Fine organization of Bombyx mori fibroin heavy chain gene

Orientation Distribution of Crystalline β-Sheet Domains in Bombyx mori Silk Fiber Studied with Vibrational Sum Frequency Generation Spectroscopy

Silk fibers have good biocompatibility and mechanical properties, which make them attractive in biomaterial applications as well as textile industries. It is believed that the superior mechanical property is associated with the crystalline β-sheet structure in the fiber; but a deeper understanding of the structure-property relationship is still needed for full exploitation of its physical properties. Especially, accurate information on hydrogen-bonding interactions within β-sheet domains at the nanoscale and their spatial distributions at the mesoscale are critically needed. In this study, we demonstrate the selective detection of crystalline β-sheet domains in Bombyx mori silk fiber using sum frequency generation (SFG) spectroscopy and its use to determine the angular distribution of the β-sheet crystallites with respect to the fiber axis. Numerical simulations of the SFG signal of the amide-I band were carried out using tensors based on the B2 symmetry of the D2 point group and compared with experimental data. This comparison found that the crystalline β-sheet domains are aligned along the fiber axis with a standard deviation of ∼27° and parallel to the fiber surface with a standard deviation of ∼5°. It was also found that the amide bands in the SFG spectra cannot be fully explained with the assumption that the crystalline β-sheet vibrations can be described with the D2 point group. Being able to monitor the amide group vibrations sensitive to both interchain hydrogen bonding and crystallite orientations, SFG analysis has a potential to unveil the structure-mechanical property relationship that may not be readily assessable with other characterization techniques.

Chain-Folded Lamellar Stacking Structure of the Crystalline Fraction of Bombyx mori Silk Fibroin with Silk II Form Studied by 2D 13C-13C Homonuclear Correlation NMR Spectroscopy

The structure of Bombyx mori silk fibroin (SF) is a subject of significant interest due to its remarkable physical properties; however, its atomic-level structure is still not conclusive. We previously proposed a lamellar stacking structure for the crystalline fraction (Cp) with β-turns occurring every eighth amino acid. In this study, we took the following steps: At first, a model of the chain-folded lamellar stacking structure in antipolar and antiparallel β-sheet layers was constructed. Then, dipolar-assisted rotational resonance solid-state NMR spectra were observed to determine the effective internuclear distance (rj,keff) for the uniformly 13C-labeled Cp fraction sample. By comparing the experimentally obtained rj,keff (obs) values with the calculated rj,keff (calc) values from our structural model, a fairly good correlation between the observed and calculated values of the internuclear distances was obtained with a standard deviation of 0.37 Å. This supports the existence of the chain-folded lamellar stacking structure in the SF fiber. These findings contribute to our understanding of the atomic-level structure of SF and its exceptional properties.

Genomic resources of aquatic Lepidoptera, Elophila obliteralis and Hyposmocoma kahamanoa, reveal similarities with Trichoptera in amino acid composition of major silk genes

While most species of butterflies and moths (Lepidoptera) have entirely terrestrial life histories, ∼0.5% of the described species are known to have an aquatic larval stage. Larvae of aquatic Lepidoptera are similar to caddisflies (Trichoptera) in that they use silk to anchor themselves to underwater substrates or to build protective cases. However, the physical properties and genetic elements of silks in aquatic Lepidoptera remain unstudied, as most research on lepidopteran silk has focused on the commercially important silkworm, Bombyx mori. Here, we provide high-quality PacBio HiFi genome assemblies of 2 distantly-related aquatic Lepidoptera species [Elophila obliteralis (Pyraloidea: Crambidae) and Hyposmocoma kahamanoa (Gelechioidea: Cosmopterigidae)]. As a step toward understanding the evolution of underwater silk in aquatic Lepidoptera, we used the genome assemblies and compared them to published genetic data of aquatic and terrestrial Lepidoptera. Sequences of the primary silk protein, h-fibroin, in aquatic moths have conserved termini and share a basic motif structure with terrestrial Lepidoptera. However, these sequences were similar to aquatic Trichoptera in that the percentage of positively and negatively charged amino acids was much higher than in terrestrial Lepidoptera, indicating a possible adaptation of silks to aquatic environments.

How Do Butterflies Use Silk to Attach their Pupae to Trees?

Butterflies constitute approximately 10% of lepidopteran insects, and along with silkworms, they can produce silk; however, this feature is often ignored. In the present study, we observed two primary methods used by butterflies to hang pupae on trees using silk: pupa adheraena (Danaus chrysippus) and pupa contigua (Papilio polytes). Anchoring the abdominal ends of pupae with a silk pad was the most common method used in both cases, whereas wrapping silk around the body using a silk girdle was a method unique to pupa contigua. The connection between the cremaster and silk pad was observed to be similar to that between the hook and loop of a Velcro fastener, except that the cremaster hook is anchor-shaped rather than being a single hook. Such a connection will remain secure, ensuring the safety of the pupae during exposure to wind and rain. Through determining the mechanical properties of silk, the performance of butterfly silk was found to be weaker than that of silkworm silk. Therefore, the P. polytes silk girdle adopts the strategy of merging a dozen silk threads to improve its strength and toughness, thereby making it difficult to break. In addition, we explained how the protein sequence and structure of butterfly silk impact its performance. In conclusion, we discovered that butterfly pupae develop unique body features to establish secure bonds with silk. This enables them to effectively undergo metamorphosis and endure harsh weather conditions and surroundings.

A comprehensive gene expression analysis of the unique three-layered cocoon of the cecropia moth, Hyalophora cecropia

The larvae of the moth Hyalophora cecropia spin silk cocoons with morphologically distinct layers. We investigated the expression of the individual silk protein components of these cocoons in relation to the morphology of the silk gland and its affiliation to the different layers of the cocoon. The study used transcriptomic and proteomic analyses to identify 91 proteins associated with the silk cocoons, 63 of which have a signal peptide indicating their secretory nature. We checked the specificity of their expression in different parts of the SG and the presence of the corresponding protein products in each cocoon layer. Differences were observed among less abundant proteins with unclear functions. The representation of proteins in the inner envelope and intermediate space was similar, except for a higher proportion of probable contaminating proteins, mostly originating from the gut. On the other hand, the outer envelope contains a number of putative enzymes with unclear function. However, the protein most specific to the outer layer has sequence homology to putative serine/threonine kinase-like proteins and some adhesive proteins, and its closest homolog in Bombyx mori was found in the scaffold silk. This research provides valuable insights into the silk production of the cecropia moth, highlighting both similarities and differences to other moth species.

