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Recently, the number of patients infected by drug-resistant pathogenic microbes has increased remarkably worldwide, and a number of studies have reported new antibiotics from natural sources. Among them, chitosan, with a high molecular weight and α-conformation, exhibits potent antimicrobial activity, but useful applications as an antibiotic are limited by its cytotoxicity and insolubility at physiological pH. In the present study, the antibacterial activity of low molecular weight water-soluble (LMWS) α-chitosan (α1k, α5k, and α10k with molecular masses of 1, 5, and 10 kDa, respectively) and β-chitosan (β1k, β5k, and β10k) was compared using a range of pathogenic bacteria containing drug-resistant bacteria isolated from patients at different pH. Interestingly, β5k and β10k exhibited potent antibacterial activity, even at pH 7.4, whereas only α10k was effective at pH 7.4. The active target of β-chitosan is the bacterial membrane, where the leakage of calcein is induced in artificial PE/PG vesicles, bacterial mimetic membrane. Moreover, scanning electron microscopy showed that they caused significant morphological changes on the bacterial surfaces. An in vivo study utilizing a bacteria-infected mouse model found that LMWS β-chitosan could be used as a candidate in anti-infective or wound healing therapeutic applications.

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Insulin-incorporated nanoparticles were prepared by polyelectrolyte complex formation using lowmolecular weight water soluble chitosan (LMWSC). Insulin-incorporated nanoparticles showed spherical shapes with a particle size of approximately 200 nm. The average particle size, drug content and loading efficiency increased with increasing insulin feed. The zeta potential decreased with increasing insulin feed, indicating that the electrostatic interaction increased with increasing insulin feed. At 1 H nuclear magnetic resonance (NMR) spectra, insulin and LMWSC had intrinsic peaks while the peaks of the nanoparticles were similar to LMWSC itself at D 2 O. However, the specific peaks for insulin appeared as a result of the breakdown of nanoparticles using DCl. When polyelectrolyte complex had dissociated, fluorescein isothiocyanate (FITC)-labeled insulin in the nanoparticles showed similar UV absorption peaks to FITC-labeled insulin only. At the release study, insulin was released continuously from the nanoparticles over 120 h at all formulations. Higher insulin contents induced a decrease in the rate of insulin released from nanoparticles. Consequently, LMWSC and insulin successively formed polyelectrolyte complexes as a nanocarriers and LMWSC can be considered a good candidate for insulin delivery.

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