Cheng Sheng Liu

Antibacterial mechanism of chitosan microspheres in a solid dispersing system against E. coli

In this study, we investigated the antibacterial mechanism through the interfacial contacting inhibition behaviors of chitosan antimicrobials against Escherichia coli in solid dispersing state. Chitosan microspheres (CMs) were prepared by emulsification cross-linking reaction, and oleoyl-CMs (OCMs) were obtained by introduction of oleoyl groups to the chitosan. The CMs were with smooth surface and spherical shape of diameter of about 124 microm. The antibacterial activity was directly proportional to the concentration and the hydrophobic property of CMs. The fluorescence experiments indicated CMs had influenced the structure of membrane, especially the OCMs were speculated to interact with proteins on the cell membrane. SEM photographs showed E. coli adhered to the surface of the CMs and provided evidences for the disruption of the cells, while the bacterium conglomerated on the surface of the OCMs. The CMs changed the permeability of membrane and caused cellular leakage that correlated with the hydrophobic interaction between CMs and cytoplasmic membrane phospholipids of Gram-negative bacteria. Solid dispersing system makes the antibacterial activities of CMs counted as a sequent event-driven to study the antibacterial mechanism of chitosan originally.

Enhancement of Dissolution Rate of Valdecoxib Using Solid Dispersions with Polyethylene Glycol 4000

The aim of the present study was to enhance the dissolution rate of valdecoxib using its solid dispersions (SDs) with polyethylene glycol (PEG) 4000. The phase solubility behavior of valdecoxib in the presence of various concentrations of PEG 4000 in water was obtained at 37°C. The solubility of valdecoxib increased with increasing amount of PEG 4000 in water. Gibbs free energy (ΔG°tr) values were all negative, indicating the spontaneous nature of valdecoxib solubilization, and they decreased with increase in the PEG 4000 concentration, demonstrating that the reaction conditions became more favorable as the concentration of PEG 4000 increased. The SDs of valdecoxib with PEG 4000 were prepared at 1:1, 1:2, 1:5, and 1:10 (valdecoxib: PEG 4000) ratio by melting method. Evaluation of the properties of the SDs was performed by using dissolution, Fourier-transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and scanning electron microscopy (SEM) studies. The SDs of valdecoxib with PEG 4000 exhibited enhanced dissolution rate of valdecoxib, and the rate increased with increasing concentration of PEG 4000 in SDs. Mean dissolution time (MDT) of valdecoxib decreased significantly after preparation of SDs and physical mixture with PEG 4000. The FTIR spectroscopic studies showed the stability of valdecoxib and absence of well-defined valdecoxib-PEG 4000 interaction. The DSC and XRD studies indicated the amorphous state of valdecoxib in SDs of valdecoxib with PEG 4000. The SEM pictures showed the formation of effective SDs of valdecoxib with PEG 4000, since well-defined changes in the surface nature of valdecoxib, SDs, and physical mixture were observed.

Oleoyl-chitosan nanoparticles inhibits Escherichia coli and Staphylococcus aureus by damaging the cell membrane and putative binding to extracellular or intracellular targets

A novel chitosan antibacterial dispersion system was prepared by oleoyl-chitosan (OCS) nanoparticles (OCNP). We further investigated the antimicrobial mode of OCNP against Escherichia coli and Staphylococcus aureus using a combination of approaches, including measurement of the effect of lecithin and phosphate groups, the conformation of membrane protein, internalization of fluorescein isothiocyanate (FITC)-labeled OCS nanoparticles (FITC-OCS nanoparticles) observed under fluorescence microscopy and DNA/RNA binding assay. Results of fluorescence experiments indicated that OCNP influenced the structure of bacterial membranes. The lecithin effect showed that OCNP bound to cytoplasmic membrane phospholipids of S. aureus, and phosphate groups played an important role. Fluorescence microscopy observations demonstrated that the way OCNP entered into bacteria varied against strains. The gel-retardation experiment showed that OCNP bound strongly to DNA/RNA and retarded their migration in the gels in a concentration-dependent manner. These results indicate that OCNP exerts its antibacterial activity by damaging the structures of cell membrane and putative binding to extracellular targets such as phosphate groups or intracellular targets such as DNA and RNA.

