Sericin Content Research Articles

Channel structure design and biological properties of silk fibroin/sericin sponge nerve scaffolds

Sponge materials with different ratios of silk fibroin and sericin and different channel structures were prepared as neural brackets to explore their physicochemical properties. The brackets were fabricated by cross-linking silk protein and sericin through glutaraldehyde and solution casting method, the aggregation state structure of the material was detected by fourier infrared, the morphology and structure of the material was observed by scanning electron microscope, and the physicochemical properties were detected by in vitro dissolution experiments, degradation experiments, and mechanical property experiments. The above analysis showed that the material is a porous mesh structure, and the pore size decreases with the increase of sericin content, while the swelling rate increases with the increase of channel area, the degradation rate increases, and the mechanical properties decrease. The proportion of 1:0.5 shows the best physicochemical performance in terms of the ratio of silk fibroin to sericin, The cytotoxicity and animal experiments indicated that this material has no cytotoxicity, and could promote cell proliferation and differentiation, the different types of brackets suggest promotion effects on nerve regeneration. In this paper, three kinds of nerve brackets, including porous structure, 24-channel structure and 4-channel structure, were designed to explore which structure is more conducive to nerve regeneration and lays a foundation for the design of biomimetics nerve scaffolds in the future, and it is expected to play a role in various peripheral nerve injuries. In the present study, a 4-channel nerve scaffold with a fibroin/sericin ratio of 1:0.5 showed the best effect in repairing a 10-mm sciatic nerve deficit in rats.

Enhanced mechanical properties of poly(butylene succinate)/silk sericin composite monofilaments with silane coupling agent KH570

Biodegradable Poly (butylene succinate) (PBS) composites with natural polymers have been widely developed, the compatibility of PBS and natural polymers is often the first consideration in terms of performance. In this work, PBS/silk sericin composite monofilaments (content of silk sericin is 6 wt%) with γ-methacryloxypropyltrimethoxysilane (KH570) as the coupling agent were fabricated by reactive melt-mixing, spinning, and stretching. The effect of KH570 content (1–3 wt%) on the morphology, mechanical property and biodegradation was studied. The reaction between the hydroxyl groups of silk sericin and -Si-OH of KH570 was analyzed by Fourier transform infrared spectroscopy. The cross-section morphology of the monofilaments obtained from SEM and EDS images indicates that the dispersion of silk sericin is improved with the increase of KH570 content. Compared with unmodified composite monofilaments, the composite monofilament with 2 wt% KH 570 shows the best mechanical performance (102% and 80% improvement in tensile strength and elongation at break respectively). The incorporation of silk sericin, which possesses skin-friendly properties, imparts composite monofilaments with advantages in the fields of clothing, headgear, shoe uppers and other related applications. Otherwise, the silk sericin can enhance the biodegradability velocity of PBS/silk sericin composite monofilaments. And the weight loss of the composite monofilaments buried in soil can be adjusted by the synergistic effect of silk sericin and KH570.

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

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

Development of Eco-Friendly Method for Degumming of Eri Cocoons

In this study, a new eco-friendly degumming technique was developed for Eri cocoons without any chemicals. A newly developed eco-Eri degumming process was tried at 110 °C, 120 °C, 130 °C and 140 °C temperatures for 10, 20 and 30 min with soft and hard water. The novel eco-friendly degumming method was compared with the existing method of degumming viz. Soap-soda along with the enzymatic method. After degumming, weight loss per cent, changes in the fibre surface morphology concerning SEM imaging and fibre properties concerning tensile strength and elongation were studied. The eco-Eri degumming method at 130 °C for 30 min using soft water removed the maximum sericin content (degumming loss 15.7%) from Eri cocoon shells and had optimum degumming efficiency. In the eco-Eri degumming method, the degummed Eri cocoons were uniformly softened. The soap soda method of degumming resulted in 14.5% weight loss whereas enzymatic degumming resulted in a maximum of 13% weight loss (12% dosage). Enzymatic degumming significantly reduced the tensile strength but no results found in the tensile properties of Eri silk fibres were observed in new eco-friendly and soap-soda methods. SEM images indicated optimal fibre surface with the smoother surface until 130 °C, but fibre damage and fibrillation occurred at 140 °C and also with the Soap-soda method. An optimal condition for degumming Eri cocoons with the new eco-Eri degumming process is 130 °C for 30 min using soft water. The eco-Eri degumming method is better compared to other methods used presently in the industry.

Effect of cocooning conditions on the structure, carbon and nitrogen isotope ratios of silks.

