Effect of metallic ions on silk formation in the Mulberry silkworm, Bombyx mori

Microstructured silk fiber scaffolds with enhanced stretchability

Despite extensive research, current methods for creating three-dimensional (3D) silk fibroin (SF) scaffolds lack control over molecular rearrangement, particularly in the formation of β-sheet nanocrystals that severely embrittle SF, as well as hierarchical fiber organization at both micro- and macroscale. Here, we introduce a fabrication process based on electrowriting of aqueous SF solutions followed by post-processing using an aqueous solution of sodium dihydrogen phosphate (NaH2PO4). This approach enables gelation of SF chains via controlled β-sheet formation and partial conservation of compliant random coil structures. Moreover, this process allows for precise architecture control in microfiber scaffolds, enabling the creation of 3D flat and tubular macro-geometries with square-based and crosshatch microarchitectures, featuring inter-fiber distances of 400 μm and ∼97% open porosity. Remarkably, the crosslinked printed structures demonstrated a balanced coexistence of β-sheet and random coil conformations, which is uncommon for organic solvent-based crosslinking methods. This synergy of printing and post-processing yielded stable scaffolds with high compliance (modulus = 0.5-15 MPa) and the ability to support elastic cyclic loading up to 20% deformation. Furthermore, the printed constructs supported in vitro adherence and growth of human renal epithelial and endothelial cells with viability above 95%. These cells formed homogeneous monolayers that aligned with the fiber direction and deposited type-IV collagen as a specific marker of healthy extracellular matrix, indicating that both cell types attach, proliferate, and organize their own microenvironment within the SF scaffolds. These findings represent a significant development in fabricating organized stable SF scaffolds with unique microfiber structures and mechanical and biological properties that make them highly promising for tissue engineering applications.

Metal ions guide the production of silkworm silk fibers

Silk fibers' unique mechanical properties have made them desirable materials, yet their formation mechanism remains poorly understood. While ions are known to support silk fiber production, their exact role has thus far eluded discovery. Here, we use cryo-electron microscopy coupled with elemental analysis to elucidate the changes in the composition and spatial localization of metal ions during silk evolution inside the silk gland. During the initial protein secretion and storage stages, ions are homogeneously dispersed in the silk gland. Once the fibers are spun, the ions delocalize from the fibroin core to the sericin-coating layer, a process accompanied by protein chain alignment and increased feedstock viscosity. This change makes the protein more shear-sensitive and initiates the liquid-to-solid transition. Selective metal ion doping modifies silk fibers' mechanical performance. These findings enhance our understanding of the silk fiber formation mechanism, laying the foundations for developing new concepts in biomaterial design.

The architecture of silk-secreting organs during the final larval stage of silkworms revealed by single-nucleus and spatial transcriptomics

Natural silks are renewable proteins with impressive mechanical properties and biocompatibility that are useful in various fields. However, the cellular and spatial organization of silk-secreting organs remains unclear. Here, we combined single-nucleus and spatially resolved transcriptomics to systematically map the cellular and spatial composition of the silk glands (SGs) of mulberry silkworms late in larval development. This approach allowed us to profile SG cell types and cell state dynamics and identify regulatory networks and cell-cell communication related to efficient silk protein synthesis; key markers were validated via transgenic approaches. Notably, we demonstrated the indispensable role of the ecdysone receptor (ultraspiracle) in regulating endoreplication in SG cells. Our atlas presents the results of spatiotemporal analysis of silk-secreting organ architecture late in larval development; this atlas provides a valuable reference for elucidating the mechanism of efficient silk protein synthesis and developing sustainable products made from natural silk.

Overview and Evolution of Insect Fibroin Heavy Chain (FibH)

The FibH gene, crucial for silk spinning in insects, encodes a protein that significantly influences silk fiber mechanics. Due to its large size and repetitive sequences, limited known sequences of insect FibH impede comprehensive understanding. Here, we analyzed 114 complete FibH gene sequences from Lepidoptera (71 moths, 24 butterflies) and 13 Trichoptera, revealing single-copy FibH in most species, with 2-3 copies in Hesperinae and Heteropterinae (subfamily of skippers). All FibH genes are structured with two exons and one intron (39-45 bp), with the second exon being notably longer. Moths exhibit higher GC content in FibH compared to butterflies and Trichoptera. The FibH composition varies among species, with moths and butterflies favoring Ala, Gly, Ser, Pro, Gln, and Asn, while Trichoptera FibH is enriched in Gly, Ser, and Arg, and has less Ala. Unique to Trichoptera FibH are Tyr, Val, Arg, and Trp, whereas Lepidoptera FibH is marked by polyAla (polyalanine), polySer (polyserine), and the hexapeptide GAGSGA. A phylogenetic analysis suggests that Lepidoptera FibH evolved from Trichoptera, with skipper FibH evolving from Papilionoidea. This study substantially expands the FibH repertoire, providing a foundation for the development of artificial silk.

Engineering a High-Strength and Superior-Electrolyte-Wettability Silk Fibroin-Based Gel Interface Achieving Dendrite-Free Zn Anode

Zn metal anode is confronted with notorious Zn dendrite growth caused by inhomogeneous Zn2+ deposition, rampant dendrite growth, and serious interface side reactions, which significantly hinder their large-scale implication. Interface modification engineering is a powerful strategy to improve the Zn metal anode by regulating Zn2+ deposition behavior, suppressing dendrite formation, and protecting the anode from electrolyte corrosion. Herein, we have designed a high-strength and superior-electrolyte-wettability composite gel protective layer based on silk fibroin (SF) and ionic liquids (ILs) on the Zn anode surface by a straightforward spin-coating strategy. The Zn ion transport kinetics and mechanical properties were further improved by following the incubation process to construct a more well-ordered β-sheet structure. Consequently, the incubated composite gel coating serves as a command station, guiding the Zn ion's preferential growth along the (002) plane, resulting in a smooth and uniform deposition morphology. Driven by these improvements, the zinc anode modified with this composite gel exhibits a remarkably long-term cycling lifespan up to 2200 h at 2 mA cm-2, while also displaying superior rate capability. This study represents a landmark achievement in the realm of electrochemical science, delineating a clear pathway toward the realization of a highly reversible and enduring Zn anode.

Harvesting Silk Fibers from Plodia interpunctella: Role of Environmental Rearing Conditions in Fiber Production and Properties

Silk fibers are produced by a wide variety of insects. The silkworm Bombyx mori (Bombyx) was domesticated because the physical properties of its silk fibers were amenable to the production of fine textiles. Subsequently, engineers have regenerated silk fibroin to form biomaterials. The monocular focus on Bombyx silk has underutilized the expanse of diverse silk proteins produced by more than 100,000 other arthropods. This vast array of silk fibers could be utilized for biomedical engineering challenges if sufficient rearing and purification processes are developed. Herein, we show that the moth, Plodia interpunctella (Plodia), represents an alternative silk source that is easily reared in highly regulated culture environments allowing for greater consistency in the silk produced. We controlled the temperature, resource availability (larvae/gram diet), and population density (larvae/mL) with the goal of increasing silk fiber production and improving homogeneity in Plodia silk proteins. We determined that higher temperatures accelerated insect growth and reduced life cycle length. Furthermore, we established initial protocols for the production of Plodia silk with optimal silk production occurring at 24 °C, with a resource availability of 10 larvae/gram and a population density of 0.72 larvae/mL. Population density was shown to be the most prominent driving force of Plodia silk mat formation among the three parameters assessed. Future work will need to link gene expression, protein production and purification, and resulting mechanical properties as a function of environmental cues to further transition Plodia silk into regenerated silk fibroin biomaterials.

