Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) from sulfuric acid solution

Quiescent and strain-induced crystallization of poly(p-phenylene terephthalamide) (PPTA) from sulfuric acid solution has been studied. Negative spherulites (SA-PPTA spherulites) are formed from hot concentrated solutions by cooling. The spherulite consists of radiating fibrous lamellae several hundred angstroms wide. The electron diffraction pattern indicates that PPTA molecules are oriented perpendicular to the long axes of the fibrous lamellae and that the [010] or [110] direction of the modification I crystal and [010] direction of the modification II crystal are parallel to the long axes of the fibrous lamellae. The width of the lamellae is much smaller than the chain length of the starting PPTA. It appears that hydrolysis of PPTA during melting crystallization determines the chain length, i.e., the width of the fibrous lamella. Stacked, lamellar structures like “row structures” are formed under shear. The longer axes of the fibrous lamellae are oriented perpendicular to the shear direction. It is confirmed by electron diffraction studies that the PPTA molecules are oriented parallel to the shear direction. Well-developed fibrils with the PPTA molecules oriented to the fibril axis, are formed by adding the SA-PPTA spherulites to water with vigorous stirring.     

The role of asbestos morphology on their cellular toxicity: an in vitro 3D Raman/Rayleigh imaging study

Amphiboles caused cohorts of deaths in exposed workers, leading to some of the largest class actions in the industry. Once inhaled, these inorganic fibers are thought to be both chemically and morphologically toxic, and their biopersistence in the lungs over decades lead to progressive pathologies, mesothelioma, and asbestosis. However, this exceptionally long chronicity for human pathologies suggests that chemical toxicity is certainly low, suggesting that morphological parameters could be more relevant in the pathology. Here, we developed a 3D Raman/optical imaging methodology in vitro to characterize both morphological and chemical parameters of cell/fiber interactions. We determined that lung cells could vesiculate amphiboles with length below 5 μm or could embed those not exceeding 15 μm in their fibrous extracellular matrix. Lung cells can thus develop defense strategies for handling the biopersistence of inorganic species, which may thus have major impact for biosafety issues related to nanomaterials.     

可调制润湿性和力学性能的电纺纤维膜的制备与性能研究

采用静电纺丝技术分别制备了无规排列和高度取向排列的聚对苯二甲酸乙二醇酯(PET)和PET/CA(柠檬酸)4种纤维膜,对它们的润湿性能和力学性能进行了研究,同时研究了纤维膜厚度对膜的力学性能的影响.研究结果表明,与无规排列的PET纤维膜相比,取向排列的PET纤维膜沿纤维取向方向的力学性能有了很大的提高,而断裂伸长率略有下降;加入柠檬酸(CA)后,PET/CA复合纤维膜的表面水接触角从132.3!减少到0!,且取向排列的纤维膜比无规排列的纤维膜更易润湿;无规排列的复合纤维膜的力学性能因加入CA而大幅下降,取向排列的PET/CA纤维膜沿纤维取向方向的力学性能下降较小,而无规排列的PET/CA纤维膜的断裂伸长率从284.1%增加到444.5%.无规排列纤维膜的力学性能随膜厚度的增加先提高,后来又下降,而取向排列的纤维膜沿纤维取向方向的力学性能随膜厚度增加而单调增加.     

Engineering and optimization of nano- and mesoporous silica fibers using sol-gel and electrospinning techniques for sorption of heavy metal ions

In this paper, we report on a novel design strategy of an efficient sorbent for removal of trace contaminants from water. This kind of sorbent is composed of a nonporous core of SiO(2) nanofiber and a mesoporous shell (denoted as nSiO(2)@mSiO(2) ("n" means "nonporous" and "m" means "mesoporous")). The nSiO(2)@mSiO(2) fiber possesses a continuously long fibrous shape and mesoporous micromorphology, thus, showing both high sorption capacity and separability. The flexible nonporous SiO(2) nanofiber was prepared with electrospinning first, followed by covering a mesoporous SiO(2) shell based on a modified St?ber method using CTAB (cetyltrimethylammonium bromide) as the directing agent for formation of the mesopores. Also, functional thiol groups were grafted on the nSiO(2)@mSiO(2) to enhance its performance. With a large specific surface area and long fibrous morphology, the nSiO(2)@mSiO(2) fiber and its thiol-functionalized counterpart exhibit impressive performance on removal of Pb(2+) and Cd(2+) from water. Furthermore, the flexible texture and fibrous morphology of the nSiO(2)@mSiO(2) fiber also made the removal of metal ions and the separation process more convenient and efficient, implying that the nSiO(2)@mSiO(2) fiber could have great potential for industrial applications.     

