Abstract. Hybrid polymeric networks composed of polyacrylamide and chitosan were developed to determine their swelling and ascorbic acid delivery kinetics at various chitosan concentrations. The hybrid acrylamide/chitosan hydrogels were synthesized in aqueous itaconic acid solution (1% w/w). Young's modulus was also evaluated for the hydrogels, and the results were correlated with the swelling properties. Swelling experiments were carried out using three different pH solutions: acidic (pH 4 buffer solution), neutral (distilled water) and basic (pH 10 buffer solution). The results of the swelling study showed that the swelling properties of the network varied with the changes of the pH in the swelling solution, as well as concentration of chitosan. When chitosan concentration increased, the swelling capacity diminished, and therefore Young's modulus increased. The results indicated that the swelling process followed a second order kinetics. The ascorbic acid diffusion inside the hydrogel follows a Fickian mechanism. The ascorbic acid diffusion coefficients are reported as a function of chitosan concentration.
The synthesis, characterization and degradation of a hybrid chitosan (CTS)/glycidyl methacrylate (GMA) material are reported. These versatile materials (natural-synthetic materials) are potential candidates for dental restoratives. All materials were characterized by infrared spectroscopy (FT-IR), X-ray diffraction and thermal (DSC) analysis. Particular attention was paid to the thermal stability and chemical resistance of the hybrid CTS materials. From dynamical rheological tests, it was concluded that CTS-GMA solutions behave as physical hydrogels. These pH-sensitive gels are an example of stimuli-responsive polymers, also known as 'smart polymers'.
A detailed analysis of the dynamic flow properties of chitosan in solution at different temperatures (25 - 45°C), chitosan concentration (0.5% - 2.0%), solvent type (acetic, lactic, and hydrochloric acid), and ionic strength (0 and 0.2M NaCl) has been undertaken. The storage modulus, G’, loss modulus, G’’ and complex viscosity, η* have been determined over a wide range of frequencies and the results are presented using master curves. For the conditions studied, at low frequencies chitosan solutions show a constant complex viscosity which decreases as frequency increases. Likewise, storage modulus, G’ and loss modulus, G’’ increase as frequency increases with G’’ being always greater than G’ (η’ > η’’) indicating that viscous effects are more important than elastic effects. For modelling the oscillatory-shear results we used the generalized Maxwell model. Two empirical equations were used to correlate the data: Cox-Merz rule for viscosity and Laun's rule for primary normal stress difference. Both relations were found to represent our data for the experimental conditions studied.
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