Mutation in the Bombyx mori BmGMC2 gene impacts silk production and silk protein synthesis

Silk is a natural protein fiber that is predominantly comprised of fibroin and sericin. In addition, it contains seroins, protease inhibitors, enzymes, and other proteins. We found an ecdysone oxidase BmGMC2, notably, which is specifically and highly expressed only in the silk glands of silkworms (Bombyx mori L.). It is also one of the main components of non-cocoon silk, however, its precise function remains unclear. In this study, we examined the spatiotemporal expression pattern of this protein and obtained a homozygous mutant strain (K-GMC2) using the CRISPR-Cas9 system. Compared to the wild-type strain (WT), the silk production and main silk proteins significantly decreased in the larval stage, and the adhesive strength of native silk proteins decreased in the final instar. Proteomic data indicated the abundance of ribosomal proteins decreased significantly in K-GMC2, differentially expressed proteins (DEPs) were enriched in pathways related to neurodegenerative diseases and genetic information processing, indicating that knockout may lead to a certain degree of cell stress, affecting the synthesis of silk proteins. This study investigated the expression pattern and gene function of ecdysone oxidase BmGMC2 in silk and silk glands, laying the groundwork for understanding the role of enzymes in the production of silk fibers.

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.

Bridging Nature and Engineering: Protein-Derived Materials for Bio-Inspired Applications

The sophisticated, elegant protein-polymers designed by nature can serve as inspiration to redesign and biomanufacture protein-based materials using synthetic biology. Historically, petro-based polymeric materials have dominated industrial activities, consequently transforming our way of living. While this benefits humans, the fabrication and disposal of these materials causes environmental sustainability challenges. Fortunately, protein-based biopolymers can compete with and potentially surpass the performance of petro-based polymers because they can be biologically produced and degraded in an environmentally friendly fashion. This paper reviews four groups of protein-based polymers, including fibrous proteins (collagen, silk fibroin, fibrillin, and keratin), elastomeric proteins (elastin, resilin, and wheat glutenin), adhesive/matrix proteins (spongin and conchiolin), and cyanophycin. We discuss the connection between protein sequence, structure, function, and biomimetic applications. Protein engineering techniques, such as directed evolution and rational design, can be used to improve the functionality of natural protein-based materials. For example, the inclusion of specific protein domains, particularly those observed in structural proteins, such as silk and collagen, enables the creation of novel biomimetic materials with exceptional mechanical properties and adaptability. This review also discusses recent advancements in the production and application of new protein-based materials through the approach of synthetic biology combined biomimetics, providing insight for future research and development of cutting-edge bio-inspired products. Protein-based polymers that utilize nature's designs as a base, then modified by advancements at the intersection of biology and engineering, may provide mankind with more sustainable products.

Silk Fibroin and Its Nanocomposites for Wound Care: A Comprehensive Review

For most individuals, wound healing is a highly organized, straightforward process, wherein the body transitions through different phases in a timely manner. However, there are instances where external intervention becomes necessary to support and facilitate different phases of the body's innate healing mechanism. Furthermore, in developing countries, the cost of the intervention significantly impacts access to treatment options as affordability becomes a determining factor. This is particularly true in cases of long-term wound treatment and management, such as chronic wounds and infections. Silk fibroin (SF) and its nanocomposites have emerged as promising biomaterials with potent wound-healing activity. Driven by this motivation, this Review presents a critical overview of the recent advancements in different aspects of wound care using SF and SF-based nanocomposites. In this context, we explore various formats of hemostats and assess their suitability for different bleeding situations. The subsequent sections discuss the primary causes of nonhealing wounds, i.e., prolonged inflammation and infections. Herein, different treatment strategies to achieve immunomodulatory and antibacterial properties in a wound dressing were reviewed. Despite exhibiting excellent pro-healing properties, few silk-based products reach the market. This Review concludes by highlighting the bottlenecks in translating silk-based products into the market and the prospects for the future.

Green, Low-carbon Silk-based Materials in Water Treatment: Current State and Future Trends

The improper and inadequate treatment of industrial, agricultural, and household wastewater exerts substantial pressure on the existing ecosystem and poses a serious threat to the health of both humans and animals. To address these issues, different types of materials have been employed to eradicate detrimental pollutants from wastewater and facilitate the reuse of water resources. Nevertheless, owing to the challenges associated with the degradation of these traditional materials post-use and their incompatibility with the environment, natural biopolymers have garnered considerable interest. Silk protein, as a biomacromolecule, exhibits advantageous characteristics including environmental friendliness, low carbon emissions, biodegradability, sustainability, and biocompatibility. Considering recent research findings, this comprehensive review outlines the structure and properties of silk proteins and offers a detailed overview of the manufacturing techniques employed in the production of silk-based materials (SBMs) spanning different forms. Furthermore, it conducts an in-depth analysis of the state-of-the-art SBMs for water treatment purposes, encompassing adsorption, catalysis, water disinfection, desalination, and biosensing. The review highlights the potential of SBMs in addressing the challenges of wastewater treatment and provides valuable insights into prospective avenues for further research.

Effect of silk fibroin protein hydrolysis on biochemistry, gelation kinetics, and NF-kB bioactivity in vitro

Fibroin is a structural protein derived from silk cocoons, which may be used in a variety of biomedical applications due to its high biocompatibility and controllable material properties. Conversely, fibroin solution is inherently unstable in solution, which limits its potential utility. Fibroin hydrolysates possess enhanced aqueous solubility and stability, with known anti-inflammatory bioactivity. Here, silk-derived protein (SDP) was produced through controlled time, temperature, and pressure conditions to generate a novel and reproducible hydrolysate population. Both regenerated fibroin and SDP solution stability were characterized for MWD, amino acid content, solubility, viscosity, surface interaction, secondary structure formation, and in vitro assessment of NF-kB pathway activity. Mechanistic studies indicate that hydrolysis processing is required to enhance material stability by abolishing fibroin's ability to self-associate. In vitro assays using HCLE cells indicate SDP has dose dependent potency for inhibiting NF-kB driven gene expression of TNF-α and MMP-9. Collectively, the results support SDP's use as an anti-inflammatory wetting agent compatible with a wide range of both biomedical and industrial applications. Furthermore, the conditions used to generate SDP hydrolysates are readily accessible, produce a highly consistent material from batch-to-batch, and permit widespread investigation of this novel population for these purposes.

The Biologically Active Biopolymer Silk: The Antibacterial Effects of Solubilized Bombyx mori Silk Fibroin with Common Wound Pathogens

Antibacterial properties are desirable in wound dressings. Silks, among many material formats, have been investigated for use in wound care. However, the antibacterial properties of liquid silk are poorly understood. The aim of this study is to investigate the inherent antibacterial properties of a Bombyx mori silk fibroin solution. Silk fibroin solutions containing ≥ 4% w/v silk fibroin do not support the growth of two common wound pathogens, Staphylococcus aureus and Pseudomonas aeruginosa. When liquid silk is added to a wound pad and placed on inoculated culture plates mimicking wound fluid, silk is bacteriostatic. Viability tests of the bacterial cells in the presence of liquid silk show that cells remain intact within the silk but could not be cultured. Liquid silk appears to provide a hostile environment for S. aureus and P. aeruginosa and inhibits growth without disrupting the cell membrane. This effect can be beneficial for wound healing and supports future healthcare applications for silk. This observation also indicates that liquid silk stored prior to processing is unlikely to experience microbial spoilage.

