The aim of this work was to study the formulation of pharmaceutically relevant polyelectrolyte complex nanoparticles (NPs) composed of hyaluronic acid (HA) and chitosan (CS) containing no crosslinkers. The influence of polymer mixing ratio, concentration and molecular weight as well as the type of counterion in chitosan salt on properties of the resulting NPs was examined. Formulations and their components were studied by laser light scattering, viscosity, infrared spectroscopy and microscopy. Physical stability, isoelectric points and cytotoxicity of selected NPs were determined. By appropriate modification of HA molecular weight, stable and non-sedimenting NPs were successfully formed. Sonication was found to be an effective method to reduce the molecular weight of HA from 2882±25 to 176±4 kDa with no chemical changes in the HA structure observed. High molecular weight CS formed micron-sized entities at all compositions investigated. Positively and negatively charged NPs were obtained depending on the mixing ratio of the polymers, with CS glutamate NPs yielding more negatively charged particles compared to CS chloride NPs. The smallest NPs (149±11 nm) were formed using HA with molecular weight of 176 kDa. Cytotoxicity of NPs was dependent on environmental pH but HA was found to exert cytoprotective effects on Caco-2 cells.
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