Application of electrospun silk fibroin nanofibers as an immobilization support of enzyme

Silk fibroin (SF) nanofibers were prepared by electrospinning and their application as an enzyme immobilization support was attempted. By varying the concentration of SF dope solution the diameter of SF nanofiber was controlled. The SF nanofiber web had high capacity of enzyme loading, which reached to 5.6 wt%. The activity of immobilizedα-chymotrypsin (CT) on SF nanofiber was 8 times higher than that on silk fiber and it increased as the fiber diameter decreased. Sample SF8 (ca. 205 nm fiber diameter) has excellent stability at 25°C by retaining more than 90 % of initial activity after 24 hours, while sample SF11 (ca. 320 nm fiber diameter) shows higher stability in ethanol, retaining more than 45% of initial activity. The formation of multipoint attachment between enzyme and support might increase the stability of enzyme. From these results, it is expected that the electrospun SF nanofibers can be used as an excellent support for enzyme immobilization.     

Covalent immobilization of urease to modified ethyl cellulose

Graft polymerization technology is a good way to modify polymers. New functional groups are added to polymer structure using graft polymerization. Enzyme immobilization could be done from these added functional groups. Ethyl cellulose was selected as a support for enzyme immobilization and no many studies has been conducted about it. It is insoluble in water and suitable for reuse. In this study, methacrylic acid was graft polymerized to ethyl cellulose using benzophenone. In graft polymerization studies, optimum amounts of methacrylic acid and benzophenone were determined as 60 mmol and 0.6 g, respectively. Percentage of graft polymerization was maximum in toluene as solvent and optimum graft polymerization time was found as 3 hours. The graft polymerization percentage was 225.7 % at optimum conditions. This value was very good for UV-induced graft polymerization technique. FT-IR spectra of ethyl cellulose and methacrylic acid graft polymerized ethyl cellulose showed that graft polymerization was carried out successfully. -COOH groups were added to ethyl cellulose structure after graft polymerization. Then, urease was immobilized to methacrylic acid graft polymerized ethyl cellulose using 1-ethyl-3-(3-dimetylaminopropyl)-carbodiimide as the condensing agent which accelerates the reaction between -COOH from methacrylic acid graft polymerized ethyl cellulose and -NH2 from urease. Optimization studies were also performed for the immobilization of urease. Optimized values for urease immobilization; optimum amount of 1-ethyl-3-(3-dimetylaminopropyl)-carbodiimide was found as 5 mg, temperature was determined as 37 °C, 2 hours were selected as optimum time, pH and amount of urease were found to be pH 7 and 10 mg, respectively. Remained activity of immobilized urease was 1.74 % before optimization studies. After optimization of immobilization studies, this ratio has increased to 29.85 %. The immobilized urease activity was increased 17.2 times.     

Antibacterial Bombyx Mori silk fabric modified with reactive chitosan quaternary ammonium salt and its laundering durability

A new fiber-reactive chitosan derivative was synthesized in two steps from a chitosan of low molecular weight. First, a water-soluble chitosan derivative, N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride (short for HTCC), was prepared by reacting chitosan with 2,3-epoxypropyltrimethylammonium chloride. Second, HTCC was further modified by reacting with N-(hydroxymethyl)-acrylamide to prepare a fiber-reactive chitosan derivative, O-methyl acrylamide quaternary ammonium salt of chitosan (short for NMA-HTCC), which can form covalent bonds with silk fiber under alkaline conditions. The chemical structure of NMA-HTCC was characterized by Fourier transform infrared spectrum (FTIR) and nuclear magnetic resonance (NMR). The substitution degree of HTCC and the double-bond content of NMA-HTCC were tested. Then NMA-HTCC was used for antibacterial finishing of Bombyx Mori silk fabric. The results showed that silk fabric treated with NMA-HTCC had a significantly improved antibacterial activity to Staphylococcus aureus and Escherichia coli, and the antibacterial activity of silk fabric finished by NMA-HTCC was much better than that finished by chitosan and HTCC. Bombyx Mori silk fabric modified with NMA-HTCC demonstrated excellent durable antibacterial activity, even after 50 repeated launderings, the bacterial reduction rate of silk fabric maintained over 95 %.     

