Suspension Cross-linking Research Articles

Synthesis and characterization of magnetic chitosan microspheres as low-density and low-biotoxicity adsorbents for lake restoration

We propose a novel magnetic adsorbent for optimal Phosphorus (P) removal from the upper sediment layers. For this aim, magnetic chitosan microparticles were prepared using a reverse-phase suspension cross-linking technique. The resulting particles and suspensions were characterized using scanning electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, magnetometry, thermogravimetric analysis, electrophoretic mobility and turbidity measurements. The hybrids are multicore particles consisting of well dispersed magnetite nanoparticles (approx. 10% w/w) homogeneously distributed within the biopolymer matrix. These microparticles can be easily separated from the water column and sediment using magnetic field gradients. Their P adsorption capacity is evaluated in batch conditions resulting in a maximum P adsorption capacity of ML = 4.84 mg g−1 at pH = 7. We demonstrate that these particles are excellent candidates to remove P from water column and also P mobile from the upper sediment layers due to two main reasons: they sediment slower and present lower potential toxicity (due to a their larger size) than conventional iron/iron oxide microparticles previously proposed for lake restoration.

Synthesis of Depo-Medrol-chitosan hydrogel as new drug slow-release appliance and investigation of release kinetics by high-performance liquid chromatography.

The present study deals with preparation and optimization of a novel chitosan hydrogel-based matrix by suspension cross-linking method for controlled release of Depo-Medrol. The controlled release of Depo-Medrol for effective Rheumatoid arthritis disease has become an imperative field in the drug delivery system. In this context, it was intended to optimize loading circumstances by experimental design and also study the release kinetics of Depo-Medrol entrapped in the chitosan matrix in order to obtain maximal efficiency for drug loading. The optimum concentrations of chitosan (2.5 g), glutaraldehyde (3.05 μL) and Depo-Medrol (0.1 mg) were set up to achieve the highest value of drug loaded and the most sustained release from the chitosan matrix. In vitro monitoring of drug release kinetic using high-performance liquid chromatography showed that 73% of the Depo-Medrol was released within 120 min, whereas remained drug was released during the next 67 h. High correlation between first-order and Higuchi's kinetic models indicates a controlled diffusion of Depo-Medrol through the surrounding media. Moreover, recovery capacity >82% and entrapment efficiency of 58-88% were achieved under optimal conditions. Therefore, the new synthesized Depo Medrol-chitosan is an applicable appliance for arthritis therapy by slow release mechanism. Copyright © 2016 John Wiley & Sons, Ltd.

An effective β-cyclodextrin polyurethane spherical adsorbent for the chromatographic enrichment of corilagin from Phyllanthus niruri L. extract

A novel β-cyclodextrin polyurethane (β-CD-PU) spherical adsorbent was prepared by the reversed-phase suspension crosslinking technique for the chromatographic enrichment of a polyphenolic compound corilagin. β-Cyclodextrin (β-CD) and PEG1000 were co-crosslinked with hexamethylene diisocyanate, and the polyurethane skeleton was formed and confirmed by FTIR, TGA and 13C CP/MAS NMR analysis. A chromatographic operation was carried out with the raw Phyllanthus niruri L. extract directly loaded onto the adsorbent, and one-step capture of corilagin had been realized. The ethanol aqueous solution of 20%(w/w) was favorable for corilagin elution with recovery and purity of 49.4% and 64.8%, respectively. The adsorption kinetic experiments showed that the pseudo-second order model provided a good fit with the data, but the values of equilibrium adsorption capacity deviated notably, revealing the complexity of the adsorption mechanism. It was considered that the formation of inclusion complex corilagin/β-CD played a significant role on corilagin adsorption and recovery, which was illustrated by the inclusion property investigation. The inclusion complex preferred 1:1 stoichiometry and the association constant was determined as 1.69×103Lmol−1 at 298K, indicating the β-CD cavity showed excellent affinity to corilagin. Moreover, there was evidence that the crystal pattern of β-CD-PU changed when it adsorbed corilagin by XRD analysis, which indirectly revealed the mechanism of adsorption. These results suggested that β-CD-PU adsorbent was a promising candidate for the recovery and enrichment of corilagin or other polyphenolic natural products from plant materials.

