Cross-linker Ethylene Research Articles

Ether cross-link formation in the R2-like ligand-binding oxidase

R2-like ligand-binding oxidases contain a dinuclear metal cofactor which can consist either of two iron ions or one manganese and one iron ion, but the heterodinuclear Mn/Fe cofactor is the preferred assembly in the presence of MnII and FeII in vitro. We have previously shown that both types of cofactor are capable of catalyzing formation of a tyrosine–valine ether cross-link in the protein scaffold. Here we demonstrate that Mn/Fe centers catalyze cross-link formation more efficiently than Fe/Fe centers, indicating that the heterodinuclear cofactor is the biologically relevant one. We further explore the chemical potential of the Mn/Fe cofactor by introducing mutations at the cross-linking valine residue. We find that cross-link formation is possible also to the tertiary beta-carbon in an isoleucine, but not to the secondary beta-carbon or tertiary gamma-carbon in a leucine, nor to the primary beta-carbon of an alanine. These results illustrate that the reactivity of the cofactor is highly specific and directed.

A facile and efficient single-step approach for the fabrication of vancomycin functionalized polymer-based monolith as chiral stationary phase for nano-liquid chromatography

A facile single-step preparation strategy for fabricating vancomycin functionalized organic polymer-based monolith within 100μm fused-silica capillary was developed. The synthetic chiral functional monomer, i.e 2-isocyanatoethyl methacrylate (ICNEML) derivative of vancomycin, was co-polymerized with the cross-linker ethylene dimethacrylate (EDMA) in the presence of methanol and dimethyl sulfoxide as the selected porogens. The co-polymerization conditions were systematically optimized in order to obtain satisfactory column performance. Adequate permeability, stability and column morphology were observed for the optimized poly(ICNEML-vancomycin-co-EDMA) monolith. A series of chiral drugs were evaluated on the monolith in either polar organic-phase or reversed-phase modes. After the optimization of separation conditions, baseline or partial enantioseparation were obtained for series of drugs including thalidomide, colchicine, carteolol, salbutamol, clenbuterol and several other β-blockers. The proposed single-step approach not only resulted in a vancomycin functionalized organic polymer-based monolith with acceptable performance, but also significantly simplified the preparation procedure by reducing time and labor.

UV Photopolymerization of Vinyl Ether Based Polymer Electrolytes for Solid-State Lithium Batteries

The utilization of solid lithium metal in lithium ion batteries increases performance and capacities but introduces safety issues when combined with liquid electrolytes. This prevents its use in practical energy dense electrochemical cells, like those required for electric vehicles or consumer electronics. Safety can be increased by using polymer or gel electrolytes which are less flammable and provide a more formidable barrier to dendrite formation. However, the production of polymer electrolytes can often be complicated and involve several stages, making the processing time-consuming and expensive to apply on the industrial scale. In this work we developed a simple bulk polymerization method in the presence of lithium salt to produce quick-curing vinyl ether based polymer electrolytes in a one-step cationic UV photopolymerization. These electrolytes are composed of ethyl vinyl ether (EVE) monomer and poly(ethylene glycol) divinyl ether (DVEp) crosslinker with triarylsulfonium hexafluorophosphate salt photoinitiator and bis(trifluoromethane) sulfonimide (LiTFSI) lithium salt. Systems with varying crosslinker to monomer (DVEp:EVE) volume ratios and lithium salt concentration ratios were produced to see the effects of crosslinking density and [O]:[Li] ratio on electrolyte properties. Attenuated Total Reflectance Fourier-transform Infrared spectroscopy (ATR-FTIR) was used to quantify polymer composition and verify complete polymerization. Ionic conductivities were measured from 0 to 80 °C using electrochemical impedance spectroscopy. The highest ionic conductivities were seen in samples with the lowest crosslinker concentrations and the highest lithium salt concentrations. The most conductive sample produced had composition 10:1 [O]:[Li] and 15% crosslinker by volume and reached an ionic conductivity of 1.2x10-6 S/cm at 20°C. Glass transition temperatures (Tg) were measured with differential scanning calorimetry (DSC) for various salt-free DVEp:EVE ratios; Tg was determined to be -15°C for composition with 15% crosslinker in the absence of salt. Investigation of the effect of salt on Tg’s and the electrochemical stability of these compositions is currently underway and will be reported.