The stable isotope technique provides the possibility to trace ancient textiles because the technique is associated with advantages such as trace indication, fast detection, and accurate results. Since different cocooning conditions may impact cocoons even under identical habitats, it is important to investigate the effects of different cocooning temperatures and humidity on the isotope incorporation values in the cocoons. In this study, silk fibers were reeled under different conditions of temperature and humidity, followed by analysis of the secondary structure of cocoon proteins and isotope incorporation patterns. We found that the deviations in carbon isotope values of silk under different cocooning conditions could reach up to 0.76‰, while the deviation in carbon isotope values at different locations of a single silk was 2.75‰. Further, during the cocooning process, depletion of the 13C-isotope at different locations of the silk fibers was observed, reducing the δ13C values. We proposed that the changes in carbon isotopes in silk were related to the content of sericin and silk fibroin in silk. Finally, we did not observe a significant difference in isotope ratios in degummed cocoons. In summary, the 13C isotope was enriched in sericin, whereas 15N was enriched in fibroin, and these findings provide basic information for tracing the provenance of silks.

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

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

Cold-stored mulberry leaves affect antioxidant system and silk proteins of silkworm (Bombyx mori) larva.

Cold storage has been widely used to maintain the quality of vegetables, but whether eating cold-stored vegetables affects health remains unknown. This study used silkworms as an animal model to evaluate the effects of nutrient changes in cold-stored mulberry leaves (CSML) on health. Compared with fresh mulberry leaves (FML), CSML contained lower vitamin C, soluble sugars and proteins, and higher H2 O2 , suggesting decreased antioxidant ability and nutrition. The CSML did not obviously affect larval survival rate, body weight or dry matter rate, cocoon shape, weight and size, or final rates of cluster and cocooning relative to the FML, suggesting CSML did not alter overall growth and development. However, the CSML increased the initial rates of cluster and cocooning and upregulated BmRpd3, suggesting CSML shortened larval lifespan and enhanced senescence. CSML upregulated BmNOX4, downregulated BmCAT, BmSOD and BmGSH-Px and increased H2 O2 in silkworms, suggesting CSML caused oxidative stress. CSML upregulated ecdysone biosynthesis and inactivation genes and elevated ecdysone concentration in silkworms, suggesting that CSML affected hormone homeostasis. CSML upregulated apoptosis-related genes, downregulated sericin and silk fibroin genes and decreased sericin content rate in silkworms, suggesting oxidative stress and protein deficiency. Cold storage reduced nutrition and antioxidant capability of mulberry leaves. CSML did not influence growth and development of silkworm larva, but affected health by causing oxidative stress and reducing protein synthesis. The findings show that the ingredient changes in CSML had negative effects on health of silkworms. © 2023 Society of Chemical Industry.

Extraction and Characterization of Sericin from Cocoon of Four Different Silkworm Races Bombyx Mori L.

The removal and use of sericin could have a strong economic, social, and environmental impact, particularly in countries where sericulture is practiced, especially in Bangladesh. Because in our country Bangladesh, sericin is a waste material in the sericulture industry. Several techniques have been adopted for sericin extraction, but maintaining its chemical properties after extraction and environment-friendly extraction methods are still a major challenge. Sericin is fully or partially hydrolyzed and solubilized during the degumming of the cocoon. Consequently, it is important to create sericin extraction procedures that require less energy, don't release any chemicals, and don't harm the environment. Numerous research has been done to extract sericin but the differences in sericin content and chemical properties of Bivoltine and Multivoltine silkworm cocoon have not been studied yet. In this work, sericin was extracted from the silkworm cocoon of four different silkworm races at two different temperatures and durations. Significant differences were observed in yield% with different silkworm races and different treatments. Extracted sericin was characterized through SDS PAGE, FTIR & UV spectroscopy, and TGA.

Study on Structure and Anti-UV Properties of Sericin Cocoons

Abstract Through biogenetic engineering, the posterior silk glands of Bombyx mori larvae are degenerated, and only the middle silk glands are retained to secrete sericin to produce sericin fibers, so as to obtain sericin cocoons with high sericin content (>98.5%). For this paper, sericin cocoons were studied, and the morphological structure characteristics and properties of sericin cocoons and common Bombyx mori cocoons were compared and analyzed through such modern test techniques as SEM, FTIR, and XRD. Results show that sericin cocoons have the basic morphological structure of cocoons, but because of the brittleness and hardness of sericin, the ssericin cocoons have poor integrity with a thermal decomposition rate that is higher than that of cocoons; the two cocoons are of a similar protein structure, with both α-helix and β-sheet structures, and dominantly the β-sheet structure; and the crystallinity of sericin cocoons (10.48%) is lower than that of the common Bombyx mori cocoons (27.10%). Sericin was extracted from both cocoons to obtain a mixed sericin solution respectively, which were coated on base fabrics of polyester taffeta (210T) for coating finish and subjected to qualitative research for their anti-UV properties. The base fabrics coated with mixed sericin solutions of sericin cocoons and Bombyx mori cocoons have an anti-UV performance index (UPF) of 23.9% and 22.5% respectively, which are higher than that of the base fabric (8.9%)..

