fabrics. As the sericin content increased, the silk nonwoven fabrics became more compact with reduced porosity and thickness. Further, with increasing sericin content, the crystallinity and elongation of the silk nonwoven fabrics decreased while the moisture regain and the maximum stress increased. The thermal stability of most silk nonwoven fabrics was not affected by the sericin content. However, silk nonwoven fabrics without sericin had a lower thermal decomposition temperature than other nonwoven fabrics. Regardless of the sericin content, all silk nonwoven fabrics exhibited optimal cell viability and are promising candidates for cosmetic and biomedical applications.

Spider dragline silk fibres maintain rectangular columnar liquid crystalline phase

ABSTRACT The liquid crystalline phase of spider silk is thought to enable for the silk protein to be stored at high concentration in the gland without gelation, facilitating the instant fibre formation at the spinning duct. Nevertheless, it has never been revealed whether the liquid crystalline state of the silk protein maintains after the fibre formation. In this study, we conducted the X-ray liquid crystal structure analysis to reveal the details of molecular assemblies of the native spider silk proteins. Based on the wide- and small angle X-ray scattering data using the uniaxial bundle of spider draglines, the spider dragline silk fibres maintain a rectangular columnar liquid crystalline phase with a P21/a (p2gg) symmetry. The liquid crystalline state of the spider silk fibre is not nematic, cholesteric, nor hexagonal columnar, as previously proposed, but rectangularly packed columnar liquid crystal. The movable silk molecular chains along the long fibre axis in the rectangular columnar liquid crystalline structure help to explain the mechanical strength of the native spider dragline silk fibres. The results obtained in this study will contribute to understanding the biological basis underlying the silk fibre formation and will be useful to the biomimicry of spider silk fibres.

Microstructure similarity analysis between synthetic phase-separated block copolymers and natural spider silk

This papers primary purpose is to explore why the microstructure of synthetic block copolymers and natural spider silk is similar at the nanoscale. This paper analyses the main chain segments and secondary structures of natural spider silk, clarifies the aggregation order, and introduces the contribution of secondary systems to the properties of natural block copolymers. Secondly, combined with the synthesis mechanism of natural spider silk, this paper summarizes and analyzes the general process of the synthesized block copolymer. Finally, the conditions of self-assembly of artificial fragments to form the structure are analyzed by employing mean-field theory and a phase diagram. Natural and ideal synthetic spider silk block copolymers have high similarity in performance. To achieve this, scientists can only start from the primary segment to understand their arrangement order in the secondary structure. Then the influence of each block on the properties of the silk fiber is analyzed. At the same time, the size and shape of self-assembled block copolymers are controlled at the micro-scale, thereby changing their properties. The mechanism above shows that the synthesized spider silk block copolymer is similar to natural spider silk in microscopic morphology.

Influence of experimental methods on the mechanical properties of silk fibers: A systematic literature review and future road map.

Spider silk fibers are of scientific and industrial interest because of their extraordinary mechanical properties. These properties are normally determined by tensile tests, but the values obtained are dependent on the morphology of the fibers, the test conditions, and the methods by which stress and strain are calculated. Because of this, results from many studies are not directly comparable, which has led to widespread misconceptions in the field. Here, we critically review most of the reports from the past 50 years on spider silk mechanical performance and use artificial spider silk and native silks as models to highlight the effect that different experimental setups have on the fibers' mechanical properties. The results clearly illustrate the importance of carefully evaluating the tensile test methods when comparing the results from different studies. Finally, we suggest a protocol for how to perform tensile tests on silk and biobased fibers.

Bioinspired Robust Helical‐Groove Spindle‐Knot Microfibers for Large‐Scale Water Collection

AbstractHelical structure is ubiquitous in nature with high‐order configuration, specific paths, large superficial areas, providing an approach to bioinspired wettability control. Owing to its special hydrophilic rough surfaces and periodic knot and joint structure, natural spider silk can catch tiny droplets in fog and transport them directionally, sparking scientific interest in bioinspired knotted microfibers to address the risk of water scarcity. To further enhance the water collection ability, a bioinspired helical‐groove‐modified spindle‐knot (HSK) microfiber is continuously fabricated in this work by a simple coating method combined with crack regulation. The formation and morphology can be precisely manipulated by adjusting the drawing velocity and concentration of the coating solution. Compared with smooth spindle‐knot microfibers, HSK exhibits greater performances of wetting speed, droplets growth rate, and hanging ability, which can be attributed to the unique helical paths that bring capillary force difference and offer extra three‐phase contact line lengths for water collection behavior. The maximum droplet volume is almost 2114 times that of the microfiber knots, which is the highest compared with previous reports. Moreover, HSK microfibers are endowed with repairable wettability, long‐term durability, excellent mechanical properties, and flexibility, showing great potential in the realm of applications for large‐scale water collection.