Chitosan Activated with Genipin: A Nontoxic Natural Carrier for Tannase Immobilization and Its Application in Enhancing Biological Activities of Tea Extract

In this work, a non-toxic chitosan-based carrier was constructed via genipin activation and applied for the immobilization of tannase. The immobilization carriers and immobilized tannase were characterized using Fourier transform infrared spectroscopy and thermogravimetric analysis. Activation conditions (genipin concentration, activation temperature, activation pH and activation time) and immobilizations conditions (enzyme amount, immobilization time, immobilization temperature, immobilization pH, and shaking speed) were optimized. The activity and activity recovery rate of the immobilized tannase prepared using optimal activation and immobilization conditions reached 29.2 U/g and 53.6%, respectively. The immobilized tannase exhibited better environmental adaptability and stability. The immobilized tannase retained 20.1% of the initial activity after 12 cycles and retained 81.12% of residual activity after 30 days storage. The catechins composition analysis of tea extract indicated that the concentration of non-ester-type catechins, EGC and EC, were increased by 1758% and 807% after enzymatic treatment. Biological activity studies of tea extract revealed that tea extract treated with the immobilized tannase possessed higher antioxidant activity, higher inhibitory effect on α-amylase, and lower inhibitory effect on α-glucosidase. Our results demonstrate that chitosan activated with genipin could be an effective non-toxic carrier for tannase immobilization and enhancing biological activities of tea extract.     

Synthesis,characterization, and properties of ethoxylated azo dyes

The nonionic surfactant properties of ethoxylated azo dyes, such as cloud point and surface tension have been investigated. The synthesized ethoxylated azo dyes could dye polyester fabric without any special pre-treatment. When the average number of ethylene oxide (EO) in the ethoxylated azo dye reached 6, its fixation could exceed 90% from the thermosol dyeing process. The average degree of condensation of ethylene glycol in the chain was interrelated with the dyeing results and did not affect on the maximum absorption wavelength (λmax) of the polyoxyethylene dye. When the average length of polyoxyethylene chain decreased, the molecular weight of dyes became smaller and the fixation of dyes was improved.     

Photocatalytic degradation of formaldehyde by silk mask paper loading nanometer titanium dioxide

Silk mask paper with different adsorbability was prepared by changing the beating degree of silk pulp and the basis weight of silk paper, and photocatalytic silk mask paper was prepared by loading nanometer titanium dioxide (nano-TiO₂) on the silk mask paper, then degradation of formaldehyde by silk mask paper loading nano-TiO₂ under daylight lamps and ultraviolet lamps were investigated, respectively. Results showed that silk mask paper could adsorb formaldehyde and had higher adsorption efficiency in the initial stage, and the adsorption/desorption equilibrium could be basically achieved in 60 minutes. The adsorption capacity of silk mask paper made from silk pulp with beating degree of 45 ^oSR was relatively low, and it increased with the increase of beating degree, but there was little change in adsorption when the beating degree of silk pulp exceeded 65 ^oSR. Under daylight lamps, 26.61 %, 31.42 % and 38.21 % of formaldehyde could be degraded in 180 minutes by silk mask paper loading 1 wt%, 3 wt% and 5 wt% nano-TiO₂, respectively. However, under ultraviolet (UV) lamps, 46.23 %, 55.47 % and 66.38 % of formaldehyde could be degraded within the same time, respectively. More formaldehyde could be degraded by photocatalytic silk mask paper under UV lamps than under daylight lamps, and the more the load of nano-TiO₂ on the silk mask paper, the higher the degradation rate of formaldehyde within the same time.     