Regenerated Fiber's Ideal Target: Comparable to Natural Fiber

The toughness of silk naturally obtained from spiders and silkworms exceeds that of all other natural and man-made fibers. These insects transform aqueous protein feedstocks into mechanically specialized materials, which represents an engineering phenomenon that has developed over millions of years of natural evolution. Silkworms have become a new research hotspot due to the difficulties in collecting spider silk and other challenges. According to continuous research on the natural spinning process of the silkworm, it is possible to divide the main aspects of bionic spinning into two main segments: the solvent and behavior. This work focuses on the various methods currently used for the spinning of artificial silk fibers to replicate natural silk fibers, providing new insights based on changes in the fiber properties and production processes over time.

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.

Selenium-silk microgels as antifungal and antibacterial agents

Antimicrobial resistance is a leading threat to global health. Alternative therapeutics to combat the rise in drug-resistant strains of bacteria and fungi are thus needed, but the development of new classes of small molecule therapeutics has remained challenging. Here, we explore an orthogonal approach and address this issue by synthesising micro-scale, protein colloidal particles that possess potent antimicrobial properties. We describe an approach for forming silk-based microgels that contain selenium nanoparticles embedded within the protein scaffold. We demonstrate that these materials have both antibacterial and antifungal properties while, crucially, also remaining highly biocompatible with mammalian cell lines. By combing the nanoparticles with silk, the protein microgel is able to fulfill two critical functions; it protects the mammalian cells from the cytotoxic effects of the bare nanoparticles, while simultaneously serving as a carrier for microbial eradication. Furthermore, since the antimicrobial activity originates from physical contact, bacteria and fungi are unlikely to develop resistance to our hybrid biomaterials, which remains a critical issue with current antibiotic and antifungal treatments. Therefore, taken together, these results provide the basis for innovative antimicrobial materials that can target drug-resistant microbial infections.

3D-printed nanohydroxyapatite/methylacrylylated silk fibroin scaffold for repairing rat skull defects

The repair of bone defects remains a major challenge in the clinic, and treatment requires bone grafts or bone replacement materials. Existing biomaterials have many limitations and cannot meet the various needs of clinical applications. To treat bone defects, we constructed a nanohydroxyapatite (nHA)/methylacrylylated silk fibroin (MASF) composite biological scaffold using photocurable 3D printing technology. In this study, scanning electron microscopy (SEM) was used to detect the changes in the morphological structure of the composite scaffold with different contents of nanohydroxyapatite, and FTIR was used to detect the functional groups and chemical bonds in the composite scaffold to determine the specific components of the scaffold. In in vitro experiments, bone marrow mesenchymal stem cells from SD rats were cocultured with scaffolds soaking solution, and the cytotoxicity, cell proliferation, Western blot analysis, Quantitative real-time PCR analysis, bone alkaline phosphatase activity and alizarin red staining of scaffolds were detected to determine the biocompatibility of scaffolds and the effect of promoting proliferation and osteogenesis of bone marrow mesenchymal stem cells in vitro. In the in vivo experiment, the skull defect was constructed by adult SD rats, and the scaffold was implanted into the skull defect site. After 4 weeks and 8 weeks of culture, the specific osteogenic effect of the scaffold in the skull defect site was detected by animal micro-CT, hematoxylin and eosin (HE) staining and Masson's staining. Through the analysis of the morphological structure of the scaffold, we found that the frame supported good retention of the lamellar structure of silk fibroin, when mixed with nHA, the surface of the stent was rougher, the cell contact area increased, and cell adhesion and lamellar microstructure for cell migration and proliferation of the microenvironment provided a better space. FTIR results showed that the scaffold completely retained the β -folded structure of silk fibroin, and the scaffold composite was present without obvious impurities. The staining results of live/dead cells showed that the constructed scaffolds had no significant cytotoxicity, and thw CCK-8 assay also showed that the constructed scaffolds had good biocompatibility. The results of osteogenic induction showed that the scaffold had good osteogenic induction ability. Moreover, the results also showed that the scaffold with a MASF: nHA ratio of 1: 0.5 (SFH) showed better osteogenic ability. The micro-CT and bone histometric results were consistent with the in vitro results after stent implantation, and there was more bone formation at the bone defect site in the SFH group.This research used photocurable 3D printing technology to successfully build an osteogenesis bracket. The results show that the constructed nHA/MASF biological composite material, has good biocompatibility and good osteogenesis function. At the same time, in the microenvironment, the material can also promote bone defect repair and can potentially be used as a bone defect filling material for bone regeneration applications.

High mechanical property silk produced by transgenic silkworms expressing the Drosophila Dumpy

Extensive research has been conducted on utilizing transgenic silkworms and their natural spinning apparatus to produce high-performance spider silk fibers. However, research on using non-spider biological proteins to optimize the molecular structure of silk protein and improve the mechanical performance of silk fibers is still relatively scarce. Dumpy, a massive extracellular matrix polypeptide, is essential for preserving the shape and structural integrity of the insect cuticle due to its remarkable tension and elasticity. Here, we constructed two transgenic donor plasmids containing the fusion genes of FibH-Dumpy and FibL-Dumpy. The results indicated the successful integration of two exogenous gene expression cassettes, driven by endogenous promoters, into the silkworm genome using piggyBac-mediated transgenic technology. Secondary structure analysis revealed a 16.7% and 13.6% increase in the β-sheet content of transgenic silks compared to wild-type (WT) silk fibers. Mechanical testing demonstrated that, compared to the WT, HDUY and LDUY transgenic silk fibers exhibited respective increases of 39.54% and 21.45% in maximum stress, 44.43% and 45.02% in toughness, and 24.91% and 28.51% in elastic recovery rate. These findings suggest that Drosophila Dumpy significantly enhanced the mechanical properties of silk, positioning it as an excellent candidate for the development of extraordinary-performance fibers. This study provides rich inspiration for using other biological proteins to construct high-performance silk fibers and expands the possibilities for designing and applying novel biomaterials.

Silk Fibroin Materials: Biomedical Applications and Perspectives

The golden rule in tissue engineering is the creation of a synthetic device that simulates the native tissue, thus leading to the proper restoration of its anatomical and functional integrity, avoiding the limitations related to approaches based on autografts and allografts. The emergence of synthetic biocompatible materials has led to the production of innovative scaffolds that, if combined with cells and/or bioactive molecules, can improve tissue regeneration. In the last decade, silk fibroin (SF) has gained attention as a promising biomaterial in regenerative medicine due to its enhanced bio/cytocompatibility, chemical stability, and mechanical properties. Moreover, the possibility to produce advanced medical tools such as films, fibers, hydrogels, 3D porous scaffolds, non-woven scaffolds, particles or composite materials from a raw aqueous solution emphasizes the versatility of SF. Such devices are capable of meeting the most diverse tissue needs; hence, they represent an innovative clinical solution for the treatment of bone/cartilage, the cardiovascular system, neural, skin, and pancreatic tissue regeneration, as well as for many other biomedical applications. The present narrative review encompasses topics such as (i) the most interesting features of SF-based biomaterials, bare SF's biological nature and structural features, and comprehending the related chemo-physical properties and techniques used to produce the desired formulations of SF; (ii) the different applications of SF-based biomaterials and their related composite structures, discussing their biocompatibility and effectiveness in the medical field. Particularly, applications in regenerative medicine are also analyzed herein to highlight the different therapeutic strategies applied to various body sectors.

