Phosphorylated chitosan membranes for the separation of ethanol-water mixtures by pervaporation

Dense membranes of chitosan were prepared and ionically crosslinked with phosphoric acid for varying intervals of time. The membranes were characterized by FTIR and XRD to confirm cross-linking. TGA and IEC studies were conducted to assess the thermal stability and estimate the number of interactive groups left in the membrane after crosslinking. Sorption studies were carried out to evaluate the extent of interaction and degree of swelling of the membranes in pure liquids as well as binary mixtures. The phosphorylated chitosan membrane crosslinked for 2 h showed good mechanical strength and strong potential for breaking the azeotrope of 95.58 wt% ethanol by exhibiting a high pervaporation selectivity of 213 with substantial water flux of 0.58 kg/(m² h). Pervaporation experimental parameters such as feed composition, membrane thickness and permeate pressure were varied to identify optimum operating conditions.     

Synthesis and characterization of chitosan/ZnO nanoparticle composite membranes

Novel chitosan/ZnO nanoparticle (CS/nano-ZnO) composite membranes were prepared via the method of sol-cast transformation and studied by UV-vis absorption spectroscopy (UV-vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray fluorescence spectrometry (EDX). The characterization revealed that ZnO nanoparticles dispersed homogeneously within the chitosan matrix. The mechanical and antibacterial properties of the product were investigated. The results showed that the ZnO content had an effect on the mechanical properties of CS/nano-ZnO composite membranes, and that the antibacterial activities of CS membranes for Bacillus subtilis, Escherichia coli, and Staphylococcus aureus were enhanced by the incorporation of ZnO. Further, CS/nano-ZnO composite membranes with 6-10 wt % ZnO exhibited high antibacterial activities.     

Effect of carboxymethylation conditions on the water-binding capacity of chitosan-based superabsorbents

A superabsorbent polymer (SAP) from chitosan was provided via carboxymethylation of chitosan, followed by cross-linking with glutaraldehyde and freeze-drying. This work was focused on an investigation of the effects of monochloroacetic acid (MCAA), sodium hydroxide, and reaction time on preparation of carboxymethyl chitosan (CMCS). The CMCS products were characterized using FTIR spectroscopy, and their degrees of substitution (DS) were measured using conductimetry and FTIR analysis. The highest DS value was obtained when the carboxymethylation reaction was carried out using 1.75 g MCAA and 1.75 g NaOH per g of chitosan in 4 h. The water solubilities of the CMCS products at various pHs were also evaluated, and the results indicated a significant impact of the reaction parameters on the solubility of CMCS. The CMCSs with the highest DS value resulted in SAPs having the highest water-binding capacity (WBC). The WBC of the best SAP measured after 10 min exposure in distilled water, 0.9% NaCl solution, synthetic urine, and artificial blood was 104, 33, 30, and 57 g/g, respectively. The WBC of this SAP at pH 2-9 passed a maximum at pH 6.     

Development of cesium phosphotungstate salt and chitosan composite membrane for direct methanol fuel cells

A novel composite membrane has been developed by doping cesium phosphotungstate salt (Cs_xH_3−xPW₁₂O₄₀ (0 ≤ x ≤3), Cs_x-PTA) into chitosan (CTS/Cs_x-PTA) for application in direct methanol fuel cells (DMFCs). Uniform distribution of Cs_x-PTA nanoparticles has been achieved in the chitosan matrix. The proton conductivity of the composite membrane is significantly affected by the Cs_x-PTA content in the composite membrane as well as the Cs substitution in PTA. The highest proton conductivity for the CTS/Cs_x-PTA membranes was obtained with x = 2 and Cs₂-PTA content of 5 wt%. The value is 6 × 10⁻³ S cm⁻¹ and 1.75 × 10⁻² S cm⁻¹ at 298 K and 353 K, respectively. The methanol permeability of CTS/Cs₂-PTA membrane is about 5.6 × 10⁻⁷, 90% lower than that of Nafion-212 membrane. The highest selectivity factor (φ) was obtained on CTS/Cs₂-PTA-5 wt% composite membrane, 1.1 × 10⁴/S cm⁻³ s. The present study indicates the promising potential of CTS/Cs_x-PTA composite membrane as alternative proton exchange membranes in direct methanol fuel cells.     