Application of modified chitosan microspheres for nitrate and phosphate adsorption from aqueous solution

Modified chitosan microspheres were prepared by inverse suspension crosslinking and used for nitrate and phosphate adsorption from aqueous solution. Their surface was coarse and porous compared to pure chitosan microspheres and they were about 100 μm in size.

Effective biosorption of patulin from apple juice by cross-linked xanthated chitosan resin

In this work, cross-linked xanthated chitosan resin (CXCR) was prepared by inverse suspension cross-linking method, using glutaraldehyde as cross-linking agent and carbon disulfide as modification agent. The biosorption of CXCR for patulin from apple juice was investigated. Batch adsorption experiments were performed to evaluate the effect of pH, temperature, contact time and initial concentration. The adsorption of CXCR for patulin was characterized by Fourier Transform Infrared Spectroscopy (FTIR). The results showed that the optimum adsorption conditions of CXCR for patulin was achieved at pH 4, 30 °C for 18 h. The adsorption data could be fitted with pseudo–second order kinetic model and Freundlich isotherm model. It indicated that CXCR is an appropriate adsorbent for the removal of patulin from apple juice.

Synthesis and Characterization of Magnetic Polyvinyl Alcohol (PVA) Hydrogel Microspheres for the Embolization of Blood Vessel.

Vascular embolization has exhibited increasing significance in treatment of terminal cancer. In order to achieve better embolic effects, magnetic polyvinyl alcohol hydrogel microspheres were synthesized for magnetic field-controlled vascular embolization. Inverse suspension crosslinking method was adopted to synthesize the magnetic hydrogel microspheres by loading magnetic nanoparticles inside. The magnetic property, CT angiography, drug release, and magnetothermal performance were characterized in vitro, respectively. The fluidity of microspheres was also showed by simulation and experiment in vitro. The microspheres were shown to have capability of drug loading, CT imaging, and magnetothermal behavior. Both the simulated and the experimental results exhibited that the microspheres can be controlled to aggregate in the fluid in the presence of magnetic field. The magnetic hydrogel microspheres exhibited the specific fluidity-like iodized oil, but were able to form solid embolus. Because of the advantages of this novel material, it is expected to get extensive application in the clinic embolotherapy.

Synthesis and Characterization of Superparamagnetic Zinc Ferrite–Chitosan Composite Nanoparticles

Single-phase ZnFe2O4 nanoparticles have been prepared by coprecipitation method without any subsequent calcination. The ZnFe2O4–chitosan magnetic composite nanoparticles were also synthesized by two steps via a suspension cross-linking method. The crystallite size, microstructure and magnetic properties were studied using X-ray diffraction (XRD), Fourier transmission infrared (FTIR) spectroscopy, transmission electron microscope (TEM) and vibrating sample magnetometer (VSM). The TEM and XRD results showed that the composite magnetic nanoparticles contained single-phase zinc ferrite with a diameter of 20–30 nm. The magnetic measurements also exhibited that the zinc ferrite–chitosan nanoparticles were superparamagnetic with the magnetization of 4.2 emu/g at 10 kOe.

Lead(II) and methylene blue removal using a fully biodegradable hydrogel based on starch immobilized humic acid

A novel biodegradable adsorbent: starch-humic acid composite hydrogel beads (ST-HA), was prepared via inverse suspension crosslinking method in this study. Adsorptive removal of Pb(II) and MB using ST-HA in respective single-component and binary systems were studied. ST-HA showed efficient removal of Pb(II) and MB. The adsorption of Pb(II) and MB on ST-HA was pH dependent with uptake dropping in acidic solutions. The adsorption mechanisms of Pb(II) and MB were also different, the latter involves π–π interactions besides ion exchanging. It was also observed that ST-HA can selectively remove MB in acidic solutions. The adsorption equilibrium study indicated that the adsorptions of Pb(II) and MB were monolayer and spontaneous processes. The adsorption kinetics followed pseudo-second-order equation and activation energy calculation indicated that the adsorption was a chemical process. Furthermore, ST-HA could be easily regenerated and reused with little loss of adsorption capacity. Overall, ST-HA is an efficient and versatile adsorbent for Pb(II) and MB removal.

