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.     

Preparation and Properties of Poly(lactic Acid)/PLA-<Emphasis Type="Italic">g</Emphasis>-ABS Blends

PLA/PLA-g-ABS blends were prepared and evaluated for mechanical properties performance. Firstly, carboxylic acid functionalized ABS particles were synthesized by grafting polymethacrylic acid (PMAA) onto ABS particle surface using potassium persulfate as an initiator. The reaction was followed by FTIR analysis. The resultant carboxylated ABS was melt mixed with virgin PLA in an internal mixer to obtain PLA/PLA-g-ABS blends. The obtained PLA/PLA-g-ABS blends were subject to injection molding to obtain specimens for testing evaluation. It was found that impact resistance values significantly outperformed neat PLA by 60 %, 87 %, and 150 % for PLA/PLA-g-ABS 10 wt%, PLA/PLA-g-ABS 20 wt%, and PLA/PLA-g-ABS 30 wt%, respectively. A significant increase in impact strength was contributable to ABS rubber which exhibited even dispersion and good interfacial adhesion. The impact strength was dependent on the percent loading of PLAg-ABS; the more the PLA/PLA-g-ABS the higher the impact strength value. In a similar manner, tensile strength increases when loaded with PLA/PLA-g-ABS albeit at lesser effect. Considering the percent elongation, a massive increase in percent elongation was recorded in case of PLA/PLA-g-ABS 20 wt% and PLA/PLA-g-ABS 30 wt%, implying that these blends were extremely flexible and tough when compared to neat PLA, control, and PLA/PLA-g-ABS 10 wt%.     

Effect of surface treatment of jute fibers on the interfacial adhesion in poly(lactic acid)/jute fiber biocomposites

Jute fibers have immense potential to be used as natural fillers in polymeric matrices to prepare biocomposites. In the present study jute fibers were surface treated using two methods: i) alkali (NaOH) and ii) alkali followed by silane (NaOH+Silane) separately. Effects of surface treatments on jute fibers surface were characterized using fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analyses. Further, the effects of surface treatments on jute fibers properties such as crystallinity index, thermal stability, and tensile properties were analyzed by X-ray diffraction method (XRD), thermo gravimetric analysis (TGA), and single fiber tensile test respectively. The effects of surface treatment of jute fibers on interphase adhesion between of poly(lactic acid) (PLA) and jute fibers were analyzed by performing single fiber pull-out test and was examined in terms of interfacial shear strength (IFSS) and critical fiber length.     

Properties of thermoplastic starch from cassava bagasse and cassava starch and their blends with poly (lactic acid)

Cassava bagasse is an inexpensive and broadly available waste byproduct from cassava starch production. It contains roughly 50% cassava starch along with mostly fiber and could be a valuable feedstock for various bioproducts. Cassava bagasse and cassava starch were used in this study to make fiber-reinforced thermoplastic starch (TPS_B and TPS_I, respectively). In addition, blends of poly (lactic acid) and TPS_I (20%) and TPS_B (5, 10, 15, 20%) were prepared as a means of producing low cost composite materials with good performance. The TPS and PLA blends were prepared by extrusion and their morphological, mechanical, spectral, and thermal properties were evaluated. The results showed the feasibility of obtaining thermoplastic starches from cassava bagasse. The presence of fiber in the bagasse acted as reinforcement in the TPS matrix and increased the maximum tensile strength (0.60 MPa) and the tensile modulus (41.6 MPa) compared to cassava starch TPS (0.40 and 2.04 MPa, respectively). As expected, blending TPS with PLA reduced the tensile strength (55.4 MPa) and modulus (2.4 GPa) of neat PLA. At higher TPS_B content (20%) the maximum strength (19.9 MPa) and tensile modulus (1.7 GPa) were reduced about 64% and 32%, respectively, compared to the PLA matrix. In comparison, the tensile strength (16.7) and modulus (1.2 GPa) of PLA blends made with TPS_I were reduced 70% and 51% respectively. The fiber from the cassava bagasse was considered a filler since no increase in tensile strength of PLA/TPS blends was observed. The TPS_I (33.1%) had higher elongation to break compared to both TPS_B (4.9%) and PLA (2.6%). The elongation to break increased from 2.6% to 14.5% by blending TPS_I with PLA. In contrast, elongation to break decreased slightly by blending TPS_B with PLA. Thermal analysis indicated there was some low level of interaction between PLA and TPS. In PLA/TPS_B blends, the TPS_B increased the crystallinity of the PLA component compared to neat PLA. The fiber component of TPS_B appeared to have a nucleating effect favoring PLA crystallization.     