Spider Silk Protein Forms Amyloid-Like Nanofibrils through a Non-Nucleation-Dependent Polymerization Mechanism.

Amyloid fibrils-nanoscale fibrillar aggregates with high levels of order-are pathogenic in some today incurable human diseases; however, there are also many physiologically functioning amyloids in nature. The process of amyloid formation is typically nucleation-elongation-dependent, as exemplified by the pathogenic amyloid-β peptide (Aβ) that is associated with Alzheimer's disease. Spider silk, one of the toughest biomaterials, shares characteristics with amyloid. In this study, it is shown that forming amyloid-like nanofibrils is an inherent property preserved by various spider silk proteins (spidroins). Both spidroins and Aβ capped by spidroin N- and C-terminal domains, can assemble into macroscopic spider silk-like fibers that consist of straight nanofibrils parallel to the fiber axis as observed in native spider silk. While Aβ forms amyloid nanofibrils through a nucleation-dependent pathway and exhibits strong cytotoxicity and seeding effects, spidroins spontaneously and rapidly form amyloid-like nanofibrils via a non-nucleation-dependent polymerization pathway that involves lateral packing of fibrils. Spidroin nanofibrils share amyloid-like properties but lack strong cytotoxicity and the ability to self-seed or cross-seed human amyloidogenic peptides. These results suggest that spidroins´ unique primary structures have evolved to allow functional properties of amyloid, and at the same time direct their fibrillization pathways to avoid formation of cytotoxic intermediates.

Bridging Biocondensation and Biomimetic Fibrillation by Regulating Intra- And Interchain Hydrogen Bonds in Artificial Biomacromolecular Condensates.

Utilizing biocondensates as feedstocks can be a state-of-the-art strategy for emulating natural silk spinning. Although current biocondensates can form solid fibers using a biomimetic draw spinning method, the fibrillation is primarily achieved through evaporation of highly concentrated biocondensates rather than structural conversion in natural spinning. Current artificial biocondensates lack biomimetic features of stress-induced fibrillation since they are unable to replicate the structural complexity of native proteins in the dope. Herein, we successfully achieved biomimetic fibrillation at significantly reduced concentrations by constructing artificial biocondensates using naturally derived silk fibroin. The biomimetic features of stress-induced fibrillation in native proteins are replicated in our artificial biocondensates by tailoring multivalent interactions in biocondensation. Our findings unravel the fundamental correlations between biocondensation and stress-induced fibrillation. This work can not only provide a framework for designing artificial biocondensates in biomimetic spinning but also improve the molecular insights into natural spinning.

Pendapatan Tenaga Kerja Perempuan Pada Agribinis Sutera Alam

The contribution of women to family income can be seen from the income earned based on the outpouring of working time allocated by women workers in natural silk agribusiness. The purpose of this study is analyzing the income of women workers in each activity in the natural silk agribusiness in Soppeng Regency. The research was conducted from December 2021 to June 2022 in Donri-Donri Subdistrict and Lilirilau Subdistrict, Soppeng Regency. The method useddescriptive quantitative and the data is obtained by means of field observations, interviews and questionnaires. Analysis of the data in this study used income analysis. The results obtained the average income earned by women workers in each natural silk agribusiness sub-system in one production cycle, namely: (1) in mulberry cultivation activities the average is Rp. 430.834 in a working time span of 2 hours/day, (2) in silkworm cultivation the average amount is Rp. 274.204 in a working time span of 6,25 hours/day, (3) in spinning activities the average amount is Rp. 644.148 in a working time span of 6,38 hours/day, (4) in weaving the average amount is Rp. 336.581 in a working time span of 5,5 hours/day, (5) as well as in silk distribution and marketing activities, the average received by Cantika Sabbena Brand is Rp. 9.530.000 in a working time span of 8 hours/day. The income obtained from each activity has a fluctuating nature caused by production conditions in the upstream part and the demand for genuine silk by consumers in the downstream.

