Mechanically robust surface-degradable implant from fiber silk composites demonstrates regenerative potential

Through millions of years of evolution, bones have developed a complex and elegant hierarchical structure, utilizing tropocollagen and hydroxyapatite to attain an intricate balance between modulus, strength, and toughness. In this study, continuous fiber silk composites (CFSCs) of large size are prepared to mimic the hierarchical structure of natural bones, through the inheritance of the hierarchical structure of fiber silk and the integration with a polyester matrix. Due to the robust interface between the matrix and fiber silk, CFSCs show maintained stable long-term mechanical performance under wet conditions. During in vivo degradation, this material primarily undergoes host cell-mediated surface degradation, rather than bulk hydrolysis. We demonstrate significant capabilities of CFSCs in promoting vascularization and macrophage differentiation toward repair. A bone defect model further indicates the potential of CFSC for bone graft applications. Our belief is that the material family of CFSCs may promise a novel biomaterial strategy for yet to be achieved excellent regenerative implants.

Natural down fiber-reinforced and polypyrrole-modified silk fibroin composite aerogel for efficient solar steam generation toward seawater desalination and wastewater treatment

Poor mechanical properties and low photothermal efficiency of silk fibroin (SF)-based aerogels are current challenges that need to be addressed. Herein, SF composite aerogel was developed to enhance the mechanical properties through physical interpenetration of natural down fiber (Df) and hydrogen bonds formed among SF, Df, and polypyrrole (PPy) and to improve the evaporation performance via in-situ polymerization of PPy. The resultant Df/PPy@SF aerogel showed significant improvement of compressive stress (194.29 kPa), which was 6.96 times than that of SF aerogel (27.91 kPa), and also good compression resiliency. Furthermore, due to uniform distribution of PPy and high porosity of 95.27 %, Df/PPy@SF aerogel possessed high light absorbance of 99.87 % and low thermal conductivity (0.043 W·m-1·K-1). Thus, the Df/PPy@SF aerogel evaporator demonstrated high evaporation rates of 2.12 kg·m-2·h-1 for 3.5 wt% saline water, 2.04-2.15 kg·m-2·h-1 for various dye water, and 2.10 kg·m-2·h-1 for actual dye wastewater. Moreover, the developed aerogel exhibited evaporation stability and outstanding salt-resistance when treating seawater due to continuous water supply by superhydrophilic porous aerogel. Therefore, these findings demonstrate the excellent performance of Df/PPy@SF aerogel and will inspire further research on developing natural fiber-reinforced aerogels for use in the fields of solar water evaporation, energy, and other related applications.

Silk fibroin-derived electrospun materials for biomedical applications: A review

Electrospinning is a versatile technique for fabricating polymeric fibers with diameters ranging from micro- to nanoscale, exhibiting multiple morphologies and arrangements. By combining silk fibroin (SF) with synthetic and/or natural polymers, electrospun materials with outstanding biological, chemical, electrical, physical, mechanical, and optical properties can be achieved, fulfilling the evolving biomedical demands. This review highlights the remarkable versatility of SF-derived electrospun materials, specifically focusing on their application in tissue regeneration (including cartilage, cornea, nerves, blood vessels, bones, and skin), disease treatment (such as cancer and diabetes), and the development of controlled drug delivery systems. Additionally, we explore the potential future trends in utilizing these nanofibrous materials for creating intelligent biomaterials, incorporating biosensors and wearable sensors for monitoring human health, and also discuss the bottlenecks for its widespread use. This comprehensive overview illuminates the significant impact and exciting prospects of SF-derived electrospun materials in advancing biomedical research and applications.

