Degradation markers of fibroin in silk through infrared spectroscopy

Mixed organic acids as an effective green modifier for enhancing PAH degradation by ZIF-8@ B. subtilis ZL09-26

Although a protective shell based on a metal-organic framework (MOF) can effectively improve the remediation of polycyclic aromatic hydrocarbons (PAHs) by microorganisms, the functional characteristics of the shell are often limited by the surface charge, chemical properties and intrinsic strain characteristics. This study explored the potential of mixed organic acids (MA) as an eco-friendly modifier for zeolite imidazolate framework-8 (ZIF-8), facilitating the formation of a biomimetic mineralized shell around Bacillus subtilis ZL09-26. The addition of MA into the ZIF-8 protective shell was found to stimulate growth and bolster cell viability. Notably, adding MA contribute resulted in a 1.98- fold enhancement of the PHE degradation efficiency. After five cycles of reuse, ZIF-8-MA@B. subtilis ZL09-26 still maintained almost 90% of the initial PHE degradation ability. Proteomic analysis revealed a coordinated regulation of multiple metabolic pathways that facilitated PHE uptake and degradation, including central carbon metabolism, direct PHE biodegradation, oxidative phosphorylation, aminoacyl-tRNA biosynthesis, fatty acid biosynthesis, ABC transporters, and the biosynthesis of valine, leucine, isoleucine, and lysine. This work broadens the application potential of biomineralized microorganisms, providing novel strategies for the sustainable bioremediation of xenobiotic pollutants in the environment.

Characterization of the second type of tubuliform spidroin (TuSp1 variant 2) elucidates the essential role of cysteine within the repetitive domain in liquid-liquid phase separation-mediated silk formation and the mechanical properties of silk fibers

Orb-weaver spiders utilize morphologically differentiated abdominal glands to produce up to seven types of silks throughout their life cycles. Tubuliform silk is unique as it serves to protect developing embryos and hatchlings. However, our current understanding of the relationship between structure and function of tubuliform silk protein remains limited. Here, we present the full-length gene sequence of the second type of tubuliform spidroin (TuSp1 variant 2) from the orb-weaver spider Leucauge blanda. The L. blanda TuSp1 variant 2 (TuSp1-v2) contains 18 tandemly arrayed repeats, with each repeat having a cysteine residue. We demonstrate that the cysteine in L. blanda TuSp1-v2 repeats can form intermolecular disulfide bond and promote the liquid-liquid phase separation (LLPS) for silk formation. Moreover, the presence of cysteine partially enhances the thermostability of soluble spidroins and the mechanical properties of fibers, as demonstrated by comparative analyses of miniature TuSp1-v2 and its mutants. The integration of mechanical and structural data indicates that the recombinant TuSp1-v2 fiber exhibits high UV-A stability in both its mechanical and structural properties. This study provides new insights into the functions of cysteine in repetitive region and implies promising potentials for development new spidroin-based biomaterials.

Non-invasive identification of historical textiles and leather by means of external reflection FTIR spectroscopy

Identifying the fibres in historical textiles presents a complex challenge due to the wide variety of plant, animal and early synthetic materials that have been used. Traditionally, this identification process involves sampling followed by either microscopic examination or ATR-FTIR spectroscopy. However, there are instances when sampling is restricted due to the good condition or significant value of the object under analysis. Additionally, the presence of leather components alongside textiles can further complicate the identification. This paper proposes a novel non-invasive method for fibre identification based on External Reflection (ER) FTIR spectroscopy, which has been rarely applied to textiles or leather. The current research demonstrates that ER-FTIR spectrum is a viable tool for fibre identification on both recent and historical textiles. The non-invasiveness of the analytical approach enables a comprehensive investigation without compromising the number or position of samples. Respect to ATR-FTIR spectra, the ER-FTIR spectra frequently exhibit an amplification of certain diagnostic bands, facilitating the identification of the various fibres examined in this study (cotton, hemp, viscose, silk, wool, leather, polyamide, acrylic, polyester). The extended spectral range (7500-375 cm-1) which is provided by ER-FTIR spectrometry also contains extra bands in the near infrared region, which can provide key information for the discrimination due to the lack of distortion phenomena. The technique was applied to the characterisation of textile materials coming from a collection of 10 traditional Japanese samurai armours spanning from the 16th to the 20th century (Museo delle Culture, Lugano, Switzerland). For the first time, the results provided a comprehensive overview of the textiles utilized in Japanese armours across various historical periods. Overall, the appearance of materials in samurai armours reflects the evolution of armour-making techniques and the influence of socio-cultural factors throughout Japanese history. Synthetic and semi-synthetic materials were easily detected, revealing the occurrence of a past conservation treatment or the early adoption of modern man-made materials in the manufacturing of traditional armours. The approach outlined in this case study can be applied to textile collections of various kinds, offering a reliable mean to discern the yarn composition and detect non-original components. The method also appears as a valuable prescreening tool for designing a less intrusive yet more informative sampling strategy, should additional details about fibre type and dyeing be necessary.