New biopolymer nanocomposites based on epoxidized soybean oil plasticized poly(lactic acid)/fatty nitrogen compounds modified clay: Preparation and characterization

Biodegradable polymers, such as poly(lactic acid) (PLA) have attracted a lot of attention in the scientific community recently due to a rapid growth of intensive interest in the global environment for alternatives to petroleum-based polymeric materials. Fatty nitrogen compounds (FNCs), fatty amides (FA), fatty hydroxamic acids (FHA), and carbonyl difatty amides (CDFA), which were synthesized from vegetable oils, were used as one of organic compounds to modify natural clay (sodium montmorillonite). The clay modification was carried out by stirring the clay particles in an aqueous solution of FA, FHA, and CDFA, by which the clay layer thickness increased from 1.23 to 2.61, 2.84 and 3.19 nm, respectively. The modified clay was then used in the preparation of the PLA/epoxidized soybean oil (ESO) blend nanocomposites. They were prepared by incorporating 2% of CDFA-MMT and 3% of both FA-MMT and FHA-MMT. The interaction of the modifier in the clay layer was characterized by X-ray diffraction (XRD), and Fourier transform infrared (FTIR). Elemental analysis was used to estimate the presence of FNCs in the clay. The nanocomposites were synthesized by solution casting of the modified clay and a PLA/ESO blend at the weight ratio of 80/20, which has the highest elongation at break. The XRD and transmission electron microscopy (TEM) results confirmed the production of nanocomposites. PLA/ESO modified clay nanocomposites show higher thermal stability and significant improvement of mechanical properties in comparison with those of the PLA/ESO blend. The novelty of this study is use of FNCs which reduces the dependence on petroleum-based surfactants.     

Influence of Poly(lactic acid) Layer on the Physical and Antibacterial Properties of Dry Bacterial Cellulose Sheet for Potential Acute Wound Healing Materials

Dry bacterial cellulose nanofiber (BC) sheet coated with poly(lactic acid) (PLA) was developed and characterized towards acute wound healing applications. This new approach of PLA coating on BC revealed enhanced physical and antibacterial properties. Commercial BC sheets originated from the manufacturing of nata de coco jelly were dried and coated with the PLA at various concentrations of 2, 4, 6, 8, 10 and 12 % w/v for the purpose of improving the mechanical properties and followed by loading of antiseptic such as benzalkonium chloride (BAC). PLA has been proposed for the use of coating materials at a concentration of 8 %, the biocomposite sheet started exhibiting a low moisture uptake, prolonged swelling in simulated wound fluid solution and high tear (9.17 Nm²/kg) and burst indices (32.5 kPa·m²/g). The 8 % PLA coating revealed porous fiber-like morphology as observed under scanning electron microscope. Therapeutic loading capacity of the BC/8 PLA was substantially higher than the pristine BC. Furthermore strong antimicrobial activities against Staphylococcus aureaus and Escherichia coli were observed for the BC/8PLA biocomposite film. These reports were clearly suggestive of the fact that synthetic biodegradable polymers, such as PLA, may be exploited for the synergistic combination with BC for antimicrobial and acute wound management. This new and modified fiber source material could reduce the dependency on plant based cellulose for more demanding biomedical applications such as wound healing materials, vascular graft, cartilage replacement, drug delivery and tissue engineering.     