Preparation and characterization of films based on zirconium sulfophenyl phosphonate and chitosan

Zirconium sulfophenyl phosphonate (ZrSP), Zr(O₃P-C₆H₄SO₃H)₂, was synthesized and characterized to prepare nanocomposites based on chitosan (CS). The effects of ZrSP on the structure, morphology, and thermal properties, as well as the mechanical properties of the films were investigated by Fourier-transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and tensile tests. FTIR spectroscopy revealed that electrostatic interactions had been formed in the nanocomposites, which improved the compatibility between CS and ZrSP. XRD and SEM results indicated the ZrSP nanoparticles were uniformly distributed in the chitosan matrix at low loading, and obvious aggregations existed at high loading. In addition, compared with neat CS, the values of tensile strength (σ_b), elongation at break (ε_b), and water resistance of CS/ZrSP-3 containing 0.6 wt % ZrSP had been improved by 60.0%, 69.7%, and 41.8%, respectively.     

Preparation and characterization of nano-cellulose with new shape from different precursor

Three different precursor materials – 1. China cotton, 2. South African cotton, 3. Waste tissue papers were used to produce nano-cellulose by acid hydrolysis route. No chemical pretreatment has been done for the production of nano-cellulose from these precursors. Prepared nano-cellulose and their corresponding precursor materials were characterized by transmission electron microscopy (TEM), particle size analysis, X-ray diffraction (XRD) study, thermo gravimetric analysis (TGA), differential scanning calorimetric (DSC) analysis and Fourier transformed infra red (FTIR) spectroscopy. A comparative study of the characteristics was done with the properties of raw materials and with that of nano-cellulose. Shape and size of the nano cellulose generally depends on nature of the precursor and hydrolysis condition. Morphology study of nano-cellulose from different sources revealed range of length from 50 to 200 nm and diameter from 10 to 90 nm. Higher thermal stability and crystallinity of nano-cellulose were observed compared to that of precursor from TGA/DSC study.     

Core-shell structured PEO-chitosan nanofibers by coaxial electrospinning

Core-shell structured PEO-chitosan nanofibers have been produced using a coaxial electrospinning setup. PEO and chitosan solutions, both in an aqueous acetic acid solvent, were used as the inner (core) and outer (shell) layer, respectively. Uniform-sized defect-free nanofibers of 150-190 nm diameter were produced. In addition, hollow nanofibers could be obtained subsequent to PEO washing of the membranes. The core-shell nanostructure and existence of chitosan on the shell layer were confirmed by TEM images obtained before and after washing the PEO content with water. The presence of chitosan on the surface of the composite nanofibers was further supported by XPS studies. The chitosan and PEO compositions in the nanofibrous mats were determined by TGA analysis, which were similar to their ratio in the feed solutions. The local compositional homogeneity of the membranes and the efficiency of the washing step to remove PEO were also verified by FTIR. In addition, DSC and XRD were used to characterize the crystalline structure and morphology of the co-electrospun nonwoven mats. The prepared coaxial nanofibers (hollow and solid) have several potential applications due to the presence of chitosan on their outer surfaces.     

