2.2.3. In vitro release kinetics study

In order to investigate the release behavior of CUR from nanocarriers the dialysis method described by Kumar et al. was used with minor modifications [30]. Dialysis of each sample was carried out through dialysis bag with high retention capacity (99.99 %) and a molecular mass cut off 12.4 kDa, (dialysis tubing, Sigma Aldrich, Darmstadt, Germany). A mixture of PBS/EtOH (1:1, v/v) and 0.1 % l-ascorbic acid was used as the dissolution medium (pH = 5.5, citric acid 0.1 M). Before using them, the dialysis bags were soaked under continuous water flow for 30 min and then for 15 min under heated (50 °C) distilled water. An aliquot of 1.0 mL (equivalent to 0.5 mg CUR) freshly prepared CUR-SLN; CUR-NLC or CUR-NE dispersion was transferred into the dialysis bag and placed in a beaker containing 200 mL of dissolution medium. The beakers were placed in a shaking water bath and maintained at 32 ± 0.5 °C throughout the experiment. Aliquots of 3 mL of the dissolution medium were withdrawn at the predefined time points (10, 30, 60, 120, 180, 240, 480, 720, 1440, and 1920 min) and replaced by fresh medium. CUR concentration was determined by spectrophotometry, measuring UV absorbance at 425 nm (UV-1800, UV–vis Spectrophotometer, Shimadzu, Duisburg, Germany), and finally the percentage of released CUR was calculated against calibration curves. The experiment was performed in triplicate for all formulations tested. To study the release mechanism of CUR from prepared lipid nanocarriers, data obtained from in vitro release studies were fitted to various mathematical models [31] such as zero order, first order, Higuchi, Hixson-Crowell, Korsmeyer-Peppas, and Kopcha release kinetic equations (Table 2). The plotted experimental data were fitted using the linear regression fitting option of the Microsoft Excel and the regression coefficient (R²) was obtained for each graphical presentation. The value of the coefficient determines the most suitable mathematical model that describes drug release kinetics [[32], [33], [34], [35]].

Mathematical models used for the description of release kinetics.

(i) Q₀ : the initial amount of CUR in nanoparticles, (ii) Q_t : the amount of CUR released at time t, (iii) M_t/M_∞ : the fraction of CUR released at time t, (iv) K₀, K₁, K_H, K_HC, K_KP: the model kinetic constant, (v) n: the diffusion exponent, (vi) A: the diffusion rate constant, (vii) B: the erosion rate constant.