Photocrosslinked methacrylated chitosan-based nanofibrous scaffolds as potential skin substitute

Nanofibers based on natural polymers have recently been attracting research interest as promising materials for use as skin substitutes. Here, we prepared photocrosslinked nanofibrous scaffolds based on methacrylated chitosan (MACS) by photocrosslinking electrospun methacrylated chitosan/poly (vinyl alcohol) (PVA) mats and subsequently removing PVA from the nanofibers. We comprehensively investigated the solution properties of MACS/PVA precursors, the intermolecular action between MACS and PVA components, and the morphology of MACS/PVA nanofibers. Results indicated that the fiber diameter and morphology of the photocrosslinked methacrylated chitosan-based nanofibrous scaffolds were controlled by the MACS/PVA mass ratio and showed highly micro-porous structures with many fibrils. In vitro cytotoxicity evaluation and cell culture experiments confirmed that MACS-based mats with micro-pore structure were biocompatible with L929 cells and facilitated cellular migration into the 3D matrix, demonstrating their potential application as skin replacements for wound repair.     

Thermal stability of the cellulose synthase complex of Acetobacter xylinum

The thermal stability of the cellulose synthase complex of Acetobacter xylinum has been analyzed in terms of enzyme activity loss as well as detection of its two major components (83kDa and 93kDa polypeptides) in polyacrylamide gels under different electrophoretic sample treatment conditions. The cellulose synthase complex intrinsically is a thermally unstable enzyme and quickly loses its in vitro activity beyond 35°C. The 83 kDa polypeptide has been found to be more labile than the 93 kDa polypeptide. When boiled in lithium dodecyl sulfate (LDS) buffer, the 83 kDa polypeptide is destroyed through peptide hydrolysis while the 93 kDa polypeptide remains uncleaved. The 83 kDa polypeptide is destroyed in LDS buffer at elevated temperatures beyond 55°C. When boiled in the absence of LDS buffer, the 83 kDa polypeptide is completely aggregated, while the 93 kDa polypeptide is only partially aggregated. In the absence of LDS buffer, the complete thermal aggregation of the 83 kDa polypeptide occurs at elevated temperatures beyond 85°C. The aggregation process has been quantitatively analyzed by a newlyintroduced quantitative index, Td (the temperature at which half the quantity of 83kDa polypeptide disappears due to aggregation). The Td determined for the 83kDa polypeptide in the productentrapped fraction is 48°C.     

Formation of nanocrystalline ZnO particles into bacterial cellulose pellicle by ultrasonic-assisted in situ synthesis

Nanocrystalline zinc oxide particles were synthesized and simultaneously incorporated into a three-dimensional nanofibrous matrix of bacterial cellulose (BC) pellicles by a newly created method called “ultrasonic-assisted in situ synthesis”. The BC pellicles were first immersed in a zinc acetate solution. Then the Zn²⁺-absorbed BC pellicle was further immersed in ammonium hydroxide solution with simultaneous ultrasonic treatment. The effect of immersion time of the BC pellicles in zinc acetate solution and ultrasonic treatment time on crystalline size and percent incorporation of ZnO into the BC pellicles were determined. The crystalline size of ZnO incorporated in BC pellicles was in the range of ~54–63 nm that were similar to the diameter of BC nanofibrils. The amount of ZnO into the BC pellicles was found to increase with increasing immersion time. A longer ultrasonic treatment time resulted in smaller crystalline size of the incorporated ZnO. The particle size, morphology and dispersion of the synthesized ZnO in the BC matrix were examined by transmission electron microscope and scanning electron microscope with inbuilt energy dispersive X-ray analysis. The mechanism of the formation of the nanocrystalline ZnO particles onto the BC nanofibrils was discussed. Moreover, the antibacterial activity of the nanocrystalline ZnO particle-incorporated BC sheet against Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive) was also evaluated.     