Effect of degumming degree on the structure and tensile properties of RSF/RSS composite films prepared by one-step extraction

Regenerated silk fibroin (RSF) and regenerated sericin (RSS) have attracted much attention for tissue engineering due to excellent biocompatibility and controllable degradation. However, pure RSF films prepared by existing methods are brittle, which limits applications in the field of high-strength and/or flexible tissues (e.g. cornea, periosteum and dura). A series of RSF/RSS composite films were developed from solutions prepared by dissolving silks with different degumming rates. The molecular conformation, crystalline structure and tensile properties of the films and the effect of sericin content on the structure and properties were investigated. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction results revealed more β-sheets in films prepared by boiling water degumming than in Na2CO3-degummed RSFC film. Analysis of mechanical properties showed that the breaking strength (3.56 MPa) and elongation (50.51%) of boiling water-degummed RSF/RSS film were significantly increased compared with RSFC film (2.60 MPa and 32.31%), and the flexibility of films could be further improved by appropriately reducing the degumming rate.

A Novel Method for the Quantitative Detection of Sericin Content in Silk Fiber Based on the Ratio of Aspartate to Alanine

The development of a method for the quantitative determination of the sericin content ratio (SCR) is urgently needed for silk refining and the purification of silk fibroin for biomedical applications. In this work, a series of sericin/fibroin mixed samples with known SCRs were prepared by mixing initial samples of extracted sericin and fibroin from Bombyx mori silk. Significant differences were found in the contents of characteristic hydrophilic amino acids abundant in sericin and hydrophobic amino acids abundant in fibroin, and several linear relationships of SCR associated with the content ratios of Ser/Ala, Asp/Ala, Lys/Ala, Asp/Gly and Ser/Gly were established by amino acid analysis. Subsequently, the linear equation expressing SCR (%) as a function of the Asp to Ala content ratio X (%) was established as SCR = 2.5634X − 12.5587 (R2= 0.9972). The results indicated that the SCR of degummed silks calculated by the equation is more objective and effective than the results obtained by the traditional weight loss method. Our study provides a novel approach for the sensitive and quantitative detection of the sericin content within the detection limit in unknown silks, which can contribute to quality control in the silk production process.

BmSuc1 Affects Silk Properties by Acting on Sericin1 in Bombyx mori.

BmSuc1, a novel animal-type β-fructofuranosidase (β-FFase, EC 3.2.1.26) encoding gene, was cloned and identified for the first time in the silkworm, Bombyx mori. BmSuc1 was specifically and highly expressed in the midgut and silk gland of Bombyx mori. Until now, the function of BmSuc1 in the silk gland was unclear. In this study, it was found that the expression changes of BmSuc1 in the fifth instar silk gland were consistent with the growth rate of the silk gland. Next, with the aid of the CRISPR/Cas9 system, the BmSuc1 locus was genetically mutated, and homozygous mutant silkworm strains with truncated β-FFase (BmSUC1) proteins were established. BmSuc1 mutant larvae exhibited stunted growth and decreased body weight. Interestingly, the molecular weight of part of Sericin1 (Ser1) in the silk gland of the mutant silkworms was reduced. The knockout of BmSuc1 reduced the sericin content in the silkworm cocoon shell, and the mechanical properties of the mutant line silk fibers were also negatively affected. These results reveal that BmSUC1 is involved in the synthesis of Ser1 protein in silk glands and helps to maintain the homeostasis of silk protein content in silk fibers and the mechanical properties of silk fibers, laying a foundation for the study of BmSUC1 regulation of silk protein synthesis in silk glands.