Phosphate barrier on pore-filled cation-exchange membrane for blocking complexing ions in presence of non-complexing ions

In present work, an approach has been used to form a phosphate groups bearing surface barrier on a cation-exchange membrane (CEM). Using optimized conditions, the phosphate bearing monomer bis[2-(methacryloyloxy)ethyl] phosphate has been grafted on the surface of the host poly(ethersulfone) membranes using UV light induced polymerization. The detailed characterizations have shown that less than a micron layer of phosphate barrier is formed without disturbing the original microporous structure of the host membrane. The pores of thus formed membrane have been blocked by cationic-gel formed by in situ UV-initiator induced polymerization of 2-acrylamido-2-methyl-1-propane sulphonic acid along with crosslinker ethylene glycol dimethacrylate in the pores of the membrane. UV-initiator is required for pore-filling as UV light would not penetrate the interior matrix of the membrane. The phosphate functionalized barrier membrane has been examined for permselectivity using a mixture of representative complexing Am3+ ions and non-complexing Cs+ ions. This experiment has demonstrated that complex forming Am3+ ions are blocked by phosphate barrier layer while non-complexing Cs+ ions are allowed to pass through the channels formed by the crosslinked cationic gel.

Silicon nanoparticles coated with an epitope-imprinted polymer for fluorometric determination of cytochrome c.

The authors describe a composite consisting of silicon nanoparticles that were first coated with SiO2 and then with a molecularly imprinted polymer (SiNP@SiO2@MIP). The MIP was generated by dual epitope imprinting such that it can recognize cytochrome c (Cyt c). The MIP on the NPs was prepared from the functional monomer zinc(II) acrylate (ZnA), the crosslinker ethylene glycol dimethacrylate and the initiator 2,2'-azoisobutyronitrile. Dual epitope templates for Cyt c included (a) a C-terminal nonapeptide (AYLKKATNE), and (b) an N-terminal nonapeptide (GDVEKGKKI). The chelation between Zn(II) of ZnA and the amino groups or hydroxy groups of the template nonapeptides warrants good recognition and capture of Cyt c. The fluorescence originating from SiNPs has excitation/emission peaks at 360/480nm and is quenched by Cyt c in the 0.50-40.0μM concentration range. The correlation coefficient for the calibration plot of the imprinted NPs is 0.9937. The detection limit is 0.32 ± 0.01μM, the precisions of six replicate detections at levels of 0.5, 20 and 40μM Cyt c are 3.2, 2.7 and 2.8%, respectively, and the imprinting factor is 2.43. Compared to single epitope template imprinting, dual epitope imprinting results in improved selectivity. The imprinted nanoparticles can discriminate Cyt c even if one amino acid is mismatched. The method was applied to the determination of Cyt c in spiked diluted human serum and gave recoveries between 94.0 and 107.5%. Graphical Abstract A fluorescent material of the architecture silicon nanoparticle@SiO2@molecularly imprinted polymer (SiNP@SiO2@MIP) was fabricated by dual epitope imprinting and a metal-chelating method. The chelation between Zn(II) of the functional monomer zinc(II) acrylate and the amino groups or hydroxy groups of template warrants that the material recognizes and captures cytochrome c well, and this results in fluorescence quenching.

Thermoreversibly Cross-Linked EPM Rubber Nanocomposites with Carbon Nanotubes.