Formation of a composite from Se0 nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films

Formation of a composite from Se⁰ nanoparticles stabilized with polyvinylpyrrolidone and Acetobacter xylinum cellulose gel films was studied. The optimal sorption parameters at which the amorphous form of the selenium complex is preserved in the composite were suggested.     

Electroaddressing agarose using Fmoc-phenylalanine as a temporary scaffold

Electroaddressing, the use of imposed electrical stimuli to guide assembly, is attractive because electrical stimuli can be conveniently applied with high spatial and temporal resolution. Several electroaddressing mechanisms have been reported in which electrode-induced pH gradients trigger stimuli-responsive materials to undergo localized sol-gel transitions to form hydrogel matrices. A common feature of existing hydrogel electrodeposition mechanisms is that the deposited matrix retains residual charged, acidic, or basic (macro)molecules. Here, we report that pH-responsive fluorenyl-9-methoxycarbonyl-phenylalanine (Fmoc-Phe) can be used to codeposit the neutral and thermally responsive polysaccharide agarose. Upon cooling, an agarose network is generated and Fmoc-Phe can be removed. The Fmoc-Phe-mediated codeposition of agarose is simple, rapid, spatially selective, and allows for the electroaddressing of a bioactive matrix.     

Stable preservation of hemoglobin vesicles as a blood substitute

Long‐term preservation of hemoglobin (Hb) vesicles, the so‐called artificial red cell (ARC), in dry powder was studied. Carbonylhemoglobin (COHb) was encapsulated in the vesicle of 1,2‐bis(2,4‐octadecadienoyl)‐sn‐glycero‐3‐phosphocholine (DODPC) and the polymerizable membrane components were polymerized by γ‐ray irradiation. The obtained ARC suspension was then freeze‐dried in the presence of sucrose. The factors influencing the shelf‐life of the freeze‐dried ARC, such as sucrose concentration, moisture and storage temperature, were elucidated. After storage in the dry state for more than one year, the oxygen‐carrying capacity was recovered by rehydration of the freeze‐dried ARC with distilled water and substitution of the carbon monoxide ligand with oxygen. Copyright © 1999 John Wiley & Sons, Ltd.     

Nitromethane as a substitute for nitric oxide in chemical ionization

Nitromethane chemical ionization mass spectra of some alkenes, alkynes and alcohols show that the spectra are similar in many respects to those obtained under nitric oxide chemical ionization conditions.     

Effect of different additives on bacterial cellulose production by Acetobacter xylinum and analysis of material property

Bacterial cellulose (BC) demonstrates unique properties including high mechanical strength, high crystallinity, and high water retention ability, which make it an useful material in many industries, such as food, paper manufacturing, and pharmaceutical application. In this study, different additives including agar, carboxymethylcellulose (CMC), microcrystalline cellulose, and sodium alginate were added into fermentation medium in agitated culture to enhance BC production by Acetobacter xylinum. The optimal additive was chosen based on the amount of BC produced. The produced BC was analyzed by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). Among the evaluated additives, CMC yielded highest BC production (8.2 g/L) compared to the control (1.3 g/L). The results also indicated that CMC-altered BC production increased with CMC addition and reached saturation around 1%. The variation between replicates for all analysis was <5%. From XRD analysis, however, the crystallinity and crystal size decreased as CMC addition increased. FESEM results showed CMC-altered BC produced from agitated culture retained its interweaving property. TGA results demonstrated that CMC-altered BC had about 98% water retention ability, which is higher than BC pellicle produced with static culture. CMC-altered BC also exhibited higher T _max compared to control. Finally, DMA results showed that BC from agitated culture loses its mechanical strength in both stress at break and Young’s modulus when compared to BC pellicle. This study clearly demonstrated that addition of CMC enhanced BC production and slightly changed its structure.     

Hydroxyethyl methyl cellulose as a modifier of gypsum properties

Journal of Thermal Analysis and Calorimetry - The study is focused on the influence of a water-soluble polymer (in weight fraction up to 1.5%), cellulose derivatives—hydroxyethyl methyl...     

