The present investigation describes the synthesis and characterization of novel biodegradable nanoparticles based on chitosan for biomedical applications. Natural di- and tricarboxylic acids were used for intramolecular cross-linking of the chitosan linear chains. The condensation reaction of carboxylic groups and pendant amino groups of chitosan was performed by using water-soluble carbodiimide. This method allows the formation of polycations, polyanions, and polyampholyte nanoparticles. The prepared nanosystems were stable in aqueous media at low pH, neutral, and mild alkaline conditions. The structure of products was determined by NMR spectroscopy, and the particle size was identified by laser light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that particle size depends on the pH, but at a given pH, it was independent of the ratio of cross-linking and the cross-linking agent. Particle size measured by TEM varied in the range 60-280 nm. In the swollen state, the average size of the particles measured by DLS was in the range 270-370 nm depending on the pH. The biodegradable cross-linked chitosan nanoparticles, as solutions or dispersions in aqueous media, might be useful for various biomedical applications.

The present investigation describes the synthesis and characterization of novel biodegradable nanoparticles based on chitosan. Poly(ethylene glycol) dicarboxylic acid was used for intramolecular cross-linking of the chitosan linear chains. The condensation reaction of carboxylic groups and pendant amino groups of chitosan was performed by using water-soluble carbodiimide. The prepared nanosystems were stable in aqueous media. The structure of the products was determined by nuclear magnetic resonance (NMR) spectroscopy, and the particle size was identified by dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. It was found that biodegradable cross-linked chitosan nanoparticles experienced considerable swelling because of the length and flexibility of the cross-linking agent. The aqueous solutions or dispersions of nanoparticles were stable and clear or mildly opalescent systems depending on the ratio of cross-linking and molecular weight of chitosan, findings consistent with values of transmittance above 75%. Particle size measured by TEM varied in the range of 4-24 nm. In the swollen state, the average size of the individual particles measured by DLS was in the range of 50-120 nm depending on the molecular weight of chitosan and the ratio of cross-linking.

Copolymerization of ST (styrene) with EDM (ethylene glycol dimethacrylate) gives nonlinear polymers. The average molecular weight and polydispersity of copolymers composed of ST and EDM were measured using the GPC (gel permeation chromatography) technique, and an exponential increase in both quantities with reaction time was observed. 1 H and 13 C NMR spectra of the copolymers were taken to prove the structure and purity of the products and to calculate the composition and pendant content of the copolymers. The ratio of the pendant double bonds of the copolymers was determined from the 1 H NMR spectra. A remarkable increase in the ratio of the pendant double bonds with reaction time was observed. The mechanism for the chain propagation was studied and found to follow the terminal model. Reacitvity ratios were found to be r1 ) 0.452 ( 0.031 for monomer ST and r2 ) 0.297 ( 0.027 for monomer EDM. According to the size distribution of the copolymers measured by DLS (dynamic light scattering) and the average radii of gyration measured by SLS (static light scattering) techniques, the samples showed strong polydispersity and an increase in molecular size with reaction time. Unusually high molecular weight values were observed after a certain reaction time.

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