Probing the Physicochemical, Nanomorphological, and Antimicrobial Attributes of Sustainable Silk Fibroin/Copaiba Oleoresin-Loaded PVA Films for Food Packaging Applications

We explore the development of biodegradable poly(vinyl alcohol) (PVA) films loaded with silk fibroin (SF) functionalized with copaiba oleoresin (SFCO) for potential use in active food packaging. The films were characterized, showing significant improvements in both their physicochemical and nanomorphological properties. Films containing 10% SFCO exhibited superior mechanical strength, with a Young modulus of 145 MPa and an elongation at break of 385%, compared to the control film with 42 MPa and 314%, respectively. The films also demonstrated barrier properties, with water vapor transmission rates (WVTRs) as low as 25.95 g/h·m2. Antimicrobial activity against Staphylococcus aureus and Escherichia coli was significantly improved, showing inhibition zones of up to 10 ± 1 mm and a minimum inhibitory concentration (MIC) of 100 µg∙mL-1. Three-dimensional nanomorphological analysis via atomic force microscopy (AFM) showed increased roughness in films with higher SFCO content, with root mean square (RMS) roughness values ranging from 2.70 nm to 11.5 nm. These results highlight the potential of SFCO-loaded PVA films as robust, eco-friendly alternatives to conventional packaging materials. They provide improved mechanical and antimicrobial properties, essential for extending the shelf life of perishable foods and advancing sustainability in the packaging industry.

In Situ Gelling Silk Fibroin/ECM Hydrogel With Sustained Oxygen Release for Neural Tissue Engineering Applications

In situ gelling, cell-laden hydrogels hold promise for regenerating tissue lesions with irregular shapes located in complex and hard-to-reach anatomical sites. A notable example is the regeneration of neural tissue lost due to cerebral cavitation. However, hypoxia-induced cell necrosis during the vascularization period imposes a significant challenge to the success of this approach. Oxygen-releasing hydrogels have been developed to address this issue, but they suffer from fast oxygen release over a short period, limiting their efficacy. This study develops an in situ gelling hydrogel system based on silk fibroin (SF) and decellularized brain extracellular matrix (dECM) with sustained oxygen release and tunable gelation time. Calcium peroxide nanoparticles (CPO NPs) served as the oxygen generating material, which were encapsulated within SF microparticles before incorporation into the SF-dECM hydrogel, aiming to regulate the oxygen release rate. The total CPO content of the hydrogels was only 2%-4% w/w. Characterization of hydrogels containing various SF concentrations (2%, 4% or 6% w/v) and microparticle loadings (10%, 15% or 20% w/w) demonstrated that SF concentration in the hydrogel matrix significantly affects the swelling, resorption rate and mechanical properties, while microparticle loading has a milder effect. On the other hand, microparticle loading strongly affected the oxygen release profile. High SF concentration in the hydrogel matrix (6% w/v) led to slow resorption rate and high stiffness, likely unsuitable for intended application. Low SF concentration (2% w/v), on the other hand, led to a high swelling ratio and a less sustained oxygen release. Among 4% w/v SF hydrogels, increased microparticle loading led to a slower resorption rate, increased stiffness and enhanced oxygen release. However, cell viability was reduced at 20% w/w microparticle loading, likely due to decreased cell attachment. The 4% w/v SF hydrogels containing 10% w/w SF-CPO microparticles exhibited relatively low swelling ratio (12.8% ± 2.4%), appropriate resorption rate (70.16% ± 10.75% remaining weight after 28 days) and compressive modulus (36.9 ± 1.7 kPa) and sustained oxygen release for over 2 weeks. This sample also showed the highest viability under hypoxic conditions among tested hydrogel samples (87.6% ± 15.9%). Overall, the developed hydrogels in this study showed promise for potential application in brain tissue engineering.

The influence of plasticizer on the mechanical, structural, thermal and strain recovery properties following stress-relaxation process of silk fibroin/sodium alginate biocomposites for biomedical applications

The influence of plasticizer glycerol (GLY) on the mechanical, structural, and thermal properties of silk fibroin (SF)/sodium alginate (SA) biocomposite films was investigated in detail. As the SF/SA ratio increased up to 65%, the SF content significantly improved the Tensile strength (σT), Young's modulus (Ey) but reduced the elongation at break (εb). To modify and enhance the elasticity and flexibility of the biocomposite films, the GLY as a plasticizer was used at different ratio from 20 to 50% for each SF/SA biocomposite films. Although the extensibility of the films was improved greatly with increasing GLY ratio, σT and Ey reduced significantly. The effect was observed more apparently for the GLY ratio starting from 35%. It was also shown that crystallinity index in the Amide I region increased as the SF/SA ratio increased to 65%. Increasing SF content improved the thermal stability of the SF/SA biocomposites. The XRD results showed that crystallinity was increased as SF/SA ratio increased. Stress-relaxation of SF/SA (30%) biocomposite films plasticized with GLY revealed that each kind of plasticized films showed a viscoelastic behavior and a fast relaxation in the first stage (1-2 min) of the processes and then continued slowly. The GLY increased the extensibility and elasticity limit of the SF/SA (30%) composite films. During the strain recovery processes, the plasticized composite films recovered completely in a quite shorter time than that of unplasticized films. It was observed higher the GLY content, the recovery times became shorter.

MOF-818 nanoparticles as radical scavengers to improve the aging resistance of silk fabric

Silk fabrics hold immense historical value as precious legacies left by our ancestors, yet they face significant damage during archaeological excavations, necessitating urgent protective measures. However, The current protective materials can't effectively prevent the degradation of silk fabrics. Nanotechnology has emerged as a promising avenue for the consolidation and preservation of silk fabrics, offering novel concepts and materials. In this study, we propose an innovative and cost-effective method that uses the MOF-818 with a radical scavenging ability to enhance the protection of silk fabrics. The resulting demonstrates that the MOF-818 was the large surface area and porous properties, which exhibited excellent superoxide dismutase (SOD)-like activity at 10 ug/mL. The silk fabrics treated by MOF-818 displays small color difference, reduced the oxidation of functional group and prevents the degradation of silk fabrics. The successful development of this nanocomposite marks a significant advancement in silk protection, opening new horizons for the preservation of silk cultural relics.