Rheological properties of chitosan-tripolyphosphate complexes: From suspensions to microgels

Complex fluids formed by crosslinking of chitosan (CS, 330 kDa) with sodium tripolyphosphate (TPP) have been studied by dynamic light scattering (DLS), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and rheology. The effects of chitosan/TPP ratios, initial chitosan or TPP concentrations, and ultrasonication time on the chitosan-TPP complex formation have been investigated. It was found that the optimum condition for CS-TPP nanoparticle formation occurred at CS/TPP mass ratio of 3.75 and with 9 min sonication treatment (energy output 3.75 W/mL). At the same initial chitosan concentration, small particle sizes (i.e., particle size < 300 nm) resulted in the formation of CS-TPP nanoparticle suspensions, which showed a lower viscosity than pure chitosan solutions, and their viscosities increased as the CS-TPP nanoparticles sizes increased. Centrifugation of CS-TPP particles of larger particle sizes (i.e., 360-870 nm) at 11,000 × g caused the formation of CS-TPP microgels. Dynamic rheological studies indicated that both storage modulus (G′) and loss modulus (G″) increased with particle sizes. During centrifugation processing, strong centrifugal force surmounted the electrostatic repulsion between CS-TPP particles and caused particles to stick with each other to form CS-TPP microgels. The water contents of microgels negligibly depended on particle size, suggesting that the free volumes of microgels were not affected by particle size, therefore supporting our pseudo-hard sphere assumption for CS-TPP nanoparticles.     

Genipin cross-linked alginate-chitosan microcapsules: membrane characterization and optimization of cross-linking reaction

The genipin cross-linked alginate-chitosan (GCAC) microcapsule, composed of an alginate core and a genipin cross-linked chitosan membrane, was recently proposed for live cell encapsulation and other delivery applications. This article for the first time describes the details of the microcapsule membrane characterization using a noninvasive and in situ method without any physical or chemical modifications on the samples. Results showed that the cross-linking reaction generated the fluorescent chitosan-genipin conjugates. The cross-linked chitosan membrane was clearly visualized by confocal laser scanning microscopy (CLSM). A straightforward assessment on the membrane thickness and relative intensity was successfully achieved. CLSM studies showed that the shell-like cross-linked chitosan membranes of approximately 37 microm in thickness were formed surrounding the microcapsule. The reaction variables, including cross-linking temperature and time significantly affected the fluorescence intensity of the membranes. Elevating the cross-linking temperature from 4 to 37 degrees C drastically intensified the membrane fluorescence, suggesting the attainment of a high degree of cross-linking on the chitosan membrane. Extended cross-linking time altered the cross-linked membranes in modulation. Although genipin concentration and cross-linking time had little effects on the membrane thickness, cross-linking at higher temperatures tended to form relatively thinner membranes.     

Clay nanopaper composites of nacre-like structure based on montmorrilonite and cellulose nanofibers—Improvements due to chitosan addition

Clay nanopaper are nanocomposites with nacre-like structure and multifunctional characteristics including high modulus, significant strength and toughness as well as fire retardancy and low oxygen transmission rate (OTR). Montmorrilonite (MTM) and nanofibrillated cellulose (NFC) hydrocolloids are combined with a chitosan (CS) solution to form high MTM content nanopaper structures by the use of a previously developed papermaking approach. Chitosan functions as flocculation agent and decreases dewatering time to less than 10% compared with MTM-NFC clay nanopaper. The effect of chitosan on the clay nanopaper structure was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Properties were measured by uniaxial tensile testing, thermogravimetric analysis (TGA), OTR and moisture adsorption experiments. A nacre-like multilayered structure was confirmed and the chitosan-clay nanopaper showed favorable mechanical properties at clay contents as high as 44-48 wt%.     

Influence of silicone oil modification on properties of ramie fiber reinforced polypropylene composites

This paper focused on the analyses of the composition, microstructure, thermal stability and mechanical behavior of modified ramie fiber and its reinforced polypropylene composites. Ramie fiber (RF) was treated with epoxy-silicone oil (ESO) at 160 °C in argon gas. The FTIR and XRD analyses indicated that some silicone molecular chains were bonded on the surface of modified RF, which decreased the crystallinity of the fiber without changing the crystalline type of cellulose. The SEM results of fracture surface showed that the modified RF/PP composite had better interfacial bonding between RF and PP. The mechanical tests showed that the impact strength and the elongation at break of RF/PP were increased by 17.0% and 196% after modification, respectively. The tensile strength of 30RF/PP was improved from 18.95 MPa to 25.96 MPa compared to pure PP. The results of TGA showed that fiber treatment could improve the degradation temperature of RF/PP composites.     