胶原蛋白组装过程原子力显微镜的观测

阐述一种特殊胶原蛋白物质的组装过程,即加入1α-酸性醣蛋白后形成的纤维长距胶原蛋白.通过透析改变胶原蛋白溶液与α1-酸性醣蛋白混合液的pH值,在不同的pH值阶段利用原子力显微镜法(AFM)来辨析稳定的中间结构,获得可靠且分辨率高的样品图像.从而观察到了每个阶段中间纤维的形态和直径.结果表明纤维长距胶原蛋白形成过程中存在明显的中间体.     

In situ detection of birefringent mesoscopic H and J aggregates of thiacarbocyanine dye in solution

Polarized-light microscopy, fluorescence microscopy, atomic force microscopy as well as absorption and fluorescence spectroscopy were used to characterize mesoscopic structures of both supramolecular H and J aggregates of 3,3'-disulfopropyl-5,5'-dichloro-9-methyl thiacarbocyanine dye in aqueous solution. Polarized-light microscopy visualizes in situ the mesoscopic morphology of the H and J aggregates and distinguishes between them by their own colors. The H aggregate having a fibrous structure showed negative birefringence, namely, the refractive index along the fiber short axis was higher than that of the long axis, so that pi-electron chromophores of the dye molecule are likely to orient along the short axis of the elongated fibers. The degree of birefringence of the H aggregate fiber was approximately -0.3. Investigations on the concentration dependence of the absorption spectra showed that the amount of J aggregates increased at the expense of a decrease in the amount of H aggregates. With respect to the J aggregates, a small dot morphology was observed at a relatively low dye concentration of 3.0 mM. With an increase of the dye concentration up to 10 mM, the morphology changed into mesoscopic fibers. In contrast, fluorescence microscopy for the fibrous J aggregates reveals that the constituent molecules are approximately aligned along the long axis of the fibers.     

Measurement of thermal radiative properties of penguin down and other fibrous materials using FTIR

Penguins live in the extremely cold Antarctic. Understanding the thermal radiative properties of penguin down may help us to develop super insulating materials. In this study, Fourier transform infrared spectroscopy (FTIR) was applied to measure the thermal radiative properties of penguin down and compare them with those of other fibrous materials. It was found that penguin and duck down are superior to other fibrous materials, such as polyester, Thinsulate and wool, at the same fibre volume fraction, in shielding the radiative heat transmission, largely due to their fine fibre diameter. There is an optimum fibre diameter at which the fibrous materials are at their best in blocking thermal radiation. The fibre diameter of penguin down is very close to this optimum value. The study further found that the relationship between the effective thermal radiative conductivity and fibre fineness may be better fitted with a quadratic curve.     

Electrospinning-based synthesis of highly ordered mesoporous silica fiber for lab-in-syringe enrichment of plasma peptides

Silica fiber with highly ordered mesoporous structure and continuously long fibrous property was synthesized on a large-scale for the first time. It can be applied to the rapid (less than 3 min) and effective enrichment of endogenous peptides with a novel lab-in-syringe approach.     

Valve leaflet‐inspired elastomeric scaffolds with tunable and anisotropic mechanical properties

Fibrous scaffolds, which can mimic the elastic and anisotropic mechanical properties of native tissues, hold great promise in recapitulating the native tissue microenvironment. We previously fabricated electrospun fibrous scaffolds made of hybrid synthetic elastomers (poly(1,3‐diamino‐2‐hydroxypropane‐co‐glycerol sebacate)‐co‐poly (ethylene glycol) (APS‐co‐PEG) and polycaprolactone (PCL)) to obtain uniaxial mechanical properties similar to those of human aortic valve leaflets. However, conventional electrospinning process often yields scaffolds with random alignment, which fails to recreate the anisotropic nature of most of the soft tissues such as native heart valves. Inspired by the structure of native valve leaflet, we designed a novel valve leaflet‐inspired ring‐shaped collector to modulate the electrospun fiber alignment and studied the effect of polymer formulation (PEG amount [mole %] in APS‐co‐PEG; ratio between APS‐co‐PEG and PCL; and total polymer concentration) in tuning the biaxial mechanical properties of the fibrous scaffolds. The fibrous scaffolds collected on the ring‐shaped collector displayed anisotropic biaxial mechanical properties, suggesting that their biaxial mechanical properties are closely associated with the fiber alignment in the scaffold. Additionally, the scaffold stiffness was easily tuned by changing the composition and concentration of the polymer blend. Human valvular interstitial cells (hVICs) cultured on these anisotropic scaffolds displayed aligned morphology as instructed by the fiber alignment. Overall, we generated a library of biologically relevant fibrous scaffolds with tunable mechanical properties, which will guide the cellular alignment.     