New fluorimetric determination of hemoglobin used as a substitute of mimietic peroxidase

Hemoglobin (Hb) could be used as a substitute of peroxidase in the catalytic oxidation of tetra-substituted amino aluminum phthalocyanine (TAA1Pc) by H2O2. We found that the fluorescence of TAA1Pc (a red-region fluorescent dye with a maximum excitation wavelength at 606 nm and a maximum emission wavelength at 673 nm) could significantly be quenched by H2O2 in the presence of Hb. The value of F0/F (where the relative fluorescence intensity of blank solution and that of the sample solution containing Hb were given by F0 and F, respectively) is linearly related to the concentration of Hb. Based on this, a novel fluorimetric method was developed for the determination of Hb in aqueous solution. Under optimal conditions, Hb could be determined in the concentration range of 5 x 10(-11) - 12 x 10(-8) mol L(-1) with a detection limit of 1.5 x10(-11) mol L(-1). The relative standard deviation of ten replicate measurements was 1.95% for solution containing 1 x10(-9 ) mol L(-1) Hb. The proposed method has been applied to the analysis of Hb in human blood and the results were in good agreement with those reported by a hospital laboratory. So this is a new, high sensitive and precise fluorescence quenching method to determine Hb.     

Phenothiazine as a redox-active DNA base substitute: comparison with phenothiazine-modified uridine

Phenothiazine can be incorporated as a redox-active probe into DNA in two conceptually different ways: the non-nucleosidic DNA base surrogate exhibits similar properties to 10-methylphenothiazine but with no preferential base-pairing properties, whereas the phenothiazine-modified uridine has different optical and electrochemical properties, but exhibits preferred Watson-Crick base pairing with adenine.     

Phloxine B as a probe for entrapment in microcrystalline cellulose

The photophysical behaviour of phloxine B adsorbed onto microcrystalline cellulose was evaluated by reflectance spectroscopy and laser induced time-resolved luminescence in the picosecond-nanosecond and microsecond-millisecond ranges. Analysis of the absorption spectral changes with concentration points to a small tendency of the dye to aggregate in the range of concentrations under study. Prompt fluorescence, phosphorescence and delayed fluorescence spectral decays were measured at room temperature and 77 K, without the need of sample degassing because cellulose protects triplet states from oxygen quenching. In all cases, spectral changes with time and lifetime distribution analysis were consistent with the dye coexisting in two different environments: dyes tightly entrapped between polymer chains in crystalline regions of cellulose showed longer fluorescence and phosphorescence lifetimes and more energetic triplet states, while dyes adsorbed in more amorphous regions of the support showed shorter lifetimes and less energetic triplet states. This behaviour is discussed in terms of the different dye-support interactions in both kinds of adsorption sites.     

An evaluation of cellulose as a substrate for room-temperature phosphorescence

Cotton-linter pulps, wood pulps and several filter papers have been evaluated as substrates for room-temperature phosphorescence. A variety of chemical treatments of one filter paper is discussed in terms of reducing the background phosphorescence of the cellulose and in evaluating possible trace contaminants in cotton fibres. In order to account for uniformity of filter paper used in room temperature phosphorescence, a final evaluation of several different lots of one type of filter paper is presented.     

Self-doped polyaniline as new polyaniline substitute for solid-phase microextraction

This work is a first study on extraction efficiency and thermal stability of nano-structured self-doped polyaniline (SPAN) as a coating of solid-phase microextraction (SPME) fibers. SPAN-based fibers were prepared using electrochemical deposition on platinum wires. The particle sizes of prepared nano-structure were in the range of 50–100 nm. Extraction properties of the fiber to 1,4-dioxane were examined using headspace solid-phase microextraction (HS-SPME) coupled to gas chromatography-flame ionization detection (GC-FID). The results have proved higher thermal stability of the proposed fiber compared to common PANI fiber. The SPAN coating was proved to be very stable at relatively high temperatures (up to 350 °C) with high extraction capacity and long lifespan (more than 50 times). Therefore, it can be a good substitute of polyaniline (PANI) as a SPME coating. The extraction procedure was optimized by selecting the appropriate extraction parameters including extraction time, extraction temperature, salt concentration, stirring rate and headspace volume. Calibration graph was linear in the concentration range of 1–100 ng mL⁻¹ (R² > 0.993) with detection limit of 0.1 ng mL⁻¹. Single fiber and fiber-to-fiber repeatability were lower than 6.0% and 10.4%, respectively. Different water samples were analyzed as real samples and good recoveries (98–120%) were obtained.     