In situ preparation of magnetic Fe3O4-chitosan nanoparticles for lipase immobilization by cross-linking and oxidation in aqueous solution

A new and simple method has been proposed to prepare magnetic Fe₃O₄-chitosan (CS) nanoparticles by cross-linking with sodium tripolyphosphate (TPP), precipitation with NaOH and oxidation with O₂ in hydrochloric acid aqueous phase containing CS and Fe(OH)₂, and these magnetic CS nanoparticles were used to immobilize lipase. The effects on the sequence of adding NaOH and TPP, the reaction temperature, and the ratio of CS/Fe(OH)₂ were studied. TEM showed that the diameter of composite nanoparticles was about 80 nm, and that the magnetic Fe₃O₄ nanoparticles with a diameter of 20 nm were evenly dispersed in the CS materials. Magnetic measurement revealed that the saturated magnetisation of the Fe₃O₄-CS nanoparticles could reach 35.54 emu/g. The adsorption capacity of lipase onto nanoparticles could reach 129 mg/g; and the maximal enzyme activity was 20.02 μmol min⁻¹ mg⁻¹ (protein), and activity retention was as high as 55.6% at a certain loading amount.     

Dehydration of 1,4-dioxane by pervaporation using modified blend membranes of chitosan and nylon 66

The pervaporation separation of 1,4-dioxane/water mixtures was carried out using crosslinked blend membranes of chitosan (CS) and nylon 66 (NYL). These membranes were characterized by FTIR, TGA, XRD, and tensile strength to assess intermolecular interactions, thermal stability, crystallinity and mechanical strength, respectively. Sorption studies were carried out in pure liquids and binary mixtures of different compositions to evaluate polymer–liquid interactions. The effects of CS/NYL ratio, membrane thickness, feed concentration on the transmembrane permeation rate and separation factor were investigated. Optimum CS/NYL ratio was determined as 90/10 (w/w) for 4.3 wt% feed water concentration at 40 °C. Increasing barrier from 30 to 120 μm improved the separation factor from 767 to 1123 at the cost of flux, which lowered from 0.118 to 0.028 kg/m² h. The membrane performance was also investigated for the separation of various feed compositions of 1,4-dioxane–water mixtures and permeate pressures. The azeotrope formed at 82-wt% dioxane was easily broken with a selectivity of 865 and water flux of 0.089 kg/m² h.     

The cytoprotection of chitosan based hydrogels in xenogeneic islet transplantation: An in vivo study in streptozotocin-induced diabetic mouse

Immune rejection and scarcity of donor tissues are the restrictions of islets transplantation. In this study, the cytoprotection of chitosan hydrogels in xenogeneic islet transplantation was demonstrated. Wistar rat islets encapsulated in chitosan hydrogels were performed glucose challenge test and live/dead cell staining in vitro. Islets/chitosan hydrogels were transplanted into the renal subcapsular space of diabetic C57BL/6 mice. Non-fasting blood glucose level (NFBG), body weight, intraperitoneal glucose tolerance test (IPGTT), and glucose disappearance rate were determined perioperatively. The serum insulin level was analyzed, and the kidney transplanted with islets/chitosan hydrogels were retrieved for histological examination after sacrifice. The present results showed that islets encapsulated in chitosan hydrogels secreted insulin in response to the glucose stimulation as naked islets with higher cell survival. The NFBG of diabetic mice transplanted with islets/chitosan hydrogels decreased from 487 ± 46 to 148 ± 32 at one day postoperation and maintained in the range of 201 ± 36 mg/dl for four weeks with an increase in body weight. IPGTT showed the glucose disappearance rate of mice transplanted with islets/chitosan hydrogels was significant faster than that of mice transplanted with naked islets; the serum insulin level increased from 0.29 ± 0.06 to 1.69 ± 0.65 μg/dl postoperatively. Histological examination revealed that the islets successfully engrafted at renal subcapsular space with positive insulin staining. The immunostain was negative for neither the T-cell lineages nor the monocyte/macrophages. This study indicates that the chitosan hydrogels deliver and protect encapsulated islets successfully in xenotransplantation.     