The novel synthesis of magnetically chitosan/carbon nanotube composites and their catalytic applications

Chitosan-modified magnetic carbon nanotubes (CS-MCNTs) were synthesized and were investigated by FT-IR, EDX, FE-SEM, elemental analysis, XRD, VSM and TGA. In order to synthesize the CS-MCNTs composites, Fe3O4 decorated carbon nanotubes (CNTs-Fe3O4) were modified with a silica layer by the ammonia-catalysed hydrolysis of tetraethyl orthosilicate (CNTs-Fe3O4@SiO2). Then, CS-MCNTs were successfully grafted on the surface of CNTs-Fe3O4@SiO2via a suspension cross-linking method. The CS-MCNT was found to be an excellent heterogeneous catalyst for the synthesis of 1,4-dihydropyridines (DHPs). The attractive advantages of the present process include short reaction times, milder and cleaner conditions, higher purity and yields, easy isolation of products, easier work-up procedure and lower generation of waste or pollutions. This catalyst was easily separated by an external magnet and the recovered catalyst was reused several times without any significant loss of activity. A combination of the advantages of CNTs, chitosan and magnetic nanoparticles provides an important methodology for carrying out catalytic transformations. Therefore, this method provides a green and much improved protocol over the existing methods.

Immobilization of laccase on chitosan–halloysite hybrid porous microspheres for phenols removal

In this paper, we used natural resources of halloysite nanotubes and chitosan to prepare new porous organic/inorganic hybrid microspheres with diameter of about 100–150μm by reversed-phase suspension cross-linking technique. The SEM image revealed that halloysite nanotubes overlapped together within hybrid microspheres and formed a hybrid porous structure. We demonstrated that the resulted porous microspheres could be used as a new kind of support to immobilize laccase, which showed excellent loading capacity for laccase immobilization as high as 123.1 mg/g. The stability of laccase was also greatly improved after immobilization on the support. While the immobilized laccase was used as biocatalyst to remove phenols from wastewater, the removal efficiency could reach as high as 95.0%.

Synthesis, Characterization and Antibacterial Activity of Chitosan/TiO<sub>2</sub> Microspheres

In this study, chitosan (CS)/titanium dioxide (TiO2) microspheres with different nanoTiO2 content were obtained by suspension cross-linking technique and characterized by FT-IR and SEM. The strong peak of C=N stretching vibrations at 1641 cm-1 were found which demonstrated that amino groups of CS reacted with aldehyde group of glutaraldehyde. SEM photographs showed that the CS/TiO2 microspheres were spherical, and the size of the CS/TiO2 microspheres ranging from 50 to 170 μm was analyzed with the software of Image J. The entrapment efficiency of the CS/TiO2 microspheres was up to 67.7%. Compared with CS, CS/TiO2 microspheres had better antibacterial activity against S. aureus and E. coli with a MIC value of 0.0125%.

Encapsulation of oil in silk fibroin biomaterials

ABSTRACTMicroencapsulation is becoming increasingly important in the food, cosmetics, and medicinal industries due to its potential for stabilization and delivery of volatile and delicate compounds. Novel food‐safe techniques for encapsulating oil in silk biomaterials using emulsion‐based processes that exploit silk's unique properties (including amphiphilicity, biocompatibility, aqueous and ambient processing, and tunable physical crosslinking behavior) are described. The sonication‐induced self‐assembly of silk previously applied to hydrogel fabrication replaced the use of the thermal or chemical suspension crosslinking traditionally used to stabilize the aqueous protein phase in emulsions. Stable, physically crosslinked silk micro‐ and macro‐particles loaded with oil or water‐soluble dye were produced by aliquoting sonicated silk solutions into an oil bath. Oil micro‐droplets emulsified in aqueous silk solutions did not impede the self‐assembly of silk into films or hydrogel networks. In O/W/O emulsions, particle morphology and silk permeability to a model lipophilic dye in the interior phase were controllable via processing. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39990.