A review on complete silk gene sequencing and de novo assembly of artificial silk

Silk, especially spider and insect silk, is a highly versatile biomaterial with potential applications in biomedicine, materials science, and biomimetic engineering. The primary structure of silk proteins is the basis for the mechanical properties of silk fibers. Biotechnologies such as single-molecule sequencing have facilitated an increasing number of reports on new silk genes and assembled silk proteins. Therefore, this review aims to provide a comprehensive overview of the recent advances in representative spider and insect silk proteins, focusing on identification methods, sequence characteristics, and de novo design and assembly. The review discusses three identification methods for silk genes: polymerase chain reaction (PCR)-based sequencing, PCR-free cloning and sequencing, and whole-genome sequencing. Moreover, it reveals the main spider and insect silk proteins and their sequences. Subsequent de novo assembly of artificial silk is covered and future research directions in the field of silk proteins, including new silk genes, customizable artificial silk, and the expansion of silk production and applications are discussed. This review provides a basis for the genetic aspects of silk production and the potential applications of artificial silk in material science and biomedical engineering.

DRGD-linked charged EKKE dimeric dodecapeptide: pH-based amyloid nanostructures and their application in lead and uranium binding

Peptides have been reported to undergo self-assembly into diverse nanostructures, influenced by several parameters, including their amino acid sequence, pH, charge, solvent, and temperature. Inspired by natural systems, researchers have developed biomimetic peptides capable of self-assembling into supramolecular functional structures. The present study explored a newly designed peptide sequence, EKKEDRGDEKKE, where E = glutamic acid, K = lysine, D = aspartic acid, G = glycine, and R = arginine, with a metal binding DRGD sequence incorporated between the exclusively charged EKKE peptide. We investigated the formation and the potential of the EKKEDRGDEKKE peptide in retaining the structure and morphology adopted by the individual EKKE peptide. According to a combination of experimental techniques such as thioflavin T fluorescence, field emission-scanning electron microscopy, atomic force microscopy, and circular dichroism, it was evident that the EKKEDRGDEKKE peptide displayed a pH-dependent propensity to adopt amyloid-like structures. Furthermore, the self-assembled entities formed under acidic, basic, and neutral conditions exhibited morphological variations, which resembled that observed for the exclusively charged EKKE peptide. Furthermore, the incorporation of the functional DRGD motif resulted in promising binding to two toxic metal ions, lead (Pb) and uranium (U), as evidenced by a range of spectroscopic techniques, including UV-visible spectroscopy, atomic absorption spectroscopy, fluorescence spectroscopy, and X-ray photoelectron spectroscopy. The use of the amyloid-forming EKKEDRGDEKKE scaffold can also be extended to potential biomedical applications.

The ratio of fibroin to sericin in the middle silk gland of Bombyx mori and its correlation with the extensional behavior of the silk dope

Understanding how native silk spinning occurs is crucial for designing artificial spinning systems. One often overlooked factor in Bombyx mori is the secretion of sericin proteins. Herein, we investigate the variation in amino acid content at different locations in the middle silk gland (MSG) of B. mori. This variation corresponds to an increase in sericin content when moving towards the anterior region of the MSG, while the posterior region predominantly contains fibroin. We estimate the mass ratio of sericin to fibroin to be ~25/75 wt% in the anterior MSG, depending on the fitting method. Then, we demonstrate that the improvement in the extensional behavior of the silk dope in the MSG correlates with the increase in sericin content. The addition of sericin may decrease the viscosity of the silk dope, a factor associated with an increase in the spinnability of silk. We further discuss whether this effect could also result from other known physicochemical changes within the MSG.

The silk gland proteome of Stenopsyche angustata provides insights into the underwater silk secretion

Caddisworms (Trichoptera) spin adhesive silks to construct a variety of underwater composite structures. Many studies have focused on the fibroin heavy chain of caddisworm silk and found that it contains heavy phosphorylation to maintain a stable secondary structure. Besides fibroins, recent studies have also identified some new silk proteins within caddisworm silk. To better understand the silk composition and its secretion process, this study reports the silk gland proteome of a retreat-building caddisworm, Stenopsyche angustata Martynov (Trichoptera, Stenopsychidae). Using liquid chromatography tandem mass spectrometry (LC-MS/MS), 2389 proteins were identified in the silk gland of S. angustata, among which 192 were predicted as secreted silk proteins. Twenty-nine proteins were found to be enriched in the front silk gland, whereas 109 proteins were enriched in the caudal silk gland. The fibroin heavy chain and nine uncharacterized silk proteins were identified as phosphorylated proteins. By analysing the sequence of the fibroin heavy chain, we found that it contains 13 Gly/Thr/Pro-rich regions, 12 Val/Ser/Arg-rich regions and a Gly/Arg/Thr-rich region. Three uncharacterized proteins were identified as sericin-like proteins due to their larger molecular weights, signal peptides and repetitive motifs rich in serine. This study provides valuable information for further clarifying the secretion and adhesion of underwater caddisworm silk.

Real-Time Monitoring of the Structural Transition of Bombyx mori Liquid Silk under Pressure by Solid-State NMR

Silk fibroin is stored in the silk glands of Bombyx mori silkworms as a condensed aqueous solution called liquid silk. It is converted into silk fibers at the silkworm's spinnerets under mechanical forces including shear stress and pressure. However, the detailed mechanism of the structural transition of liquid silk to silk fibers under pressure is not well understood. Magic angle spinning (MAS) in solid-state nuclear magnetic resonance (NMR) can exert pressure on liquid samples in a quantitative manner. In this study, solid-state NMR was used to quantitatively analyze the impact of pressure on the structural transition of liquid silk. A combination of 13C DD-MAS and CP-MAS NMR measurements enabled the conformation and dynamics of the crystalline region of the silk fibroin (both before (Silk Ip) and after (Silk IIp) the structural transition) to be detected in real time with atomic resolution. Spectral analyses proposed that the pressure-induced structural transition from Silk Ip to Silk IIp proceeds by a two-step autocatalytic reaction mechanism. The first reaction step is a nucleation step in which Silk Ip transforms to single lamellar Silk IIp, and the second is a growth step in which the single lamellar Silk IIp acts as a catalyst that reacts with Silk Ip molecules to further form Silk IIp molecules, resulting in stacked lamellar Silk IIp. Furthermore, the rate constant in the second step shows a significant pressure dependence, with an increase in pressure accelerating the formation of large stacked lamellar Silk IIp.