Sericin cocoon bio-compatibilizer for reactive blending of thermoplastic cassava starch

Cassava starch was blended with glycerol to prepare thermoplastic starch (TPS). Thermoplastic starch was premixed with sericin (TPSS) by solution mixing and then melt-blended with polyethylene grafted maleic anhydride (PEMAH). The effect of sericin on the mechanical properties, morphology, thermal properties, rheology, and reaction mechanism was investigated. The tensile strength and elongation at break of the TPSS10/PEMAH blend were improved to 12.2 MPa and 100.4%, respectively. The TPS/PEMAH morphology presented polyethylene grafted maleic anhydride particles (2 μm) dispersed in the thermoplastic starch matrix, which decreased in size to approximately 200 nm when 5% sericin was used. The melting temperature of polyethylene grafted maleic anhydride (121 °C) decreased to 111 °C because of the small crystal size of the polyethylene grafted maleic anhydride phase. The viscosity of TPS/PEMAH increased with increasing sericin content because of the chain extension. Fourier-transform infrared spectroscopy confirmed the reaction between the amino groups of sericin and the maleic anhydride groups of polyethylene grafted maleic anhydride. This reaction reduced the interfacial tension between thermoplastic starch and polyethylene grafted maleic anhydride, which improved the compatibility, mechanical properties, and morphology of the blend.

Comparative Analysis of Structure and Properties of Stereoscopic Cocoon and Flat Cocoon

Abstract Cocoon is a kind of natural biopolymer material with reasonable structure and various functions. However, its structure and functions are often destroyed in practical application. In this study, we took common Bombyx Mori as the research object, and provided different cocooning sites for single or multiple silkworms to construct common stereoscopic cocoons (“normal cocoons” [NC]) and flat cocoons (“single-silkworm flat cocoons” [SFC] and “multi-silkworm flat cocoons” [MFC]), respectively, and compared the morphological structure and basic properties of these cocoons. The study found that the flat cocoons have similar multi-layered variable structure and characteristics compared to those of the common cocoons; also, morphological characteristics and physical and chemical properties of silk fiber from outer layer to inner layer, such as sericin content, fiber fineness, and change rule of basic mechanical properties, are completely consistent with those of the common cocoons. It can be considered that the flat cocoons are constructed by silkworms in the same “procedural” process as that of common cocoons. Due to the expansion of cocooning space, the mechanical properties of fibers are significantly improved. By controlling the size of the cocooning space or the quantity of silkworms cocooning simultaneously, and the time of spinning, a cocoon material with controllable thickness, weight per square meter, porosity, and number of cocoon layers can be obtained as a composite material for direct application.

Sericin from mulberry and non-mulberry silk using chemical-free degumming

In this study we report the extraction and characterization of sericin using water alone, from two non-mulberry silks - Antheraea assamensis (A. assamensis) and Philosamia ricini (P. ricini) compared with Bombyx mori (B. mori) silk. Degumming at 130 °C offered the highest sericin removal for A. assamensis; P. ricini had the lowest sericin removal among the varieties, because of its lower overall sericin content. Along with sericin degumming, fiber tensile properties were also reported. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of sericin revealed minimal sericin degradation even for degumming temperatures above 100 °C. The spectra from Fourier Transform Infrared Spectroscopy (FTIR) confirmed random coil motifs for B. mori sericin but a higher proportion of β-sheets in A. assamensis and P. ricini sericin which is likely to contribute to their lower water solubility. Thus, high temperature, water-based processing can be a potential approach for chemical- free degumming of silk fibers and to obtain high molecular weight sericin for different biomaterial applications.

Effect of Silk Sericin Content on the Electrospun Silk Nanofibrous Membrane Property

Background: Silk sericin has a significant influence on the regenerated silk solution and silk-based materials property, while few reports were found to investigate this topic. Aim: The aim is to discuss the effect of silk sericin content on the electrospun silk nanofibrous membrane. Methods: Four degumming conditions (none degumming, boiling water degumming, 0.05 % Na2CO3 degumming, 0.5 % Na2CO3 degumming) were carried out for a systematic investigation in terms of (1) the silk sericin content after degumming; (2) the morphology of regenerated silk nanofibrous membrane was characterized by a Scanning Electron Microscope (SEM); and (3) structural properties of regenerated silk nanofibrous membrane by Fourier transform infrared (FTIR) spectroscopy, X-Ray Diffraction (XRD). Results and Conclusion: The results show that 0.5 % Na2CO3 degumming results in poor spinnability. The solutions derived from none degumming and boiling water degumming present high viscosity, leading to a hard silk nanofiber fabrication process. The silk nanofiber from the 0.05 % Na2CO3 degumming shows an easier fabrication process and better nanofiber morphology. These results will benefit the silk-based materials preparation, biomedical and separation application.

Minerals as exogenous modulators in enhancing silk productivity of silkworm, Bombyx mori L.