Comparative Analysis of Silk Fibroin Membranes across Cross-Linking Methods: Processing and Characterization

Silk fibroin (SF) extracted from silkworm silk can be transformed into transparent membranes with well-suited physical properties for ophthalmic applications. There is ample literature on the fabrication and characterization of SF-based membranes; however, the use of diverse SF extraction protocols and characterization methods or their settings makes it difficult to compare different silk membrane properties across studies. In this work, we fabricated 10 families of SF-based membranes by physical cross-linking and one non-cross-linked as a control. We evaluated transparency (ranging from 84.5 to 95.3% in the visible spectrum), enzyme stability (from 24 h to 200 days in protease XIV), decomposition temperature (280-290 °C), water uptake (40-60%), Young's modulus (8-30 MPa), roughness (1.6-22.7 nm), and FTIR spectra for the secondary structure. We found correlation between water uptake and the Young's modulus (the lower the water uptake, the higher the Young's modulus) and a relationship between membrane stability in protease XIV and the secondary structure of the proteins. Higher surface roughness and faster degradation were found in membranes cross-linked with polyethylene glycol, and conversely, lower roughness and lower degradation were found in methanol, ethanol, or isopropanol crossed-link membranes. This ample compilation of materials and their characterization will aid in the selection of a SF-based material according to the needs of the application.

Investigation of the Structural Changes in Silk Due to Tin Weighting

In the 19th century, the weighting of silk with metal salts, such as tin, was a common practice to enhance certain properties of silk fabrics and compensate for the weight loss incurred during the degumming process. This technique induces both physical and chemical modifications to the fibres, contributing to their long-term degradation, which requires thorough investigation. This study aims to examine the structural changes in silk fibres caused by the accumulation of metal salts from the tin-weighting process, using mock-up samples prepared through successive loading with weighting agents using a traditional tin-phosphate treatment method. Unweighted and tin-weighted silk samples were compared using scanning electron (SEM) micrographs, which presented the dispersed nanoparticles on the fibres, while through energy-dispersive X-ray spectroscopy (EDS) elemental mapping, the presence and uniform distribution of the weighting agents were confirmed. Fourier-transform infrared spectroscopy (FTIR) analysis revealed structural changes in tin-weighted silk samples compared to untreated ones, including shifts in amide bands, altered water/hydroxyl and skeletal stretching regions, and increased skeletal band intensities suggesting modifications in hydrogen bonding, β-sheet content, and structural disorder without significantly impacting the overall crystallinity index. X-ray diffraction (XRD) analysis of both pristine and tin-weighted silk samples revealed significant alterations, predominantly in the amorphous regions of the silk upon weighting. These structural changes were further examined using small-angle X-ray scattering (SAXS) and small- and wide-angle X-ray scattering (SWAXS), which provided detailed insights into modifications occurring at the nanometre scale. The analyses suggested disruptions in β-sheet crystals and intermolecular packing, especially in the amorphous regions, with increasing amounts of tin-weighting. Contact angle analysis (CA) revealed that the tin-phosphate-weighting process significantly impacted silk surface properties, transforming it from moderately hydrophobic to highly hydrophilic. These changes indicate that the incorporation of tin-phosphate nanoparticles on and within silk fibres could restrict the flexibility of polymer chains, impacting the physical properties and potentially the degradation behaviour of silk textiles. By studying these structural changes, we aim to deepen our understanding of how tin-weighting impacts silk fibre structure, contributing valuable insights into the longevity, conservation, and preservation strategies of silk textiles in the context of cultural heritage.

Study on the Structure and Properties of Silk Fibers Obtained from Factory All-Age Artificial Diets

The traditional production mode of the sericulture industry is no longer suitable for the development requirements of modern agriculture; to facilitate the sustainable development of the sericulture industry, factory all-age artificial diet feeding came into being. Understanding the structural characteristics and properties of silk fibers obtained from factory all-age artificial diet feeding is an important prerequisite for application in the fields of textiles, clothing, biomedicine, and others. However, there have been no reports so far. In this paper, by feeding silkworms with factory all-age artificial diets (AD group) and mulberry leaves (ML group), silk fibers were obtained via two different feeding methods. The structure, mechanical properties, hygroscopic properties, and degradation properties were studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Structurally, no new functional groups appeared in the AD group. Compared with the ML group, the structure of the two groups was similar, and there was no significant difference in mechanical properties and moisture absorption. The structure of degummed silk fibers is dominated by crystalline regions, but α-chymotrypsin hydrolyzes the amorphous regions of silk proteins, so that after 28 d of degradation, the weight loss of both is very small. This provides further justification for the feasibility of factory all-age artificial diets for silkworms.