A brief review on the mechanisms and approaches of silk spinning-inspired biofabrication

Silk spinning, observed in spiders and insects, exhibits a remarkable biological source of inspiration for advanced polymer fabrications. Because of the systems design, silk spinning represents a holistic and circular approach to sustainable polymer fabrication, characterized by renewable resources, ambient and aqueous processing conditions, and fully recyclable "wastes." Also, silk spinning results in structures that are characterized by the combination of monolithic proteinaceous composition and mechanical strength, as well as demonstrate tunable degradation profiles and minimal immunogenicity, thus making it a viable alternative to most synthetic polymers for the development of advanced biomedical devices. However, the fundamental mechanisms of silk spinning remain incompletely understood, thus impeding the efforts to harness the advantageous properties of silk spinning. Here, we present a concise and timely review of several essential features of silk spinning, including the molecular designs of silk proteins and the solvent cues along the spinning apparatus. The solvent cues, including salt ions, pH, and water content, are suggested to direct the hierarchical assembly of silk proteins and thus play a central role in silk spinning. We also discuss several hypotheses on the roles of solvent cues to provide a relatively comprehensive analysis and to identify the current knowledge gap. We then review the state-of-the-art bioinspired fabrications with silk proteins, including fiber spinning and additive approaches/three-dimensional (3D) printing. An emphasis throughout the article is placed on the universal characteristics of silk spinning developed through millions of years of individual evolution pathways in spiders and silkworms. This review serves as a stepping stone for future research endeavors, facilitating the in vitro recapitulation of silk spinning and advancing the field of bioinspired polymer fabrication.

Silk fibroin scaffolds with stable silk I crystal and tunable properties

It is crucial to develop a three-dimensional scaffold with tunable physical properties for the biomedical application of silk fibroin (SF). The crystallization of polymers dictates their bulk properties. The presence of two unique crystal types, silk I and silk II, provides a mechanism for controlling the properties of SF biomaterials. However, it remains challenging to manipulate silk I crystallization. In this study, we demonstrate the stability and tunability of SF scaffolds with silk I structure prepared by a freezing-annealing processing. The porous structure and mechanical properties of the scaffolds can be readily regulated by SF concentration. XRD results show that the typical peaks representing silk I do not shift when subjected to various post-treatments, such as ethanol soaking, heating, water vapor annealing, UV irradiation, and high-temperature/high-pressure, indicating the stability of silk I crystal type. Moreover, the crystallization kinetics can be regulated by changing annealing time. This physical process can regulate the transition from non-crystalline to silk I, in turn controlling the mechanical properties and degradation rate of the SF scaffolds. Our result show that this green, all-aqueous strategy provides new directions for the design of SF-based biomaterials with controllable properties.

Self-Assembled Protein Nanofilm Regulating Uniform Zn Nucleation and Deposition Enabling Long-Life Zn Anodes

Rechargeable zinc-ion batteries (RZIBs) have gained promising attention as a feasible alternative for large-scale energy storage by the virtue of their intrinsic security, environmental benignity, low cost, and high volumetric capacity (5849 mAh cm-3 ). Nevertheless, the deep-rooted issues of dendrite formation and side reactions in unstable Zn metal anode have impeded RZIBs from being dependably deployed in their proposed applications. Herein, silk fibroin (SF) and lysozyme (ly), as natural biomacromolecules with abundant polar groups arranged in polypeptide backbones, are in situ self-assembled on the Zn anode surface to construct a homogeneous and compact protein nanofilm. Such protein nanofilm protecting layer presents a negative charge surface and significantly regulates Zn2+ deposition behavior. Meanwhile, synergistic flexible and robust features of protein nanofilm function as artificial solid electrolyte interface (SEI), accommodates the dynamic volume deformation during deposition/dissolution, and blocks corrosion of side reactions. Consequently, the electrochemical stability of protein nanofilm-modified Zn anode is greatly improved, with an excellent extended lifespan of over 1100 h at a high current density of 10 mA cm-2 and a high cycling capacity of 10 mAh cm-2 , corresponding to a high depth of discharge (83% DODZn ). Furthermore, the highly reversible Zn electrode remarkably improved the overall performance of MnO2 ||Zn full-cells.

The Fractal Network Structure of Silk Fibroin Molecules and Its Effect on Spinning of Silkworm Silk

Animal silk is usually considered to exist as a solid fiber with a highly ordered structure, formed by the hierarchical assembly starting from a single silk fibroin (SF) chain. However, this study showed that silk protein molecules existed in the form of a fractal network structure in aqueous solution, rather than as a single chain. This type of network was relatively rigid with low fractal dimension. Finite element analysis revealed that this network structure significantly helped in the stable storage of SF prior to the spinning process and in the rapid formation of a β-sheeted nanocrystalline and nematic texture during spinning. Further, the strong but brittle mechanical properties of Bombyx mori silk could also be well-explained through the fractal network model of silk fibroin. The strength was mainly derived from the dual network structure, consisting of nodes and β-sheet cross-links, whereas the brittleness could be attributed to the rigidity of the SF chains between these nodes and cross-links. In summary, this study presents insights from network topology for understanding the spinning process of natural silk and the structure-property relationship in silk materials.

Dynamic Changes and Characterization of the Metal Ions in the Silk Glands and Silk Fibers of Silkworm

Metal ions are involved in the conformational transition of silk fibroin and influence the structure and mechanical properties of silk fibers. However, the dynamic characteristics of metal ions during the formation of silk fibers remain unclear. In this study, we found that the silk glands of silkworms contain various metal elements, with varying levels of the metal elements in different zones of the glands and higher levels in the anterior silk glands. Additionally, the content of various metallic elements in the silk glands varied greatly before and after spinning, similar to their content in different cocoon layers, thus, indicating that the anterior silk glands maintain a certain metal ion environment for the transport and conformational transformation of the silk proteins. Most of the metallic elements located in fibroin were confirmed using degumming experiments. For the first time, a scanning electron microscope energy spectrometry system was used to characterize the metal elements in the cross-section of silk and cocoons. These findings have deepened our understanding of the relationship between the overall metal ion environment and silk fiber formation and help us further conceptualize the utilization of metal ions as targets to improve the mechanical properties of the silk fibers.

Biological Materials Processing: Time-Tested Tricks for Sustainable Fiber Fabrication

There is an urgent need to improve the sustainability of the materials we produce and use. Here, we explore what humans can learn from nature about how to sustainably fabricate polymeric fibers with excellent material properties by reviewing the physical and chemical aspects of materials processing distilled from diverse model systems, including spider silk, mussel byssus, velvet worm slime, hagfish slime, and mistletoe viscin. We identify common and divergent strategies, highlighting the potential for bioinspired design and technology transfer. Despite the diversity of the biopolymeric fibers surveyed, we identify several common strategies across multiple systems, including: (1) use of stimuli-responsive biomolecular building blocks, (2) use of concentrated fluid precursor phases (e.g., coacervates and liquid crystals) stored under controlled chemical conditions, and (3) use of chemical (pH, salt concentration, redox chemistry) and physical (mechanical shear, extensional flow) stimuli to trigger the transition from fluid precursor to solid material. Importantly, because these materials largely form and function outside of the body of the organisms, these principles can more easily be transferred for bioinspired design in synthetic systems. We end the review by discussing ongoing efforts and challenges to mimic biological model systems, with a particular focus on artificial spider silks and mussel-inspired materials.