Microencapsulation of a probiotic bacteria with alginate–gelatin and its properties

Lactobacillus casei ATCC 393-loaded microcapsules based on alginate and gelatin had been prepared by extrusion method and the product could increase the cell numbers of L. casei ATCC 393 to be 107 CFU g−1 in the dry state of microcapsules. The microparticles homogeneously distributed with size of 1.1 ± 0.2 mm. Four kinds of microcapsules (S1, S2, S3 and S4) exhibited swelling in simulated gastric fluid (SGF) while the beads eroded and disintegrated rapidly in simulated intestinal fluid (SIF). Cells of L. casei ATCC 393 could be continuously released from the microcapsules during simulated gastrointestinal tract (GIT) and the release amounts and speeds in SIF were much higher and faster than that in SGF. Encapsulation in alginate–gelatin microcapsules successfully improved the survival of L. casei ATCC 393 and this approach might be useful in delivery of probiotic cultures as a functional food.

Uptake of oleoyl-chitosan nanoparticles by A549 cells

The aim of the present study was to evaluate cellular uptake of oleoyl-chitosan (OCH) nanoparticles by using A549 cells, a human lung carcinoma cell line, for drug and gene delivery applications. In this study, self-assembled OCH nanoparticles encapsulating a fluorescent marker molecule, fluorescein isothiocyanate (FITC), were prepared and characterized. The effects of particle size, concentration, and incubation time on the cellular uptake of the nanoparticles (FITC-OCH nanoparticles) were quantified by spectrofluorometric measurement and confirmed using fluorescence microscopy studies. The nanoparticles were taken up by the cells, and levels of binding and uptake increased with the decrease of particle size and the increase of particle concentration and incubation time. These results implied that the OCH nanoparticles have great potential to be applied as a drug carrier system to deliver drugs into the cells.

Chitosan Acetate as an Active Coating Material and Its Effects on the Storing of Prunus avium L.

In this article, chitosan acetate (CA) was prepared by the method of solid-liquid reaction. CA was a stable faint yellow powder with water solubility. CA kept the same backbone in the chemical structure as the raw material of chitosan, and it also had the similar antibacterial properties with chitosan. CA could form a coating film on the outside surface of the sweet cherries, could effectively retard the loss of the water, titratable acidity, and ascorbic acid of sweet cherries, and could induce a significant increase in the peroxidase and catalase activities in the fruit. The CA coating could also increase the ratio of the total soluble solids and titratable acidity in the fruit. The application of CA effectively maintained quality attributes and extended postharvest life of the sweet cherries. The results revealed that the CA salts had potential application in active edible coating materials in the storage of fresh fruit.

Drug Release Kinetics of Spray-Dried Chitosan Microspheres

The aim of this article was to investigate the drug release kinetics of spray-dried chitosan microspheres using various kinetic models. The mean particle size and encapsulation efficiency of cross-linked chitosan microspheres was between 3.8 and 4.2 μm and 96.3 and 98.7%, respectively. Spray-dried chitosan microspheres were spherical in shape with smooth surface. The surface morphology of spray-dried chitosan microspheres was affected by the crystallinity of the loaded drug and cross-linking agent. The release data of the spray-dried chitosan microspheres were treated with zero-order, first-order, Higuchi, Korsmeyer, and Kopcha kinetic models and best fit was observed with Higuchi model, indicating the release of drug from spray-dried chitosan microspheres followed Ficks law of diffusion.