Functional modification of silk fibroin from silkworms and its application to medical biomaterials: A review

Silk fibroin (SF) from the silkworm Bombyx mori is a fibrous protein identified as a widely suitable biomaterial due to its biocompatibility, tunable degradation, and mechanical strength. Various modifications of SF protein can give SF fibers new properties and functions, broadening their applications in textile and biomedical industries. A diverse array of functional modifications on various forms of SF has been reported. In order to provide researchers with a more systematic understanding of the types of functional modifications of SF protein, as well as the corresponding applications, we comprehensively review the different types of functional modifications, including transgenic modification, modifications with chemical groups or biologically active substance, cross-linking and copolymerization without chemical reactions, their specific modification methods and applications. Furthermore, recent applications of SF in various medical biomaterials are briefly discussed.

Evaluation of the Modification Effects of Heparin/Dalteparin on Silk Fibroin Structure and Physical Properties for Skin Wound Healing

We have developed a functionalized silk fibroin (BSF) that can serve as an improved fundamental material for dressings by specifically capturing growth factors secreted during the healing process and supplying them to cells accumulated in the wound area to enhance the tissue regeneration efficiency. When considering the design of heparin-modified BSF, there is a difficulty with binding to high-molecular-weight polysaccharides without disrupting the hydrophobic crystalline structure of the BSF. In this study, a low-molecular-weight pharmaceutical heparin, dalteparin, was selected and cross-linked with the tyrosine residue presence in the BSF non-crystalline region. When targeting 3D porous applications like nanofiber sheets, as it is crucial not only to enhance biological activity but also to improve handling by maintaining stability in water and mechanical strength, a trade-off between improved cell affinity and reduced mechanical strength depending on crystalline structure was evaluated. The use of dalteparin maintained the mechanical strength better than unfractionated heparin by reducing the effect on disturbing BSF recrystallization. Film surface hydrophilicity and cell proliferation induction were significantly higher in the dalteparin group. For BSF functionalization, using purified heparin was an effective approach that achieved a balance between preserving the mechanical properties and induction of tissue regeneration, offering the potential for various forms in the future.

Highly strong and tough silk by feeding silkworms with rare earth ion-modified diets

Nature-derived silk fibers possess excellent biocompatibility, sustainability, and mechanical properties, yet producing strong and tough silk fibers in a facile and large-scale manner remains a significant challenge. Herein, we report a simple method for preparing strong and tough silk fibers by feeding silkworms rare earth ion-modified diets. The resulting silk fibers exhibit significantly increased tensile strength and toughness, with average values of 0.85 ± 0.07 GPa and 156 ± 13 MJ m-3, respectively, and maximum values of 0.97 ± 0.04 GPa and 188 ± 19 MJ m-3, approaching those of spider dragline silk. Our findings suggest that the incorporation of rare earth ions (La3+ or Eu3+) into the silk fibers contributes to this enhancement. Structure analysis reveals a reduction in content and an improvement in orientation of β-sheet nanocrystals in silk fibers. X-ray photoelectron spectroscopy analysis confirms the chemical interaction between rare earth ions with β-sheet nanocrystals. The structural evolution and chemical interactions lead to the simultaneous enhancement in both strength and toughness. This work presents a simple, scalable, and effective strategy for producing ultra-strong and tough silk fibers with potential applications in areas requiring super structural materials, such as personal protection and aerospace.

Self-assembled silk fibroin cross-linked with genipin supplements microbial carbonate precipitation in building material

The process of microbially induced carbonate precipitation (MICP) is known to effectively improve engineering properties of building materials and so does silk fibroin (SF). Thus, in this study, an attempt was taken to see the improvement in sand, that is, basic building material coupled with MICP and SF. Urease producing Bacillus megaterium was utilized for MICP in Nutri-Calci medium. To improve the strength of SF itself in bacterial solution, it was cross-linked with genipin at the optimized concentration of 3.12 mg/mL. The Fourier transform infrared (FTIR) spectra confirmed the crosslinking of SF with genipin in bacterial solution. In order to understand how such cross-linking can improve engineering properties, sand moulds of 50 mm3 dimension were prepared that resulted in 35% and 55% more compressive strength than the one prepared with bacterial solution with SF and bacterial solution only, respectively with higher calcite content in former one. The FTIR, SEM, x-ray powder diffraction spectrometry and x-ray photoelectron spectroscopy analyses confirmed higher biomineral precipitation in bacterial solution coupled with genipin cross-linked SF. As the process of MICP is proven to replace cement partially from concrete without negatively influence mechanical properties, SF cross-linked with genipin can provide additional significance in developing low-carbon cement-based composites.

Insights into nanomechanical behavior of B. mori silk fibroin-hydroxyapatite bio-nanocomposite using MD simulations: Role of varying hydroxyapatite content

Nanocomposite material composed of Bombyx mori Silk Fibroin and hydroxyapatite (B. mori SF-HA) is a potential biomaterial for bone tissue engineering. Here, Bombyx mori Silk Fibroin (B. mori SF) is a flexible and tough organic, polymer phase, and hydroxyapatite (HA) is hard and stiff mineral phase. Knowledge about mechanical deformation behavior together with governing mechanisms, and the role of the two phases (SF and HA phase) and interfacial interactions between them, in B. mori SF-HA biomaterial, at fundamental level is an important factor to consider while developing the tissue grafts. Such nanometer scale behavior is often preferably investigated using molecular dynamics method. Present study aims at understanding the mechanical deformation behavior and associated physical mechanisms in B. mori SF-HA bio-nanocomposite, at nanoscale. For this purpose, computational atomistic models of B. mori SF-HA bio-nanocomposite are developed with varying HA content. Mechanical behavior analysis of these composite models under tensile loading were performed using Molecular Dynamics (MD) simulations. Elastic modulus and tensile strength values in the range of 7-20 GPa and 200-700 MPa, respectively, are obtained for B. mori SF-HA composite, in case of different HA contents, wherein, increased mechanical properties are observed with increase in HA content. Analyses of the deformation trajectories show that the deformation flow behavior in B. mori SF-HA bio-nanocomposites is mainly defined by the soft SF phase. However, energetics analyses show that, the HA phase and SF-HA interfacial interactions also play a considerable role in mechanical performance of B. mori SF-HA bio-nanocomposite. Additionally, interfacial shear strength values in B. mori SF-HA bio-nanocomposite, for different HA contents, have also been obtained. The observations made and insights gained in present work has contribution and impact in gaining an insight into the mechanistic interactions occurring at nanoscale between SF and HA phases in B. mori SF-HA bio-composite.

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.