Silk Nanofibril-Palygorskite Composite Membranes for Efficient Removal of Anionic Dyes

To develop membrane materials with good performance for water purification that are green and low cost, this work reports an organic-inorganic composite membrane composed of silk nanofibrils (SNFs) and palygorskite (PGS). To improve the stability of the the composite membrane, genipin was used as a crosslinking agent to induce the conformational transition of SNF chains from random coils to β-sheets, reducing the swelling and hydrolysis of the membrane. The separation performance can be adjusted by tailoring the component ratio of the nanomaterial. The results showed that these membranes can effectively remove anionic dyes from water, and they exhibit excellent water permeability. The SNF-based membrane had strong mechanical and separation properties, and the PGS could tune the structure of composite membranes to enhance their permeability, so this green composite membrane has good prospects in water treatment and purification applications.

Bioengineered and functionalized silk proteins accelerate wound healing in rat and human dermal fibroblasts

Wound healing is an intrinsic process directed towards the restoration of damaged or lost tissue. The development of a dressing material having the ability to control the multiple aspects of the wound environment would be an ideal strategy to improve wound healing. Though natural silk proteins, fibroin, and sericin have demonstrated tissue regenerative properties, the efficacy of bioengineered silk proteins on wound healing is seldom assessed. Furthermore, silk proteins sans contaminants, having low molecular masses, and combining with other bioactive factors can hasten the wound healing process. Herein, recombinant silk proteins, fibroin and sericin, and their fusions with cecropin B were evaluated for their wound-healing effects using in vivo rat model. The recombinant silk proteins demonstrated accelerated wound closure in comparison to untreated wounds and treatment with Povidone. Among all groups, the treatment with recombinant sericin-cecropin B (RSC) showed significantly faster healing, greater than 90% wound closure by Day 12 followed by recombinant fibroin-cecropin B (RFC) (88.86%). Furthermore, histological analysis and estimation of hydroxyproline showed complete epithelialization, neovascularization, and collagenisation in groups treated with recombinant silk proteins. The wound healing activity was further verified by in vitro scratch assay using HADF cells, where the recombinant silk proteins induced cell proliferation and cell migration to the wound area. Additionally, wound healing-related gene expression showed recombinant silk proteins stimulated the upregulation of EGF and VEGF and regulated the expression of TGF-β1 and TGF-β3. Our results demonstrated the enhanced healing effects of the recombinant silk fusion proteins in facilitating complete tissue regeneration with scar-free healing. Therefore, the recombinant silks and their fusion proteins have great potential to be developed as smart bandages for wound healing.

Molecular Characterization of the Functional Genes Associated with Silk Assembly, Transport, and Protection in the Silk Glands of Popular Multivoltine Breeds of Silkworm Bombyx mori. L

Bombyx mori is an agriculturally important insect used extensively for silk production. India, especially the eastern regions, is mostly dependent on the multivoltine breeds of silkworm Bombyx mori and their hybrids/crossbreeds. The multivoltine breeds are indigenous and superior in survival and hardiness but are relatively inferior in terms of qualitative traits, typically the silk quality. Therefore, it is highly relevant to understand the mechanism of silk production in the multivoltine breeds to decipher the reasons for the inferior quality of silk produced by the multivoltine breeds and thus gain leads to improve the quality of silk production in multivoltine breeds. With this background, study was carried to identify differential expression of the major genes associated with silk proteins in the silk gland region of the popular multivoltine breeds. Our results indicated that although fib-L, fib-H, Sericins, and P25 are the major genes associated with silk filament, a few other genes associated with silk assembly, transport, and protection in the silk glands are the ones that largely contribute towards efficient silk production. The differential expression of these genes had a major effect on the movement of silk proteins within the silk gland and the efficiency of silk production as well. The Pearson correlation revealed a positive correlation amongst the genes dealt with in this study, indicating that the concurrent increase in expression of both the types of genes in the silk glands, significantly improves the silk production.

Silk Fibroin Coating Enables Dendrite-free Zinc Anode for Long-Life Aqueous Zinc-Ion Batteries

Due to the advantages of the low cost of Zn and the safety of aqueous electrolytes, the aqueous Zn ion battery (AZIB) is expected to become the next-generation battery after lithium-ion batteries. However, the problems of Zn anode dendrite growth, self-corrosion, and passivation in AZIBs lead to short cycle life and short circuit of the battery. In this work, uniform and stable Silk II-silk fibroin (Silk II-SF) coating was prepared on the surface of Zn anode by a simple method. Experiments showed that the SF coating could prevent dendritic growth and hydrogen evolution corrosion. Therefore, symmetric cells using Silk II-SF@Zn anode achieved a cycle life over 3300 and 1500 h at current densities of 10 and 20 mA cm^-2 , respectively. Using Silk II-SF coating to protect Zn anode is a simple and effective strategy to realize dendrite-free Zn anode and long-cycle-life AZIBs.

A single-cell transcriptomic atlas characterizes the silk-producing organ in the silkworm

The silk gland of the domesticated silkworm Bombyx mori, is a remarkable organ that produces vast amounts of silk with exceptional properties. Little is known about which silk gland cells execute silk protein synthesis and its precise spatiotemporal control. Here, we use single-cell RNA sequencing to build a comprehensive cell atlas of the silkworm silk gland, consisting of 14,972 high-quality cells representing 10 distinct cell types, in three early developmental stages. We annotate all 10 cell types and determine their distributions in each region of the silk gland. Additionally, we decode the developmental trajectory and gene expression status of silk gland cells. Finally, we discover marker genes involved in the regulation of silk gland development and silk protein synthesis. Altogether, this work reveals the heterogeneity of silkworm silk gland cells and their gene expression dynamics, affording a deeper understanding of silk-producing organs at the single-cell level.

Chitin and cuticle proteins form the cuticular layer in the spinning duct of silkworm

Chitin is found in the exoskeleton and peritrophic matrix of arthropods, but recent studies have also identified chitin in the spinning duct of silk-spinning arthropods. Here, we report the presence and function of chitin and cuticle proteins ASSCP1 and ASSCP2 in the spinning duct of silkworm. We show that chitin and these proteins are co-located in the cuticular layer of the spinning duct. Ultrastructural analysis indicates that the cuticular layer has a multilayer structure by layered stacking of the chitin laminae. After knocking down ASSCP1 and ASSCP2, the fine structure of this layer was disrupted, which had negative impacts on the mechanical properties of silk. This work clarifies the function of chitin in the spinning duct of silkworm. Chitin and cuticle proteins are the main components of the cuticular layer, providing the shearing stress during silk fibrillogenesis and regulating the final mechanical properties of silk. STATEMENT OF SIGNIFICANCE: Recent studies have identified chitin in the spinning duct of silk-spinning arthropods. However, the role of chitin in this specific organ remains unclear. This study reports that chitin and cuticle proteins form the cuticular layer, a unique structure of the spinning duct of silkworm. This layer with a precise laminate structure gives the spinning duct flexible properties, provides shearing forces for silk fibrillogenesis, and contributes to silk final mechanical properties. Our work clarifies the component, ultrastructure, and biological significance of the silkworm cuticular layer, describes the specific process of silk fiber formation, and proposes new molecular targets (chitin and cuticle proteins) for the improvement of animal silks.