F-Actin reassembly during focal adhesion impacts single cell mechanics and nanoscale membrane structure

Focal adhesions play an important role in cell spreading,migration,and overall mechanical integrity.The relationship of cell structural and mechanical properties was investigated in the context of focal adhesion processes.Combined atomic force microscopy(AFM) and laser scanning confocal microscopy(LSCM) was utilized to measure single cell mechanics,in correlation with cellular morphology and membrane structures at a nanometer scale.Characteristic stages of focal adhesion were verified via confocal fluorescent studies,which confirmed three representative F-actin assemblies,actin dot,filaments network,and long and aligned fibrous bundles at cytoskeleton.Force-deformation profiles of living cells were measured at the single cell level,and displayed as a function of height deformation,relative height deformation and relative volume deformation.As focal adhesion progresses,single cell compression profiles indicate that both membrane and cytoskeleton stiffen,while spreading increases especially from focal complex to focal adhesion.Correspondingly,AFM imaging reveals morphological geometries of spherical cap,spreading with polygon boundaries,and elongated or polarized spreading.Membrane features are dominated by protrusions of 41-207 nm tall,short rods with 1-6 μm in length and 10.2-80.0 nm in height,and long fibrous features of 31-246 nm tall,respectively.The protrusion is attributed to local membrane folding,and the rod and fibrous features are consistent with bilayer decorating over the F-actin assemblies.Taken collectively,the reassembly of F-actin during focal adhesion formation is most likely responsible for the changes in cellular mechanics,spreading morphology,and membrane structural features.     

Looking at long molecules in solution: what happens when they are subjected to Couette flow?

Knowing the structure of a molecule is one of the keys to deducing its function in a biological system. However, many biomacromolecules are not amenable to structural characterisation by the powerful techniques often used namely NMR and X-ray diffraction because they are too large, or too flexible or simply refuse to crystallize. Long molecules such as DNA and fibrous proteins are two such classes of molecule. In this article the extent to which flow linear dichroism (LD) can be used to characterise the structure and function of such molecules is reviewed. Consideration is given to the issues of fluid dynamics and light scattering by such large molecules. A range of applications of LD are reviewed including (i) fibrous proteins with particular attention being given to actin; (ii) a far from comprehensive discussion of the use of LD for DNA and DNA-ligand systems; (iii) LD for the kinetics of restriction digestion of circular supercoiled DNA; and (iv) carbon nanotubes to illustrate that LD can be used on any long molecules with accessible absorption transitions.     

Mechanically Strong Globular‐Protein‐Based Fibers Obtained Using a Microfluidic Spinning Technique

Proteins used for the formation of light weight and mechanically strong biological fibers are typically composed of folded rigid and unfolded flexible units. In contrast to fibrous proteins, globular proteins are generally not regarded as a good candidate for fiber production due to their intrinsic structural defects. Thus, it is challenging to develop an efficient strategy for the construction of mechanically strong fibers using spherical proteins. Herein, we demonstrate the production of robust protein fibers from bovine serum albumin (BSA) using a microfluidic technique. Remarkably, the toughness of the fibers was up to 143 MJ m^?3, and after post‐stretching treatment, their breaking strength increased to almost 300 MPa due to the induced long‐range ordered structure in the fibers. The performance is comparable to or even higher than that of many recombinant spider silks or regenerated silkworm fibers. Thus, this work opens a new way for making biological fibers with high performance.     

Fibrous membranes electrospinning from acrylonitrile-based polymers: specific absorption behaviors and states of water

Fibrous membranes with a fiber diameter ranging from 80 to 800 nm are prepared from polyacrylonitrile and poly[acrylonitrile-co-(N-vinyl-2-pyrrolidone)] by the electrospinning process. The parameters can be controlled to fabricate fibrous membranes with similar fiber diameters (between 600 and 800 nm) for further studies on the swelling behaviors and water states. Water swelling experiments indicate that the fibrous membrane has a great capacity for water sorption, which reaches a maximum in a few minutes because of its extremely high porosity. Furthermore, a remarkable overshoot occurs as a result of polymer chain relaxation and the non-compact structure of the fibrous membranes. Contrary to the dense membrane, the equilibrium water content in the fibrous membrane decreases with the content of hydrophilic NVP though the maximum is almost the same. Results from DSC experiments demonstrate that only non-freezable bound water and free water can be distinguished in the fibrous membrane. On the basis of the results of water swelling and DSC experiments, it is concluded that the specific behaviors of the fibrous membranes are induced by the non-compact and pore-fiber discontinuous structure, which is different from either dense membranes or hydrogels. [GRAPHS: SEE TEXT] DSC curves of fully swollen electrospun fibrous membranes and of fully swollen dense membranes with different NVP contents.     