Microcompartmentalization Controls Silk Feedstock Rheology.

The rheological characteristics of pre-spun native silk protein, which is stored as a viscous pulp inside the silk gland, are the key factors that determine the mechanical performance of the endpoint material: the spun silk fibers. In silkworms and arthropods, microcompartmentalization was shown to play an important regulatory role in storing and stabilizing the aggregation-prone silk and in initiating the fibrillar self-assembly process. However, our current understanding of the mechanism of stabilization of the highly unstable protein pulp in its soluble state inside the microcompartments and of the conditions required for initiating the structural transition in protein inside the microcompartments remains limited. Here, we exploited the power of droplet microfluidics to mimic the silk protein's microcompartmentalization event; we introduced changes in the chemical environment and analyzed the storage-to-spinning transition as well as the accompanying structural changes in silk fibroin protein, from its native fold into an aggregative β-sheet-rich structure. Through a combination of experimental and computational simulations, we established the conditions under which the structural transition in microcompartmentalized silk protein is initiated, which, in turn, is reflected in changes in the silk-rich fluid behavior. Overall, our study sheds light on the role of the independent parameters of a dynamically changing chemical environment, changes in fluid viscosity, and the shear forces that act to balance silk protein self-assembly, and thus, facilitate new exploratory avenues in the field of biomaterials.

Simultaneous dyeing and finishing of wool and natural silk fabrics using Azolla pinnata extract

Simultaneous dyeing and finishing of wool and natural silk fabrics using Azolla pinnata extract

Optimization of extraction and dyeing conditions of the Parkia roxburghii pod’s peel as a natural substantive silk dye

Natural dyes are soft, eco-friendly, and non-toxic colours for silk fabric, imparting high compatibility with the environment. Among the different natural dyestuffs derived from different parts of plants, the peel of the Parkia roxburghii pod is thriving as one of the potential natural substantive dyes. The study reveals optimization of dye extraction for dyeing silk fabric. Colour strength (K/S) and absorbance of dye extract were evaluated for optimization of extraction and dyeing parameters. The optimized ML ratio (material and solvent proportions) was 1:30 for 60 min of boiling at 80 °C under acidic medium. Use of natural and synthetic mordants produced different colour patterns giving two classes, YR, light to dark brownish colour. CuSO4, lime juice and Terminalia chebula mordants produced better wash fastness and light fastness in meta-mordant conditions. Dyeing silk with parkia peel without mordant also produces better fastness properties, thus acts as a natural substantive silk dye.

The NiCo Bimetal Catalyst Loaded on Polyvinylidene Fluoride Coated on the Self-Supporting Silk Electrode as an Advanced Electrocatalyst for the Hydrogen Evolution Reaction

In this work, a NixCox/Silk-PVDF bimetallic catalyst electrode was prepared for the hydrogen evolution reaction (HER) in hydropower. This cheap, durable, and efficient electrode has good practical application prospects. Green natural silk, which will pollute the environment. The electrodes (obtained by varying the Ni:Co ratio and hydrothermal times) were prepared hydrothermally. Ni and Co elements were revealed by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Ni2Co2/silk-PVDF was identified as an effective catalyst in 1 M KOH alkaline electrolyte with an overpotential of 89.4 mV at 20 mA cm−2 and a Tafel slope of 47.46 mv dec−1. It showed low resistance and a high specific surface area in EIS and CV tests, respectively, proving its superior HER performance. Finally, the stability and durability of the electrode coated with PVDF were demonstrated via testing at a voltage of −0.1 V over 24 h. This work provides an environmentally friendly and simple method to load metal on a self-supporting electrode to be used in the hydrogen evolution reaction.