Active coatings based on oxidized chitin nanocrystals and silk fibroins for the control of anthracnose in 'Hass' avocados

Postharvest avocado losses are mainly due to anthracnose disease caused by Colletotrichum gloeosporioides. Chemical fungicides are effective, but their negative effects on health and the environment have led to the search for sustainable alternatives such as biopolymer-based coatings and natural compounds. Therefore, chitin nanocrystals (NCChit) were extracted using a sustainable deep eutectic solvent (DES) and chemically modified into oxidized chitin nanocrystals (O-NCChit) or deacetylated chitin nanocrystals (D-NCChit) to modulate and increase the charge surface density and the dispersibility of the crystals. The modified NCChits were dispersed with silk fibroins (SF), essential oil (EO), melatonin (MT) and/or phenylalanine (Phe) to elaborate active coatings. Antioxidant and antifungal in vitro analyses showed that the O-NCChit/SF-based coating had the best performance. In addition, in vivo tests were carried out through the artificial inoculation of C. gloeosporioides on coated avocados. O-NCChit/SF/MT-based coatings reduced the severity of anthracnose by 45 %, the same effect as the chemical fungicide (Prochloraz®). Moreover, avocado quality parameters during cold storage and the shelf-life period were also evaluated, where nonsignificant differences were observed. Therefore, this study demonstrates the great potential of O-NCChit and SF in combination with active compounds for the control of anthracnose in 'Hass' avocados.

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.

Porous Thermoplastic Molded Regenerated Silk Crosslinked by the Addition of Citric Acid

Thermoplastic molded regenerated silk fibroin was proposed as a structural material in tissue engineering applications, mainly for application in bone. The protocol allows us to obtain a compact non-porous material with a compression modulus in the order of a Giga Pascal in dry conditions (and in the order of tens of MPa in wet conditions). This material is produced by compressing a lyophilized silk fibroin powder or sponge into a mold temperature higher than the glass transition temperature. The main purpose of the produced resin was the osteofixation and other structural applications in which the lack of porosity was not an issue. In this work, we introduced the use of citric acid in the thermoplastic molding protocol of silk fibroin to obtain porosity inside the structural material. The citric acid powder during the compression acted as a template for the pore formation. The mean pore diameter achieved by the addition of the higher amount of citric acid was around 5 μm. In addition, citric acid could effectively crosslink the silk fibroin chain, improving its mechanical strength. This effect was proved both by evaluating the compression modulus (the highest value recorded was 77 MPa in wet conditions) and by studying the spectra obtained by Fourier transform infrared spectroscopy. This protocol may be applied in the near future to the production of structural bone scaffolds.

Green tea catechin-grafted silk fibroin hydrogels with reactive oxygen species scavenging activity for wound healing applications

BACKGROUND

Overproduction of reactive oxygen species (ROS) is known to delay wound healing by causing oxidative tissue damage and inflammation. The green tea catechin, (-)-Epigallocatechin-3-O-gallate (EGCG), has drawn a great deal of interest due to its strong ROS scavenging and anti-inflammatory activities. In this study, we developed EGCG-grafted silk fibroin hydrogels as a potential wound dressing material.

METHODS

The introduction of EGCG to water-soluble silk fibroin (SF-WS) was accomplished by the nucleophilic addition reaction between lysine residues in silk proteins and EGCG quinone at mild basic pH. The resulting SF-EGCG conjugate was co-crosslinked with tyramine-substituted SF (SF-T) via horseradish peroxidase (HRP)/H2O2 mediated enzymatic reaction to form SF-T/SF-EGCG hydrogels with series of composition ratios.

RESULTS

Interestingly, SF-T70/SF-EGCG30 hydrogels exhibited rapid in situ gelation (< 30 s), similar storage modulus to human skin (≈ 1000 Pa) and superior wound healing performance over SF-T hydrogels and a commercial DuoDERM® gel dressings in a rat model of full thickness skin defect.

CONCLUSION

This study will provide useful insights into a rational design of ROS scavenging biomaterials for wound healing applications.

