Preparation and antibacterial activity of chitosan nanoparticles
Graphical abstract
Atomic force micrographs (AFMs) of chitosan nanoparticles at pH 5.0. Chitosan nanoparticles (A) and copper-loaded nanoparticles (B).
Introduction
Chitosan is a natural nontoxic biopolymer derived by the deacetylation of chitin. Chitosan and its derivatives have attracted considerable interest due to their antimicrobial and antifungal activity.[1], [2], [3] Chitosan exhibits its antibacterial activity only in an acidic medium because of its poor solubility above pH 6.5.4 The antibacterial activity of chitosan is influenced by a number of factors that include the type of chitosan, the degree of chitosan polymerization and some of its other physicochemical properties. Chitosan exhibits higher antibacterial activity against Gram-positive bacteria than Gram-negative bacteria. The antibacterial activity of chitosan also depends on the molecular weight and solvent,5 and is inversely affected by pH, with higher activity at lower pH values.6
Chitosan is a mucoadhesive polymer that is able to open tight junctions and allow the paracellular transport of molecules across mucosal delivery of vaccines.7 Chitosan microparticles and nanoparticles loaded with DNA plasmids were reported to induce protective immune responses in mice.[8], [9]
Chitosan nanoparticles have been synthesized as drug carriers as reported in previous studies.[10], [11], [12] Insulin-loaded chitosan nanoparticles could enhance intestinal absorption of insulin and increase its relative pharmacological bioavailability.13 Chitosan nanoparticles had also been employed as a gene carrier to enhance gene-transfer efficiency in cells.[14], [15] Chitosan microspheres have been used for gastric drug delivery. Reacetylated chitosan microspheres have been prepared for controlled release of active antimicrobial agents, such as amoxycillin and metronidazole in the gastric cavity.16 However, the antibacterial activity of chitosan nanoparticles has only seldom been reported elsewhere. The unique character of nanoparticles for their small size and quantum size effect could make chitosan nanoparticles exhibit superior activities.
Chitosan nanoparticles and copper-loaded nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions. Their antibacterial activities against various microorganism were studied. The morphological changes of S. choleraesuis treated with chitosan nanoparticles were examined by atomic force microscopy (AFM).
Section snippets
Materials
Chitosan was obtained from the Chitosan Company of Pan’an (Zhejiang Province, China) and refined twice by dissolving it in dilute HOAc solution. The solution was filtered, the chitosan was precipitated with aqueous sodium hydroxide, and the precipitate was dried in vacuum at room temperature.17 The degree of deacetylation was about 85% as determined by elemental analysis, and the average molecular weight of the chitosan was 220 kDa as determined by viscometric methods.18 Tripolyphosphate and
Size, zeta potential, and morphology of chitosan nanoparticles and copper-loaded nanoparticles
The preparation of chitosan nanoparticles is based on an ionic gelation interaction between positively charged chitosan and negatively charged tripolyphosphate at room temperature.[11], [12] The chitosan nanoparticles prepared in the experiment exhibit a white powdered shape and are insoluble in water, dilute acidic and alkali solutions. The mean size and size distribution of each batch of nanoparticle suspension was analyzed using the Zetasizer analysis. The size distribution profile, as shown
Conclusions
In summary, chitosan nanoparticles and copper-loaded nanoparticles have been synthesized and characterized in the present study. The nanoparticles obtained in the present study have small particle size and positive surface charges, which may improve their stability in the presence of biological cations37 and improve for their antibacterial activities due to the interaction with negatively charged biological membranes and site-specific targeting in vivo.38 These studies show that chitosan
Acknowledgement
The financial support of the Zhejiang Science and Technology Council (No. 021102680) is gratefully acknowledged.
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