Preparation, characterization and adsorption properties of chitosan modified magnetic graphitized multi-walled carbon nanotubes for highly effective removal of a carcinogenic dye from aqueous solution

Novel chitosan-modified magnetic graphitized multi-walled carbon nanotubes (CS-m-GMCNTs) were synthesized via a suspension cross-linking method. Composition, morphology and magnetic properties of as-prepared CS-m-GMCNTs were characterized by XRD, SEM-EDS, BET and VSM. The large saturation magnetization (12.27emug−1) allows fast separation of CS-m-GMCNTs from treated aqueous solution. The adsorption of congo red (CR) on CS-m-GMCNTs was strongly dependent on pH, temperature of the aqueous phase and adsorbent dosage. Up to 100 and 94.58% color removal could be achieved in 100min contact time with 10 and 50mgL−1 of initial concentrations, respectively. The adsorption capacity of CR onto CS-m-GMCNTs could reach 262.9mgg−1. The pseudo-second-order kinetic model with high correlation coefficients (R2>0.999) was suitable to describe the process of CR adsorption onto CS-m-GMCNTs. The Langmuir model fitted the adsorption isotherm data better than the Freundlich model. Values of thermodynamic parameters (ΔG°, ΔH° and ΔS°) indicated that the adsorption process was strongly dependent on temperature of the aqueous phase, and spontaneous and endothermic process in nature. Therefore, CS-m-GMCNTs adsorbent displays main advantages of excellent dispersion, convenience separation and high adsorption capacity, which implies their potential application in the environmental cleanup.

Characterization and bisphenol A adsorption capacity of β-cyclodextrin–carboxymethylcellulose-based hydrogels

Novel hydrogel beads having molecular adsorption abilities were prepared from carboxymethylcellulose sodium salt (CMC) and β-cyclodextrin (β-CD) by suspension crosslinking, using ethylene glycol diglycidyl ether (EGDE) in basic medium as a crosslinking agent. FTIR and solid-state NMR spectroscopic analysis revealed that the amount of incorporated β-CD and crosslinking densities within the hydrogel bead structures are strongly dependent on the molar feed ratio of β-CD to CMC during preparation. The hydrogel beads showed water-swelling capacities of 70–200mL/g-polymer, with decreases in capacity associated with increased amounts of β-CD incorporated in the gel structure. The hydrogel beads also showed a high adsorption capacity toward bisphenol A (BPA) in water. Batch BPA-adsorption experiments were analyzed employing Langmuir isotherm models; hydrogel bead adsorption isotherms for BPA could be fitted to the Langmuir model. The maximum BPA-adsorption among the prepared series of hydrogel beads amounted to 167μmolg−1.

Immobilization of Rhizopus oryzae lipase on magnetic Fe3O4-chitosan beads and its potential in phenolic acids ester synthesis

A novel and simple method was developed for the preparation of magnetic Fe3O4 nanoparticles by chemical co-precipitation method and subsequent coating with 3-aminopropyltrimethoxysilane (APTMS) through silanization process. Magnetic Fe3O4-chitosan particles were prepared by the suspension cross-linking and covalent technique to be used in the application of magnetic carrier technology. The synthesized immobilization supports were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). Using glutaraldehyde as the coupling agent, the lipase from R. oryzae was successfully immobilized onto the functionalized magnetic Fe3O4-chitosan beads. The results showed that 86.60% of R. oryzae lipase was bound on the synthesized immobilization support. This immobilized lipase was successfully used for the esterification of phenolic acid which resulted in esterification of phenolic acid in isooctane solvent reaction system for 8 consecutive cycles (totally 384 h), 72.6% of its initial activity was retained, indicating a high stability in pharmaceutical and industrial applications.

Different preparation methods and characterization of magnetic maghemite coated with chitosan

The preparation of maghemite (γ-Fe2O3) micro- and nanoparticles coated with chitosan, used as carriers for immobilized enzymes, was investigated. γ-Fe2O3 nanoparticles were synthesized by coprecipitation of Fe2+ and Fe3+ ions in the presence of ammonium. They were coated with chitosan by the microemulsion process, suspension cross-linking technique, and covalent binding of chitosan on the γ-Fe2O3 surface. The methods distinguished the concentration of chitosan, concentration of acetic acid solution, concentration of a cross-linking agent, temperature of synthesis, pH of the medium, and time of synthesis. γ-Fe2O3 micro- and nanoparticles coated with chitosan prepared after three preparation methods were evaluated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy analysis, energy dispersive spectrometry, thermogravimetric analysis, differential scanning calorimetry analysis, vibrating sample magnetometry, dynamic light scattering, laser diffraction granulometry, and X-ray diffractometry. These positive attributes demonstrated that these magnetic micro- and nanoparticles coated with chitosan may be used as a promising carrier for further diverse biomedical applications.