Ambient-conditions spinning of functional soft fibers via engineering molecular chain networks and phase separation

Producing functional soft fibers via existing spinning methods is environmentally and economically costly due to the complexity of spinning equipment, involvement of copious solvents, intensive consumption of energy, and multi-step pre-/post-spinning treatments. We report a nonsolvent vapor-induced phase separation spinning approach under ambient conditions, which resembles the native spider silk fibrillation. It is enabled by the optimal rheological properties of dopes via engineering silver-coordinated molecular chain interactions and autonomous phase transition due to the nonsolvent vapor-induced phase separation effect. Fiber fibrillation under ambient conditions using a polyacrylonitrile-silver ion dope is demonstrated, along with detailed elucidations on tuning dope spinnability through rheological analysis. The obtained fibers are mechanically soft, stretchable, and electrically conductive, benefiting from elastic molecular chain networks via silver-based coordination complexes and in-situ reduced silver nanoparticles. Particularly, these fibers can be configured as wearable electronics for self-sensing and self-powering applications. Our ambient-conditions spinning approach provides a platform to create functional soft fibers with unified mechanical and electrical properties at a two-to-three order of magnitude less energy cost under ambient conditions.

The Export Pattern of Commercial Crops and Related Products of India: A Comparative Study

India has completed two and a half decades of economic reforms. There are studies related to the impact of reforms on India’s export. Most of the studies have analyzed India’s foreign trade as a whole and in terms of value in specific. The present study is an attempt to evaluate the impact of reforms on India’s commercial crops and related products in India, in terms of quantity and value. The impact has been measured through decadal value, Compound Growth Rate (CGR), Instability Index (II) and Dummy Semi-Logarithmic Regression Estimation. It has been observed that reforms accelerated the export performance of all commercial crops during the reform period comparable to the pre-reform and overall study periods. During the reform period, some of the commercial crops viz. Natural rubber (12.50), silk (8.76), jute (10.84) and tobacco unmanufactured (6.50) have moved to positive growth rate from a negative growth rate during the pre-reform period and three products were moved from low CGR to high CGR viz. Cotton lint (20.92), rubber natural dry (38.40) and textile fibers (20.32) during the reform period. The Instability Index for all the commercial crops has decreased during the reform period, compared to the pre-reform period, except rubber natural dry (3.89) but compared to the overall period the Instability Index has registered a high value during the reform period. The jute and silk have moved to a low Instability Index group during the reform period from the medium Instability Index during the pre-reform period. The rubber natural has moved to a medium Instability Index during the reform period from a low Instability Index group during the pre-reform period. The estimation of the semi-log regression model has confirmed that there has been a positive significant change in the export of commercial crop items during the reform period.

Quartz-Enhanced Photoacoustic Spectroscopy-Conductance Spectroscopy for Gas Mixture Analysis.

A novel spectroscopic method, named quartz-enhanced photoacoustic spectroscopy-conductance spectroscopy (QEPAS-CS), was first developed for gas mixture analysis. In QEPAS-CS, the advantage of photoacoustic detection and conductance analysis was realized by a quartz tuning fork (QTF). Two-component gas analysis was done by photoacoustic detection and conductance detection. For an explicit application, natural spider silk was used as a water vapor transducer to modify the QTF, making a conductance sensing channel. A 2004 nm laser diode was used as an excitation source for a photoacoustic sensing channel. Such a QEPAS-CS sensor was used for H2O/CO2 gas mixture analysis in a cell incubator. This provides a solution to calibrate an infrared photoacoustic spectroscopy gas sensor. This example effectively confirms the capacity of multigas analysis by the QEPAS-CS sensor.

Flow-Induced Protein Chain Deformation, Segmental Orientation, and Phase Separation in Native Silk Feedstock.

The ability of many arthropods to spin silk and its many uses bear testament to its importance in Nature. Despite over a century of research, however, the spinning process is still not fully understood. While it is widely accepted that flow and chain alignment may be involved, the link to protein gelation remains obscure. Using combinations of rheology, polarized light imaging, and infrared spectroscopy to probe different length scales, this work explored flow-induced gelation of native silk feedstock from Bombyx mori larvae. Protein chain deformation, orientation, and microphase separation were observed, culminating in the formation of antiparallel β-sheet structures while the work rate during flow appeared as an important criterion. Moreover, infrared spectroscopy provided direct observations suggesting a loss of protein hydration during flow-induced gelation of fibroin in native silk feedstock, which is consistent with recently reported hypotheses.