Study on the rheological properties of microcrystalline chitosan hydrogels
used as drug carriers (English version)
Polimery 2000, No 11-12, 818
SummaryThe flow behavior of gel-like water dispersions containing 2–4 wt. % of microcrystalline chitosan (MCCh) (Table 1), selected anti-inflammatory drugs (diclofenac acid, ketoprofen acid, diclofenac Na, ibuprofen Na) (Table 2); and various auxiliary substances (triethanolamine, glycerol, etc.), viz., viscosity (η) and yield stress (τo), were studied in relation to MCCh content, drug content (Table 4), temperature, shear rate, and storage time. Methylcellulose was used as a model gel-forming substance. The power-law Ostwald—de Waele  (eqn. 1) and the Herschel—Bulkley (eqn. 2) models were used for the diluted and for the MCCh-rich hydrogels, respectively; the adjustable parameters, k and n, and activation energy (Ea) were established (Tables 3, 4, Fig. 5). Measurements were carried out immediately after preparation and after a year's long storage (Table 5). Low-polymer MCCh hydrogels are non-Newtonian fluids with n < 1, shear-thinned, and with no yield stress. Polymer-rich hydrogels, n < 1 and τo > 0, are viscoelastic fluids, shear-thinned; they have a yield stress. As the temperature was raised, τo decreased. For most hydrogel systems, the Arrhenius equation adequately described the variation of apparent viscosity with temperature. As the shear rate was increased, η and Ea decreased. In one year's long storage at 20°C the viscosity of the MCCh hydrogel was lower and that of the hydrogel containing an active substance was slightly higher. The polymer content decides whether the MCCh hydrogel is a pseudoplastic or a plastic fluid. Glycerol and 1,2-propylene glycol as hydrophilizing agents and methylcellulose hydrogel were found to be useful additives ensuring spreading over, and adhesion to, the surface of the human skin.