Sideritis raeseri-Modified Coatings on Ti-6Al-4V as a Carrier for Controlled Delivery Systems of Active Substances

The search for the ideal metallic material for an implant is still a difficult challenge for scientists due to the phenomenon of corrosion and the consequent disruption of the implant structure. Prevention is the application of coatings that protect the implant, activate the tissues for faster regeneration, and also prevent inflammation through antibacterial and antiviral effects. The present study focuses on the selection of components for a Ti-6Al-4V alloy coating. These days, researchers are taking an intense interest in extracts of natural origin. It was decided to take a look at Sideritis raeseri, which contains vitamins and valuable elements and is rich in polyphenols, as well as antioxidants. The composition of coatings based on a PEG polymer reinforced with brushite and the S. raeseri extract with the proteins L-carnosine, fibroin, or sericin was developed. The samples were subjected to detailed physiochemical analysis, including potentiometry and electrical conductivity analysis, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and UV-VIS spectroscopy. The study demonstrated that polyphenols were successfully released from the coatings during incubation in vitro. The osteointegration process can be supported by a number of factors, such as the release of polyphenols from implant coatings to prevent bacterial, viral, and fungal infections. Subjecting the samples to 14 days of incubation demonstrated their interactions with the incubation fluids, an ion exchange between the medium and the materials. An analysis of the surface morphology exhibited the presence of brushite crystals and their increased number after incubation, indicating the bioactivity of the formed coatings.

Polydopamine/SWCNT Ink Functionalization of Silk Fabric to Obtain Electroconductivity at a Low Percolation Threshold

This study presents the functionalization of silk fabric with SWCNT ink. The first step was the formation of a polydopamine (PDA) thin coating on the silk fabric to allow for effective bonding of SWCNTs. PDA formation was carried out directly on the fabric by means of polymerization of dopamine in alkali conditions. The Silk/PDA fabric was functionalized with SWCNT ink of different SWCNT concentrations by using the dip-coating method. IR and Raman analyses show that the dominant β-sheet structure of silk fibroin after the functionalization process remains unchanged. The heat resistance is even slightly improved. The hydrophobic silk fabric becomes hydrophilic after functionalization due to the influence of PDA and the surfactant in SWCNT ink. The ink significantly changes the electrical properties of the silk fabric, from insulating to conductive. The volume resistance changes by nine orders of magnitude, from 2.4 × 1012 Ω to 2.3 × 103 Ω for 0.12 wt.% of SWCNTs. The surface resistance changes by seven orders of magnitude, from 2.1 × 1012 Ω to 2.4 × 105 Ω for 0.17 wt.% of SWCNTs. The volume and surface resistance thresholds are determined to be about 0.05 wt.% and 0.06 wt.%, respectively. The low value of the percolation threshold indicates efficient functionalization, with high-quality ink facilitating the formation of percolation paths through SWCNTs and the influence of the PDA linker.

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.

Weak-Water-Coordination Electrolyte to Stabilize Zinc Anode Interface for Aqueous Zinc Ion Batteries

The performance of zinc-ion batteries is severely hindered by the uncontrolled growth of dendrites and the severe side reactions on the zinc anode interface. To address these challenges, a weak-water-coordination electrolyte is realized in a peptone-ZnSO4 -based electrolyte to simultaneously regulate the solvation structure and the interfacial environment. The peptone molecules have stronger interaction with Zn2+ ions than with water molecules, making them more prone to coordinate with Zn2+ ions and then reducing the active water in the solvated sheath. Meantime, the peptone molecules selectively adsorb on the Zn metal surface, and then are reduced to form a stable solid-electrolyte interface layer that can facilitate uniform and dense Zn deposition to inhabit the dendritic growth. Consequently, the Zn||Zn symmetric cell can exhibit exceptional cycling performance over 3200 h at 1.0 mA cm-2 /1.0 mAh cm-2 in the peptone-ZnSO4 -based electrolyte. Moreover, when coupled with a Na2 V6 O16 ·3H2 O cathode, the cell exhibits a long lifespan of 3000 cycles and maintains a high capacity retention rate of 84.3% at 5.0 A g-1 . This study presents an effective approach for enabling simultaneous regulation of the solvation structure and interfacial environment to design a highly reversible Zn anode.

Molecular Evidence of Structural Changes in Silk Using Unlimited Degradation Mass Spectrometry

Proteomics has important uses in archeological science because it can distinguish species, reveal the evolution of paleontology, and provide biological evidence of historical events. However, this technique still has full potential in the study of silk aging mechanisms. In this work, we propose a strategy combining unlimited degradation with mass-spectrometry-based proteomics techniques, which interpret protein fragmentation propensity and secondary structure changes by detecting content changes of specific peptide groups in complex proteomes. This approach was employed to study the conformational changes in silk microscopic crystals after heat treatment. Combining conventional mechanics and crystallographic characterization, a thermal aging degradation mechanism model was proposed. At the same time, it explained the interesting problem that the crystallinity remained unchanged, but the mechanical properties decreased significantly. Focusing on the unlimited degradation process, this method will be widely applicable to the study of silk and wool aging processes and regenerated silk fibroin.

Development of Salmon Sperm DNA/Regenerated Silk Bio-Based Films for Biomedical Studies on Human Keratinocyte HaCaT Cells under Solar Spectrum

In this study, we fabricated adhesive patches from silkworm-regenerated silk and DNA to safeguard human skin from the sun's rays. The patches are realized by exploiting the dissolution of silk fibers (e.g., silk fibroin (SF)) and salmon sperm DNA in formic acid and CaCl₂ solutions. Infrared spectroscopy is used to investigate the conformational transition of SF when combined with DNA; the results indicated that the addition of DNA provides an increase in the SF crystallinity. UV-Visible absorption and circular dichroism spectroscopy showed strong absorption in the UV region and the presence of B-form of DNA once dispersed in the SF matrix, respectively. Water absorption measurements as well as thermal dependence of water sorption and thermal analysis, suggested the stability of the fabricated patches. Biological results on cellular viability (MTT assay) of keratinocyte HaCaT cells after exposures to the solar spectrum showed that both SF and SF/DNA patches are photo-protective by increasing the cellular viability of keratinocytes after UV component exposure. Overall, these SF/DNA patches promise applications in wound dressing for practical biomedical purposes.