A promising approach for bio-finishing of cotton using immobilized acid-cellulase

In this research, cellulases were immobilized on Eudragit S-100 to minimize the tensile strength loss of cotton fabric caused by the enzymatic hydrolysis. About 76 % of the enzyme activity and 81 % of the amount of protein were recovered after the immobilization process, and the immobilized cellulase exhibited good reuse ability. The immobilized cellulase had the better adsorptive performance on cotton than the free cellulase. In addition, the results revealed that the catalytic efficiency of the immobilized cellulase on cotton was degradation, perhaps because the diffusion of the enlarged cellulase molecules is significantly inhibited in the interior of the cotton fiber. Moreover, the cotton fabric treated with the immobilized cellulase showed less weight and strength losses. SEM pictures further indicated that the cotton fabric treated with the immobilized cellulase suffered less damage.     

Reducing silk fibrillation through MMA graft method

Silk fibrillation, one major weakness of silk fibers, can lead to undesirable fabric appearance. In this research, an effective method for reducing the fibrillation of silk fibers through the graft copolymerization with methyl methacrylate (MMA) has been developed. The major copolymerization factors such as the initiator concentration, MMA monomer concentration, reaction time and temperature were investigated. An AATCC Crockmeter was used to rub the fabric to simulate the abrasion in production to generate the fibrillation. The microscope observation and the evaluation of fibrillation index (FI) were applied to assess the degree of fibrillation of silk fibers. The optimum graft copolymerization factors were obtained. Instrumental analyses, such as FTIR, TG and SEM, proved that the silk fabric had been successfully grafted with MMA monomers. The fibrillation of the grafted silk fibers was considerably reduced since the coated PMMA can protect the silk fiber. In addition, the physical properties such as the crease recovery, breaking strength, and the breaking length of the grafted silk fabrics were also improved.     

Fabrication and characterization of nanofibers based on poly(lactic acid)/chitosan blends by electrospinning and their functionalization with phospholipase A1

In this work, electrospinning of poly(lactic acid) (PLA), chitosan and their blends has been investigated, and nanofibers with a diameter ranging from 90 nm to 1.9 microns were produced and used as carriers for immobilization of the phospholipase A1. A strong influence of chitosan (CS) and the solvent trifluoroacetic acid (TFA) on the morphology, distribution of the nanofibers diameter and on their hydrophobicity was observed. The yield of phospholipase A1 (PLA1) on non-woven fibers was evaluated using the method of Bradford. Their activities and their reutilisability were assessed titrimetrically using soybean lecithin as substrate. The results showed that the degree of immobilization on the non-woven fibers of pure PLA and mixtures PLA/CS4 and PLA/SC6 are 73, 54, 45 % respectively and can be reused up to 4 cycles without significant loss of enzyme activity. Moreover, a remarkable improvement of the activity of phospholipase A1 on non-woven based on pure PLA fibers was observed, indicating that most of the enzymes were probably in their active form.     

An effective and simple process for obtaining high strength silkworm (Bombyx mori) silk fiber

This article describes a new process for strengthening natural silk fibers. This process is simple yet effective for mass production of high strength silk fibers, enabled by drawing at a lower temperature and immediately heat setting at a higher temperature. The processing conditions were investigated and optimized to improve the strength. Silk fibers drawn to the maximum ratio at room temperature and then heat set at 200 °C show best tensile properties. Some salient features of the resulting fibers are tensile strength at break reaching 533±10.2 MPa and Young’s modulus attaining 12.9±0.57 GPa. These values are significantly higher than those of natural silk fibers (tensile strength increased by 44 % and Young’s modulus by 135 %). Wide-angle X-ray diffraction and FTIR confirm the transformation of silk I to silk II crystalline structure for the fiber obtained from this process. DSC and TGA data also provide support for the structural change of the silk fiber.     