Conductive rubber nanocomposites were prepared by dispersing conductive nanotubes (CNT) in thermoreversibly cross-linked ethylene propylene rubbers grafted with furan groups (EPM-g-furan) rubbers. Their features were studied with a strong focus on conductive and mechanical properties relevant for strain-sensor applications. The Diels-Alder chemistry used for thermoreversible cross-linking allows for the preparation of fully recyclable, homogeneous, and conductive nanocomposites. CNT modified with compatible furan groups provided nanocomposites with a relatively large tensile strength and small elongation at break. High and low sensitivity deformation experiments of nanocomposites with 5 wt % CNT (at the percolation threshold) displayed an initially linear sensitivity to deformation. Notably, only fresh samples displayed a linear response of their electrical resistivity to deformations as the resistance variation collapsed already after one cycle of elongation. Notwithstanding this mediocre performance as a strain sensor, the advantages of using thermoreversible chemistry in a conductive rubber nanocomposite were highlighted by demonstrating crack-healing by welding due to the joule effect on the surface and the bulk of the material. This will open up new technological opportunities for the design of novel strain-sensors based on recyclable rubbers.

Investigation of the thermal properties of glycidyl methacrylate\u2013ethylene glycol dimethacrylate copolymeric microspheres modified by Diels\u2013Alder reaction

The study describes the thermal properties of functional microspheres composed of glycidyl methacrylate (GMA) and crosslinking agent ethylene glycol dimethacrylate (EGDMA). Copolymeric poly(GMA-co-EGDMA) microspheres were prepared via suspension–emulsion polymerization in the presence of toluene and decan-1-ol as porogens. In order to introduce functional groups, the porous methacrylate network was modified by epoxy ring opening with the use of sodium cyclopentadienide and then the Diels–Alder addition with maleic anhydride. The thermal properties of poly(GMA-co-EGDMA) materials were evaluated by thermogravimetry and differential scanning calorimetry. By TG/FTIR, it was observed that new functional materials exhibited multi-staged decomposition patterns, different from parent poly(GMA-co-EGDMA) microspheres. The synthesized poly(GMA-co-EGDMA) microspheres exhibited rather high thermal stability in inert atmosphere. Their initial decomposition temperature determined at the temperature of 2% of mass loss was about 210 °C; however, after the chemical modification it was slightly lower. The thermal degradation of parent poly(GMA-co-EGDMA) copolymer runs mainly according to the depolymerization mechanism, while functionalized by cyclopentadienyl group and maleic anhydride microspheres decompose through the chain scission mechanism.

Synthesis, characterization and toxicological evaluation of pH-sensitive polyelectrolyte Nanogels

Nanogels are polymeric nanoparticles that have similar characteristic to hydrogels, but have the size in nano range. The pH-sensitive nanogel have gained much interest in the field of pharmaceutical nanotechnology as they have potential to be used as nanocarriers in drug delivery system. The aim of the present study was to synthesize pH-sensitive polyelectrolyte MMA/IA nanogels using free radical polymerization containing methyl methacrylate (MMA), itaconic acid (IA), and a crosslinker ethylene glycol dimethacrylate (EGDMA). In the synthesis of nanogels four parameters i.e. ethanol/water ratios (v/v), dilution volume using ethanol/water (v/v), crosslinker EGDMA concentration, and monomers MMA/IA ratios were optimized. Their effect on particle size, PdI, zeta potential and swelling ratio were evaluated. The swelling behaviour of the nanogels was studied by measuring swelling ratio using gravimetric method. The optimized nanogels were characterized by proton nuclear magnetic resonance (1H NMR), Fourier transform infrared spectroscopy (FTIR), liquid chromatography/time-of-flight/mass spectrometry (LC-TOF-MS), X-ray powder diffraction (X-RD) and transmission electron microscopy (TEM). Polyelectrolyte characteristic was confirmed by measuring isoelectric point using aqueous electrophoresis. The in-vitro and in-vivo toxicity studies were performed by MTT assays using Caco-2 cells and Limit test using female Sprague Dawly rats, respectively. The nanogels were amorphous in nature, exhibited pH-responsive property and polyelectrolyte characteristics, which showed an isoelectric point at pH 2.78. They had an average particle size <250 nm, narrow size distribution (PdI < 0.3), and negative zeta potential. The in-vitro MTT assays indicated that the nanogels had no sign of cytotoxicity. The in vivo Limit test showed that the LD50 was greater than 2000 mg/kg body weight. The necrospy, histopathology and hematological studies also revealed no sign of toxicity. These findings suggested that the MMA/IA nanogels are pH-sensitive, non-toxic and have potential to form a polyelectrolyte complex with oppositely charged of macromolecular drugs.