Historical Silk: A Novel Method to Evaluate Degumming with Non-Invasive Infrared Spectroscopy and Spectral Deconvolution

To correctly manage a collection of historical silks, it is important to detect if the yarn has been originally subjected to degumming. This process is generally applied to eliminate sericin; the obtained fiber is named soft silk, in contrast with hard silk which is unprocessed. The distinction between hard and soft silk gives both historical information and useful indications for informed conservation. With this aim, 32 samples of silk textiles from traditional Japanese samurai armors (15th-20th century) were characterized in a non-invasive way. ATR-FTIR spectroscopy has been previously used to detect hard silk, but data interpretation is challenging. To overcome this difficulty, an innovative analytical protocol based on external reflection FTIR (ER-FTIR) spectroscopy was employed, coupled with spectral deconvolution and multivariate data analysis. The ER-FTIR technique is rapid, portable, and widely employed in the cultural heritage field, but rarely applied to the study of textiles. The ER-FTIR band assignment for silk was discussed for the first time. Then, the evaluation of the OH stretching signals allowed for a reliable distinction between hard and soft silk. Such an innovative point of view, which exploits a "weakness" of FTIR spectroscopy-the strong absorption from water molecules-to indirectly obtain the results, can have industrial applications too.

Structural insight on the liquid silk from the middle silk gland of non-mulberry silkworm Antheraea assamensis

This study highlights the preliminary characterization of liquid silk from the middle silk gland (MSG) along with the in-silico analysis of the sericin protein of a less explored non mulberry silkworm Antheraea assamensis which is endemic to the North Eastern region of India. Various biophysical methods have been applied to elucidate the conformational patterns of the liquid silk present inside the MSG without removing the sericin layer. This will help us to know the actual features of the in vivo transitional status of the silk in the MSG which travel towards the anterior silk gland (ASG) prior to spinning. The SDS PAGE analysis represented the existence of the both fibroin and sericin bands in the sample. The structural pattern of the MSG liquid silk as revealed by various methods denoted the occurrence of β-sheet component along with some random coil and β-turn components which in turn suggests the transitional state of the liquid silk attributed to the existence of both the crystalline and amorphous contents. The thermo gravimetric study and the aggregation behavior analysis results proposed the occurrence of intermolecular hydrogen bonding between the sericin and fibroin in the MSG. This study will sensitize the better understanding of the behavior of the liquid silk in the MSG of non-mulberry silkworm A. assamensis and will open avenues for various application-based studies of this silk.Communicated by Ramaswamy H. Sarma.

Fabrication of silk fibroin film enhanced by acid hydrolyzed silk fibroin nanowhiskers to improve bacterial inhibition and biocompatibility efficacy

In this study, silk fibroin nanowhiskers (SNWs) were extracted from natural silk fiber by sulfuric acid hydrolysis with the assistance of ultrasonic wave treatment. The obtained SNWs were mixed with regenerated silk fibroin (RSF) solution to fabricate the SNWs/RSF films. The fabricating SNWs were systematically characterized by using SEM, FTIR, and the SNWs/RSF films were observed by digital camera, PM, etc. The results show that the monodisperse SNWs are evenly distributed in the RSF film. The presence of SNWs in RSF film significantly improves the performances of the film, including the swelling ability, mechanical properties, hydrophilicity, antibacterial efficacy, cytocompatibility. Meanwhile, the SNWs/RSF film can endorse the wound healing efficiency in vivo mice wound site. The proposed techniques for extracting SNWs and fabricating silk fibroin composite film may provide a valuable method for creating an ideal silk-based material for biomedical applications.

Biomolecular Regulation of Zinc Deposition to Achieve Ultra-Long Life and High-Rate Zn Metal Anodes

Aqueous zinc-ion batteries (ZIBs) have been extensively studied due to their inherent safety and high energy density for large-scale energy storage. However, the practical application is significantly limited by the growing Zn dendrites on metallic Zn anode during cycling. Herein, an environmental biomolecular electrolyte additive, fibroin (FI), is proposed to guide the homogeneous Zn deposition and stabilize Zn anode. This work demonstrates that the FI molecules with abundant electron-rich groups (NH, OH, and CO) can anchor on Zn anode surface to provide more nucleation sites and suppress the side reactions, and the strong interaction with water molecules can simultaneously regulate the Zn²⁺ coordination environment facilitating the uniform deposition of Zn. As a consequence, only 0.5 wt% FI additive enables a highly reversible Zn plating/stripping over 4000 h at 1 mA cm^-2 , indicating a sufficient advance in performance over state-of-the-art Zn anodes. Furthermore, when applied to a full battery (NaVO/Zn), the cell exhibits excellent capacity retention of 98.4% after 1000 cycles as well as high Coulombic efficiency of 99%, whereas the cell only operates for 68 cycles without FI additive. This work offers a non-toxic, low-cost, effective additive strategy to solve dendrites problems and achieve long-life and high-performance rechargeable aqueous ZIBs.