Modification of fibrous silicates surfaces with organic derivatives: an infrared spectroscopic study

This contribution explores the interaction of the fibrous silicates, palygorskite, sepiolite and chrysotile with a wide range of organic agents. Infrared spectroscopy (IR) methods are essential for the characterization of solid surfaces and for the investigation of the kind of bonds formed between the surface of these silicates and the organic moieties. Thus, when sepiolite or palygorskite are treated, e.g., with polyurethanes, alcohols, isocyanates, amines or pyridines, specific SiNHC or SiOC bonds are derived from the linkage of the differently located OH groups in these fibrous silicates with the organic moieties. On the other hand, more stable, covalent SiOSiC bondings are formed when the fibrous silicates, especially chrysotile, are reacted with heterofunctional silylating agents like chlorosilanes or ethoxysilanes carrying, alkyl, alkenyl or aryl groups. Such reactions may occur in the presence or absence of HCl. An absorption band at 960 cm(-1)--which we assigned to SiOH groups--is detected only in the presence of HCl. The evolution of this band is related to the degree of grafting of the organic radicals with the silanol groups of the silicates. HCl-generated silanol groups are the main bridges for the coupling of organosilyl groups on chrysotile and other silicates by covalent bonding, leading the way to the preparation of interesting new materials, including fibrous sheet polymers.     

A review on wound dressings with an emphasis on electrospun nanofibrous polymeric bandages

Wound dressings have experienced continuous and significant changes since the ancient times. The development starts with the use of natural materials to simply cover the wounds to the materials of the present time that could be specially made to exhibit various extraordinary functions. The modern bandage materials made of electrospun biopolymers contain various active compounds that are beneficial to the healing of wounds. These materials are fibrous in nature, with the size of fibers segments ranging from tens of nanometers to micrometers. With the right choices of biopolymers used for these fibrous materials, they could enhance the healing of wounds significantly compared with the conventional fibrous dressing materials, such as gauze. These bandages could be made such that they contain bioactive ingredients, such as antimicrobial, antibacterial, and anti‐inflammatory agents, which could be released to the wounds enhancing their healing. In an active wound dressing (AWD), the main purpose is to control the biochemical states of a wound in order to aid its healing process. This review provides an overview of different types of wounds, effective parameters in wound healing and different types of wound dressing materials with a special emphasis paid to those prepared by electrospinning. Copyright © 2009 John Wiley & Sons, Ltd.     

Validation of new microvolume Couette flow linear dichroism cells

Long molecules such as fibrous proteins are particularly difficult to characterise structurally. We have recently designed a microvolume Couette flow linear dichroism (LD) cell whose sample volume is only 20-40 microL in contrast to previous cells where the volume of sample required has typically been of the order of 1000-2000 microL. This brings the sample requirements of LD to a level where it can be used for biological samples. Since LD is the difference in absorption of light polarised parallel to an orientation direction and perpendicular to that direction, it is the ideal technique for determining relative orientations of subunits of e.g. fibrous proteins, DNA-drug systems, etc. For solution phase samples, Couette flow orientation, whereby the sample is sandwiched between two cylinders, one of which rotates, has proved to be the optimal technique for LD experiments in many laboratories. Our capillary microvolume LD cell has been designed using extruded quartz rods and capillaries and focusing and collecting lenses. We have developed applications with PCR products, fibrous proteins, liposome-bound membrane proteins, as well as DNA-dye systems. Despite this range of applications, to date there is nothing reported in the literature to enable one to validate the performance of Couette flow LD cells. In this paper we establish validation criteria and show that the data from the microvolume cells are reproducible, vary by less than 1% with sample reloading, follow the Beer-Lambert law, and have signals linear in voltage over a wide voltage range. The microvolume cell data are consistent with those from the large-volume cells for DNA samples. Surprisingly, upon extending the wavelength range by adding the intercalator ethidium bromide, the spectra in the microvolume and large-volume cells differ by a wavelength dependent orientation parameter. This wavelength variation was concluded to be the result of Taylor-vortices in the large-volume cells which have inner rotating cylinders in our laboratory. Thus the microvolume LD cells can be concluded to provide better data than our large-volume LD cells, though the latter are still to be preferred for titration series as it is extremely difficult to add sample to the capillary cells without introducing artefacts.     