Insignificant Difference in Biocompatibility of Regenerated Silk Fibroin Prepared with Ternary Reagent Compared with Regenerated Silk Fibroin Prepared with Lithium Bromide

Bombyx mori silk fibroin (SF) is widely used in the field of biomaterials due to its excellent biocompatibility and mechanical properties. However, SF cannot be used directly in many applications and needs to be dissolved first. Lithium bromide (LiBr) is a traditional solvent which is usually used to dissolve SF. However, LiBr has several limitations, e.g., it is expensive, it is toxic to organisms, and it is environmentally unfriendly. Herein, we investigate the possibility of developing a ternary reagent system that is inexpensive, non-toxic to organisms, and environmentally friendly as an alternative for silk fibroin solubilization. The results confirm that regenerated silk fibroin (RSF) prepared using a ternary reagent has the same morphology and amino acid composition as that prepared using LiBr, but the RSF prepared using a ternary reagent still had a small amount of calcium residue even after long-term dialysis. Further research found that the residual calcium does not cause significant differences in the structure and biological performance of the RSF, such as its cytotoxicity, blood compatibility, and antibacterial properties. Therefore, we believe that ternary reagents are an ideal alternative solvent for dissolving SF.

131I-Labeled Silk Fibroin Microspheres for Radioembolic Therapy of Rat Hepatocellular Carcinoma

Transarterial radioembolization (TARE) is a promising technology in hepatocellular carcinoma (HCC) therapy, which utilizes radionuclide-labeled microspheres to achieve arterial embolization and internal irradiation. However, the therapeutic effect of liver cancer can be affected by low radionuclide labeling rate and stability, as well as poor biocompatibility, and non-biodegradability of microspheres. Here, ¹³¹I-labeled silk fibroin microspheres (¹³¹I-SFMs) were developed as radioembolization material for effective TARE therapy against HCC. Silk fibroin rich in 10.03% of tyrosine was extracted from silkworm cocoons and then emulsified and genipin-crosslinked to prepare SFMs. SFMs show a good settlement rate, biodegradability, hemocompatibility, and low cytotoxicity. Afterward, ¹³¹I-SFMs were obtained by radiolabeling ¹³¹I onto the SFMs through the chloramine-T method. ¹³¹I-SFMs possess a high ¹³¹I labeling rate of over 84% and good radioactive stability and are thus conducive to internal radiotherapy. Significantly, ¹³¹I-SFMs with diameters around 11 μm were successfully radioembolized at the hepatic artery. ¹³¹I-SFMs were diffused in the liver, indicating the favorable biodistribution and biosafety in vivo. Based on the combination of embolization and local radiotherapy, the administration of ¹³¹I-SFMs shows a favorable inhibitive effect against the progression of HCC. Overall, the newly developed ¹³¹I-SFMs as radioembolization microspheres provide a promising application for effective TARE therapy against liver cancer.

The Contribution of Silk Fibroin in Biomedical Engineering

Silk fibroin (SF) is a natural protein (biopolymer) extracted from the cocoons of Bombyx mori L. (silkworm). It has many properties of interest in the field of biotechnology, the most important being biodegradability, biocompatibility and robust mechanical strength with high tensile strength. SF is usually dissolved in water-based solvents and can be easily reconstructed into a variety of material formats, including films, mats, hydrogels, and sponges, by various fabrication techniques (spin coating, electrospinning, freeze-drying, and physical or chemical crosslinking). Furthermore, SF is a feasible material used in many biomedical applications, including tissue engineering (3D scaffolds, wounds dressing), cancer therapy (mimicking the tumor microenvironment), controlled drug delivery (SF-based complexes), and bone, eye and skin regeneration. In this review, we describe the structure, composition, general properties, and structure-properties relationship of SF. In addition, the main methods used for ecological extraction and processing of SF that make it a green material are discussed. Lastly, technological advances in the use of SF-based materials are addressed, especially in healthcare applications such as tissue engineering and cancer therapeutics.