Poly(ethylene 2,6-naphthalate)/MWNT nanocomposites prepared by in situ polymerization: Rheological and mechanical properties

Poly(ethylene 2,6-naphthalate)/multi-walled carbon nanotube (PEN/MWNT) nanocomposites are prepared by in situ condensation polymerization in the presence of various acid-treated MWNT (a-MWNT) contents and their morphology, rheological and mechanical properties are investigated as a function of the a-MWNT content. SEM image of a plasma-etched nanocomposite exhibits that a-MWNTs are dispersed well in the PEN matrix by forming an interconnected network structure. Accordingly, rheological properties such as complex viscosities and shear moduli of PEN/a-MWNT nanocomposites at the terminal region of low frequency are much higher than those of pure PEN. Glass transition temperatures of nanocomposites also increase with the increment of the a-MWNT content, which stems from the reduced chain mobility due to the specific interaction between a-MWNTs and PEN matrix. Dynamic and tensile mechanical properties of nanocomposites are also higher than those of pure PEN and they increase with the increment of the a-MWNT content. The highly improved mechanical properties of PEN/a-MWNT nanocomposites are explained to originate from the interconnected network structure of a-MWNTs in PEN matrix as well as the strong interfacial adhesion between a-MWNTs and PEN matrix.     

Bio-composites: Development and mechanical characterization of banana/sisal fibre reinforced poly lactic acid (PLA) hybrid composites

The work focuses on the influencing effect of fiber surface treatment by BP towards mechanical properties of BSF reinforced PLA composites. BSF were treated by BP to improve the adhesion between fibres and matrix. BSF (30 wt %) reinforced PLA (70 wt %) hybrid composites were fabricated by means of twin screw extrusion followed by injection molding process. Tensile strength, flexural strength and modulus were tested by means of UTM. The morphological analysis of the untreated and treated BSF reinforced PLA composites in comparison with virgin PLA was carried out by SEM to examine the existence of interfacial adhesion between BSF and PLA. The resultant data reveals that treated BSF restricts the motion of the PLA matrix due to better wettability and bonding. Consequently, mechanical properties like tensile and flexural moduli of BSF reinforced PLA composites were enhanced in comparison to virgin PLA and untreated BSF reinforced PLA composites. The results are discussed in detail.     

Tensile behavior and structural evolution of poly(lactic acid) monofilaments in glass transition region

A series of amorphous poly(lactic acid) (PLA) monofilaments with various D-isomer contents of 1∼9 mol% have been prepared and then elongated uniaxially at 25∼65 °C in the glass transition region. Both initial modulus and maximum strength of PLA monofilaments are appreciably decreased with increasing the temperature, especially at ∼50 °C, and they were somewhat lower for the monofilament with higher D-isomer content. Structural evolution, chain orientation, and thermal properties of PLA monofilaments drawn uniaxially with various draw ratios at 65 °C were then investigated by using wide-angle X-ray diffraction, polarized Raman spectroscopy, and differential scanning calorimetry, respectively. X-ray diffraction patterns clearly exhibited the development of chain orientation and stain-induced crystallization of the monofilaments as a function of draw ratio (DR). The dichroic ratio, a measure of the chain orientation, was quantitatively evaluated from the polarized Raman spectra. It was revealed that the dichroic ratios increased up to DR=4 and decreased slightly at DR>4 owing to the strain-induced crystallization for PLA monofilaments with D-isomer contents of 1 and 4 mol%. The glass transition and cold-crystallization temperatures of PLA monofilaments increased and decreased, respectively, with the increment of DR. The strain-induced enthalpy relaxation endothermic peak appearing in glass transition region became intense with increasing the DR.     

