Hyo Won Kwak

Extraction conditions of Antheraea mylitta sericin with high yields and minimum molecular weight degradation

Although the technique for extracting the Bombyx mori sericin has been extensively known, the extraction of sericin from wild-silkworm cocoons is not yet standardized. The aim of this study was to find the optimal conditions for the extraction of sericin from Antheraea mylitta cocoons, with high yields and minimum degradation. We attempted to apply various protocols for the extraction of the A. mylitta sericin (AmS). Among these, we found that the extraction of AmS with a sodium carbonate solution exhibited the highest yield except the conventional soap-alkali extraction. To find the optimal conditions for the AmS extraction with the sodium carbonate, we changed the concentration of sodium carbonate and the treatment time. With an increase in the sodium carbonate concentration and the extraction time, the yield of AmS increased, but the molecular weight (MW) of AmS decreased. Considering the yield, molecular weight distribution (MWD) and amino acid composition of AmS, we suggest that the optimal conditions for the AmS extraction require treatment with 0.02 M sodium carbonate and boiling for 60 min.

Preparation and characterization of silk sericin/glycerol/graphene oxide nanocomposite film

Sericin (SS) is a protein that is secreted by silkworms, but it is usually discarded during the degumming process. To obtain and make use of the sericin, we prepared sericin/glycerol/graphene oxide nanocomposite film. The inherent brittleness of pure sericin film was improved by the addition of glycerol (Glc) as a plasticizer. To compensate for the reduced stiffness, we added graphene oxide (GO) into the SS/Glc film. At concentrations of up to 0.8 wt% relative to SS, GO dispersed evenly in the SS matrix without any agglomeration. The maximum tensile strength (9.5±0.7 MPa) and Young’s modulus (414.4±23.2 MPa) were obtained when the GO content was 0.8 wt% relative to SS. The elongation of SS/Glc/GO nanocomposite film also increased by approximately 40 % compared to SS/Glc film. The strong interfacial interaction between the SS and the GO was responsible for the increased stiffness. The increased elongation was due to the reduced crystallinity of the sericin matrix in the presence of GO.

The role of glycerol and water in flexible silk sericin film.

Silk sericin (SS) can be obtained as a byproduct during the silk fiber process, but its application has been limited due to the brittleness of the SS film. To enhance the flexibility of the SS film, glycerol (Glc) has been added as a plasticizer. The addition of Glc enhanced the elongation property of the SS film when the Glc content was 50-70 wt% of SS. Glc also induced the structural transition of SS from a random coil structure to a β-sheet structure. The inconsistent increase of elongation and β-sheet structure of the SS/Glc film were explained by the content of moisture in the SS/Glc film. The moisture content of the SS/Glc film increased proportionally when the Glc content was higher than 50 wt% of SS, which was the same Glc content range that exhibited the plasticizing effect. Therefore, the plasticizing effect on the SS film may occur not only because of Glc but also because of water. Furthermore, water also contributed to the increase in the β-sheet structure development. Our results suggest that the moisture content in the plasticized protein film may play an important role when the plasticizer has hygroscopic properties.

Fabrication of Phaeodactylum tricornutum extract-loaded gelatin nanofibrous mats exhibiting antimicrobial activity

Microalgae have recently been recognized as a valuable resource for various applications. Phaeodactylum tricornutum is a diatom that lives in marine water and has an unusually high content of lipids. In this study, we added P. tricornutum into a gelatin dope solution to examine the effect of this diatom using electrospinning. The addition of P. tricornutum extracts increased the conductivity of the dope solution but had little effect on the viscosity. Due to the increased conductivity, the fiber diameter was reduced compared with the neat gelatin nanofiber. The loading of P. tricornutum extracts was confirmed using fluorescence microscopy, and the incorporation of lipids was detected through gas chromatography. The P. tricornutum-loaded nanofiber mat exhibited anti-microbial activity against Escherichia coli and multidrug-resistant Staphylococcus aureus (MRSA). The cell viability test showed that the P. tricornutum-loaded nanofiber has no cytotoxicity. We expect that this antimicrobial P. tricornutum-loaded gelatin nanofiber mat can be applied as a wound dressing.

Structural characteristics and biological performance of silk fibroin nanofiber containing microalgae spirulina extract

Silk fibroin (SF) nanofiber scaffold containing microalgae Spirulina extract were prepared by electrospinning and the performance and functionality of the scaffold were evaluated. The viscosity and conductivity of the dope solution of Spirulina containing SF were examined for electrospinability and we found that the morphological structure of SF nanofiber is affected by the concentration of Spirulina extract added. The platelet adhesion and coagulation time test confirmed that the Spirulina containing SF nanofiber scaffold had excellent ability to prevent blood clotting or antithrombogenicity that is comparable to heparin. Low cytotoxicity and excellent cell adhesion and proliferation were also observed for Sprulina containing SF nanofiber scaffold by methylthiazolyldiphenyl-tetrazolium bromide assay and confocal fluorescence microscope using fibroblast and human umbilical vein endothelial cells. Based on these results, we believe SF nanofiber scaffold containing Spirulina extract has the potential to be used as tissue engineering scaffold that requires high hemocompatibility.

Effect of shear viscosity on the preparation of sphere-like silk fibroin microparticles by electrospraying.