Experiments were conducted by supplementing minerals viz., zinc sulphate, magnesium sulphate and potassium chloride with mulberry leaves to improve the silk yield of B. mori. Per os administration of minerals to silkworm larvae during third, fourth and fifth instars significantly enhanced the larval, cocoon and silk reeling related parameters. Among the different minerals studied, it was found that the treatment with Zinc sulphate @ 100 ppm + Magnesium sulphate @ 200 ppm + Potassium chloride @ 100 ppm recorded significantly higher mature larval weight (4.45 g), ERR (97.16%), cocoon weight (2.30 g), shell weight (0.55 g), pupal weight (1.76 g) and shell ratio (23.19%), filament length (1458 m), filament weight (0.431 g) and silk productivity (6.35 cg/day). The proteins in silk gland (62.70 mg/g) and haemolymph (46.00 mg/g) were also found be higher in the above treatment apart from fibroin (410 mg/shell) and sericin (102.0 mg/shell) contents in cocoons.

Structure and Functions of Cocoons Constructed by Eri Silkworm.

Eri silkworm cocoons (E cocoons) are natural composite biopolymers formed by continuous twin silk filaments (fibroin) bonded by sericin. As a kind of wild species, E cocoons have characteristics different from those of Bombyx mori cocoons (B cocoons). E cocoons have an obvious multilayer (5–9 layers) structure with an eclosion hole at one end and several air gaps between the layers, which can be classified into three categories—cocoon coat, cocoon layer, and cocoon lining—with varying performance indexes. There is a significant secondary fracture phenomenon during the tensile process, which is attributed to the high modulus of the cocoon lining and its dense structure. Air gaps provide cocoons with distinct multistage moisture transmission processes, which form a good moisture buffer effect. Temperature change inside cocoons is evidently slower than that outside, which indicates that cocoons also have an obvious temperature damping capability. The eclosion hole does not have much effect on heat preservation of E cocoons. The high sericin content of the cocoon coat, as well as the excellent ultraviolet absorption and antimicrobial abilities of sericin, allows E cocoons to effectively prevent ultraviolet rays and microorganisms from invading pupae. The ultraviolet protection factor (UPF) of the E cocoon before and after degumming were found to be 17.8% and 9.7%, respectively, which were higher than those of the B cocoon (15.3% and 4.4%, respectively), indicating that sericin has a great impact on anti-UV performance. In the cocoon structure, the outer layer of the cocoon has 50% higher content than the inner layer, and the E cocoon shows stronger protection ability than the B cocoon. Understanding the relationship between the structure, property, and function of E cocoons will provide bioinspiration and methods for designing new composites.

The beta-1, 4-N-acetylglucosaminidase 1gene, selected by domestication and breeding, is involved in cocoon construction of Bombyx mori.

Holometabolous insects have distinct larval, pupal, and adult stages. The pupal stage is typically immobile and can be subject to predation, but cocoon offers pupal protection for many insect species. The cocoon provides a space in which the pupa to adult metamorphosis occurs. It also protects the pupa from weather, predators and parasitoids. Silk protein is a precursor of the silk used in cocoon construction. We used the silkworm as a model species to identify genes affecting silk protein synthesis and cocoon construction. We used quantitative genetic analysis to demonstrate that β-1,4-N-acetylglucosaminidase 1 (BmGlcNase1) is associated with synthesis of sericin, the main composite of cocoon. BmGlcNase1 has an expression pattern coupled with silk gland development and cocoon shell weight (CSW) variation, and CSW is an index of the ability to synthesize silk protein. Up-regulated expression of BmGlcNase1 increased sericin content by 13.9% and 22.5% while down-regulation reduced sericin content by 41.2% and 27.3% in the cocoons of females and males, respectively. Genomic sequencing revealed that sequence variation upstream of the BmGlcNase1 transcriptional start site (TSS) is associated with the expression of BmGlcNase1 and CSW. Selective pressure analysis showed that GlcNase1 was differentially selected in insects with and without cocoons (ω1 = 0.044 vs. ω2 = 0.154). This indicates that this gene has a conserved function in the cocooning process of insects. BmGlcNase1 appears to be involved in sericin synthesis and silkworm cocooning.

A transparent sericin-polyacrylamide interpenetrating network hydrogel as visualized dressing material

High transparent and biocompatible hydrogel dressing with bioactivity is attractive for clinical skin repair. Here we report a high optically transparent interpenetrating network (IPN) hydrogel that was fabricated by sericin and polyacrylamide. The hydrogels possess pH-dependent degradation as well as high porosity and porous structures with different sized diameters and distribution. Moreover, the swelling behaviors, degradation dynamics, and mechanical strength can be flexibly regulated by adjusting the content of sericin. In addition, the hydrogel system is compatible with hosting cells owing to its excellent cell-adhesive capability, effectively promoting cell attachment, proliferation and long-term survival. Together, our study demonstrates that the sericin-polyacrylamide interpenetrating network hydrogel may serve as a visualized dressing material for real-time monitoring of wounds.