Tissue engineered skin substitutes: A comprehensive review of basic design, fabrication using 3D printing, recent advances and challenges

The multi-layered skin structure includes the epidermis, dermis and hypodermis, which forms a sophisticated tissue composed of extracellular matrix (ECM). The wound repair is a well-orchestrated process when the skin is injured. However, this natural wound repair will be ineffective for large surface area wounds. Autografts-based treatment is efficient but, additional pain and secondary healing of the patient limits its successful application. Therefore, there is a substantial need for fabricating tissue-engineered skin constructs. The development of a successful skin graft requires a fundamental understanding of the natural skin and its healing process, as well as design criteria for selecting a biopolymer and an appropriate fabrication technique. Further, the fabrication of an appropriate skin graft needs to meet physicochemical, mechanical, and biological properties equivalent to the natural skin. Advanced 3D bioprinting provides spatial control of the placement of functional components, such as biopolymers with living cells, which can satisfy the prerequisites for the preparation of an ideal skin graft. In this view, here we elaborate on the basic design requirements, constraints involved in the fabrication of skin graft and choice of ink, the probable solution by 3D bioprinting technique, as well as their latest advancements, challenges, and prospects.

Fibroin heavy chain gene replacement with a highly ordered synthetic repeat sequence in Bombyx mori

The exceptional quality of silkworm silk is attributed to the amino acid sequence of its fibroin heavy chain (Fib-H) protein. The large central domain of Fib-H, which consists of glycine- and alanine-rich crystalline regions interspersed with amorphous motifs of approximately 30 amino acid residues, is considered crucial for fibrilization and determines the properties of the silk fiber. We established a technical platform to modify the Fib-H core region systematically using transcription activator-like effector nuclease-mediated homologous recombination through a somatic and germline gene knockin assay along with PCR-based screening. This efficient knockin system was used to generate a silkworm strain carrying a mutant Fib-H allele, in which the core region was replaced with a highly ordered synthetic repeat sequence of a length comparable with native Fib-H core. Heterozygous knockin mutants produced seemingly normal cocoons, whereas homozygotes did not and exhibited considerable degradation in their posterior silk glands (PSGs). Cross-sectional examination of the PSG lumen and tensile tests conducted on reeled silk threads indicated that the mutant Fib-H, which exhibited reduced stability in the PSG cells and lumen, affected the mechanical properties of the fiber. Thus, sequence manipulation of the Fib-H core domain was identified as a crucial step in successfully creating artificial silk using knockin technology.

Unique Material Properties of Bombyx mori Silk Fiber Incorporated with 3-Azidotyrosine

Silk fiber produced by the silkworm Bombyx mori is a nature-derived proteinous fiber with excellent mechanical strength and broad biocompatibility. To alter its material properties and make it more suitable for textile, biomedical, and electronics applications, chemical modifications and genetic engineering methods have been extensively studied. Here, we report that the translational incorporation of a synthetic amino acid, 3-azidotyrosine (3-AzTyr), into B. mori silk fiber can improve its material properties. Such an incorporation considerably increased the fiber's mechanical strength and remarkably changed its solubility, whereas its crystalline hierarchical structure was not perturbed, as shown by X-ray analyses. These changes were probably caused by the intra- and/or intermolecular crosslinkings involving the azido group of 3-AzTyr during the degumming process to remove a coating protein. These findings indicate that the incorporation of synthetic amino acids could be an efficient method to improve the properties of silk-based materials.

Challenging level of rigid-body approach involving numerical elements (CHLORAINE) applied to repeated elastin peptides

Elastic proteins and derived biomaterials contain numerous tandemly repeated peptides along their sequences, ranging from a few copies to hundreds. These repetitions are responsible for their biochemical, biological and biomechanical properties. These sequences are considered to be intrinsically disordered, and the variations in their behavior are actually mainly due to their high flexibility and lack of stable secondary structures originating from their unique amino acid sequences. Consequently, the simulation of elastic proteins and large elastomeric biomaterials using classical molecular dynamics is an important challenge. Here, we propose a novel approach that allows the application of the DURABIN protocol to repeated elastin-like peptides (r-ELPs) in a simple way. Four large r-ELPs were studied to evaluate our method, which was developed for simulating extracellular matrix proteins at the mesoscopic scale. After structure clustering applied on molecular dynamic trajectories of constitutive peptides (5-mers and 6-mers), the main conformations were used as starting points to define the corresponding primitives, further used as rigid body fragments in our program. Contributions derived from electrostatic and molecular hydrophobicity potentials were tested to evaluate their influence on the interactions during simple mesoscopic simulations. The CHLORAINE approach, despite the thinner granularity due to the size of the patterns used, was included in the DURABIN protocol and emerges as a promising way to simulate elastic macromolecular systems.

Multifunctional silk vinyl sulfone-based hydrogel scaffolds for dynamic material-cell interactions

Biochemical and mechanical interactions between cells and the surrounding extracellular matrix influence cell behavior and fate. Mimicking these features in vitro has prompted the design and development of biomaterials, with continuing efforts to improve tailorable systems that also incorporate dynamic chemical functionalities. The majority of these chemistries have been incorporated into synthetic biomaterials, here we focus on modifications of silk protein with dynamic features achieved via enzymatic, "click", and photo-chemistries. The one-pot synthesis of vinyl sulfone modified silk (SilkVS) can be tuned to manipulate the degree of functionalization. The resultant modified protein-based material undergoes three different gelation mechanisms, enzymatic, "click", and light-induced, to generate hydrogels for in vitro cell culture. Further, the versatility of this chemical functionality is exploited to mimic cell-ECM interactions via the incorporation of bioactive peptides and proteins or by altering the mechanical properties of the material to guide cell behavior. SilkVS is well-suited for use in in vitro culture, providing a natural protein with both tunable biochemistry and mechanics.

Advances in Preparation and Properties of Regenerated Silk Fibroin

Over the years, silk fibroin (SF) has gained significant attention in various fields, such as biomedicine, tissue engineering, food processing, photochemistry, and biosensing, owing to its remarkable biocompatibility, machinability, and chemical modifiability. The process of obtaining regenerated silk fibroin (RSF) involves degumming, dissolving, dialysis, and centrifugation. RSF can be further fabricated into films, sponges, microspheres, gels, nanofibers, and other forms. It is now understood that the dissolution method selected greatly impacts the molecular weight distribution and structure of RSF, consequently influencing its subsequent processing and application. This study comprehensively explores and summarizes different dissolution methods of SF while examining their effects on the structure and performance of RSF. The findings presented herein aim to provide valuable insights and references for researchers and practitioners interested in utilizing RSF in diverse fields.

Characterization of the primary structure of the major silk gene, h-fibroin, across caddisfly (Trichoptera) suborders

Larvae of caddisflies (Trichoptera) produce silk to build various underwater structures allowing them to exploit a wide range of aquatic environments. The silk adheres to various substrates underwater and has high tensile strength, extensibility, and toughness and is of interest as a model for biomimetic adhesives. As a step toward understanding how the properties of underwater silk evolved in Trichoptera, we used genomic data to identify full-length sequences and characterize the primary structure of the major silk protein, h-fibroin, across the order. The h-fibroins have conserved termini and basic motif structure with high variation in repeating modules and variation in the percentage of amino acids, mainly proline. This finding might be linked to differences in mechanical properties related to the different silk usage and sets a starting point for future studies to screen and correlate amino acid motifs and other sequence features with quantifiable silk properties.