Biochemical Properties and Anti-Biofilm Activity of Chitosan-Immobilized Papain

Chitosan, the product of chitin deacetylation, is an excellent candidate for enzyme immobilization purposes. Here we demonstrate that papain, an endolytic cysteine protease (EC: 3.4.22.2) from Carica papaya latex immobilized on the matrixes of medium molecular (200 kDa) and high molecular (350 kDa) weight chitosans exhibits anti-biofilm activity and increases the antimicrobials efficiency against biofilm-embedded bacteria. Immobilization in glycine buffer (pH 9.0) allowed adsorption up to 30% of the total protein (mg g chitosan⁻¹) and specific activity (U mg protein⁻¹), leading to the preservation of more than 90% of the initial total activity (U mL⁻¹). While optimal pH and temperature of the immobilized papain did not change, the immobilized enzyme exhibited elevated thermal stability and 6–7-fold longer half-life time in comparison with the soluble papain. While one-half of the total enzyme dissociates from both carriers in 24 h, this property could be used for wound-dressing materials design with dosed release of the enzyme to overcome the relatively high cytotoxicity of soluble papain. Our results indicate that both soluble and immobilized papain efficiently destroy biofilms formed by Staphylococcus aureus and Staphylococcus epidermidis. As a consequence, papain, both soluble and immobilized on medium molecular weight chitosan, is capable of potentiating the efficacy of antimicrobials against biofilm-embedded Staphylococci. Thus, papain immobilized on medium molecular weight chitosan appears a presumably beneficial agent for outer wound treatment for biofilms destruction, increasing antimicrobial treatment effectiveness.     

Expanding Application of Immobilized <Emphasis Type="Italic">Candida Antarctica</Emphasis> Lipase B: A Green Enzyme Catalyst for Knoevenagel Condensation Reaction

We propose a green synthesis of benzopyran compound based on immobilized lipase. Firstly, by using a combined electrospun membrane and biocompatible chitosan, we show that the chitosan-functionalized electrospun PMA-co-PAA fibrous membrane can provide effective anchoring sites for immobilization of the Candida antarctica lipase B (CALB), and a maximum loading amount of CALB (152 mg/g) can be achieved. Then, the resulting membrane displays enhanced stability in catalyzing Knoevenagel condensation reaction of salicylaldehyde with active methylene compound in mixed aqueousorganic media. The catalytic activity and stability of the CALB on chitosan-modified fiber is better than its non-immobilized counterpart. Furthermore, this immobilize CALB catalyst still retained about 45 % of the initial activity after 5 cycles, which potentially had implications for the design of “green” enzyme catalyst for sustainable organic synthesis.     

Curcuma Dye with Modified Treatment Using Chitosan for Superior Fastness

Curcuma dye could never gain popularity in natural dyeing as the intrinsic nature of the colorant Curcumin did not have the requisite adhering property towards natural fabrics such as silk and cotton, thereby making it very fugitive. In this paper attempts have been made to activate Curcumin molecule by complexation with chitosan (another natural linear polysaccharide). The binding took place at intrinsic pH (7–8) very effectively without any surfactant or enzyme. Dyeing with this new composite showed excellent wash and light fastnesses as compared to curcuma dye. The novelty of this dyeing process is the remarkable enhancement of wash and light fastnesses levels by 1.0–1.5 for silk and cotton fabric dyeing in just 1 hour at 40–45 °C. It is fast and energy conserving dyeing process. Three subsequent washing of the dyed samples showed very small change in CIE Lab.     

龙井茶摊放过程中β葡萄糖苷酶活性变化

对龙井茶鲜叶摊放过程中β 葡萄糖苷酶活性的变化研究表明: 鲜叶摊放2 小时, 酶活性就达到最高水平, 而后便逐渐下降, 品种间虽有差异, 但趋势基本一致。3 个品种摊放叶的酶活性以水古茶最高, 其次是龙井43 和鸠坑种。在温度较低(20 ℃左右) 和相对湿度较大(90% 左右) 时, 酶活性在6 ～8 小时仍保持较高水平, 而在温度较高(25 ℃) 和相对湿度较低(75 % —80 % ) 时, 摊放2 小时后, 酶活性就大幅度下降到较低的水平, 因此, 要达到传统工艺上的摊放要求, 宜以低温(20 ℃以下) 高湿( 相对湿度90 % 以上) 环境下摊放为妥。     