Synthesis of γ-cyclodextrin/chitosan composites for the efficient removal of Cd(II) from aqueous solution

The synthesis of chitosan-graft-γ-cyclodextrin (Ch-g-γ-CD) using persulfate/ascorbic acid redox system was done and characterized by FTIR, XRD, TGA and SEM/EDX. The optimum yield of the copolymer was obtained using 16 × 10⁻³ M γ-cyclodextrins (γ-CD), 2.8 × 10⁻² M ascorbic acid (AA), 1.8 × 10⁻² M K₂S₂O₈ and 0.1 g chitosan in 25 mL of 2% aqueous formic acid at 45 ± 0.2 °C. The highest percent grafting samples were evaluated for cadmium metal ion (Cd(II)) removal from the aqueous solutions where the sorption capacities were found proportional to the grafting extent. The sorption was pH and concentration dependent where, pH = 8.5 was found to be the optimum value. The adsorption data were modeled using Langmuir and Freundlich isotherms. The equilibrium data followed the Langmuir isotherm model with maximum sorption capacity of 833.33 mg/g. The influence of electrolytes, sodium chloride (NaCl) and sodium sulphate (Na₂SO₄) on Cd(II) uptake was also studied. Desorption of the cadmium loaded Ch-g-γ-CD was accomplished with 0.01 N H₂SO₄. The adsorbent exhibited high reusability and could be successfully recycled for nine cycles where in the ninth cycle 27% adsorption was feasible.     

Synthesis and evaluation of physicochemical properties of cross-linked sago starch

Highly substituted sago starch phosphate was synthesized using POCl₃ as cross-linking reagent. Titrimetric and Fourier transform infra red (FT-IR) spectral analysis were used to characterize the substitution. Studying the different factors affecting the reaction parameters showed that the optimal conditions for starch phosphorylation were: 4 h reaction time and reagent concentration 1.5% (w/w). The physicochemical properties of cross-linked sago starch (CLSS) were done using Scanning electron micrograph (SEM), X-ray powder diffractometer (XRD and Thermogravimetric analysis (TGA). The results revealed that crystalline nature of native sago starch was transformed after cross-linking. TGA report exhibited higher thermal stability, which makes it suitable for various industrial applications. Swelling behavior showed high swelling at low temperature (30 and 60 °C) as compared to high temperature (90 °C).     

Magnetic single-enzyme nanoparticles with high activity and stability

Magnetic single-enzyme nanoparticles (SENs) encapsulated within a composite inorganic/organic polymer network were fabricated via the surface modification and in situ aqueous polymerization of separate enzyme molecule. The resultant nanoparticles were characterized by transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectrometer and X-ray diffraction (XRD). These particles are almost spherical in shape and have a unique size of about 50 nm in diameter. Electrical and magnetic measurements reveal that the magnetic SENs have a conductivity of 2.7 × 10⁻³ S cm⁻¹, and are superparamagnetic with a saturation magnetization of 14.5 emu g⁻¹ and a coercive force of 60 Oe. Compared with free enzyme, encapsulated enzyme exhibits a strong tolerance to the variation of solution pH, high temperature, organic solvent and long-term storage, thus showing significantly enhanced enzyme performance and stability.     