Development of a non-destructive methodology using ATR-FTIR and chemometrics to discriminate wild silk species in heritage collections

This paper aims to develop a non-destructive methodology applicable to heritage artifacts in order to discriminate between different species of wild silks. Wild silks are less known than domestic silk from Bombyx mori, but they are numerous and have been used in textile weaving for thousands of years. Archaeological artifacts, museum artifacts, and ethnographic collections deserve to be better documented regarding wild silks. The developed methodology is based on Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) coupled with chemometric analyses such as Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA). Discriminant statistical analysis has enabled within a corpus of wild silks, including cocoons from the collections of the musée du quai Branly-Jacques Chirac (Paris, France), to differentiate cocoons of the species Borocera madagascariensis (Lasiocampidae) from samples belonging to the Saturniidae family. These very encouraging results are promising for future studies involving more species and more diverse artifacts.

Textile ageing due to atmospheric gases and particles in indoor cultural heritage

Textile fibre degradation can be due to many factors. The most common cause is light exposure, but upon the lifespan of a textile, many other environmental factors are to be taken into account. This study focuses on the role of atmospheric compounds-both particulate and gaseous species-on natural textiles ageing, more specifically cotton, silk and wool. To achieve this, reference samples of textiles were exposed to contrasted environments (marine, urban and semi-rural museums and historical buildings) for natural ageing. These conditions were also reproduced in an experimental chamber dedicated to the study of the impact of airborne pollutants on heritage materials. Experimental ageing allowed to highlight degradation mechanisms for each fibre: SO₂ and HCOOH cause the cleavage of cotton's glyosidic links and silk's peptide bonds, while NO₂ promotes the oxidation of the fibres. The most harmful pollutant towards cotton is NO₂ since it causes both its oxidation and hydrolysis. The case of wool is more complicated: HCOOH provokes peptide link cleavage (similarly to silk) but this fibre is less sensitive to SO₂ attacks than silk and even seems to be protected against future alterations after having been firstly exposed to this pollutant. In any case, this experimental study evidences that damages caused by gaseous pollutants are fostered by the presence of particles, regardless of the chemical composition of the particle coating.

Silk fibroin directs the formation of monetite nanocrystals and their assembly into hierarchical composites

Natural biominerals are usually composite materials produced through mineralization of inorganic crystals within an organic matrix. Silk fibroin is known to be capable of directing the nucleation and growth of hydroxyapatite crystals. Here, we used silk films as the substrate to induce the mineralization of calcium phosphate. We show that the silk fibroin in solution could induce the formation of monetite crystals with a hierarchical structure, which are assembled by well aligned single crystals of monetite. In addition, we show that silk fibroins are incorporated inside the crystals. Therefore, the self-assembly of silk fibroin during the crystallization process is critical for the formation of such hierarchical structures.

Silk Powder from Cocoons and Woven Fabric as a Potential Bio-Modifier

Silk, as a protein fiber characterized by high biocompatibility, biodegradability, and low toxicity, is mainly used as textile structures for various purposes, including for biological applications. The key issue for unlimited silk applicability as a modifier is to prepare its relevant form to cover or introduce to other materials. This study presents silk powder fabrication from Bombyx mori cocoons and non-dyed silk woven fabric through cryogenic milling. The cocoons were milled before and after the degumming process to obtain powders from raw structures and pure fibroin. The powder morphology and composition were analyzed using scanning electron microscopy and energy dispersive spectroscopy. The influence of the milling on the silk structure was studied using infrared and Raman spectroscopies, indicating that silk powders retained dominant β-sheet structure. The powders were also analyzed by differential scanning calorimetry and thermogravimetric techniques. The thermal endothermic peak and onset temperature characteristic for silk decomposition shifted to the lower values for all powders, indicating less thermal stability. However, the process was found to be an efficient way to obtain silk powders. The new milled form of silk can allow its introduction into different matrices or form coatings without using any harsh solvents, enriching them with new features and make more biologically friendly.

A preliminary evaluation of chemical interaction between sanitizing products and silk

The ongoing Coronavirus crisis involved almost all sectors as well as museums, collections, and historical sites all over the world. Even though artworks do not have the ability to spread the virus, the pandemic officially introduced in cultural sites alcohol-based products (even by visitors for personal use) as these products were indicated to be able to inactivate the virus and were imposed by many local authorities. In this context, the need to conciliate the safety of the visitors and the protection of artworks represents a challenging task. The possibility that accumulation of vapour coming from the sanitizing solutions or from accidental spills, potentially caused also by visitors, should be considered. The study focuses specifically on the possible interactions between sanitizing alcohol-based products and silk, since this material is present in many cultural sites all over the world on upholsteries and tapestries. The recommended sanitising solution (75% ethanol, 20% water, 5% benzalkonium chloride) selected by the Italian Ministry for Cultural Heritage (MIBACT) was considered. Pure distilled water, absolute ethanol and water/ethanol blends in different concentrations were also tested. Chemical and morphological variations on the silk have been evaluated with Scanning Electron Microscopy - SEM, Atomic Force Microscopy - AFM and portable instruments (contact microscope, colorimeter, Infrared and Raman spectroscopy). IR and Raman analyses did not detect significant chemical changes in silk. However, Raman spectra showed, after immersion treatments, minor variations in the intensity of peaks attributed to dyes. Residues of benzalkonium chloride after immersion tests in sanitising solution are present, confirmed also by SEM and AFM analyses. Even if chemical spectroscopic changes were not relevant, the colour of few samples seemed to consistently fade after immersion treatments, thus affecting the visual appearance of textiles.

