Silkworm Cocoon Silk Research Articles

Enhancing the In Vitro Biological Activity of Degraded Silk Sericin and Its Analog Metabolites.

Two sericins of high and low molecular weight (HS and LS) were prepared from commercial silkworm cocoon silk with a boiling water and Ca(OH)2 solution with ultrasonic treatments, respectively. This study first investigated the release concentration of the two abovementioned sericins in simulated saliva, gastric juice, and intestinal juice (pH 6.8, 2.0, and 7.4, respectively) within 10 h. The results showed that the order of sericin release rate and its amount in the simulated environment was gastric juice > saliva > intestinal juice. Second, the molecular weights of both sericin metabolites formed by in vitro enzymatic degradation were lower than 15 kDa. The α-glucosidase inhibitory activities of both sericins and their analog metabolites were positively correlated with their concentrations. The IC50 values of the HS- and LS-derived metabolites were 1.02 ± 0.12 mg/mL and 0.91 ± 0.15 mg/mL, respectively, which were five to seven times lower than those of both original sericins. The total antioxidant capacities and hydroxyl radical scavenging capacities of both metabolites were enhanced by one- to three-fold compared with HS and LS. These results indicate that both sericins, regardless of molecular size, have significantly enhanced antioxidant, superoxide free radical scavenging, and glycosidase inhibitory activities after simulated metabolism, and that LS is better than HS regardless of simulated digestion. These results confirm that sericin is important in the sustainable development and utilization of silk resources, especially the reduction in environmental pollution, and provides new ideas for the development of adjuvant treatments for diabetes and the development of foods with anti-hyperglycemic functions.

Identification and location of sericin in silkworm with anti-sericin antibodies

Sericin, as the main component of silkworm cocoon silk, surrounds and protects the silk fibroin. Sericin is a natural macromolecular protein complex encoded by the genes Ser1, Ser2, and Ser3. At present, there are no available antibodies against sericin that may be used to identify and locate it at the protein level, hindering the study of its secretion mechanism and materials application. Therefore, the development of effective antibodies against sericin is an urgent necessity. To address this problem, we prepared polyclonal antibodies against the Ser1, Ser2 and Ser3 proteins using synthesized peptides for the first time. The specificity of the antibodies was confirmed using dot blot, immunoblotting and mass spectrometry on the hybrid bands of the middle silk gland. The immunoblotting results of anti-sericin antibodies showed that sericin has different molecular weights in different regions of the middle silk gland and strains in the 5th instar. Through immunohistochemistry, anti-sericin antibodies revealed that sericin presented different distributions in the anterior part of the middle silk gland of 872 strain at the 7th day of 5th instar. In addition, the prepared antibodies not only detected intact sericin molecules, but also detected degraded sericin that was dissolved in five different solvents. In summary, this work prepared effective sericin antibodies for silk protein synthesis and secretion research and provides a possible molecular detection method for biological products containing silkworm sericin.

Human epidermal growth factor-functionalized cocoon silk with improved cell proliferation activity for the fabrication of wound dressings.

Human epidermal growth factor (hEGF) is a key factor involved in wound healing owing to its powerful ability to stimulate cell proliferation. In this study, we used piggyBac transposon technology to produce transgenic silkworms expressing the hEGF protein fused to truncated heavy chain (FibH-hEGF). The FibH-hEGF fusion protein was successfully expressed and secreted into silkworm cocoons. Compared to wild-type silk, the transgenic silkworm silk had the similar morphology about silks fiber surface and cocoon nets, while the secondary structure between the transgenic silk and wild-type silk was different. Most importantly, transgenic silkworm cocoon silk powder extract significantly increased human fibroblast FIB cell proliferation for a long duration with no apparent cytotoxicity. Our study provides a promising method for obtaining cost-effective and functional biomaterials for the fabrication of wound dressings.

Antibacterial Mechanism of Silkworm Seroins.

Seroin 1 and seroin 2 are abundant in silkworm cocoon silk and show strong antibacterial activities, and thus are thought to protect cocoon silk from damage by bacteria. In this study, we characterized the expression pattern of silkworm seroin 3, and found that seroin 3 is synthesized in the female ovary and secreted into egg to play its roles. After being infected, seroin 1, 2, and 3 were significantly up-regulated in the silkworm. We synthesized the full-length protein of seroin 1, 2, and 3 and their N/C-terminal domain (seroin-N/C), and compared the antimicrobial activities in vitro. All three seroins showed higher antibacterial activity against Gram-positive bacteria than against Gram-negative bacteria. Seroin 2 showed better antibacterial effect than seroin 1 and 3, whereas seroin 1/2/3-N was better than seroin 1/2/3-C. We found that seroin 2-C has stronger peptidoglycan binding ability than seroin 2-N per the ELISA test. The binding sites of seroin 2 with bacteria were blocked by peptidoglycan, which resulted in the loss of the antibacterial activity of seroin 2. Collectively, these findings suggest that seroin 1 and 2 play antibacterial roles in cocoon silk, whereas seroin 3 functions in the eggs. The three silkworm seroins have the same antibacterial mechanism, that is, binding to bacterial peptidoglycan by the C-terminal domain and inhibiting bacterial growth by the N-terminal domain.