Removal of anionic dyes from aqueous solutions by an ion-exchanger based on pullulan microspheres

Pullulan-graft-poly(3-acrylamidopropyl trimethylammonium chloride) (P-g-pAPTAC) microspheres were prepared by suspension cross-linking of the pullulan previously grafted with cationic moieties. Adsorption of Azocarmine B by the P-g-pAPTAC microspheres was used as a model to demonstrate the removal of anionic dyes from aqueous solutions. Batch adsorption studies concerning the effect of the contact time, pH, initial dye concentration, temperature, grafting, and the nature of sulfonated anionic dyes on the adsorption kinetics were investigated. Adsorption was shown to be independent of pH. The experimental data best fitted to the pseudo-second order model which provided values of the rate constant k2 of 1.4×10−4gmg−1min−1 for 100mgL−1 solution and of 3.7×10−4gmg−1min−1 for 500mgL−1 solution. From the Langmuir isotherm linear equation, the maximum adsorption capacity determined was 113.63mg of Azocarmine B per gram of adsorbent; the negative value of the free energy change indicated the spontaneous nature of the adsorption process.

The Preparation and Research of β-Chitosan/HA Composite Magnetic Microspheres

In this work, we demonstrate β-Chitosan(βCS) made from the skin of maggot has higher viscosity, better activity and lower heavy metal concentration in comparison with α-Chitosan made from shrimp shell and crab shell. This study is basedon hydroxyapatite(HA) as the matrix. The method of reverse phase suspension cross-linking was adopted in the experiment to prepare Fe3O4/βCS magnetic microspheres. Then magnetic Fe3O4/βCS/HA composite microspheres were prepared by compounding Fe3O4/βCS with HA via in situ precipitation method. Through our experiments, we found the concentration of βCS 1.5%, Fe3O4/βCS mass ratio of 9.05, and stirring speed of 1200r/min to be the optimal conditions. Furthermore, the structure and morphology of β-magnetic chitosan microspheres were analyzed with XRD and SEM, and the average particle diameters were determined to be 10μm. With the productivity of β-magnetic chitosan microspheres is above 50%, the magnetic Fe3O4/βCS/HA composite microspheres are expected to become promising multi-functional bone repair materials.

Preparation of amino‐reserved magnetic chitosan microsphere and its application in adsorbing endotoxin

AbstractIn this article, we present a novel amino‐reserved magnetic chitosan microsphere (ARMCM) prepared from chitosan and Fe3O4 through inverse suspension crosslinking by formaldehyde and epichlorohydrin. The density of ARMCM was 1.47 g/mL, and the amino content was 2.44 mmol/g. The measurements data indicated that the saturation magnetization (σs) of ARMCM was 23.2 emu/g. The adsorption results showed that these magnetic chitosan microspheres had good adsorption capacity on endotoxin: the maximum absorption capacity was about 1792.1EU/g in 40 min; the endotoxin adsorption efficiency in the protein solution was close to 80% and what is more, protein adsorption efficiency was only 23.2 and 2.0%, respectively, for acidic and basic proteins. It is expected that this ARMCM will have a feasible and useful application in adsorbing endotoxin from biological products. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Preparation and Characterization of Magnetic Chitosan Microspheres for Endotoxin Adsorption

A novel magnetic chitosan microsphere (MCM) was prepared from chitosan and Fe3O4 through inverse suspension crosslinking, epichlorohydrin activation, and grafted with ligands. The magnetometer measurements data indicated that the magnetic microspheres had superparamagnetic property as well as fast magnetic response without the magnetic hysteresis effect and thus can be well used in magnetic separation. The adsorption results showed that the magnetic chitosan microsphere grafted with ligand had good adsorption capacity on endotoxin up to 554.1 EU/g under the condition of 25.0 mg/mL adsorbent, 17.2 EU/mL endotoxin. It is expected that this new microsphere will have a feasible and useful application in adsorbing endotoxin from biological products.