Preparation and properties of Nano-TiO2 photo-catalytic silk respirator paper

In order to obtain paper respirator with dust resistance performance and antibacterial property, silk photo-catalytic respirator paper was made by loading nano-TiO₂ photo-catalyst on silk based respirator paper. The pore structure, surface topography and TiO₂ distribution, and the filtration performance of silk respirator paper were studied by using a pore size meter (PSM), a field emission scanning electron microscope (FESEM), and a filter tester, respectively. In addition, the antibacterial property of silk respirator paper was also investigated. The results showed that the pore structure and filtration performance of silk respirator paper could be controlled by changing the degree of beating of silk pulp and the basis weight of silk paper. Silk respirator paper of 45 g/m² made from silk pulp having beating degree of 85 ^oSR had high filtration efficiency and appropriate filtration resistance. Nano-TiO₂ particles were mainly attached to the surface of silk paper, and the loading of nano-TiO₂ photo-catalyst resulted in a slight decrease in filtration resistance and filtration efficiency of silk respirator paper. It, however, improved the antibacterial property of silk respirator paper effectively.     

Structure and performance of<Emphasis Type="Italic">Bombyx mori</Emphasis> silk modified with nano-TiO<Subscript>2</Subscript> and chitosan

Bombyx mori (B. mori) silk was modified with the nano-TiO₂ and chitosan dispersion system by the crosslinking reactions of citric acid (CA) and maleic anhydride (MA). The average size of the nano-TiO₂ particles in the aqueous dispersion system was 36.7 nm. The scanning electron microscopy (SEM) micrographs showed that the nano-TiO₂ particles were spherical and homogeneously dispersed in the dispersion system, and the surface ofB. mori silk fiber treated with the nano-TiO₂ and chitosan dispersion system was rougher than that of the untreated one. X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) Spectrometry indicated that the crystallinity of theB. mori silk fiber increased after treatment. It was also found that the nano-TiO₂ and chitosan contributed to significantly enhance the mechanical properties including breaking strength, breaking elongation, initial modulus, rupture work, and elastic recovery property of theB. mori silk fiber. The wrinkle-resistant performance of the treatedB. mori silk fabrics was also greatly improved.     

Experimental Study on Antimicrobial Activity of Silk Fabric Treated with Natural Dye Extract from Neem (<Emphasis Type="Italic">Azadirachta indica</Emphasis>) Leaves

In the present study, a novel eco-friendly production of silk fabrics dyed with different natural dye bath concentrations (40, 80, 120, 160, 200 and 240 g/l) extracted from neem (Azadirachta indica) leaves was developed. The surface morphology of the fabrics was examined by scanning electron microscopy (SEM) and Fourier-transform infrared (FTIR) spectroscopy to characterize the chemical structure of the fabrics. The SEM images of the undyed fabric show that the fabric was tightly woven with little porosity between the fibres with dozens of silk threads in orthogonal directions. By increasing the neem concentration, a scale of fine particles grew on the surface of the silk fabrics with little macroscopical defects was demonstrated. The fiber diameters and tightness between filaments were significantly increased. The FTIR displayed that, neem dye does not change the characteristic peaks of the silk fabrics. Also, the evaluation of the antimicrobial activity of the undyed and neem dyed silk fabrics was monitored for Gram positive and Gram negative bacteria in addition to yeasts and fungi by using the agar diffusion method. The comparison between the different dye bath concentrations was based on the inhibition zones obtained after incubation. The antimicrobial activity in leaf extract of neem was estimated in Staphylococcus aureus, Bacillus subtilis and Lactobacillus cereus (Gram positive bacteria); Escherichia coli (Gram negative bacteria); Candida albicans and Candida tropicalis (yeasts); and Aspergillus niger and Fusarium solani (fungi). The results emphasized that, the highest neem dye bath concentration (240 g/l) was found to display good inhibitory effect against the Gram positive and reasonable activity against the Gram negative bacteria. Furthermore, the different dye bath concentrations possess no activities against yeast and fungi. In conclusion, the data reveal that the increase of neem dye concentration does not damage the silk fabric; however, it improves its antimicrobial activity by incorporating with antimicrobial agent. The current study highlighted that using neem leaves had beneficial effect in controlling the pathogenic microbial organisms.     

