Porous Chitosan Microspheres Research Articles

Preparation of a novel CuI/PCMS heterogeneous catalyst for Heck-type cross-coupling reactions

A novel and environmentally friendly heterogeneous catalyst has been prepared through the wet impregnation of copper(I) species onto the highly porous chitosan microspheres (CuI/PCMS). This novel CuI/PCMS heterogeneous catalyst with no additional ligands is much better than CuI homogeneous catalysts when applied in Heck reactions. Moreover, the reaction conditions are much milder than those for the similar copper catalysts mediated cross-coupling reactions reported in the literature. PCMS has been demonstrated not only the excellent solid support, but also have many unique functional groups to chelate the copper (I) species to enhance its catalytic activity.

Poly(l-glutamic acid)/chitosan polyelectrolyte complex porous microspheres as cell microcarriers for cartilage regeneration

In this study a novel kind of porous poly(l-glutamic acid) (PLGA)/chitosan polyelectrolyte complex (PEC) microsphere was developed through electrostatic interaction between PLGA and chitosan. By adjusting the formula parameters chitosan microspheres with an average pore size of 47.5±5.4μm were first developed at a concentration of 2wt.% and freeze temperature of −20°C. For self-assembly of the PEC microspheres porous chitosan microspheres were then incubated in PLGA solution at 37°C. Due to electrostatic interaction a large amount of PLGA (110.3μgmg−1) was homogeneously absorbed within the chitosan microspheres. The developed PEC microspheres retained their original size, pore diameters and interconnected porous structure. Fourier transform infrared spectroscopy, thermal gravimetric analysis and zeta potential analysis revealed that the PEC microspheres were successfully prepared through electrostatic interaction. Compared with microspheres fabricated from chitosan, the porous PEC microspheres were shown to efficiently promote chondrocyte attachment and proliferation. After injection subcutaneously for 8weeks PEC microspheres loaded with chondrocytes were found to produce significant more cartilaginous matrix than chitosan microspheres. These results indicate that these novel fabricated porous PLGA/chitosan PEC microspheres could be used as injectable cell carriers for cartilage tissue engineering.

ChemInform Abstract: Porous Chitosan Microspheres Supported‐Palladium Catalyst for the C—N Cross‐Coupling of Aryl Halides with Secondary Amines.

AbstractThe inexpensive and simple operation of this environmental friendly Buchwald‐Hartwig amination reaction referred here should make its application attractive for industrial uses.

Microfluidic production of porous chitosan/silica hybrid microspheres and its Cu(II) adsorption performance

Waste water with heavy metal ions has been of great concern because of its increased discharge, toxic and some other bad effects on human beings or the environment. In this article, monodispersed chitosan/silica hybrid microspheres with porous structure and large specific surface area were successfully prepared by using microfluidic technology and they have advantages in mechanical property and adsorption of heavy metal ions such as Cu(II). In the optimum condition, porous chitosan/silica hybrid microspheres with 1.0wt.% TEOS in the dispersed phase and pre-solidified for 3h have enhanced mechanical intensity, faster adsorption kinetic and larger equilibrium adsorption amount of Cu(II) compared to the porous chitosan microspheres. The mechanical intensity and adsorption rate of the porous hybrid microspheres were 1.5 times and two times of porous chitosan microspheres, respectively. Meantime, the adsorption capacity was increased by 25%. The porous hybrid microspheres have good potentials in the applications of removing heavy metal ions from waste water.

Microfluidic preparation of chitosan microspheres with enhanced adsorption performance of copper(II)

This article presents facile microfluidic methods to prepare different chitosan microspheres by combining chemical crosslinking and solvent extraction. And the enhancement of Cu(II) adsorption kinetics and capacity was realized. The effects of solidifying time, initial concentration of Cu(II) and initial pH on adsorption performance were systematically studied. The adsorption isotherms can be fitted with Langmuir equation. The adsorption capacity was about 50mg/g, which is similar to that in references. To enhance the adsorption kinetics, porous chitosan microspheres were prepared by using poly(ethylene glycol) to form the pores. Many tiny pores were closely arranged on the surface, which resulted in accelerating the adsorption of Cu(II). And the adsorption time to reach equilibrium was reduced from 100h to 20h. To enhance the adsorption capacity, chitosan was crosslinked with another biocompatible polymer, poly(acrylic acid), and the blending microspheres were prepared with a two-step solidifying method. By adjusting the content of acrylic acid, the adsorption capacity could be increased to 66.3mg/g. Finally, porous chitosan-poly(acrylic acid) composite microspheres were prepared by combining the above methods. Adsorption reached equilibrium after about 25h and the adsorption capacity is about 72mg/g. Both the adsorption kinetics and capacity of the composite microspheres were enhanced.