Bioinspired engineering protein nanofibrils-based multilayered self-cleaning membranes for universal water purification

Proteinaceous materials are promising for membranes due to greater mechanical strength, in-built functionalities, amphiphilicity and high molecular loading capacity. Herein, a novel strategy of functionalization of silk nanofibrils with metal oxyhydroxide and fabrication of ultrafast permeable multi-layered and self-cleaning membrane was demonstrated. Typically, 1.9 µm thick multilayered membrane efficiently purifies macromolecules, dyes, pharmaceutical, surfactants and oil-water emulsion contaminated wastewater with rejection rate > 89% with the flux rate > 883 Lm²h^-1. Further, the potential of the multilayered membrane was tested for series of different feed concentrations of fluoride and As (V) to validate the commercial applicability of the multilayered membranes for industry wastewater. Notably, even at higher concentration of 10-30 mgL^-1, >96% for fluoride and >87% for As (V) rejection was obtained. Furthermore, the functionalized multilayered membrane exhibited outstanding performance for fluoride removal in real water streams, where, it purifies approximately 4710 L.m^-2 in two consecutive cycles, before the quality of the effluents no longer meets WHO criteria. However, the remarkable separation efficiency principally attributed to adsorption sites on the surface of the membrane. Thus, various regeneration strategies were established based on the nature of pollutants. More importantly, photocatalytic Fenton-like reaction assisted self-cleaning property of the multilayered membrane is demonstrated for regeneration of organic fouled membrane. Overall, the present multilayered membrane exhibits superior performance in purifying organic, inorganic contaminated water and oil-water emulsion with excellent recyclability; hence, envisaged its application for Universal water purification.

Boron, nitrogen co-doped biomass-derived carbon aerogel embedded nickel-cobalt-iron nanoparticles as a promising electrocatalyst for oxygen evolution reaction

The electrocatalytic performance of oxygen evolution reaction (OER) electrocatalysts is highly reliant on the activity of its catalytic active site, which may be augmented by raising the number of active sites. In this study, nanoscaled nickel-cobalt-iron (NiCoFe) alloy was embedded on conductive boron(B), nitrogen(N) co-doped/biomass-derived carbon aerogel as an OER electrocatalyst. The synthesized electrocatalysts were calcined under different temperatures and with variable dopants. The optimal electrocatalyst (BN/CA-NiCoFe-600) demonstrated a low overpotential of 321 mV (at current density of 10 mA cm^-2) and a minute Tafel slope of 42 mV dec^-1, which was even smaller than that of IrO₂ and RuO₂. Its mass activity and specific activity were calculated to be 201.7 A g^-1, and 34.1 cm^-2_ECSA, respectively. Furthermore, the electrocatalyst showed excellent stability and durability. This work provides an easy and practical synthetic strategy for acquiring very active and durable electrocatalysts for OER.

Study on the Effect of Stretching on the Strength of Natural Silk Based on Different Feeding Methods

Silk is an important biological protein fiber, which has been widely developed and used in textile and biomedical fields due to its excellent mechanical properties and good biocompatibility. Strength is an important indicator that determines the value and use of silk. Although investigations have been made on the mechanical properties of silkworm silks and their dependence relationship with the microstructures, the variation of silk strength formed in the process of silkworm spinning has not been reported. By feeding the same strain of silkworms with mulberry leaves, mulberry leaves + artificial feed, and artificial feed, silks with three filament sizes were obtained, respectively. The tensile test results showed that the strength and filament size of silk are inversely proportional. The structure and fibrosis process of different-strength silks were analyzed. The results showed that, compared with ordinary silk, the β-sheet and crystallinity content of high-strength silk is higher, indicating that its fibrosis process is more sufficient. We proposed that the stretched degree of silk protein determines its structure and properties. During the spinning process of individual silkworms, the secretion of silk protein is not stable, which will cause changes in the stretched degree. The measurement results of the intraindividual stretched degree and strength verified that the degree of stretch determines the strength of the silk. This study not only provides a deeper understanding of the properties of silk protein but also is of interest for the design and development of advanced biomimetic silk materials.

Fiber Formation and Mechanical Properties of Bombyx mori Silk Are Regulated by Vacuolar-Type ATPase

The mechanism of silk fiber formation in silkworms, Bombyx mori, is of particular scientific interest because it is closely related to the mechanical properties of silk fibers. However, there are still substantial knowledge gaps in understanding the details of this mechanism. Studies have found a pH gradient in the silk gland of silkworms. A vacuolar-type ATPase (V-ATPase) is thought to be involved in establishing this pH gradient. Although it is reported that the pH gradient plays a role in silk fibrillogenesis, the direct relationship between V-ATPase and silk mechanical properties is unclear. Thus, this study aims to clarify this relationship. We found that V-ATPase is highly and stably expressed in the anterior silk gland (ASG) and maintains the pH gradient and the fine structure of ASG. Inhibition of V-ATPase activity increased the β-sheet content and crystallinity of silk fibers. Tensile testing showed that the mechanical properties of silk fibers improved after inhibiting V-ATPase activity. All the data suggest that V-ATPase is a key factor in regulating silk fibrillogenesis and is related to the final mechanical properties of the silk fibers. V-ATPase is a potential target for silk mechanical property improvement.

Emerging Silk Material Trends: Repurposing, Phase Separation and Solution-Based Designs

Silk continues to amaze. This review unravels the most recent progress in silk science, spanning from fundamental insights to medical silks. Key advances in silk flow are examined, with specific reference to the role of metal ions in switching silk from a storage to a spinning state. Orthogonal thermoplastic silk molding is described, as is the transfer of silk flow principles for the triggering of flow-induced crystallization in other non-silk polymers. Other exciting new developments include silk-inspired liquid-liquid phase separation for non-canonical fiber formation and the creation of "silk organelles" in live cells. This review closes by examining the role of silk fabrics in fashioning facemasks in response to the SARS-CoV-2 pandemic.

Efficient Regulation of the Behaviors of Silk Fibroin Hydrogel via Enzyme-Catalyzed Coupling of Hyaluronic Acid

Pure silk fibroin (SF) hydrogel exhibits poor elasticity and low water retention ability, owing to the compact crystalline structure and high content of hydrophobic amino acids. Herein, a composite double-network hydrogel of SF and tyramine-modified hyaluronic acid (mHA) was constructed, via the laccase-catalyzed coupling reactions between the phenolic hydroxyl groups from SF and mHA chains. The obtained hydrogel exhibits improved structural stability and flexibility compared to pure SF hydrogel. Meanwhile, the swelling ratio, mechanical property, drug loading, and release behaviors can be readily regulated by alcoholization, altering pH value, and ionic strength of soaking solutions. Increasing pH values promoted the swelling capacity of SF/mHA hydrogel, resulting in an efficient loading of cationic drugs and sustained release of anionic drugs as well. The addition of inorganic salts reduced electrostatic repulsion in the hydrogel scaffold, accompanying with a noticeable improvement of toughness. Furthermore, alcohol treatment induced conformation changes of fibroin protein, and the composite hydrogel achieved a higher fracture and improved elasticity. The present work provides a biological alternative to regulate the mechanical behavior, drug loading, and sustained release capacity of the SF-based hydrogel.