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.

Mineralization of calcium phosphate induced by a silk fibroin film under different biological conditions

Silk fibroin films can have an important effect on the mineralization process of calcium phosphate in different biological environments. There was improvement of MSF with good biocompatibility that are promising in bone tissue engineering.

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.

Revealing the Influence of the Degumming Process in the Properties of Silk Fibroin Nanoparticles

Several studies have stated that the process used for sericin removal, or degumming, from silk cocoons has a strong impact in the silk fibroin integrity and consequently in their mechanical or biochemical properties after processing it into several biomaterials (e.g. fibers, films or scaffolds) but still, there is a lack of information of the impact on the features of silk nanoparticles. In this work, silk cocoons were degummed following four standard methods: autoclaving, short alkaline (Na2CO3) boiling, long alkaline (Na2CO3) boiling and ultrasounds. The resultant silk fibroin fibers were dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate and used for nanoparticle synthesis by rapid desolvation in polar organic solvents. The relative efficiencies of the degumming processes and the integrity of the resulting fibroin fibers obtained were analyzed by mass loss, optical microscopy, thermogravimetric analysis, infrared spectroscopy and SDS-PAGE. Particle sizes and morphology were analyzed by Dynamic Light Scattering and Field Emission Scanning Electronic Microscopy. The results showed that the different treatments had a remarkable impact on the integrity of the silk fibroin chains, as confirmed by gel electrophoresis, which can be correlated with particle mean size and size distribution changes. The smallest nanoparticles (156 ± 3 nm) and the most negative Z potential (-30.2 ± 1.8 mV) were obtained with the combination of long treatment (2 h) of boiling in alkaline solution (Na2CO3 0.02 eq/L). The study confirms that parameters of the process, such as composition of the solution and time of the degumming step, must be controlled in order to reach an optimum reproducibility of the nanoparticle production.

Understanding the structural degradation of South American historical silk: A Focal Plane Array (FPA) FTIR and multivariate analysis

Silk artifacts constitute an invaluable heritage, and to preserve such patrimony it is necessary to correlate the degradation of silk fibroin with the presence of dyes, pollutants, manufacturing techniques, etc. Fourier Transform Infrared Spectroscopy with a Focal plane array detector (FPA FTIR) provides structural information at the micron scale. We characterized the distribution of secondary structures in silk fibers for a large set of South American historical textiles, coupling FTIR with multivariate statistical analysis to correlate the protein structure with the age of the samples and the presence of dyes. We found that the pressure applied during attenuated total reflectance (ATR) measurements might induce structural changes in the fibers, producing similar spectra for pristine and aged samples. Reflectance spectra were thus used for the rigorous characterization of secondary structures. Some correlation was highlighted between the age of the samples (spanning over five centuries) and specific changes in their secondary structure. A correlation was found between the color of the samples and structural alterations, in agreement with the chemical nature of the dyes. Overall, we demonstrated the efficacy of reflectance FPA µ-FTIR, combined with multivariate analysis, for the rigorous and non-invasive description of protein secondary structures on large sets of samples.

Degradation Behavior and Immunological Detection of Silk Fibroin Exposure to Enzymes

The degradation behavior of silk fibroin (SF) is a significant and intriguing subject in the area of archaeological ancient silk research. In the present study, the immunological detection techniques combined with traditional characterization methods, jointly studied the degradation process of SF from Bombyx mori (B. mori) and Antheraea pernyi (A. pernyi) through exposure to alkaline proteinase, α-chymotrypsin, pepsin, and trypsin. Spectroscopic analysis revealed that different enzymes showed similar hydrolysis effects on the secondary structure, but the changes of B. mori SF and A. pernyi SF were mainly reflected in the decrease of β-sheet and the reduction of α-helical structure, respectively. In further research of immunology, two diagnostic antibodies were prepared corresponding to SF of B. mori and A. pernyi, respectively. The enzyme-linked immunosorbent assay (ELISA) and western blot indicated the enzyme-treated SF proteins still exhibited higher immunoreactivity because the epitopes on the surface of SF molecules are retained. Although α-chymotrypsin possesses the most cleavage sites among these enzymes, the α-chymotrypsin-treated SF did not exhibit significant changes in secondary structures and high antibody binding capacity. The results deepen our understanding of the SF degradation process during enzymatic hydrolysis, and show far-reaching guiding significance in trace detection of SF.

Fabrication and Characterization of Silk Fibroin/Curcumin Sustained-Release Film

In the present work, a sustained-release film composed of silk fibroin (SF), curcumin (Cur), glutaraldehyde (GA), and glycerol (Gly) was prepared successfully for wound dressings. Features relevant to wound dressings of SF/Gly/GA/Cur film were assessed. Physical and chemical properties of the fabricated materials were also characterized. The results showed that the prepared SF/Gly/GA/Cur film demonstrated a good sustained-release performance, flexibility, and gas permeability. In addition, it was found that the prepared SF/Gly/GA/Cur film possessed the capability to effectively inhibit the growth of bacteria and prevent bacterial penetration with a suitable water vapor transmission rate. Furthermore, the prepared composite film was non-cytotoxic, which makes it an ideal material for wound dressings.