Constructing Silk Fibroin-Based Three-Dimensional Microfluidic Devices via a Tape Mask-Assisted Multiple-Step Etching Technique

Regenerated silk fibroin (RSF) has been regarded as a very promising biomaterial for the preparation of microfluidic devices. However, the facile and low-cost fabrication of three-dimensional (3D) RSF microfluidic devices is still a great challenge. Herein, we developed a tape-mask-assisted multiple-step etching technique to fabricate 3D microfluidic devices based on water-annealed RSF films. Several rounds of tape adhesion- or peeling-etching cycles need to be conducted to produce 3D features on the RSF films with the LiBr aqueous solution as the etchant. The water-annealed RSF films could be effectively etched with 1.0 g·mL^-1 LiBr solution at 60 °C. The shape, width, and height of the 3D structures could be precisely tailored by controlling the mask pattern, etching conditions, and the number of etchings. Using the tape adhesion- and peeling-assisted multiple-etching techniques, the convex-pyramid-shaped and the concave-step-shaped structures could be successfully prepared on the RSF films, respectively. The RSF-film-based 3D micromixers and microfluidic separator were also manufactured with the proposed approach, exhibiting excellent liquid mixing and size-dependent particle sorting capabilities, respectively. The enzymatic degradation of RSF-film-based devices was also investigated to show their environmental friendliness. This work may not only provide a facile and low-cost method for the fabrication of RSF-based 3D microfluidic devices but also extend the applications of RSF in the fields of biomedical and chemical analysis.

Dissolution and processing of silk fibroin for materials science

In recent decades, silk fibroin (SF) from silkworm Bombyx mori has been extensively researched and applied in several fields, including: cosmetics, biomedicine and biomaterials. The dissolution and regeneration of SF fibers is the key and prerequisite step for the application of silk protein-based materials. Various solvents and dissolving systems have been reported to dissolve SF fibers. However, the dissolution process directly affects the characteristics of SF and particularly impacts the mechanical properties of the resulting silk biomaterials in subsequent processing. The purpose of this review is to summarize the common solvents, the dissolution methods for silk protein, the properties of the resulting SF protein. The suitable use of SF dissolved in the corresponding solvent was also briefly introduced. Recent applications of SF in various biomaterials are also discussed.

A Facile Strategy for Fabrication Lysozyme-Loaded Mesoporous Silica Nanotubes from Electrospun Silk Fibroin Nanofiber Templates

This paper presents a facile and low-cost strategy for fabrication lysozyme-loaded mesoporous silica nanotubes (MSNTs) by using silk fibroin (SF) nanofiber templates. The “top-down method” was adopted to dissolve degummed silk in CaCl₂/ formic acid (FA) solvent, and the solution containing SF nanofibrils was used for electrospinning to prepare SF nanofiber templates. As SF contains a large number of -OH, -NH₂ and -COOH groups, the silica layer could be easily formed on its surface by the Söber sol-gel method without adding any surfactant or coupling agent. After calcination, the MSNTs were obtained with inner diameters about 200 nm, the wall thickness ranges from 37 ± 2 nm to 66 ± 3 nm and the Brunauer–Emmett–Teller (BET) specific surface area was up to 200.48 m²/g, the pore volume was 1.109 cm³/g. By loading lysozyme, the MSNTs exhibited relatively high drug encapsulation efficiency up to 31.82% and an excellent long-term sustained release in 360 h (15 days). These results suggest that the MSNTs with the hierarchical structure of mesoporous and macroporous will be a promising carrier for applications in biomacromolecular drug delivery systems.