Does Thermal Annealing Affect the Mechanical Properties of Silkworm (Bombyx mori) Cocoon Silk?

ABSTRACTIt has been reported [1] that microwave radiation can enhance many of the mechanical properties of Bombyx mori silkworm cocoon silk, as measured in constant strain rate tensile tests to failure and in stress relaxation tests. The consequences of microwave radiation will affect decisions about the use of silk in settings subjected to significant microwave exposure – for example, as a reinforcing fiber in an epoxy matrix composite that may be microwave cured, or as a component in aircraft radomes.There are two possible mechanisms by which microwave radiation may affect a material [2]: (i) the radiation may enable chemical and/or microstructural changes – and therefore property changes – in the same way that conventional heating would, or (ii) the high heating rates that are achievable by microwaving may selectively favor changes that would be masked under conventional conditions, where heating rates are low enough to give preference to changes that have a lower activation energy. Here we explore the former possibility for silk.We characterized several mechanical properties of degummed and subsequently annealed B. mori silk, and compared them to the corresponding properties of degummed B. mori silk that was not annealed. The annealing treatment was carried out at 140 °C for 7 hours (conditions that optimally increased crystal size in an unrelated study of B. mori silk [3]), and then the fibers were allowed to cool gradually to room temperature over the course of an hour. Comparison of mechanical properties revealed no differences between the materials that we tested. Thus, for annealed silk, we do not observe the enhancements that can be achieved by microwaving. We conclude that in cases where microwaving affects the properties of silk, those changes are not a simple consequence of annealing by the microwaves.

Generation of Monodisperse Silk Microspheres Prepared with Microfluidics

Monodisperse microspheres of reconstituted silkworm cocoon silk were produced using a glass capillary-based microfluidic system and by identifying an appropriate solvent/nonsolvent fluid system. The microspheres can be produced to a range of different diameters depending on the system flow rates and have a nearly homogeneous size distribution. The silk microspheres exhibit a unique core--shell architecture and have a largely beta-sheet structure, as measured by infrared spectroscopy. Mechanical characterization was performed with AFM nanoindentation and indicates that the microspheres are unexpectedly soft for a silk material. Because silk is well established as biocompatible and biodegradable, we anticipate that these silk microspheres could have particular utility in drug delivery and controlled release.

Comparing the rheology of native spider and silkworm spinning dope

Silk production has evolved to be energetically efficient and functionally optimized, yielding a material that can outperform most industrial fibres, particularly in toughness. Spider silk has hitherto defied all attempts at reproduction, despite advances in our understanding of the molecular mechanisms behind its superb mechanical properties. Spun fibres, natural and man-made, rely on the extrusion process to facilitate molecular orientation and bonding. Hence a full understanding of the flow characteristics of native spinning feedstock (dope) will be essential to translate natural spinning to artificial silk production. Here we show remarkable similarity between the rheologies for native spider-dragline and silkworm-cocoon silk, despite their independent evolution and substantial differences in protein structure. Surprisingly, both dopes behave like typical polymer melts. This observation opens the door to using polymer theory to clarify our general understanding of natural silks, despite the many specializations found in different animal species.

Tensile behavior and morphology of differently degummed silkworm (Bombyx mori) cocoon silk fibres

Tensile tests have been performed on silkworm cocoon silk fibres degummed using five different methods: distilled water, boracic acid–sodium borate buffer, sodium carbonate, urea and succinic acid. Using an electronic single-fibre tensile instron, the force–displacement curves were obtained for each condition. Effects of degumming on silk include a decrease in the initial elastic modulus and a decrease in the proportional limit (i.e., yield point). These results suggest that degumming weakens at least one type of non-covalent interaction of core fibrion, such as hydrogen bonds and Van der waal's bonds. The stress–strain curve determined from a force–displacement curve as rescaled by the corresponding sample cross-sectional area failed to reproduce the actual mechanical properties of two fibroin core fibres because of variable degradation of the sericin coating. The two important factors associated with degumming could affect the tensile properties of silkworm silk: 1) the change in the microstructure of two core fibroin, and 2) the degumming ratio. SEM was used to observe visually the morphology and fractography of differently degummed cocoon silk fibres. Effects of different degumming treatments on the tensile behavior, mechanical properties, morphology and fractography of cocoon silk are clearly visible.