Preparation of amidoxime-modified polyacrylonitrile nanofibers immobilized with laccase for dye degradation

A novel approach to preparing multifunctional composite nanofibrous membrane was developed. Polyacrylonitrile (PAN) nanofibrous membrane was fabricated by electrospinning and then the nitrile groups in PAN copolymer was chemically modified to obtain amidoxime modified PAN (AOPAN) nanofiber membrane which was further used as a functional support for laccase immobilization. During the process of reactive dye degradation catalyzed by the AOPAN nanofiber membrane immobilized with laccase, metal ion adsorption occurred at the same time. The chemical modification was confirmed by Fourier transform spectroscopy (FTIR). Scanning electron microscope (SEM) was employed to investigate the surface morphologies of the electrospun nanofibers before and after laccase immobilization. The effects of environmental factors on laccase activity were studied in detail. It was found that the optimum pH and temperature for the activity of immobilized laccase was 3.5 and 50 °C. The relative activity retention of the immobilized laccase decreased dramatically during the initial four repeated uses. After 20 days’ storage, the activity retention of immobilized laccase was still high above 60 %. It has also proved that laccase immobilized on AOPAN nanofiber membrane performed well in dye degradation and metal ion adsorption.     

Palladium immobilized on aminated polyacrylonitrile nanofiber as an efficient heterogeneous catalyst for Heck reaction

Aminated polyacrylonitrile (PAN-NH) nanofiber mats prepared by electrospinning and then aminated by multiamines with different chemical structures have been used for the immobilization of palladium. The PAN-NH fiber morphologies were characterized by scanning electron microscopy (SEM) and the dispersion of palladium particles on the PAN-NH fiber were examined by transmission electron microscopy (TEM). The catalytic activity and recyclability of the prepared heterogeneous palladium catalysts have been evaluated by the Heck reaction of iodobenzene with n-butyl acrylate. It was found that the catalytic activities of PAN-NH-Pd catalysts could be correlated with the chelating energies of the PAN-NH fiber mats with Pd active species.     

Characterization of plant and animal based natural fibers reinforced polypropylene composites and their comparative study

Natural fibers are largely divided into two categories depending on their origin: plant based and animal based. Plant based natural jute fiber reinforced polypropylene (PP) matrix composites (20 wt% fiber) were fabricated by compression molding. Bending strength (BS), bending modulus (BM), tensile strength (TS), Young’s modulus (YM), and impact strength (IS) of the composites were found 44.2 MPa, 2200 MPa, 41.3 MPa, 750 MPa and 12 kJ/m², respectively. Animal based natural B. mori silk fiber reinforced polypropylene (PP) matrix composites (20 wt% fiber) were fabricated in the same way and the mechanical properties were compared over the silk based composites. TS, YM, BS, BM, IS of silk fiber reinforced polypropylene composites were found 55.6 MPa, 760 MPa, 57.1 MPa, 3320 MPa and 17 kJ/m² respectively. Degradation of composites in soil was measured upto twelve weeks. It was found that plant based jute fiber/PP composite losses its strength more than animal based silk fiber/PP composite for the same period of time. The comparative study makes it clear that mechanical properties of silk/PP composites are greater than those values of jute/PP composites. But jute/PP composites are more degradable than silk/PP composites i.e., silk/PP composites retain their strength for a longer period than jute/PP composites.