Alginate, a natural polysaccharide from brown algae, and chitosan, a deacetylated derivative of chitin from exoskeletons of crustaceans, are biocompatible and biodegradable polymers used in the design of pH-responsive hydrogels. These polymers are most commonly ionically crosslinked by adding calcium ions to alginate solutions and phosphate ions (sodium tripolyphosphate) to chitosan solutions. Both crosslinkers create ionic interactions between polymer chains, which increases the crosslink density and viscosity of these systems. In the experimental part, I prepared alginate solutions with the following concentrations: 0,5%, 0,6%, 0,7%, 0,8%, and 0,9% (w/v) and chitosan solutions with concentrations of 0,5%, 0,7%, and 0,9% (w/v). I measured their viscosity at different pH values. The results confirmed that viscosity increases with higher polymer concentration and the addition of crosslinking agents due to the formation of network structures. pH change also affects viscosity as it influences the ionization of functional groups in the polymers and the formation of the polymer network. I also calculated the diffusion coefficients of various substances using the Stokes-Einstein equation and monitored how the viscosity of the release medium affects the release rate of active ingredients.
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