Evaluation and Application of Silk Fibroin Based Biomaterials to Promote Cartilage Regeneration in Osteoarthritis Therapy

Osteoarthritis (OA) is a common joint disease characterized by cartilage damage and degeneration. Traditional treatments such as NSAIDs and joint replacement surgery only relieve pain and do not achieve complete cartilage regeneration. Silk fibroin (SF) biomaterials are novel materials that have been widely studied and applied to cartilage regeneration. By mimicking the fibrous structure and biological activity of collagen, SF biomaterials can promote the proliferation and differentiation of chondrocytes and contribute to the formation of new cartilage tissue. In addition, SF biomaterials have good biocompatibility and biodegradability and can be gradually absorbed and metabolized by the human body. Studies in recent years have shown that SF biomaterials have great potential in treating OA and show good clinical efficacy. Therefore, SF biomaterials are expected to be an effective treatment option for promoting cartilage regeneration and repair in patients with OA. This article provides an overview of the biological characteristics of SF, its role in bone and cartilage injuries, and its prospects in clinical applications to provide new perspectives and references for the field of bone and cartilage repair.

Raman, WAXS, and Solid-State NMR Characterizations of Regenerated Silk Fibroin Using Lanthanide Ions as Chaotropic Agents

Bombyx mori silk fibroin (SF) has been reported as a convenient natural material for regenerative medicine, optoelectronics, and many other technological applications. SF owes its unique features to the hierarchical organization of the fibers. Many efforts have been made to set up protocols for dissolution since many applications of SF are based on regenerated solutions and fibers, but chaotropic conditions required to disassemble the packing of the polymer afford solutions with poor crystalline behavior. Our previous research has disclosed a dissolution and regeneration process of highly crystalline fibers involving lanthanide ions as chaotropic agents, demonstrating that each lanthanide has its own unique interaction with SF. Herein, we report elucidation of the structure of Ln-SF fibers by the combined use of Raman spectroscopy, wide-angle X-ray scattering (WAXS), and solid-state NMR techniques. Raman spectra confirmed the coordination of metal ions to SF, WAXS results highlighted the crystalline content of fibers, and solid-state NMR enabled the assessment of different ratios of secondary structures in the protein.

Molecular mechanics and failure mechanisms in B. mori Silk Fibroin-hydroxyapatite composite interfaces: Effect of crystal thickness and surface characteristics

Bombyx mori Silk Fibroin-hydroxyapatite (B. mori SF-HA) bio-nanocomposite is a prospective biomaterial for tissue engineered graft for bone repair. Here, B. mori SF is primarily a soft and tough organic phase, and HA is a hard and stiff mineral phase. In biomaterial design, an understanding about the nanoscale mechanics of SF-HA interface, such as interfacial interaction and interface debonding mechanisms between the two phases is essential for obtaining required functionality. To investigate such nanoscale behavior, molecular dynamics method is a preferred approach. Present study focuses on understanding of the interface debonding mechanisms at SF-HA interface in B. mori SF-HA bio-nanocomposite at nanometer length scale. For this purpose, nanoscale atomistic models of SF-HA interface are also developed based on the HA crystal size and HA surface type (Ca2+ dominated and OH- dominated) in contact with SF. Mechanical behavior analysis of these SF-HA interface models under pull-out type test were performed using Molecular Dynamics (MD) simulations. Surface pull-off strength values in the range of 0.4-0.8 GPa were obtained for SF-HA interface models, for different HA crystal thicknesses, wherein, the pull-off strength values are found to increase with increase in HA thicknesses. Analyses show that deformation mechanisms in SF-HA interface deformation, is a combination of shear deformation in SF phase followed by disintegration of SF phase from HA block. Furthermore, higher rupture force values were obtained for SF-HA interface with Ca2+ dominated HA surface in contact with SF phase, indicating that SF protein has a higher affinity for Ca2+ dominated surface of HA phase. Current work contributes in developing an understanding of mechanistic interactions between organic and inorganic phases in B. mori SF-HA composite nanostructure.

A review on the structure of Bombyx mori silk fibroin fiber studied using solid-state NMR: An antipolar lamella with an 8-residue repeat

Silk fibroin (SF) fiber from the silkworm Bombyx mori in the Silk II form has been used as an excellent textile fiber for over 5000 years. Recently it has been developed for a range of biomedical applications. Further expansion of these uses builds on the excellent mechanical strength of SF fiber, which derives from its structure. This relationship between strength and SF structure has been studied for over 50 years, but it is still not well understood. In this review, we report the use of solid-state NMR to study stable-isotope labeled SF fiber and stable-isotope labeled peptides including (Ala-Gly)₁₅ and (Ala-Gly-Ser-Gly-Ala-Gly)₅ as models of the crystalline fraction. We show that the crystalline fraction is a lamellar structure with a repetitive folding using β-turns every eighth amino acid, and that the sidechains adopt an antipolar arrangement rather than the more well-known polar structure described by Marsh, Corey and Pauling (that is, the Ala methyls in each layer point in opposite directions in alternate strands). The amino acids Ser, Tyr and Val are the next most common in B. mori SF after Gly and Ala, and occur in the crystalline and semi-crystalline regions, probably defining the edges of the crystalline region. Thus, we now have an understanding of the main features of Silk II but there is still a long way to go.

Unidirectional Nanopore Dehydration Induces a Highly Stretchable and Mechanically Robust Silk Fibroin Membrane Dominated by Type II β-Turns

Aqueous silk fibroin solution is dehydrated by evaporation into a water-soluble cast film (SFM_E) with poor mechanical properties but becomes by unidirectional nanopore dehydration (UND) into silk fibroin membrane (SFM_U) with water-stable and good mechanical robustness. The thickness and tensile force of the SFM_U are almost twice those of the MeOH-annealed SFM_E. The UND-based SFM_U has a tensile strength of 15.82 MPa, an elongation of 665.23%, and a type II β-turn (Silk I) that accounts for 30.75% of the crystal structure. Mouse L-929 cells adhere, grow, and proliferate well on it. The UND temperature can be used to tune the secondary structure, mechanical properties, and biodegradability. UND induced the oriented arrangement of the silk molecules, which led to the formation of the SFM_U dominated with Silk I structure. The silk metamaterial by controllable UND technology has great potential in medical biomaterials, biomimetic materials, sustained drug release, and flexible electronic substrates.

Highly accurate long reads are crucial for realizing the potential of biodiversity genomics

BACKGROUND

Generating the most contiguous, accurate genome assemblies given available sequencing technologies is a long-standing challenge in genome science. With the rise of long-read sequencing, assembly challenges have shifted from merely increasing contiguity to correctly assembling complex, repetitive regions of interest, ideally in a phased manner. At present, researchers largely choose between two types of long read data: longer, but less accurate sequences, or highly accurate, but shorter reads (i.e., >Q20 or 99% accurate). To better understand how these types of long-read data as well as scale of data (i.e., mean length and sequencing depth) influence genome assembly outcomes, we compared genome assemblies for a caddisfly, Hesperophylax magnus, generated with longer, but less accurate, Oxford Nanopore (ONT) R9.4.1 and highly accurate PacBio HiFi (HiFi) data. Next, we expanded this comparison to consider the influence of highly accurate long-read sequence data on genome assemblies across 6750 plant and animal genomes. For this broader comparison, we used HiFi data as a surrogate for highly accurate long-reads broadly as we could identify when they were used from GenBank metadata.