Enhanced antioxidant properties of sericin-cecropin fusion protein against oxidative stress in human adult dermal fibroblasts

Chronic exposure to UVB radiation causes photoaging, immunosuppression, and ultimately photocarcinogenisis through the generation of reactive oxygen species (ROS). The ability of natural compounds in neutralizing the effects of oxidative stress is being explored with increased interest. Silk sericin, a biopolymer is reported to have diverse biological properties. In an effort to make the silk sericin pure, more effective and multifunctional, we have recombinantly expressed both functional sericin as well as sericin-cecropin B fusion proteins. Herein, we studied the antioxidant and anti-UVB potential of recombinant sericin and sericin-cecropin B proteins against oxidative stress using human primary dermal fibroblast cells. Treating the cells with recombinant sericin (RS) or sericin-cecropin B (RSC) prior to exposure to UVB and H2O2, effectively increased the cell viability by approximately 30% and 50%, respectively, in comparison to non-treated control. The protective effects were further evident in terms of significant reduction of LDH in oxidatively challenged cells treated with RS and RSC. A reduction in LDH release of at least 16 and 33% was observed with RS and RSC treatments, respectively, in comparison to exposed control. Further, elevated levels of catalase and superoxide dismutase (SOD) activity were observed. Importantly, the RSC fusion protein exhibited enhanced protective effects than cells treated with RS alone. Our results demonstrate that the functional attributes of cecropin B along with sericin activity in the fusion protein conferred enhanced protection against UVB- and H2O2-induced oxidative damage in human dermal fibroblasts. The improved antioxidant activity of recombinant sericin fusion biopolymer has great potential as a promising therapeutic agent for ROS-induced skin diseases.

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.

Programing Performance of Silk Fibroin Superstrong Scaffolds by Mesoscopic Regulation among Hierarchical Structures

To design higher-strength natural scaffold materials, wool keratin (WK) rich in α-helix structures is used as a well-defined foreign substrate, which induces the formation of β-crystallites in silk fibroin (SF). Consequently, the macroscopic properties of silk materials (such as the rheological properties of SF hydrogels and the mechanical properties of stents) can be manipulated by governing the change in the hierarchical mesoscopic structure of silk materials. In this work, by monitoring the structure and morphology in the SF gel process, the mechanism of the effect of keratin on SF network formation was speculated, which was further used to design ultra-high-strength protein scaffolds. It has been confirmed that WK accelerates the gelation of SF by reducing the multistep nucleation barrier and increasing the primary nucleation sites, and then establishing a high-density SF domain network. The modulus of the protein composite scaffold prepared by this facile strategy can reach 11.55 MPa, and the MC-3T3 cells can grow well on the scaffold surface. The results suggest that freeze-dried biocompatible SF-based scaffolds are potential candidates for bone tissue engineering.

Composition and in silico structural analysis of fibroin from liquid silk of non-mulberry silkworm Antheraea assamensis

Silk is spun from the liquid precursor known as liquid silk secreted from the posterior part and stored in the silk gland lumen with occurrence of many momentary events. The liquid silk in the silk gland is transformed to the spun silk fibre. In this study the elucidation of the protein components of liquid silk from the posterior part of the silk gland (PSG) of saturniid silkworm Antheraea assamensis along with its structural characterization has been reported. The 3D model of the N-terminal amorphous portion with some repeat crystalline motifs (19-255) of core protein fibroin has also been constructed. 1D and 2D electrophoresis revealed the homo-dimeric structure of the silk protein. Secondary structure analysis by Circular dichroism, FTIR spectroscopy showed α helical structural component as predominant conformation in the liquid silk. The crystalline structure investigated through X ray diffraction (XRD) analysis also revealed the presence of less ordered amorphous α helical conformation in the liquid silk. The 3D structural model proposed of the residues from 19 to 255 has revealed structural stability throughout the molecular dynamics simulation process. This study will provide the detailed structural information and in silico analysis of the core protein present in the liquid silk of PSG.

From Silk Spinning to 3D Printing: Polymer Manufacturing using Directed Hierarchical Molecular Assembly

Silk spinning offers an evolution-based manufacturing strategy for industrial polymer manufacturing, yet remains largely inaccessible as the manufacturing mechanisms in biological and synthetic systems, especially at the molecular level, are fundamentally different. The appealing characteristics of silk spinning include the sustainable sourcing of the protein material, the all-aqueous processing into fibers, and the unique material properties of silks in various formats. Substantial progress has been made to mimic silk spinning in artificial manufacturing processes, despite the gap between natural and artificial systems. This report emphasizes the universal spinning conditions utilized by both spiders and silkworms to generate silk fibers in nature, as a scientific and technical framework for directing molecular assembly into high-performance structures. The preparation of regenerated silk feedstocks and mimicking native spinning conditions in artificial manufacturing are discussed, as is progress and challenges in fiber spinning and 3D printing of silk-composites. Silk spinning is a biomimetic model for advanced and sustainable artificial polymer manufacturing, offering benefits in biomedical applications for tissue scaffolds and implantable devices.

Silk degumming time controls horseradish peroxidase-catalyzed hydrogel properties

Hydrogels provide promising applications in tissue engineering and regenerative medicine, with silk fibroin (SF) offering biocompatibility, biodegradability and tunable mechanical properties. The molecular weight (MW) distribution of SF chains varies from ∼80 to 400 kDa depending on the extraction and purification process utilized to prepare the protein polymer. Here, we report a fundamental study on the effect of different silk degumming (extraction) time (DT) on biomaterial properties of enzymatically crosslinked hydrogels, including secondary structure, mechanical stiffness, in vitro degradation, swelling/contraction, optical transparency and cell behaviour. The results indicate that DT plays a crucial role in determining material properties of the hydrogel; decrease in DT increases β-sheet (crystal) formation and mechanical stiffness while decreasing degradation rate and optical transparency. The findings on the relationships between properties of silk hydrogels and DT should facilitate the more rational design of silk-based hydrogel biomaterials to match properties needed for diverse purpose in biomedical engineering.

Variations in the Metallic Ion Concentration in the Silk Gland and Cocoon of Silkworm Antheraea assamensis helfer

The natural spinning process in silkworms involves the conformation transition of the liquid silk protein present in the silk gland to make fiber. This conformation transition is influenced by different factors, and some studies suggested that changes in the metallic ion concentrations is one of them (Zhou et al. 2005). This study investigated the changes in the metallic ion compositions in the silk glands (before and during spinning) and cocoons of non-mulberry silkworm Antheraea assamensis helfer. Intact silk glands were dissected from mature 5th instar A. assamensis larvae. The glands were rinsed with deionized water and divided into five divisions: posterior silk gland (PSG), middle silk gland (MSG), anterior silk gland (ASG), posterior middle (PM) and anterior middle (AM) division of silk gland. Cocoon pieces and the gland parts were dried and digested in acid mixture to quantify the metallic contents in an atomic absorption spectrophotometer (Shimadzu, AA7000). We determined seven metals (Na, K, Mg, Ca, Cu, Zn, Fe) present in the different parts of the secretory pathway as well as in the fibers of A.assamensis. Our results suggested that the concentrations of Mg, Ca, Na, and K were more abundant in the gland than the Cu and Zn. Fe concentration was found comparatively less in amount in the gland. Amount of Ca found to be higher in the cocoons. The differences in the metallic ion concentrations in the gland parts before and during spinning suggested the possibility of their role in the formation of silk thread from luminal silk.