Silk Fibroin as a Functional Biomaterial for Tissue Engineering

Tissue engineering (TE) is the approach to combine cells with scaffold materials and appropriate growth factors to regenerate or replace damaged or degenerated tissue or organs. The scaffold material as a template for tissue formation plays the most important role in TE. Among scaffold materials, silk fibroin (SF), a natural protein with outstanding mechanical properties, biodegradability, biocompatibility, and bioresorbability has attracted significant attention for TE applications. SF is commonly dissolved into an aqueous solution and can be easily reconstructed into different material formats, including films, mats, hydrogels, and sponges via various fabrication techniques. These include spin coating, electrospinning, freeze drying, physical, and chemical crosslinking techniques. Furthermore, to facilitate fabrication of more complex SF-based scaffolds with high precision techniques including micro-patterning and bio-printing have recently been explored. This review introduces the physicochemical and mechanical properties of SF and looks into a range of SF-based scaffolds that have been recently developed. The typical TE applications of SF-based scaffolds including bone, cartilage, ligament, tendon, skin, wound healing, and tympanic membrane, will be highlighted and discussed, followed by future prospects and challenges needing to be addressed.

Effects of Ultraviolet Light Irradiation on Silk Fibroin Films Prepared under Different Conditions

Silk fibroin (SF)-based materials are exposed to both natural and artificial ultraviolet (UV) light during preparation or administration. However, the effects of UV irradiation on SF films prepared under different conditions have not yet been described in detail. In this study, four SF films with different molecular weight (MW) distribution were fabricated using SF solutions, which were prepared by dissolving degummed SF for 0.5–24 h. We observed UV (365 nm) irradiation on SF films induced the increase of yellowness and absorbance at 310 nm of SF films, indicating the formation of new photo-products and di-tyrosine bonds by photo-oxidation. Due to di-tyrosine cross-links between SF chains, UV-irradiated SF films were not fully dissociated in urea solution. In addition to formation of new products, UV reduced the crystallinity of SF films by breaking hydrogen bonds of β-sheet conformation. Unlike the UV-induced decomposition of physical interactions, UV did not affect the covalent bonds (i.e., peptide bonds). Through these experiments, we could expect that SF with higher MW was more susceptible and SF with lower MW was more resistant to UV-induced photo-oxidation and photo-degradation. These results provide useful information about UV-induced aging of SF-based materials under natural sunlight and UV irradiating conditions.

Engineering of sustainable biomaterial composites from cellulose and silk fibroin: Fundamentals and applications

This review addresses composites prepared from cellulose (Cel) and silk fibroin (SF) to generate multifunctional, biocompatible, biodegradable materials such as fibers, films and scaffolds for tissue engineering. First, we discuss briefly the molecular structures of Cel and SF. Their structural features explain why certain solvents, e.g., ionic liquids, inorganic electrolyte solutions dissolve both biopolymers. We discuss the mechanisms of Cel dissolution because in many cases they also apply to (much less studied) SF dissolution. Subsequently, we discuss the fabrication and characterization of Cel/SF composite biomaterials. We show how the composition of these materials beneficially affects their mechanical properties, compared to those of the precursor biopolymers. We also show that Cel/SF materials are excellent and versatile candidates for biomedical applications because of the inherent biocompatibility of their components.

Graphene oxide and electroactive reduced graphene oxide-based composite fibrous scaffolds for engineering excitable nerve tissue

This study systematically investigates the role of graphene oxide (GO) and reduced GO (rGO)/silk-based composite micro/nano-fibrous scaffolds in regulating neuronal cell behavior in vitro, given the limited comparative studies on the effects of graphene family materials on nerve regeneration. Fibrous scaffolds can mimic the architecture of the native extracellular matrix and are potential candidates for tissue engineering peripheral nerves. Silk/GO micro/nano-fibrous scaffolds were electrospun with GO loadings 1 to 10 wt.%, and optionally post-reduced in situ to explore a family of electrically conductive non-woven silk/rGO scaffolds. Conductivities up to 4 × 10^-5 S cm^-1 were recorded in the dry state, which increased up to 3 × 10^-4 S cm^-1 after hydration. Neuronoma NG108-15 cells adhered and were viable on all substrates. Enhanced metabolic activity and proliferation were observed on the GO-containing scaffolds, and these cell responses were further promoted for electroactive silk/rGO. Neurite extensions up to 100 μm were achieved by day 5, with maximum outgrowth up to ~250 μm on some of the conductive substrates. These electroactive composite fibrous scaffolds exhibit potential to enhance the neuronal cell response and could be versatile supportive substrates for neural tissue engineering applications.