Cryogelation within cryogels: Silk fibroin scaffolds with single-, double- and triple-network structures

Mechanically strong silk fibroin cryogels with two generations of pores were produced by carrying out the cryogelation reactions within the pores of the initial single-network (SN) fibroin cryogels. In this way, cryogels with interpenetrated and interconnected double- (DN), and triple-network (TN) structures were produced from fibroin solutions frozen at −18 °C in the presence of butanediol diglycidyl ether cross-linker and N,N,N′,N′-tetramethylethylenediamine as a pH regulator. Cryogel scaffolds formed at fibroin concentrations above 25 wt% exhibit a Young's modulus between 66 and 126 MPa, and sustain around 90% compressions under 87–240 MPa stresses. These values are the largest reported so far for fibroin scaffolds and hence the materials have promising applications in bone tissue engineering. We also show that the improvement in the mechanical performance of cryogels after multiple-networking is due to their increased content of fibroin network. Both DN and TN cryogels have two generations of interconnected macropores with diameters 20–30 μm and 3–9 μm. The size of both large and small pores could be adjusted by the relative amounts of fibroin in the network components.

Fish scale-derived collagen patch promotes growth of blood and lymphatic vessels in vivo.

Currently the most common sources of collagen are of bovine and porcine origins, although the industrial use of collagen obtained from non-mammalian species is growing in importance, particularly since they have a lower risk of disease transmission and are not subjected to any cultural or religious constraints. However, unmodified collagen typically has poor mechanical and degradation stability both in vitro and in vivo. Hence, in this study, Type I collagen was successfully extracted from fish scales and chemically modified and crosslinked. In vitro studies showed overall improvement in the physicochemical properties of the material, whilst in vivo implantation studies showed improvements in the growth of blood and lymphatic host vessels in the vicinity of the implants.

KINETICS AND ISOTHERM STUDIES OF Pb(II) IMPRINTED CARBOXYMETHYL CHITOSAN–PECTIN-PEGDE

Pectin and chitosan are biomaterials that capable to act as biosorbent. Pectin has active groups, such as carboxyl, methoxyl, and hydroxyl (OH), while chitosan has amine group (–NH2) and hydroxyl (OH) as the active site metal ion absorber. Integration of two biopolymers is conducted by using a suitable cross-linker agents that are expected to form stable and more organized structure. This structure facilitate metal ions to enter and to form chelation reaction. Thus, it has great capacity for metal adsorption. A modified natural adsorbent pectin-chitosan has been synthesized by reacting of -OH group among pectin (Pec) and chitosan with Poly(ethylene glycol) Diglycidyl Ether (PEGDE) crosslinker agent to form a stable and an acidic medium-resistance adsorbent. Prior to increasing the active group of the adsorbent, chitosan was attached with acetate to form Carboxymethyl Chitosan (CMC). Furthermore, the CMC-Pec-PEGDE adsorbent was imprinted with Pb (II) to afford Pb(II) imprinted-CMC-Pec-PEGDE adsorbent in order to improve the selective sorption of Pb(II) metal ion. All of the functional groups attached on the synthesized adsorbents were characterized by Fourier Transform Infrared (FT-IR) Spectrometry. The kinetics and thermodynamics bath sorption of Pb(II) on Pb(II) imprinted-CMC-Pec-PEGDE film adsorbent have been investigated including the optimal condition for adsorption. The pseudo first-order and second-order kinetic model were investigated in order to determine the adsorption mechanism. The results indicated that all of the three adsorbent, CMC, CMC-Pec-PEGDE, and Pb(II) imprinted-CMC-Pec-PEGDE followed a pseudo-second-order kinetic model. Furthermore, adsorption studies of Pb(II) ion on CMC and CMC–Pec-PEGDE found to follow Langmuir adsorption while on imprinted-CMC-Pec-PEGDE followed Freundlich adsorption isotherm. The adsorption isotherm parameters of CMC and CMC-Pec-PEGDE adsorbents were ΔG° of 24.8 and 23.1 kJ mol-1, respectively. While Pb(II) imprinted-CMC-Pec-PEGDE followedisotherm model with ΔG° of 9.6 kJ mol-1.