Thin cellulose films as a model system for paper fibre bonds

Thin cellulose films on silicon substrates are used as a model system for paper fiber bonds. The films are formed by spincoating trimethylsilylcellulose on the substrates. The films are regenerated using HCl gas. After swelling in water, two samples can be bonded like a sandwich. It is shown that this model system can be used to measure the bond strength between the two films under controlled conditions. For a detailed characterization the films are studied in terms of roughness with atomic force microscopy (AFM). The hardness of the films is investigated by AFM-based nanoindentation. The chemistry and the thickness of the films is studied by infrared spectroscopy. It is shown that this model system enables the evaluation of different bonding mechanisms discussed in pulp and paper research. Our results clearly indicate that Coulomb interaction is an important bonding mechanism.     

Nitric acid preparation of cellulose from miscanthus as a nitrocellulose precursor

A nitric acid method for the preparation of cellulose from miscanthus is considered. The method consists in successive treatment of the raw material with nitric acid and sodium hydroxide and affords cellulose with properties suitable for the synthesis of cellulose nitrates. The data on the nitrogen weight fraction, the viscosity, and the solubility of cellulose nitrates from miscanthus in the alcohol-ether medium are given. The miscanthus cellulose was nitrated using an industrial sulfuric-nitric acid mixture to yield cellulose nitrate samples with characteristics close to those of colloxylin.

     

Reducing end-group of cellulose as a reactive site for thermal discoloration

Thermal discoloration of cellulose (Avicel PH-101 and Whatman No. 42 filter paper) was studied in N₂ at 160-280 °C with glycerol-treated and NaBH₄-reduced samples, to understand the role of the reducing end. Thermal discoloration of glycerol-treated Avicel PH-101, in which some of the reducing ends were converted into glycosides (non-reducing ends), was suppressed compared with the original cellulose, and the level of suppression was directly related to the extent of glycosylation of the reducing ends. The stabilization efficiency of glycerol-treated Whatman No. 42 filter paper suggested that the reducing ends newly formed by reduction of the degree of polymerization (DP) (to about 200) during heat treatment contributed to the discoloration. The important role of the reducing ends in thermal discoloration was supported by the stabilization of Avicel PH-101 by reduction with NaBH₄ (giving a reducing end content that was 2% of that of the original cellulose). Thermally induced discoloration was also inhibited by heating cellulose in suspension in the polyether tetraethyleneglycol dimethylether, which has been reported to inhibit the thermal degradation of reducing sugars.     

Tetraiodophenolsulfonphthalein as a spectral substitute to characterize the complexation between cationic and anionic surfactant

The complexation of cetyltrimethylammonium bromide (CTAB) with sodium dodecyl sulfate (SDS) with sodium dodecyl benzene sulfonate (SDBS), with tetraiodophenolsulfonphthalein (TIPST) as a spectral substitute was investigated at pH 5.89 and 8.30 by the microsurface adsorption--spectral correction (MSASC) technique. The aggregations of TIPST, SDS, and SDBS on CTAB obeyed the Langmuir isothermal adsorption. The aggregates TIPST-CTAB, TIPST2-CTAB3, SDS3-CTAB2, and SDBS3-CTAB2 were formed at 20 degrees C and the binding constants of all the aggregates were determined. The replacement of TIPST-binding CTAB monomer with SDS or SDBS at pH 5.89 was applied to the quantitative determination of anionic detergent (AD) in water with satisfactory recovery.