Cu(II) ion loading in silk fibroin scaffolds with silk I structure

Metal ions play important roles in the diverse biochemical reactions associated with many cell signalling pathways. The modification of biomaterials with metal ions may offer a promising approach to stimulate cellular activity for improving tissue regeneration. Here, copper ion loading as a potential therapeutic agent in silk fibroin (SF) scaffolds was investigated. Freezing-annealing was used to induce silk I crystallization for forming water-insoluble SF scaffolds. Cu(II) ions were entrapped into SF scaffolds with different ratios by forming silk I crystal networks when copper chloride dihydrate was less than 5.0 wt%, producing water-stable materials. Moreover, it was found that copper ion chelation further enhanced SF stability when a low amount copper chloride was loaded. Increasing copper chloride content weakened silk I crystallization and Cu(II) ion chelation, rendering SF scaffolds unstable in water. Above 5.0 wt% copper chloride dihydrate, silk I crystallization was prevented. Finally, silk I scaffold with 1.5 wt% copper chloride dihydrate showed the strongest water-stability and highest loading efficiency. The results provide valuable data for understanding the effect of metal ions in freezing-induced SF crystallization, and also offer options for preparing novel Cu(II)-functionalized SF scaffolds.

Enzymatically crosslinked silk and silk-gelatin hydrogels with tunable gelation kinetics, mechanical properties and bioactivity for cell culture and encapsulation

Silk fibroin (SF) was enzymatically crosslinked with tyramine-substituted silk fibroin (SF-TA) or gelatin (G-TA) to fabricate hybrid hydrogels with tunable gelation kinetics, mechanical properties and bioactivity. Horseradish peroxidase (HRP)/hydrogen peroxide (H2O2) mediated crosslinking of SF in physiological buffers results in slow gelation and limited mechanical properties. Moreover, SF lacks cell attachment sequences, leading to poor cell-material interactions. These shortcomings can limit the uses of enzymatically crosslinked silk hydrogels in injectable tissue fillings, 3D bioprinting or cell microencapsulation, where rapid gelation and high bioactivity are desired. Here SF/SF-TA and SF/G-TA composite hydrogels were characterized for hydrogel properties and the influence of conjugated cyclic arginine-glycine-aspartic acid (RGD) peptide or G-TA content on bioactivity was explored. Both SF-TA and G-TA significantly increased gelation kinetics, improved mechanical properties and delayed enzymatic degradation in a concentration-dependent manner. β-Sheet formation and hydrogel stiffening were accelerated by SF-TA content but delayed by G-TA. Both cyclic RGD and G-TA significantly improved morphology and metabolic activity of human mesenchymal stem cells (hMSCs) cultured on or encapsulated in composite hydrogels. The hydrogel formulations introduced in this study provide improved control of gel formation and properties, along with biocompatible systems that can be utilized in tissue engineering and cell delivery applications.

Top-Down Extraction of Silk Protein Nanofibers by Natural Deep Eutectic Solvents and Application in Dispersion of Multiwalled Carbon Nanotubes for Wearable Sensing

With typical nanofibrous structure, silks spun by silkworms and spiders are the representative fibrous proteins that embody excellent mechanical properties and biological functions. However, it is still a challenge to directly extract silk nanofibers (SNFs) from natural silk fibers, to retain their nanostructures and properties, by a human- and environment-friendly approach for practical applications. Here, an all-natural strategy for simple, green, and scalable extraction of silkworm and spider silk protein nanofibers in natural deep eutectic solvents has been developed. The liquid-exfoliated SNFs have adjustable diameters from 20 nm (at the single SNF scale) to 100 nm and could be dispersed in water and organic solvents, enabling the production of useful macroscopic biomaterials. The free-standing SNF membranes made from silkworm silk nanofibers (SSNFs) exhibited cytocompatibility, flexibility, and excellent mechanical performance, providing the ability to fabricate sustainable materials for tissue engineering and green electronics. Moreover, the SSNF could be used as a green and efficient dispersant of multiwalled carbon nanotubes (MWCNTs), and the SSNFs/MWCNTs nanocomposite membranes could be used in wearable devices to monitor human activities.

3D Printing of Silk Protein Structures by Aqueous Solvent-Directed Molecular Assembly

Hierarchical molecular assembly is a fundamental strategy for manufacturing protein structures in nature. However, to translate this natural strategy into advanced digital manufacturing like three-dimensional (3D) printing remains a technical challenge. This work presents a 3D printing technique with silk fibroin to address this challenge, by rationally designing an aqueous salt bath capable of directing the hierarchical assembly of the protein molecules. This technique, conducted under aqueous and ambient conditions, results in 3D proteinaceous architectures characterized by intrinsic biocompatibility/biodegradability and robust mechanical features. The versatility of this method is shown in a diversity of 3D shapes and a range of functional components integrated into the 3D prints. The manufacturing capability is exemplified by the single-step construction of perfusable microfluidic chips which eliminates the use of supporting or sacrificial materials. The 3D shaping capability of the protein material can benefit a multitude of biomedical devices, from drug delivery to surgical implants to tissue scaffolds. This work also provides insights into the recapitulation of solvent-directed hierarchical molecular assembly for artificial manufacturing.

Visible sensing of conformational transition in model silk peptides based on a gold nanoparticles indicator

To understand protein structural transition and β-sheet formation is of importance in disparate areas such as silk protein processing and disease related β-amyloid behavior. Herein, GAGSGAGAGSGAGY (GY-14), a tetradecapeptide based on the crystallizable sequence of silk fibroin, was employed as a model peptide of the crystalline regions of silk fibroin. Due to the incorporation of tyrosine (Y), GY-14 was able to reduce Au³⁺ to Au NPs and further stabilize them without any external reducing or capping reagents to produce GY-14 stabilized Au NPs (GY-14@Au NPs). The in situ prepared GY-14@Au NPs were utilized as a built-in colorimetric indicator. The influences of specified physiological factors including decreasing the pH, the addition of calcium ions and isopropanol treatment on the self-assembly behavior of GY-14@Au NPs in aqueous solution have been studied. On the basis of transmission electron microscopy (TEM), dynamic light scattering (DLS), atomic force microscopy (AFM), Fourier transform infrared (FT-IR) spectroscopy and circular dichroism (CD) measurements, the color changes and the UV-Vis absorption peak shift of GY-14@Au NPs were attributed to the conformational change of the GY-14 peptide. The colorimetric readout can be seen with the naked eye, providing an efficient indicator to study the conformational changes of peptides exposed to various environmental stimuli.

A pH-sensitive self-healing coating for biodegradable magnesium implants

Self-healing coatings have attracted attention on surface modification of magnesium alloys, as it can recover the barrier ability of the coatings from corrosion attack. Nevertheless, previous works on this aspect are not suitable for biomedical magnesium alloys owing to the lack of biocompatibility. In this study, we fabricated a self-healing coating on biomedical Mg-1Ca alloy by compositing silk fibroin and K₃PO₄. PO₄^3- ions act as corrosion inhibitor, while K³⁺ ions help to regulate the secondary structures of silk fibroin. The scratch test, scanning vibrating electrode technique (SVET), and electrochemical impedance spectroscopy (EIS) provide comprehensive results, confirming the pH-sensitive self-healing capacity of the composite coating. Moreover, cells' (MC3T3-E1) multiple responses including spreading, adhesion, proliferation, and differentiation illustrate the preferable biocompatibility as well as the osteogenic activity of the coating. These primary findings might open new opportunities in the exploration of self-healing coatings on biomedical magnesium alloys. STATEMENT OF SIGNIFICANCE: Biomedical magnesium alloys surface modifications have been studied for years, which however the biomedical self-healing coatings were rarely involved. In this work, silk fibroin and phosphate (K₃PO₄) were composited to fabricate coating on biomedical magnesium alloys. The coating not only owned the self-healing ability with pH sensitivity, but also endowed the substrate preferable corrosion resistance as well as osteogenic activity. This work gives a new insight into surface modification for biomedical Mg alloys.