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.

Species identification of Bombyx mori and Antheraea pernyi silk via immunology and proteomics

In recent years, increasing attention has been paid to the origin, transmission and communication of silk. However, this is still an unsolved mystery in archaeology. The identification of silk-producing species, especially silk produced by Bombyx mori (B. mori) and Antheraea pernyi (A. pernyi), is of key significance to address this challenge. In this study, two innovative methods, i.e. immunology and proteomics, were proposed and successfully established for the species identification of silks. ELISAs result demonstrated that the two prepared antibodies exhibited high sensitivity and specificity in distinguishing B. mori and A. pernyi silk. No cross-reactivity with each other was observed. Moreover, biomarkers were obtained for Bombyx and Antheraea through proteomic analysis. It was also confirmed that the biomarkers were suitable for identifying the species that produced a given silk sample. Compared with conventional methods for distinguishing silk species, immunological and proteomics techniques used in tandem can provide intact information and have the potential to provide accurate and reliable information for species identification.

Analysing the structure and glass transition behaviour of silks for archaeology and conservation

Silk is an iconic material in many cultures. Silk archaeology and conservation is affected by silk production technology as well as subsequent environmental effects such as humidity, temperature, UV radiation and ageing. The complex interactions and various effects on silk materials affect the practical use of silk, for example, in the conservation of ancient manuscripts. This study examines the various influences of silk provenance and processing, adhesive coatings and chemical treatments as well as natural and artificial ageing of the silk material. We use infrared spectroscopy (FTIR) and dynamic mechanical thermal analysis to investigate the glass transition behaviours in a range of archaeological and control silk samples. This allows us to establish structural differences in century-old museum silks and predict the effects of silk ageing and degradation.

Alpha mangostin loaded crosslinked silk fibroin-based nanoparticles for cancer chemotherapy

Silk fibroin has been utilized extensively for biomedical purposes, especially the drug delivery systems. This study introduced and characterized three novel α-mangostin loaded crosslinked fibroin nanoparticles (FNPs), using EDC or PEI as a crosslinker, for cancer treatment. All three formulas were spherical particles with a mean size of approximately 300 nm. By varying the type and/or amount of the crosslinkers, particle surface charge was controllable from -15 to +30 mV. Crosslinked FNPs exhibited higher drug entrapment efficiency (70%) and drug loading (7%) than non-crosslinked FNP. FT-IR, XRD, and DSC analytical methods confirmed that α-mangostin was entrapped in FNPs in molecular dispersion form. Compared to the free α-mangostin, the crosslinked FNPs increased the drug's solubility up to threefold. They also showed sustained release characteristics of more than 3 days, and reduced free α-mangostin hematotoxicity by 90%. The α-mangostin loaded FNPs were physicochemically stable for up to 24 h when dispersed in intravenous diluent and for at least 6 months when preserved as lyophilized powder at 4 °C. In terms of anticancer efficacy, on both Caco-2 colorectal and MCF-7 breast adenocarcinoma cell lines, all formulas maintain α-mangostin's apoptotic effect while exhibit greater cytotoxicity than the free drug. In conclusion, α-mangostin loaded crosslinked FNPs show high potential for cancer chemotherapy.

Species Identification of Silks from Bombyx mori, Eri Silkworm and Chestnut Silkworm Using Western Blot and Proteomics Analyses

Species identification is of key significance for exploring the origin and transmission of ancient silks. In this study, two novel methods, i.e. western blot (WB) and proteomics analyses, were proposed and established to identify the differences between silks from Bombyx mori (B. mori) and two other distinctive species (Eri silkworm and Chestnut silkworm). Three diagnostic antibodies, a polyclonal anti-silk fibroin (anti-SF) antibody (pAb), a polyclonal anti-SF-specific peptide antibody (pAsb), and a monoclonal anti-SF antibody (mAb) were designed and prepared to distinguish silk species using the antibody-based WB technique. Proteomics analysis by liquid chromatography-tandem mass spectrometry was performed to further identify silk species at the protein level. WB results indicated that the three antibodies showed high specificity and affinity and could discern B. mori silk from Eri and Chestnut silks. Biomarkers for each SF were obtained using proteomics analysis, and they have the potential to serve as standards for identifying silk species. Thus, combining WB and proteomics analyses with conventional methods can provide more accurate silk information and may be suitable for identifying other proteinaceous materials in archaeological field.

Discerning Silk Produced by Bombyx mori from Those Produced by Wild Species Using an Enzyme-Linked Immunosorbent Assay Combined with Conventional Methods

Recently, much interest has been paid to the separation of silk produced by Bombyx mori from silk produced by other species and tracing the beginnings of silk cultivation from wild silk exploitation. In this paper, significant differences between silks from Bombyx mori and other species were found by microscopy and spectroscopy, such as morphology, secondary structure, and amino acid composition. For further accurate identification, a diagnostic antibody was designed by comparing the peptide sequences of silks produced by Bombyx mori and other species. The results of the noncompetitive indirect enzyme-linked immunosorbent assay (ELISA) indicated that the antibody that showed good sensitivity and high specificity can definitely discern silk produced by Bombyx mori from silk produced by wild species. Thus, the antibody-based immunoassay has the potential to be a powerful tool for tracing the beginnings of silk cultivation. In addition, combining the sensitive, specific, and convenient ELISA technology with other conventional methods can provide more in-depth and accurate information for species identification.