Porous Chitosan Microspheres Supported-palladium Catalyst for the C–N Cross-coupling of Aryl Halides with Secondary Amines

Porous chitosan microspheres-supported palladium catalysed the amination of aryl halides with a wide variety of secondary amines to yield the corresponding cross-coupling products under aerobic conditions. Both aryl bromides and iodides gave good to excellent yields of N,N-disubstituted anilines. The procedure can tolerate common functional groups such as chloro, methoxyl and nitro. The heterogeneous catalysis is efficienct and the catalyst could be recycled seven times without obvious decreased conversion.

Microstructure-stability relations studies of porous chitosan microspheres supported palladium catalysts

In this study, polyethylene glycol (PEG) with different molecular weight, polyvinyl pyrrolidone (PVP), and polyvinyl alcohol (PVA), are chosen as porogens for preparing chitosan base porous microsphere supported palladium catalyst for coupling reactions. The pore structure of the microspheres was controlled by the compatibility of chitosan and counterpart polymers. The prepared porous chitosan microspheres supported palladium heterogeneous catalysts have been evaluated using the well-established Ullmann reductive homocoupling and the Heck cross-coupling reactions. The activities, stabilities and recyclability of the porous chitosan microspheres supported palladium catalysts are not only highly dependent upon the surface areas of the solid supports, but also upon the chemical properties of the water-soluble polymers. The degradation of the prepared heterogeneous palladium catalysts is mainly caused by a combination of the palladium leaching and the morphological transformation of the palladium species from the amorphous into the crystals.

Highly porous chitosan microspheres supported palladium catalyst for coupling reactions in organic and aqueous solutions

Porous chitosan microspheres (PCMS) were prepared from crosslinking chitosan/polyethylene glycol (PEG) interpenetrating microspheres through selective dissolution of the water-soluble PEG component for the immobilization of palladium catalyst. The resultant Pd/PCMS supported palladium has been demonstrated as a highly active and easily recyclable heterogeneous catalyst for the Ullmann-type reductive homocoupling of aromatic halides and the Heck cross-coupling of aromatic halides with acrylates. Most interestingly, the prepared Pd/PCMS heterogeneous palladium catalyst can also be employed in the environmentally-benign aqueous solution due to the highly hydrophilic hydroxyl and amino functional groups of chitosan. The large size of the microsphere structure can greatly facilitate separation and recycling of the expensive and toxic palladium catalysts from the reaction mixture and the recovered Pd/PCMS catalyst can preserve the catalytic activity and selectivity for the Heck reaction without any observable degradation over ten recycling times. The high activity and stability of the Pd/PCMS catalyst have been attributed to a combination of the high specific surface area of the porous structure as well as the strong chelation of palladium species with the abundant chitosan surface hydroxyl, amino and carbonyl functional groups.

Nanosized Vanadium, Tungsten and Molybdenum Oxide Clusters Grown in Porous Chitosan Microspheres as Promising Hybrid Materials for Selective Alcohol Oxidation

The ability of chitosan biopolymer to coordinate vanadium, tungsten and molybdenum metallic species and to control their mineralisation growth provides a new family of surface-reactive organic-inorganic hybrid microspheres. Drying the resulting materials under supercritical conditions allowed the gel network dispersion to be retained, thereby leading to a macroporous catalyst with surface areas ranging from 253 to 278 m(2) g(-1). On account of the open framework structure of these microspheres, the redox species entangled within the fibrillar network of the polysaccharide aerogels were found to be active, selective and reusable catalysts for cinamylalcohol oxidations.