Degradation behaviour of poly(lactic acid) films and fibres in soil under Mediterranean field conditions and laboratory simulations testing

Long-term degradation/disintegration behaviour, indicative of the biodegradation in soil behaviour of poly(lactic acid) films and fibres, was studied in natural Mediterranean soil environment during an eleven-month trial in the experimental field. In parallel, simulated soil burial experiments were carried out under controlled laboratory conditions. The degradation/disintegration behaviour of PLA was analysed using visual inspection, mechanical testing, DSC and FTIR analysis. The influence of the thickness and the type of the materials (film vs. fibre) on disintegration was investigated under the given mild conditions. For comparison purposes, degradation/disintegration of PLA film was also studied under low temperature composting conditions (house composting). During long-term exposure under natural soil environment dominated by complex and uncontrolled biotic-abiotic conditions and Mediterranean climatic conditions and under house composting conditions, PLA film samples of different thicknesses were partially, to a rather low degree, degraded mechanically or slightly disintegrated. The results showed that degradation behaviour of bio-based polymers like poly(lactic acid) in a real soil environment is a complex phenomenon, following different patterns regarding morphological changes.     

Tilling技术及其在小麦中的应用研究进展

Tilling（Targeting induced local lesions in genomes）技术是近年来兴起的利用化学诱变或者物理诱变方法产生一系列的点突变,经过PCR快速筛选突变体,进而验证基因功能的方法。近年来,Tilling技术被用于多种生物的研究中。对小麦这种基因组庞大、遗传背景复杂的作物来说,Tilling技术在分析基因功能、挖掘重要基因资源和改良作物品质方面比传统的转基因方法有更大的优势。然而,Tilling技术在小麦中的应用还存在筛选工作量大等问题。本文介绍了Tilling技术的操作流程、问题改进及在小麦基因功能研究和品质改良方面的研究现状。     

Relative amounts of tissues in mature wheat (Triticum aestivum L.) grain and their carbohydrate and phenolic acid composition

Hand dissection of mature grains from two common wheats (Triticum aestivum L., cv. Caphorn and cv. Crousty) were performed to quantitatively assess their tissue composition and to obtain homogeneous samples of embryonic axis, scutellum, starchy endosperm, aleurone layer, hyaline layer, outer pericarp and a composite layer made up of testa+hyaline layer+inner pericarp. Polymeric neutral sugar and phenolic acid contents of the samples were determined and used to identify specific composition patterns in each tissue irrespective of the cultivar. The scutellum and embryonic axis showed the lowest amount of carbohydrates with similar relative amounts of arabinose and xylose (Ara+Xyl), but the scutellum differed from the embryonic axis in its high phenolic acid, in particular ferulate dehydrodimer, content. The peripheral layers of the grains were mainly composed of cell wall polysaccharides, chiefly arabinoxylans but with differing structures. The hyaline layer was mostly composed of arabinoxylan with extremely low Ara/Xyl ratio (0.1), with high amounts of ferulic acid monomers and hence very weakly crosslinked. The aleurone layer differed from the outer pericarp by its much lower Ara/Xyl ratio and lower amounts of ferulic acid dimers and trimers. High proportions of ether-linked phenolic acids (released by alkali at 170 °C) were detected specifically in the seed coat and tissues in the crease region. The possible application of biochemical markers found in the various tissues to monitor wheat grain fractionation processes is discussed.     

Photo-induced changes in the concentrations of individual chlorogenic acid isomers in potato (Solanum tuberosum) tubers and their complexation with ferric ions

Summary Changes in the concentrations of 3-, 4- and 5-caffeoylquinic acids in potato tubers exposed to light have been determined by high-performance liquid chromatography. In the first 24 to 48 hours the observed increases in total chlorogenic acid content was due primarily to an increase in 5-caffeoylquinic acid content but thereafter the rate of accumulation of the other isomers increased gradually. After 24 hours exposure 4-caffeoylquinic acid accounted for 10% of the total chlorogenic acid content of the tubers compared with 33% after 168 hours. The significance of this change in isomeric ratio on the spectral characteristics of potential ferrichlorogenic acid complexes was investigated in vitro. It was concluded that potato quality, as reflected in the development of after-cooking blackening, was dependent on total chlorogenic acid content and was unaffected by the relative concentrations of the individual isomers.     