Characteristics of Rofecoxib-Polyethylene Glycol 4000 Solid Dispersions and Tablets Based on Solid Dispersions

The aim of this work was to report the properties of rofecoxib-PEG 4000 solid dispersions and tablets prepared using rofecoxib solid dispersions. Rofecoxib is a poorly water soluble nonsteroidal anti-inflammatory drug with a poor dissolution profile. This work investigated the possibility of developing rofecoxib tablets, allowing fast, reproducible, and complete rofecoxib dissolution, by using rofecoxib solid dispersion in polyethylene glycol (PEG) 4000. Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the solid state of solid dispersions. The effect of PEG 4000 concentration on the dissolution rate of rofecoxib from its solid dispersions was investigated. The dissolution rate of rofecoxib from its solid dispersions increased with an increasing amount of PEG 4000. The extent of dissolution rate enhancement was estimated by calculating the mean dissolution time (MDT) values. The MDT of rofecoxib decreased significantly after preparing its solid dispersions with PEG 4000. The FTIR spectroscopic studies showed the stability of rofecoxib and absence of well-defined rofecoxib-PEG 4000 interaction. The DSC and XRD studies indicated the amorphous state of rofecoxib in solid dispersions of rofecoxib with PEG 4000. SEM pictures showed the formation of effective solid dispersions of rofecoxib with PEG 4000 since well-defined change in the surface nature of rofecoxib and solid dispersions were observed. Solid dispersions formulation with highest drug dissolution rate (rofecoxib: PEG 4000 1:10 ratio) was used for the preparation of solid dispersion–based rofecoxib tablets by the direct compression method. Solid dispersion–based rofecoxib tablets obtained by direct compression, with a hardness of 8.1 Kp exhibited rapid drug dissolution and produced quick anti-inflammatory activity when compared to conventional tablets containing pure rofecoxib at the same drug dosage. This indicated that the improved dissolution rate and quick anti-inflammatory activity of rofecoxib can be obtained from its solid dispersion–based oral tablets.

Preparation and Characterization of Carboxymethyl Chitosan and β-Cyclodextrin Microspheres by Spray Drying

Three kinds of carboxymethyl chitosan/β-cyclodextrin microspheres loaded with theophylline were prepared by spray drying intended for pulmonary delivery. Mucociliotoxicity, permeation rate, and drug release characteristics of the product were investigated. The microspheres obtained by spray drying were found to be spherical with smooth or wrinkled surfaces. The mean particle size was between 3.39 and 6.06 µm. The microspheres demonstrated high product yield (43.7–50.2%), high drug loading (13.7–38.1%), and high encapsulation efficiency (86.9–92.8%). FT-IR indicated that there were interactions of theophylline with carboxymethyl chitosan matrix. Further studies on mucociliotoxicity and permeation confirmed that microspheres had better adaptability and high permeation rate. In vitro drug release from the microspheres was not related to the drug/polymer ratios.

Preparation, characterization, and antibacterial activity of oleic acid-grafted chitosan oligosaccharide nanoparticles

An oleic acid-grafted chitosan oligosaccharide (CSO-OA) with different degrees of amino substitution (DSs) was synthesized by the 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC)-mediated coupling reaction. Fourier transform infrared spectroscopy (FT-IR) suggested the formation of an amide linkage between amino groups of chitosan oligosaccharide and carboxyl groups of oleic acid. The critical aggregation concentrations (CACs) of CSO-OA with 6%, 11%, and 21% DSs were 0.056, 0.042, and 0.028 mg·mL−1, respectively. Nanoparticles prepared with the sonication method were characterized by means of transmission electron microscopy (TEM) and Zetasizer, and the antibacterial activity against Escherichia coli and Staphylococcus aureus was investigated. The results showed that the CSO-OA nanoparticles were in the range of 60–200 nm with satisfactory structural integrity. The particle size slightly decreased with the increase of DS of CSO-OA. The antibacterial trial showed that the nanoparticles had good antibacterial activity against E. coli and S. aureus.