Synthesis of Highly Porous Chitosan Microspheres Anchored with 1,2-Ethylenedisulfide Moiety for the Recovery of Precious Metal Ions

The highly porous chitosan microspheres (HPCM) with throughpores were performed by mixing the oil-in-water-in-oil (chitosan O/W/O) emulsions containing chitosan in the water phase with the NaCl W/O emulsions containing 15% sodium chloride in the aqueous phase. The difference of the osmotic pressure between these emulsions causes the transportation of water from chitosan O/W/O emulsions to NaCl W/O emulsions to make HPCM. Both introduction of 1,2-ethylenedisulfide moiety and cross-linking were performed at the same time by activating HPCM with 2-(chloromethyl)oxirane, followed by introducing 1,2-ethylenedisulfide moiety with 1,2-ethanedithiol. These chitosan microspheres (EDSC) had an average diameter of 143 μm and average pore size of 2−6 μm. EDSC exhibited high selectivity for precious metals such as palladium(II), gold(III), and platinum(IV) over base metal ions in hydrochloric acid solutions. The adsorbed palladium(II) was completely desorbed using aqueous thiourea solution. Furthermore, the adsorption...

Um sistema simples para preparação de microesferas de quitosana

This article describes the construction and optimization of an inexpensive apparatus for the production of uniform and porous chitosan microspheres. It also describes the control of the main operational parameters and strategies for the production of uniform chitosan microspheres.

Porous Chitosan Microcarriers for Large Scale Cultivation of Cells for Tissue Engineering: Fabrication and Evaluation

Porous chitosan microspheres with diameters ranging from 180 μm to 280 μm were successfully prepared, using an anti-phase suspension method combined with temperature controlled freeze-extraction. The mean pore diameter could be regulated from 5 μm to 60 μm by varying the freezing temperature through the cooling rate. Results with in vitro chondrocyte cultures showed that cells could attach, proliferate, and spread on these porous microspheres as well as inside the microcarriers. The materials and cell co-cultures were characterized using both optical and scanning electron microscopy. These results show that the porous chitosan microspheres are promising candidates for tissue culture for use as an injectable tissue engineering scaffold.

Porous chitosan microsphere for controlling the antigen release of Newcastle disease vaccine: preparation of antigen-adsorbed microsphere and in vitro release.

Porous chitosan microspheres suitable for the delivery of antigen were prepared using a wet phase-inversion method. The pore structure of the chitosan microsphere could be modified by the change of pH value of the coagulation medium, which is the aqueous tripolyphosphate (TPP) solution. High porosity of chitosan microsphere with an open porous structure on its surface was prepared by coagulation in TPP aq. solution of pH 8.9. The porous chitosan microspheres were modified chemically with reagents to introduce three types of functional groups; carboxyl, hydrophobic acyl and quaternary ammonium groups. Antigen of ND vaccine was immobilized into the pores of porous chitosan microspheres and the adsorbed antigen was assayed by the Hemoglobin Aggregation (HA) analytical method. Sustained-release of ND vaccine's antigen could be achieved through an adsorption-desorption release test. The chemical modifications of the porous chitosan microspheres have a strong large influence on the adsorption efficiency or release rates of the antigen investigated. The porous microspheres have a higher adsorption efficiency and the slower release rate of antigen when modified chemically with 3-chloro-2-hydroypropyltrimethylamonium chloride.

Evaluation of the factors influencing stomach-specific delivery of antibacterial agents for Helicobacter pylori infection.

Because Helicobacter pylori infection is localized in the gastric mucus layer and at the mucus layer-epithelial cell interface, we have developed amoxycillin- and metronidazole-containing chitosan microspheres for stomach-specific drug delivery. Drug-loaded porous chitosan microspheres were prepared by simultaneous crosslinking and precipitation with sodium tripolyphosphate. The release of antibacterial agents into simulated gastric fluid (SGF, pH 1.2), and the stability and permeability through gastric mucin, were examined at 37 degrees C. Because of the high porosity of drug-loaded chitosan microspheres, all the amoxycillin and metronidazole were released in 2 h. High-performance liquid chromatography assays of the antibacterial agents in SGF at 37 degrees C indicated 40% degradation of amoxycillin after 10 h. Metronidazole was completely stable for up to 24 h in SGF. Amoxycillin and metronidazole were highly permeable through the gastric mucin gel layer. The results of this study show that acid-stable antibacterial agents, such as metronidazole, that rapidly permeate the gastric mucus layer would be very effective for the complete eradication of H. pylori infection when delivered specifically at the site of infection in the stomach.