Membrane hydration correlates to cellular biophysics during freezing in mammalian cells

Cell survival during freezing applications in biomedicine is highly correlated to the temperature history and its dependent cellular biophysical events of dehydration and intracellular ice formation (IIF). Although cell membranes are known to play a significant role in cell injury, a clear correlation between the membrane state and the surrounding intracellular and extracellular water is still lacking. We previously showed that lipid hydration in LNCaP tumor cells is related to cellular dehydration. The goal of this study is to build upon this work by correlating both the phase state of the membrane and the surrounding water to cellular biophysical events in three different mammalian cell types: human prostate tumor cells (LNCaP), human dermal fibroblasts (HDF), and porcine smooth muscle cells (SMC) using Fourier Transform Infrared spectroscopy (FTIR). Variable cooling rates were achieved by controlling the degree of supercooling prior to ice nucleation (− 3 °C and − 10 °C) while the sample was cooled at a set rate of 2 °C/min. Membranes displayed a highly cooperative phase transition under dehydrating conditions (i.e. NT = − 3 °C), which was not observed under IIF conditions (NT = − 10 °C). Spectral analysis showed a consistently greater amount of ice formation during dehydrating vs. IIF conditions in all cell types. This is hypothesized to be due to the extreme loss of membrane hydration in dehydrating cells that is manifested as excess water available for phase change. Interestingly, changes in residual membrane conformational disorder correlate strongly with cellular volumetric decreases as assessed by cryomicroscopy. A strong correlation was also found between the activation energies for freezing induced lyotropic membrane phase change determined using FTIR and the water transport measured by cryomicroscopy. Reduced lipid hydration under dehydration freezing conditions is suggested as one of the likely causes of what has been termed as “solution effects” injury in cryobiology.     

Magainin 2 in action: distinct modes of membrane permeabilization in living bacterial and mammalian cells

Interactions of cationic antimicrobial peptides with living bacterial and mammalian cells are little understood, although model membranes have been used extensively to elucidate how peptides permeabilize membranes. In this study, the interaction of F5W-magainin 2 (GIGKWLHSAKKFGKAFVGEIMNS), an equipotent analogue of magainin 2 isolated from the African clawed frog Xenopus laevis, with unfixed Bacillus megaterium and Chinese hamster ovary (CHO)-K1 cells was investigated, using confocal laser scanning microscopy. A small amount of tetramethylrhodamine-labeled F5W-magainin 2 was incorporated into the unlabeled peptide for imaging. The influx of fluorescent markers of various sizes into the cytosol revealed that magainin 2 permeabilized bacterial and mammalian membranes in significantly different ways. The peptide formed pores with a diameter of ∼2.8 nm (< 6.6 nm) in B. megaterium, and translocated into the cytosol. In contrast, the peptide significantly perturbed the membrane of CHO-K1 cells, permitting the entry of a large molecule (diameter, >23 nm) into the cytosol, accompanied by membrane budding and lipid flip-flop, mainly accumulating in mitochondria and nuclei. Adenosine triphosphate and negatively charged glycosaminoglycans were little involved in the magainin-induced permeabilization of membranes in CHO-K1 cells. Furthermore, the susceptibility of CHO-K1 cells to magainin was found to be similar to that of erythrocytes. Thus, the distinct membrane-permeabilizing processes of magainin 2 in bacterial and mammalian cells were, to the best of our knowledge, visualized and characterized in detail for the first time.     

Cytocompatibility of electrospun nanofiber tubular scaffolds for small diameter tissue engineering blood vessels

A tubular scaffold was fabricated by using electrospun polymer solution blends of pNSR32 (recombinant spider silk protein), PCL (polycaprolactone) and Gt (gelatin). The physicochemical properties and cytocompatibility of these scaffolds were investigated. Afterwards, the pNSR32/PCL/Gt tubular scaffold (inner diameter = 3 mm) showed high porosity of 86.2 ± 2.9%, pore size of 2423 ± 979 nm and average fibre diameter of 166 ± 85 nm. Water uptake and contact angle of the scaffolds reached 112.0 ± 4.4% and 45.7 ± 13.7°, respectively. SDRAECs (Sprague Dawley Rat Aortic Endothelial Cells) grew and proliferated well and phenotype could be maintained on the composite scaffolds after they had been cultured on the composite scaffolds for 7 days. Compared with pure PCL scaffolds a greater density of viable cells was seen on the composites, especially the pNSR32/PCL/Gt scaffolds.