Silk fibroin (SF) is known to be a biocompatible material, and different forms of SF are used for various applications. However, the application of SF in particle form is rarely reported, compared to other forms. In this study, SF microparticles with a diameter of approximately 250 μm were prepared by the electrospray method, using 1 M LiCl/DMSO as a solvent. The dissolution time of SF in the CaCl2/CH3CH2OH/H2O solution and the concentration of the SF dope solution affected the final morphology of the microparticles. A long dissolution time and a low SF concentration led to the formation of irregular microparticles, but a short dissolution time and a high concentration produced sphere-like microparticles. The shear viscosity of the SF dope solution was the main parameter that affected the morphology of the SF microparticles. Regardless of the dissolution time in the CaCl2/CH3CH2OH/H2O solution and the concentration of the SF dope solution, the shear viscosity of the dope solution must be higher than 0.33 Pa s to produce sphere-like microparticles. Finally, cell adhesion experiments demonstrated that these SF microparticles show potential for use as cell carriers.

Silk sericin microparticles as a biosorbent for hexavalent chromium ion

AbstractSilk sericin (SS) microparticles prepared using the electrospraying method were used for the removal of Cr(VI). SS microparticles exhibited better Cr(VI) adsorption capacity than that of SS macrobeads due to the increased surface area. The optimum pH for Cr(VI) adsorption was 1–2, and the adsorption kinetics followed pseudo secondorder kinetics. The adsorption behavior followed three stages: initial external mass transportation, limited intraparticle diffusion and near equilibrium stage. From the isotherm model study, the Brunauer-Emmett-Teller (BET) model exhibited a very good fit for Cr(VI) adsorption, indicating that SS microparticle has multiple layers and homogeneous active binding sites. The adsorption capacity increased with an increase in the initial Cr(VI) concentration and a decrease in the dosage of the biosorbent.

Preparation of Silk Sericin/Lignin Blend Beads for the Removal of Hexavalent Chromium Ions

In the present study, novel adsorbents having high adsorption capability and reusability were prepared using agricultural by-products: silk sericin and lignin. Silk sericin and lignin blend beads were successfully prepared using simple coagulation methods for the removal of hexavalent chromium (Cr(VI)) from aqueous solution. A 1 M lithium chloride (LiCl)/dimethyl sulfoxide (DMSO) solvent system successfully dissolved both sericin and lignin and had sufficient viscosity for bead preparation. Compared to the conventional sericin bead adsorbent, sericin/lignin blend beads showed higher Cr(VI) adsorption capacity. The amount of lignin added to the adsorbent greatly affected the adsorption capacity of the beads, and a 50:50 sericin/lignin blend ratio was optimal. Adsorption behavior followed the Freundlich isotherm, which means the adsorption of Cr(VI) occurred on the heterogeneous surface. Cr(VI) adsorption capability increased with temperature because of thermodynamic-kinetic effects. In addition, over 90% of Cr(VI) ions were recovered from the Cr(VI) adsorbed sericin/lignin beads in a 1 M NaOH solution. The adsorption-desorption recycling process was stable for more than seven cycles, and the recycling efficiency was 82%. It is expected that the sericin/lignin beads could be successfully applied in wastewater remediation especially for hazardous Cr(VI) ions in industrial wastewater.

Fabrication of an ultrafine fish gelatin nanofibrous web from an aqueous solution by electrospinning

Electrospinning of aqueous gelatin solution obtained from bovine or porcine sources has been difficult to achieve without additional facilities, such as a temperature control oven or heating cover. Gelatin from cold-water fish has low contents of proline (Pro) and hydroxyproline (Hyp) compared with mammalian-derived gelatin. For this reason, the fish-derived gelatin maintains a sol state without showing gelation behavior at room temperature. In the present study, we prepared an ultrafine fish gelatin nanofibrous web by electrospinning from aqueous solutions without any additive polymers or temperature control facilities. The concentration and viscosity of fish gelatin are the most important factor in determining the electrospinnability and fiber diameter. Electrospinning of aqueous fish gelatin has the highest nanofiber productivity compared to other organic solvent systems. Using glutaraldehyde vapor (GTA), the water stability was improved and substantial enhancement was achieved in the mechanical properties. Finally, the cytotoxicity of a fish gelatin nanofibrous scaffold was evaluated based on a cell proliferation study by culturing human dermal fibroblasts (HDFs) compared with a fish gelatin film and nanofibrous mat from mammalian gelatin. The result shows better initial cell attachment and proliferation compared with the fish gelatin film and no significant difference compared with mammalian-derived gelatin nanofibrous mat. We expect that electrospinning of aqueous fish gelatin could be an effective alternative mammalian gelatin source.

Sericin Promotes Fibroin Silk I Stabilization Across a Phase-Separation

Natural silk spinning offers several advantages over the synthetic fiber spinning, although the underlying mechanisms of this process are yet to be fully elucidated. Silkworm silks, specifically B. mori, comprise two main proteins: fibroin, which forms the fiber, and sericin, a coextruded coating that acts as a matrix in the resulting nonwoven composite cocoon. To date, most studies have focused on fibroins self-assembly and gelation, with the influence of sericin during spinning receiving little to no attention. This study investigates sericins effects on the self-assembly of fibroin via their natural phase-separation. Through changes in sample opacity, FTIR, and XRD, we report that increasing sericin concentration retards the time to gelation and β-sheet formation of fibroin, causing it to adopt a Silk I conformation. Such findings have important implications for both the natural silk spinning process and any future industrial applications, suggesting that sericin may be able to induce long-range conformational and stability control in silk fibroin, while being in a separate phase, a factor that would facilitate long-term storage or silk feedstocks.