Selective separation and determination of glucocorticoids in cosmetics using dual-template magnetic molecularly imprinted polymers and HPLC

Molecularly imprinting polymers (MIPs) are typically prepared using a single template molecule, which allows selective separation and enrichment of only one target analyte. It is not suitable for determination of complex real samples containing multiple analytes. In order to expand the practical application of imprinted polymers, novel dual-template magnetic molecularly imprinted polymers (MMIPs) were synthesized by surface polymerization using hydrocortisone and dexamethasone as the dual-template molecules in this study. The dual-template MMIPs were prepared by copolymerization on the surface of Fe3O4@ SiO2-NH2, the template molecules, the functional monomer acrylamide (AM), the cross-linking agent ethylene glycol dimethacrylate (EGDMA), and the initiator 2,2-azobisisobutyronitrile. The morphology, magnetic properties and adsorption characteristics of the obtained dual-template MMIPs were studied by field emission scanning electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and vibrating sample magnetometry, and re-binding experiments. The results indicated that dual-template MMIPs had uniform particle size, strong magnetic properties, high thermal stability, and good mass transfer rate. To investigate the selectivity of dual-template MMIPs, the template molecules were mixed along with their structural analogs. The dual-template MMIPs revealed a significantly higher adsorption amount for the template molecule than its structure analog. The dual-template MMIPs can be used for the enrichment and determination of hydrocortisone and dexamethasone in cosmetic products with the recoveries of spiked cosmetic samples ranging from 86.8–107.5% and 91.2–104.3%, respectively. The relative standard deviation (RSD) for hydrocortisone was <2.89%, and RSD for dexamethasone was <2.62%.

Facile preparation of ODPA‐ODA type polyetherimide‐based carbon membranes by chemical crosslinking

ABSTRACTA chemical crosslinking protocol was developed to prepare carbon membranes from 3,3′,4,4′‐oxydiphthalic dianhydride‐4,4′‐oxydianiline (ODPA–ODA) type polyetherimide on the support of phenolic resin sheets. The effects of support pretreatment, membrane‐coating methods and crosslinking protocols on the resultant carbon membranes were investigated. The microstructure, functional group evolution, thermal stability, mechanics, morphology, and gas separation performance of samples were characterized by XRD, FTIR, TGA, mechanical testing technique, and gas permeation technique, respectively. Results have shown that the chemical crosslinking is more beneficial than the popular thermal crosslinking protocol to fabricate supported carbon membranes for the advantage of simple preparation process. In addition, spin‐coating is superior to drop‐coating in terms of good membrane formation on the support. Under the preferred preparation conditions of crosslinker ethylene glycol usage at 10 wt % and spin‐coating, supported carbon membranes can be obtained with good hydrogen separation performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44889.