聚合水稻温敏核不育基因和反温敏核不育基因创制永久核不育系

【目的】制种安全是影响两系杂交稻持续健康发展的关键问题。本研究旨在探索解决两系杂交水稻的制种安全隐患途径。【方法】以16个(光)温敏核不育系与4个反温敏核不育系配组并对F1育性进行观察,选择矮紫S(温敏核不育系)和矮雁s(反温敏核不育系)为构建永久核不育系的供源亲本。通过回交将矮紫S和矮雁s的育性基因导入到桥梁亲本天丰B中,分别育成天丰B的近等基因系天丰S和天丰s。【结果】天丰S和天丰s杂交获得的天丰Ss即为永久核不育系。对天丰Ss的育性、可恢性等特性的研究表明,天丰Ss在自然长日高温和短日低温下均表现不育;天丰Ss及其3个亲本与5个恢复系杂交的F1组合结实率无明显差异。【结论】永久核不育系的创制有望从根本上解决两系杂交水稻的制种安全问题。     

Electrospun curcumin loaded poly(lactic acid) nanofiber mat on the flexible crosslinked PVA/PEG membrane film: Characterization and <Emphasis Type="Italic">in vitro</Emphasis> release kinetic study

Herein, a biodegradable and biocompatible composite comprising of support membrane based on crosslinked PVA/PEG film and curcumin loaded electrospun poly(lactic acid) (PLA) nanofiber mat is introduced. The membrane film was prepared from PVA/PEG blend followed by crosslinking with an optimum amount of citric acid, 15 wt.%. After then, PLA solutions with different curcumin content, 0-11 wt.%, were electrospinned on the prepared membrane substrate. The prepared film showed high water absorption, water vapor transmission rate and superior mechanical properties with improved elastic modulus, tensile strength and with an elongation of around 320 % with respect to the non-crosslinked one. Also, the scanning electron microscopy was revealed uniformly dispersed pores throughout the membrane film with a nearly narrow in size distribution centered at 36 μm. As well, a nanostructure porous morphology was found for the electrospun fibrous curcumin loaded PLA from the scanning electron microscopy micrographs and the average fiber diameter was decreased with curcumin content. In vitro drug release from the prepared flexible composite into the vertical diffusion cell was recorded by the measuring curcuminoids content using high performance liquid chromatography and drug release kinetic evaluations were revealed that the release pattern of all prepared samples, containing different content of curcumin, well fitted to the Higuchi’s model signifying diffusion-controlled release mechanism. As well, the determined release rate at the second release stages, i.e. steady state flux (J), was varied from 0.31 to 43.53 μg·cm^-2·h^-1 with increasing drug content from 1 to 11 wt.%. Regarding this results, this flexible composite by providing the moist environment along with miraculous healing properties of curcumin, can be potential candidate for transdermal drug delivery.     

小麦 TaWRKY51基因的克隆及其参与SQ-1诱导小麦花粉败育过程的表达模式研究

为进一步深入解析化学杂交剂SQ-1诱导小麦花粉败育的机理,本研究从SQ-1诱导的生理型雄性不育系PHYMS-1376及其对照可育系CK-1376各时期花药转录组测序筛选出差异表达基因TraesCS1D02G362900.1,与小麦基因组数据库比对发现,该基因编码的氨基酸与 TaWRKY51同源度为97%,说明该差异表达基因为 TaWRKY51对其进行生物信息学分析、亚细胞定位、转录激活活性与花药表达模式研究,结果表明, TaWRKY51开放阅读框全长663 bp,可编码220个氨基酸,含有WRKY结构域和锌指结构,分子量约为23.34 kD,等电点为6.42;启动子区包含与光响应、茉莉酸甲酯响应、脱落酸响应等7类顺式作用元件,且TaWRKY51蛋白被定位在细胞核内,具有一定的转录激活活性;与CK-1376相比,PHYMS-1376植株花药中 TaWRKY51的表达量在5个发育时期均高于CK-1376,且在四分体时期、单核晚期、二核期和三核期与CK-1376的差异均达极显著水平,表明该基因与PHYMS-1376花粉败育密切相关。