Comparative analysis of proteins from Bombyx mori and Antheraea pernyi cocoons for the purpose of silk identification

Achieving efficient identification of silk protein requires highly sensitive analytical techniques and favorable extraction methods, which is of great significance to the research of ancient silk, especially for the controversial issue of the silk origin. In this paper, proteomics and western blot were proposed to analyze the silk proteins of Bombyx mori (B. mori) and Antheraea pernyi (A. pernyi) dissolved by different methods. First, the differences in secondary structure were detected via spectroscopy. LC-MS/MS was then employed to characterize the peptides of silk proteins precisely. LiBr solution exhibited outstanding dissolution effect on B. mori cocoon, with 87 proteins detected; while copper-ethylenediamine solution (CED) was more appropriate for A. pernyi cocoon, and 16 proteins were identified in A. pernyi-CED. In addition to fibroin and sericin, abundant seroins, enzymes, protease inhibitors, other functional proteins and uncharacterized proteins were detected. Based on the LC-MS/MS data, diagnostic antibodies for the two species were prepared, and fibroin was successfully identified by western blot assay because both dissolution methods were gentle and did not destroy the antigenic epitopes in the protein molecule. Owing to their good specificity and high sensitivity, these diagnostic antibodies have good application prospects in immunoassays of different silk species. SIGNIFICANCE: This study presents the comprehensive analysis on silk identification of proteins from B. mori and A. pernyi extracted by different methods via the proteomic and immunology as well as the conventional approaches. Great coverage of two cocoon proteomes was accomplished, which demonstrated the outstanding difference in components and abundance. Based on the proteomics analysis, the diagnostic antibodies against two species were prepared and identified the corresponding fibroin successfully in the completed protein mixtures. To our knowledge, the proteomic and immunology procedures with high efficiency, sensitivity and specificity are novel analysis on the silk identification and has great potential in the field of ancient silk detection.

Osteogenic and pH stimuli-responsive self-healing coating on biomedical Mg-1Ca alloy

Various coatings have been used to slow down the corrosion rate of biomedical magnesium alloys. However, these coatings usually act only as passive barriers. It is much more desirable to endow such coatings with active, biocorrosion-responsive self-repairing capacity. In the present work, a self-healing coating system (denoted as "silk-PA") was constructed in the form of a sandwich architecture of fluoride precoating (bottom), silk-phytic acid (PA) coating (middle), and silk fibroin coating (top). Here, PA was loaded in the middle coating as a corrosion inhibitor by harnessing its strong chelating ability toward dissolving Mg²⁺ and Ca²⁺ ions. The self-healing property was evaluated by scratch and SVET tests, and the corrosion resistance was evaluated by in vitro immersion and electrochemical measurements. The results showed that the silk-PA manifested intriguing self-healing capacity with pH responsiveness, hence profiting the corrosion resistance of the Mg-1Ca alloy. The biocompatibility and osteogenic activity of the coating system were further evaluated using MC3T3-E1 cells, and it demonstrated favorable responses in multiple cellular behaviors, i.e., adherence, spreading, proliferation, and differentiation. These findings open new opportunities in the study of self-healing coatings for protection against corrosion in biomedical Mg alloys. STATEMENT OF SIGNIFICANCE: In the present study, a self-healing coating system with pH stimuli-responsiveness and osteogenic activity was fabricated on Mg-1Ca alloy by integrating a silk fibroin barrier coating, a silk fibrin/phytic acid composite coating, and a fluoride precoating. This coating system demonstrated interesting self-healing ability as compared to traditional surface modification layers. Furthermore, the self-healing ability enhanced the corrosion resistance of biomedical magnesium alloys, while effective compositions of the coating system endowed the substrate with osteogenic activity. This work provides some new insights into smart surface modification for biomedical Mg alloys.

Disruption of the Metal Ion Environment by EDTA for Silk Formation Affects the Mechanical Properties of Silkworm Silk

Silk fiber has become a research focus because of its comprehensive mechanical properties. Metal ions can influence the conformational transition of silk fibroin. Current research is mainly focused on the role of a single ion, rather than the whole metal ion environment. Here, we report the effects of the overall metal ion environment on the secondary structure and mechanical properties of silk fibers after direct injection and feeding of silkworms with EDTA. The metal composition of the hemolymph, silk gland, and silk fiber changed significantly post EDTA treatment. Synchrotron FTIR analysis indicated that the secondary structure of silk fiber after EDTA treatment changed dramatically; particularly, the β-sheets decreased and the β-turns increased. Post EDTA treatment, the silk fiber had significantly decreased strength, Young’s modulus, and toughness as compared with the control groups, while the strain exhibited no obvious change. These changes can be attributed to the change in the metal ion environment in the silk fibroin and sericin in the silk gland. Our investigation provides a new theoretical basis for the natural silk spinning process, and our findings could help develop a method to modify the mechanical properties of silk fiber using metal ions.

Structure analysis of the spinneret from Bombyx mori and its influence on silk qualities

Silk is an excellent natural fiber, which has been widely used in versatile fields. Silk spinning is a complex process involving the larval spinneret. The spinneret is essential for silk spinning, but the sectional morphology of the spinneret that determines the silk monofilament, the muscular activities around the silk press as well as the relationships between the spinneret and the properties of the resulting silk remain poorly understood. We studied these factors by dissecting the spinneret and analyzing silk from different Bombyx mori strains. The sectional morphology of silk monofilament was found to be largely determined by the spinneret, especially by the silk press. Moreover, contractile activity of the muscles around the silk press is high, and the contraction frequency of the muscles was estimated to range from 11.42 to 50 HZ. A comparison of the fibroin filaments before they entered the common tube indicated that the spinneret determines both silk shape and silk size. This study provides insight into the silk spinning process, which may help develop bionic spinning in further studies and also provides a rationale to study the effect of the spinneret on silk fineness at the molecular level.

Spinning and Applications of Bioinspired Fiber Systems

Natural fiber systems provide inspirations for artificial fiber spinning and applications. Through a long process of trial and error, great progress has been made in recent years. The natural fiber itself, especially silks, and the formation mechanism are better understood, and some of the essential factors are implemented in artificial spinning methods, benefiting from advanced manufacturing technologies. In addition, fiber-based materials produced via bioinspired spinning methods find an increasingly wide range of biomedical, optoelectronic, and environmental engineering applications. This paper reviews recent developments in the spinning and application of bioinspired fiber systems, introduces natural fiber and spinning processes and artificial spinning methods, and discusses applications of artificial fiber materials. Views on remaining challenges and the perspective on future trends are also proposed.