Characterization of Ground Silk Fibroin through Comparison of Nanofibroin and Higher Order Structures

Silk fibroin, a biodegradable component of silk, is increasingly used for various applications and studied intensively. Recently, a technique for preparing nanofibers without using chemicals has been gaining attention from the environmental impact and safety perspectives. This study focuses on the structure observation of ground silk fibroin (GF) prepared using a grinding method, which is a physical nanofibrillation method. The fabricated nanofiber samples were examined in detail using the X-ray diffraction (XRD), differential scanning calorimetry (DSC), micro Raman spectroscopy, and atomic force microscopy (AFM) techniques. The nanofibrillated structures were observed in both GF and regenerated silk fibroin (RF) samples prepared using the conventional method. As results, AFM images showed that the nanofibril diameter of GF was about 1.64 nm and that of RF was about 0.32 nm. Methanol treatment induced a structural transition from a random coil to a β-sheet for the RF film, but it had no effect on the GF film. Thus, it is suggested that the grinding method provides not only ultrafine silk fibroin nanofibers without using toxic reagents but also resistance to reagents such as methanol.

Self-regenerated silk fibroin with controlled crystallinity for the reinforcement of silk

HYPOTHESIS

Silk artifacts constitute a fundamental cultural and historical heritage, yet they are affected by degradation that alters the secondary structure of fibroin and weakens the mechanical properties of textiles, hindering their conservation. Feasible and compatible consolidants for silk are still widely needed.

EXPERIMENTS

Here, we propose a robust and reliable method to restore the mechanical properties of fragile, aged silk fibers, based on the adhesion of self-regenerated silk fibroin (SRSF) with controlled crystallinity, prepared from waste silk, to the aged fibers. By varying the concentration of fibroin dispersions, the content of crystalline and amorphous domains in SRSF films can be tuned, as demonstrated by 2D micro-Fourier transform infrared spectroscopy Imaging and thermal analysis.

FINDINGS

The presence of amorphous fibroin domains, distributed between the aged silk fibers, completely recovered their mechanical properties. Instead, the presence of domains with high content of ordered structures, distributed between the fibers, reduced their tensile strength and elongation length. The different mechanical behavior is likely due to the fact that adhesion of crystalline layers produces a brittle material, while amorphous layers with higher fibroin chain mobility increase ductility. The tunability of this treatment allows easy control of desired mechanical properties of degraded silk fibers, simply controlling the crystallinity Vs amorphousness of SRSF; these findings open up new perspectives in textile conservation, in the engineering of biomaterials and materials, and in the preparation of composite materials with enhanced properties.

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.

Proteins in Ionic Liquids: Reactions, Applications, and Futures

Biopolymer processing and handling is greatly facilitated by the use of ionic liquids, given the increased solubility, and in some cases, structural stability imparted to these molecules. Focussing on proteins, we highlight here not just the key drivers behind protein-ionic liquid interactions that facilitate these functionalities, but address relevant current and potential applications of protein-ionic liquid interactions, including areas of future interest.

Ionic Liquid-Assisted Synthesis of Mesoporous Silk Fibroin/Silica Hybrids for Biomedical Applications

New mesoporous silk fibroin (SF)/silica hybrids were processed via a one-pot soft and energy-efficient sol-gel chemistry and self-assembly from a silica precursor, an acidic or basic catalyst, and the ionic liquid 1-butyl-3-methylimidazolium chloride, acting as both solvent and mesoporosity-inducer. The as-prepared materials were obtained as slightly transparent-opaque, amorphous monoliths, easily transformed into powders, and stable up to ca. 300 °C. Structural data suggest the formation of a hexagonal mesostructure with low range order and apparent surface areas, pore volumes, and pore radii of 205-263 m2 g-1, 0.16-0.19 cm3 g-1, and 1.2-1.6 nm, respectively. In all samples, the dominating conformation of the SF chains is the β-sheet. Cytotoxicity/bioactivity resazurin assays and fluorescence microscopy demonstrate the high viability of MC3T3 pre-osteoblasts to indirect (≥99 ± 9%) and direct (78 ± 2 to 99 ± 13%) contact with the SF/silica materials. Considering their properties and further improvements, these systems are promising candidates to be explored in bone tissue engineering. They also offer excellent prospects as electrolytes for solid-state electrochemical devices, in particular for fuel cells.