High-strength silk fibroin scaffolds with anisotropic mechanical properties

In contrast to isotropic morphologies of synthetic hydrogels, many biological tissues possess anisotropic hierarchical morphologies leading to extraordinary mechanical properties that cannot be mimicked by synthetic materials. Here, we report preparation of anisotropic silk fibroin cryogels and scaffolds exhibiting a Young's modulus in the range of MPa that sustain up to 20 MPa compressive stresses. The cryogels were prepared by a combined directional freezing – cryogelation process starting from an aqueous 4.2 wt% fibroin solution containing butanediol diglycidyl ether cross-linker and N,N,N′,N′-tetramethylethylenediamine. In the first step, the reactor containing the aqueous solution of fibroin, cross-linker, and TEMED was immersed into liquid nitrogen at a controlled rate to create a directionally frozen ice template. In the second step, cryogelation reactions were conducted in this frozen solution at −18 °C whereby the cryo-concentrated fibroin in the unfrozen microzones of the reaction system forms a 3D fibroin network. The scaffolds exhibit anisotropic microstructure and hence anisotropic mechanical properties, e.g., the Young's modulus is 3.4 ± 0.5 MPa and 0.8 ± 0.3 MPa when measured along the directions parallel and vertical to the freezing direction, respectively. All the cryogels could completely be compressed due to squeezing out of water from their pores. Upon removal of the load, the compressed cryogels immediately recover their original dimensions and mechanical properties by absorbing the released water into their pores.

Enhanced Lithium Ion Transport in Poly(ethylene glycol) Diacrylate-Supported Solvate Ionogel Electrolytes via Chemically Cross-linked Ethylene Oxide Pathways.

Lithium-ion solvate ionic liquids (SILs), consisting of complexed Li+ cations and a weakly basic anion, represent an emergent class of nonvolatile liquid electrolytes suitable for lithium-based electrochemical energy storage. In this report, solid-state, flexible solvate ionogel electrolytes are synthesized via UV-initiated free radical polymerization/cross-linking of poly(ethylene glycol) diacrylate (PEGDA) in situ within the [Li(G4)][TFSI] electrolyte, which is formed by an equimolar mixture of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and tetraglyme (G4). Ion diffusivity measurements reveal enhanced Li+ diffusion in PEGDA-supported solvate ionogels, as compared to poly(methyl methacrylate)-supported gels that lack ethylene oxide chains. At 21 vol% PEGDA, a maximum Li+ transport number of 0.58 and a room temperature ionic conductivity of 0.43 mS/cm have been achieved in a solvate ionogel electrolyte that exhibits an elastic modulus of 0.47 MPa. These results demonstrate the importance of polymer scaffold selection on solvate ionogel electrolyte performance for advanced lithium-based batteries.

Characterization of electron beam cross-linked ethylene–octene copolymer composites with carbon nanotubes

Characterization of electron beam cross-linked ethylene–octene copolymer composites with carbon nanotubes

Protonation State of MnFe and FeFe Cofactors in a Ligand-Binding Oxidase Revealed by X-ray Absorption, Emission, and Vibrational Spectroscopy and QM/MM Calculations.

Enzymes with a dimetal-carboxylate cofactor catalyze reactions among the top challenges in chemistry such as methane and dioxygen (O2) activation. Recently described proteins bind a manganese-iron cofactor (MnFe) instead of the classical diiron cofactor (FeFe). Determination of atomic-level differences of homo- versus hetero-bimetallic cofactors is crucial to understand their diverse redox reactions. We studied a ligand-binding oxidase from the bacterium Geobacillus kaustophilus (R2lox) loaded with a FeFe or MnFe cofactor, which catalyzes O2 reduction and an unusual tyrosine-valine ether cross-link formation, as revealed by X-ray crystallography. Advanced X-ray absorption, emission, and vibrational spectroscopy methods and quantum chemical and molecular mechanics calculations provided relative Mn/Fe contents, X-ray photoreduction kinetics, metal-ligand bond lengths, metal-metal distances, metal oxidation states, spin configurations, valence-level degeneracy, molecular orbital composition, nuclear quadrupole splitting energies, and vibrational normal modes for both cofactors. A protonation state with an axial water (H2O) ligand at Mn or Fe in binding site 1 and a metal-bridging hydroxo group (μOH) in a hydrogen-bonded network is assigned. Our comprehensive picture of the molecular, electronic, and dynamic properties of the cofactors highlights reorientation of the unique axis along the Mn-OH2 bond for the Mn1(III) Jahn-Teller ion but along the Fe-μOH bond for the octahedral Fe1(III). This likely corresponds to a more positive redox potential of the Mn(III)Fe(III) cofactor and higher proton affinity of its μOH group. Refined model structures for the Mn(III)Fe(III) and Fe(III)Fe(III) cofactors are presented. Implications of our findings for the site-specific metalation of R2lox and performance of the O2 reduction and cross-link formation reactions are discussed.