Intrinsically Disordered Tardigrade Proteins Self-Assemble into Fibrous Gels in Response to Environmental Stress

Tardigrades are remarkable for their ability to survive harsh stress conditions as diverse as extreme temperature and desiccation. The molecular mechanisms that confer this unusual resistance to physical stress remain unknown. Recently, tardigrade-unique intrinsically disordered proteins have been shown to play an essential role in tardigrade anhydrobiosis. Here, we characterize the conformational and physical behaviour of CAHS-8 from Hypsibius exemplaris. NMR spectroscopy reveals that the protein comprises an extended central helical domain flanked by disordered termini. Upon concentration, the protein is shown to successively form oligomers, long fibres, and finally gels constituted of fibres in a strongly temperature-dependent manner. The helical domain forms the core of the fibrillar structure, with the disordered termini remaining highly dynamic within the gel. Soluble proteins can be encapsulated within cavities in the gel, maintaining their functional form. The ability to reversibly form fibrous gels may be associated with the enhanced protective properties of these proteins.     

De novo design of fibrils made of short alpha-helical coiled coil peptides.

BACKGROUND: The alpha-helical coiled coil structures formed by 25-50 residues long peptides are recognized as one of Nature's favorite ways of creating an oligomerization motif. Known de novo designed and natural coiled coils use the lateral dimension for oligomerization but not the axial one. Previous attempts to design alpha-helical peptides with a potential for axial growth led to fibrous aggregates which have an unexpectedly big and irregular thickness. These facts encouraged us to design a coiled coil peptide which self-assembles into soluble oligomers with a fixed lateral dimension and whose alpha-helices associate in a staggered manner and trigger axial growth of the coiled coil. Designing the coiled coil with a large number of subunits, we also pursue the practical goal of obtaining a valuable scaffold for the construction of multivalent fusion proteins. RESULTS: The designed 34-residue peptide self-assembles into long fibrils at slightly acid pH and into spherical aggregates at neutral pH. The fibrillogenesis is completely reversible upon pH change. The fibrils were characterized using circular dichroism spectroscopy, sedimentation diffusion, electron microscopy, differential scanning calorimetry and X-ray fiber diffraction. The peptide was deliberately engineered to adopt the structure of a five-stranded coiled coil rope with adjacent alpha-helices, staggered along the fibril axis. As shown experimentally, the most likely structure matches the predicted five-stranded arrangement. CONCLUSIONS: The fact that the peptide assembles in an expected fibril arrangement demonstrates the credibility of our conception of design. The discovery of a short peptide with fibril-forming ability and stimulus-sensitive behavior opens new opportunities for a number of applications.     

树脂填充聚醚砜纤维吸附剂对牛血清蛋白吸附性能的研究

重点研究树脂填充聚醚砜(PES)纤维吸附剂与模型蛋白质牛血清蛋白(BSA)之间的吸附与脱附行为.结果表明,蛋白质BSA在树脂填充PES纤维吸附剂中的平衡吸附过程较好地符合朗格缪尔吸附模型,树脂Lewatit CNP80ws填充PES吸附剂的最大吸附容量约为139mg BSA/g吸附剂.表面具有开孔结构的树脂填充PES纤维吸附剂的吸附速率较快,在不同结构纤维吸附剂中BSA的扩散系数在1·82×10-14~8·7×10-14m2/s范围内变化.另外,考察了BSA溶液的pH与洗脱剂等因素对吸附剂吸附与脱附性能的影响,研究结果对蛋白质的实际分离纯化具有重要的参考价值.     

Toughening mechanisms in cellulose nanopaper: the contribution of amorphous regions

Cellulose nanopaper is a strong and tough fibrous network composed of hydrogen bonded cellulose nanofibres. Upon loading, cellulose nanopaper exhibits a long inelastic portion of the stress–strain curve which imparts high toughness into the material. Toughening mechanisms in cellulose nanopaper have been studied in the past but mechanisms proposed were often rather speculative. In this paper, we aim to study potential toughening mechanisms in a systematic manner at multiple hierarchical levels in cellulose nanopaper. It was proposed that the toughness of cellulose nanopaper is not, as is often assumed, entirely caused by large scale inter-fibre slippage and reorientation of cellulose nanofibres. Here it is suggested that dominant toughening mechanism in cellulose nanopaper is associated with segmental motion of molecules facilitated by the breakage of hydrogen bonds within amorphous regions .