Haesung Yun

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.

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.

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.

Methyl cellulose nanofibrous mat for lipase immobilization via cross-linked enzyme aggregates

Nanofibers prepared from cellulose derivatives are a suitable support for enzyme immobilization. We selected a methyl cellulose (MC) nanofibrous mat for enzyme immobilization. First, we established the electrospinning conditions for the preparation of the MC nanofibrous mat. A mixture of ethanol and water at a volume ratio of 1:1 was selected as the solvent of MC for electrospinning. An MC concentration of 5 wt% and a flow rate of 0.5 mL/h were employed to ensure stable electrospinning without bead formation. By varying the applied voltage, the sizes of the MC nanofibers could be controlled in the range of 50 to 80 nm, and an applied voltage of 18 kV was selected for further experimentation. The MC nanofibrous mats were cross-linked with glutaraldehyde under acidic conditions for 12 h in order to increase the stability of the mats in water. Lipase was directly immobilized onto cross-linked MC nanofibrous mats without a further activation step, and 34.82 µg of lipase was immobilized per mg of support. The reusability test showed an unexpected loss of activity after second reuse due to a loss of lipase during the washing procedure promoted by the surface erosion of the MC nanofiber. This problem was solved by introducing crosslinked enzyme aggregates (CLEA) to the surfaces of MC nanofibers. CLEA formation enhanced the activity of lipase per mg of support by almost 5-fold compared with the original lipase-immobilized MC nanofibrous mat. The reusability was also enhanced: more than 90% of the initial activity was retained after seven reuses.

Preparation and Characterization of Sericin/PVA Blend Fibers Using Recovered Sericin

Abstract: Sericin/PVA blend fibers were prepared using sericin that had been recovered during conventional degum-ming. Pure recovered sericin (RS) fibers could not be formed because of their low molecular weights. By blending theRS with PVA, it could be spun into fibers. A maximum draw ratio of 7.5 was achieved when the PVA/RS blend ratiowas 80:20. The morphologies of the PVA/RS fibers were equivalent to those of the blend fibers prepared with hot-water extracted sericin (HS). The elongations at failure and Young’s moduli of the PVA/RS and PVA/HS blend fiberswere not significantly different. However, the ultimate strengths of the PVA/RS blend fibers were lower than those ofthe PVA/HS blend fibers. XRD data revealed that the crystallinities of the blend fibers decreased in the presence of RS. Keywords: sericin, degumming, protein fiber, blend fiber, wet spinning 1. 서론 실크는 물성이 우수할 뿐만 아니라 고유의 촉감과 광택으로 과거부터 지금까지 최고급 섬유소재로 활용되었다.실크의 촉감과 광택은 고치실의 단백질 성분 중 세리신을제거한 후에 나타나게 된다. 세리신을 제거하는 방법으로는 고온의 물, 알칼리-염, 비누정련 등의 다양한 방법이 이용되고 있으며, 그 중 비누정련법이 산업 분야에서 가장 많이 이용되고 있다. 이렇게 제거된 세리신이 포함된 정련폐액은 현재 전액 폐기되고 있는 실정인데, 고치실의 무게 중약 25%가 세리신인 것을 감안하면, 실크 1M/T 생산당333 kg의 세리신이 폐기되고 있는 것이다. 이렇게 많은 양이 단백질이 포함된 정련폐액은 결국 하천의 부영양화를초래하여 환경 오염의 원인이 될 수 있으며, 폐수처리 비용을 증대시켜 경제적으로도 부담요인으로 작용하게 된다.따라서 과거로부터 세리신을 회수하여 새로운 소재로 활용하기 위한 시도가 많이 있었으며, 성공할 경우 환경 및 비용의 문제를 해결할 수 있을 것으로 기대되었다. 또한 최근에는 재생가능한 자원으로 천연고분자가 주목을 받고 있는데, 전 세계적으로 생산량이 풍부하고 폐기물에서 회수한다는 점에서 세리신은 주목해야 할 천연고분자중의 하나이다.세리신을 활용하기 위해서 많은 연구가 시도되고 있으나정작 정련폐액에서 세리신을 회수하는 연구는 성공적 사례가 많이 보고되고 있지 않다. 현재 세리신을 이용한 연구는 주로 열수추출법을 이용하여 세리신을 추출하는데, 이경우 남은 75%의 피브로인의 사용용도가 없기 때문에 실제 산업적으로 이용하기에는 부적합한 방법이다. 따라서정련폐액으로부터 세리신을 회수하는 것이 보다 현실성이있다고 판단되며, 이러한 목적을 달성하고자 많은 연구가진행되었다. 분리막을 이용한 세리신 회수방법이 가장 많이 시도되었으나 순도가 낮거나 분자량이 매우 낮은 세리신이 얻어져 고분자 재료로서 이용하기에 적합하지 않았다[1]. 또한 실험 과정에서 세리신 농도를 낮추기 위하여 약5배 가량 희석하여 실험한 경우가 있어 이를 직접 정련 폐액의 처리 과정에 적용하기에 어려움이 있다[2,3]. 키토산