Robust composite silk fibers pulled out of silkworms directly fed with nanoparticles

This paper reports the impacts of direct feeding silkworms with different nanoparticles (Cu, Fe, and TiO₂) on the morphology, structures, and mechanical properties of the resulting silk fiber (SF). The contents of the Cu nanoparticles were 38 times higher in the posterior silk glands and only 2-3 times higher in the SF and in the middle silk glands compared with the controlled groups. Significant changes of the surface morphology, structures, and diameter of the Cu nanoparticle fed SF have been observed, which are attributed to a slight SF protein reconstruction or conformational change in the mixture of silk fibroin and sericin in the silk glands. The resulting Cu-containing SF exhibits good tensile strength of 360MPa and reaches a strain of 38%, which are 89% and 36% higher than those of the natural SF. This study offers a new green strategy for the easy modification to achieve robust composite SF.

In situ assembly of Ag nanoparticles (AgNPs) on porous silkworm cocoon-based wound film: enhanced antimicrobial and wound healing activity

Preventing wound infection and retaining an appropriate level of moisture around wounds represent the most critical issues in wound treatment. Towards these ends, special focus has been placed on Bombyx mori cocoons because the protective function of the silkworm cocoon resembles the manner in which the skin protects the human body. We have designed a facile technique to develop a novel silkworm cocoon-based wound film (SCWF) wound dressing utilizing a CaCl₂-ethanol-H₂O solution. To improve the anti-bacterial performance of SCWF, we have incorporated the ability of silk sericin to act as a reducing agent for the conversion of Ag⁺ to Ag, yielding nanoparticles (AgNPs) linked together by peptide bonds of silkworm cocoon wound film (SCWF-AgNPs). SCWF-AgNP dressing exhibited excellent biocompatibility, anti-bacterial performance, and good extensibility. Furthermore, in vivo experiments indicated that SCWF-AgNP dressing was able to significantly accelerate the healing rate of infected wounds in New Zealand White rabbits and histological examination revealed that it aided in the successful reconstruction of intact and thickened epidermis during 14 days of healing of impaired wound tissue. These results demonstrate that the present approach might shed new light on the design of anti-bacterial materials such as SCWF-AgNPs with promising applications in wound dressing.

Preparation of a regenerated silk fibroin film and its adsorbability to azo dyes

In this work, a novel and sustainable biosorbent, regenerated silk fibroin film (rSFF) was successfully prepared and its adsorbability to azo dyes (acid yellow 11, naphthol orange and direct orange S) was measured. At optimal conditions, the adsorption capacity of rSFF for acid yellow 11 reached up to 59.71mg/g, which was 1.23-fold higher than that of raw silk fibroin fibers. More importantly, rSFF exhibited a high level of flexibility and functionality as well as a good shaping ability, which were crucial for its practical application. The SEM results showed that rSFF was a porous material, indicating that it had more available adsorption sites compared with raw silk fibroin fibers, which might contribute to the higher adsorption capacity of rSFF. Isotherm equilibrium studies revealed that the azo dye adsorption process followed the Langmuir model, indicating that rSFF was a structurally homogenous adsorbent. The recycle test showed that rSFF had potential to be reused in a number of treatment cycles. After five cycles, its adsorbability to acid yellow 11 remained as high as 47.20mg/g. Finally, a scale-up experiment was performed for rSFF, and the results indicated that it was feasible for rSFF to extend the practical application.