RESULTS

HiFi reads outperformed ONT reads in all assembly metrics tested for the caddisfly data set and allowed for accurate assembly of the repetitive ~ 20 Kb H-fibroin gene. Across plants and animals, genome assemblies that incorporated HiFi reads were also more contiguous. For plants, the average HiFi assembly was 501% more contiguous (mean contig N50 = 20.5 Mb) than those generated with any other long-read data (mean contig N50 = 4.1 Mb). For animals, HiFi assemblies were 226% more contiguous (mean contig N50 = 20.9 Mb) versus other long-read assemblies (mean contig N50 = 9.3 Mb). In plants, we also found limited evidence that HiFi may offer a unique solution for overcoming genomic complexity that scales with assembly size.

CONCLUSIONS

Highly accurate long-reads generated with HiFi or analogous technologies represent a key tool for maximizing genome assembly quality for a wide swath of plants and animals. This finding is particularly important when resources only allow for one type of sequencing data to be generated. Ultimately, to realize the promise of biodiversity genomics, we call for greater uptake of highly accurate long-reads in future studies.

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.

Combined CRISPR toolkits reveal the domestication landscape and function of the ultra-long and highly repetitive silk genes

Highly repetitive sequences play a major structural and function role in the genome. In the present study, we developed Cas9-assisted cloning and SMRT sequencing of long repetitive sequences (CACS) to sequence and manipulate highly repetitive genes from eukaryotic genomes. CACS combined Cas9-mediated cleavage of a target segment from an intact genome, Gibson assembly cloning, and PacBio SMRT sequencing. Applying CACS, we directly cloned and sequenced the complete sequences of fibroin heavy chain (FibH) genes from 17 domesticated (Bombyx mori) and 7 wild (Bombyx mandarina) silkworms. Our analysis revealed the unique fine structure organization, genetic variations, and domestication dynamics of FibH. We also demonstrated that the length of the repetitive regions determined the mechanical properties of silk fiber, which was further confirmed by Cas9 editing of FibH. CACS is a simple, robust, and efficient approach, providing affordable accessibility to highly repetitive regions of a genome. STATEMENT OF SIGNIFICANCE: Silkworm silk is the earliest and most widely used animal fiber, and its excellent performance mainly depends on the fibroin heavy chain (FibH) protein. The FibH gene is the main breakthrough in understanding the formation mechanism and improvement of silk fiber. In the study, we developed a CACS method for characterizing the fine structure and domestication landscape of 24 silkworm FibH genes. We used CRISPR/Cas9 to edit the repetitive sequence of FibH genes, revealing the relationship between FibH genes and mechanical properties of silkworm silk. Our study is helpful in modifying silk genes to manipulate other valuable highly repetitive sequences, and provides insight for silkworm breeding.

Selenium Silk Nanostructured Films with Antifungal and Antibacterial Activity

The rapid emergence of drug-resistant bacteria and fungi poses a threat for healthcare worldwide. The development of novel effective small molecule therapeutic strategies in this space has remained challenging. Therefore, one orthogonal approach is to explore biomaterials with physical modes of action that have the potential to generate antimicrobial activity and, in some cases, even prevent antimicrobial resistance. Here, to this effect, we describe an approach for forming silk-based films that contain embedded selenium nanoparticles. We show that these materials exhibit both antibacterial and antifungal properties while crucially also remaining highly biocompatible and noncytotoxic toward mammalian cells. By incorporating the nanoparticles into silk films, the protein scaffold acts in a 2-fold manner; it protects the mammalian cells from the cytotoxic effects of the bare nanoparticles, while also providing a template for bacterial and fungal eradication. A range of hybrid inorganic/organic films were produced and an optimum concentration was found, which allowed for both high bacterial and fungal death while also exhibiting low mammalian cell cytotoxicity. Such films can thus pave the way for next-generation antimicrobial materials for applications such as wound healing and as agents against topical infections, with the added benefit that bacteria and fungi are unlikely to develop antimicrobial resistance to these hybrid materials.

FibH Gene Complete Sequences (FibHome) Revealed Silkworm Pedigree

The highly repetitive and variable fibroin heavy chain (FibH) gene can be used as a silkworm identification; however, only a few complete FibH sequences are known. In this study, we extracted and examined 264 FibH gene complete sequences (FibHome) from a high-resolution silkworm pan-genome. The average FibH lengths of the wild silkworm, local, and improved strains were 19,698 bp, 16,427 bp, and 15,795 bp, respectively. All FibH sequences had a conserved 5' and 3' terminal non-repetitive (5' and 3' TNR, 99.74% and 99.99% identity, respectively) sequence and a variable repetitive core (RC). The RCs differed greatly, but they all shared the same motif. During domestication or breeding, the FibH gene mutated with hexanucleotide (GGTGCT) as the core unit. Numerous variations existed that were not unique to wild and domesticated silkworms. However, the transcriptional factor binding sites, such as fibroin modulator-binding protein, were highly conserved and had 100% identity in the FibH gene's intron and upstream sequences. The local and improved strains with the same FibH gene were divided into four families using this gene as a marker. Family I contained a maximum of 62 strains with the optional FibH (Opti-FibH, 15,960 bp) gene. This study provides new insights into FibH variations and silkworm breeding.

Methods for Silk Property Analyses across Structural Hierarchies and Scales

Silk from silkworms and spiders is an exceptionally important natural material, inspiring a range of new products and applications due to its high strength, elasticity, and toughness at low density, as well as its unique conductive and optical properties. Transgenic and recombinant technologies offer great promise for the scaled-up production of new silkworm- and spider-silk-inspired fibres. However, despite considerable effort, producing an artificial silk that recaptures the physico-chemical properties of naturally spun silk has thus far proven elusive. The mechanical, biochemical, and other properties of pre-and post-development fibres accordingly should be determined across scales and structural hierarchies whenever feasible. We have herein reviewed and made recommendations on some of those practices for measuring the bulk fibre properties; skin-core structures; and the primary, secondary, and tertiary structures of silk proteins and the properties of dopes and their proteins. We thereupon examine emerging methodologies and make assessments on how they might be utilized to realize the goal of developing high quality bio-inspired fibres.

Recent Developments in Biopolymer-Based Hydrogels for Tissue Engineering Applications

Hydrogels are being investigated for their application in inducing the regeneration of various tissues, and suitable conditions for each tissue are becoming more apparent. Conditions such as the mechanical properties, degradation period, degradation mechanism, and cell affinity can be tailored by changing the molecular structure, especially in the case of polymers. Furthermore, many high-functional hydrogels with drug delivery systems (DDSs), in which drugs or bioactive substances are contained in controlled hydrogels, have been reported. This review focuses on the molecular design and function of biopolymer-based hydrogels and introduces recent developments in functional hydrogels for clinical applications.