Preparation of Magnetic Surface-Imprinted Polymer Microspheres with Hydrophilic External Layers for Selective Extraction of Fluoroquinolones from Eggs

A novel method of one-pot covalently grafting a hydrophilic organic polymer imprinted layer on the surface of magnetic microspheres was developed for the preparation of restricted access materials–molecularly imprinted magnetic microspheres (RAM-MIMMs) with water compatibility and ability to exclude biomacromolecules and selectively enrich analytes. The magnetic nanoparticles were coated with silica gel, modified with vinyl groups, polymerized with the template (enrofloxacin), functional monomer (glycidyl methacrylate, methacrylic acid), and cross-linking agent (ethylene glycol dimethacrylate) in chloroform, and then the hydrophilic surface was formed by a ring-opening reaction. The RAM-MIMMs were characterized by transmission electron microscopy, FT-IR spectroscopy, and adsorption experiments and demonstrated average diameters around 400 nm and a coating thickness in the range of 50 nm. They exhibited high selectivity of the imprinted cavities and hydrophilicity of the external surface with water compatibility and exclusion of biomacromolecules. The RAM-MIMMs were used for the magnetic dispersion microextraction of fluoroquinolones from egg samples with satisfactory results.

Improving crosslinking of stabilized polyacrylonitrile fibers and mechanical properties of carbon fibers by irradiating with γ-ray

Polyacrylonitrile (PAN) fibers were stabilized continuously through a series of temperature zones, and the stabilized PAN fibers (SFs) taken out from different zones were irradiated with γ-ray, finally, some of the irradiated SFs were carbonized continuously. Structure changes of the SFs and mechanical properties of the derived carbon fibers were investigated. It is found that γ-ray not only could destroy the nitrile crosslinking bonds and form nitrile groups again in slight SFs, but could make more crosslinked structure including ether crosslinking and carbon-carbon crosslinking in slight and deep SFs, which improved thermal stability of the SFs and tensile strength of the carbon fibers. The irradiation also induced cyclization in short sequence in slight SFs, however, such a cyclization structure didn't significantly improve thermal stability.

Cell growth and proliferation on the interface of a silk fabric tubular scaffold

A silk fibroin tubular scaffold (SFTS) has been designed and fabricated using silk fabric and regenerated silk fibroin, and used in the construction of artificial blood vessels. As a replacement for blood vessels, scaffolds should have a suitable interface for the adherence and proliferation of vascular cells, and the pore structure of the internal surface is one of most important factors. In this article, we investigate the effect of SFTSs with different pore structures on cells growth. Pore structures were controlled by adjusting the concentration of both the silk fibroin and the polyethylene glycol diglycidyl ether cross-linker as well as the freezing temperature. Intuitive cell fluorescence imaging and MTT assays on fibroblasts and human umbilical vein endothelial cells (HUVEC) were used to probe interactions with internal surfaces of differing pore diameter and density. The results showed that SFTSs fabricated under different conditions exhibited no cytotoxicity. Furthermore, fibroblasts were highly migratory, occupied the interface and could bridge the macropores well when the pore diameter was 50 ∼ 75 µm. SFTSs with micropores of about 30 ∼ 50 µm in diameter were deemed suitable for the growth and proliferation of HUVECs.