A Comprehensive Review on Silk Fibroin as a Persuasive Biomaterial for Bone Tissue Engineering

Bone tissue engineering (BTE) utilizes a special mix of scaffolds, cells, and bioactive factors to regulate the microenvironment of bone regeneration and form a three-dimensional bone simulation structure to regenerate bone tissue. Silk fibroin (SF) is perhaps the most encouraging material for BTE given its tunable mechanical properties, controllable biodegradability, and excellent biocompatibility. Numerous studies have confirmed the significance of SF for stimulating bone formation. In this review, we start by introducing the structure and characteristics of SF. After that, the immunological mechanism of SF for osteogenesis is summarized, and various forms of SF biomaterials and the latest development prospects of SF in BTE are emphatically introduced. Biomaterials based on SF have great potential in bone tissue engineering, and this review will serve as a resource for future design and research.

Silk Fibroin Microneedles for Transdermal Drug Delivery: Where Do We Stand and How Far Can We Proceed?

Microneedles are a patient-friendly technique for delivering drugs to the site of action in place of traditional oral and injectable administration. Silk fibroin represents an interesting polymeric biomaterial because of its mechanical properties, thermal stability, biocompatibility and possibility of control via genetic engineering. This review focuses on the critical research progress of silk fibroin microneedles since their inception, analyzes in detail the structure and properties of silk fibroin, the types of silk fibroin microneedles, drug delivery applications and clinical trials, and summarizes the future development trend in this field. It also proposes the future research direction of silk fibroin microneedles, including increasing drug loading doses and enriching drug loading types as well as exploring silk fibroin microneedles with stimulation-responsive drug release functions. The safety and effectiveness of silk fibroin microneedles should be further verified in clinical trials at different stages.

Clinical Use of Non-Suture Silk-Containing Products: A Systematic Review

AIMS

The purpose of this systematic review is to determine how various innovative non-suture silk and silk-containing products are being used in clinical practice, and compare patient outcomes following their use.

METHODS

A systematic review of PubMed, Web of Science, and Cochrane was completed. A qualitative synthesis of all included studies was then performed.

RESULTS

Our electronic search identified 868 silk-related publications, which yielded 32 studies for full-text review. After exclusion, nine studies from 2011 to 2018 were included for qualitative analysis. A total of 346 patients were included which consisted of 37 males and 309 females. The mean age range was between 18-79 years old. The follow-up among studies ranged between one to twenty-nine months. Three studies addressed the application of silk in wound dressings, one on the topical application of silk-derived products, one on silk-derived scaffold in breast reconstruction, and three on silk underwear as adjunct for the treatment of gynecological conditions. All studies showed good outcomes alone or in comparison to controls.

CONCLUSION

This systematic review concludes that silk products' structural, immune, and wound-healing modulating properties are advantageous clinical assets. Nevertheless, more studies are needed to strengthen and establish the benefit of those products.

Influence of lyophilization primary drying time and temperature on porous silk scaffold fabrication for biomedical applications

Lyophilization of protein solutions, such as silk fibroin (silk), produces porous scaffolds useful for tissue engineering (TE). The impact of modifying lyophilization primary drying parameters on scaffold properties has not yet been explored previously. In this work, changes to primary drying duration and temperature were investigated using 3%, 6%, 9%, and 12% (w/v) silk solutions, via protocols labeled as Long Hold, Slow Ramp, and Standard. The 9% and 12% scaffolds were not successfully fabricated using the Standard protocol, while the Long Hold and Slow Ramp protocols resulted in scaffolds from all silk solution concentrations. Scaffolds fabricated using the Long Hold protocol had higher Young's moduli, smaller pore Feret diameters, and faster degradation. To investigate the utility of the different lyophilized scaffolds for in vitro cell culturing, the HepaRG liver cell line was cultured in the 3% to 12% scaffolds fabricated using the Long Hold protocol. The HepaRG cells grown in 3% scaffolds initially had greater lipid accumulation and metabolic activity than the other groups, although these differences were no longer apparent by Day 28. The deoxyribonucleic acid content of the HepaRG cells grown in 3% scaffold group was also initially significantly higher than the other groups. Significant differences in gene expression by 9% scaffolded HepaRG cells (CK19, HNFα) were seen on Day 14 while significant differences by 12% scaffolded HepaRG cells (ALB, APOA4) were seen on Day 28. Overall, modifying the primary drying parameters and silk concentration resulted in lyophilized scaffolds with tunable properties useful for TE applications.

Effects of RGD-fused silk fibroin in a solution format on fibroblast proliferation and collagen production

BACKGROUND

Collagen production in fibroblasts is important for skin tissue repair. Cell-adhesive Arg-Gly-Asp (RGD) peptides immobilized on scaffolds stimulate fibroblast collagen production, but RGD peptides in solution exhibit opposite effects. Transgenic silkworm technology enables the design of fusion positions for RGD peptides in silk fibroin molecules. The effect of RGD-fused silk fibroin in solution on fibroblast cell activity remains unclear.

OBJECTIVE

To clarify the effects of RGD peptides fused to silk fibroin heavy (H)-chain or light (L)-chain on fibroblast proliferation and collagen production when RGD-fused silk fibroin proteins were added to the culture medium.

METHODS

Silk fibers with RGD-fused H-chains (H-RGD) or L-chains (L-RGD) were degummed, dissolved, and dialyzed to prepare H-RGD or L-RGD aqueous solutions, respectively. These solutions were added to the fibroblast medium, and their proliferation and collagen production were quantified.

RESULTS

Both L- and H-RGD stimulated fibroblast proliferation at a similar level, even in a solution format, but L-RGD promoted fibroblast collagen production significantly, indicating the synergistic effect of the native H-chain and RGD-fused L-chain.

CONCLUSION

RGD-fused silk fibroin in solution stimulated fibroblast proliferation and collagen production, depending on the fusion position of the peptides.

Designing Silk-Based Cryogels for Biomedical Applications

There is a need to develop the next generation of medical products that require biomaterials with improved properties. The versatility of various gels has pushed them to the forefront of biomaterials research. Cryogels, a type of gel scaffold made by controlled crosslinking under subzero or freezing temperatures, have great potential to address many current challenges. Unlike their hydrogel counterparts, which are also able to hold large amounts of biologically relevant fluids such as water, cryogels are often characterized by highly dense and crosslinked polymer walls, macroporous structures, and often improved properties. Recently, one biomaterial that has garnered a lot of interest for cryogel fabrication is silk and its derivatives. In this review, we provide a brief overview of silk-based biomaterials and how cryogelation can be used for novel scaffold design. We discuss how various parameters and fabrication strategies can be used to tune the properties of silk-based biomaterials. Finally, we discuss specific biomedical applications of silk-based biomaterials. Ultimately, we aim to demonstrate how the latest advances in silk-based cryogel scaffolds can be used to address challenges in numerous bioengineering disciplines.