Design of experiments to develop and optimise the nanocarriers: the case of vesicles loaded with cannabidiol and coated with chitosan

The application of statistical analysis in the early stages of research allows quality to be built into the product from the outset, following a Quality by Design (QbD) approach. In formulation development, particularly for nanocarriers, the traditional “one factor at a time” method still dominates, whereas Design of Experiments (DoE) offers a more rational and efficient approach. In this study, chitosan- coated nanovesicles loaded with cannabidiol (CBD), a non-psychoactive phytocannabinoid with anti-inflammatory and neuroprotective properties, were embedded in a thermosensitive gel for topical ocular administration. A preliminary screening phase was conducted to evaluate the effect of three independent variables (% chitosan, coating time and % poloxamer 407) on five dependent variables: gelation time at 34 °C, vesicle size, polydispersity index (PDI), zeta potential and zeta potential change upon interaction with mucin. The aim was to identify the most influential factors for subsequent optimisation. Optimization was carried out using the Doehlert design, a versatile and efficient experimental design that allows three factors to be evaluated simultaneously at different levels, giving greater resolution to the most critical variables. At this stage, coating time was fixed, while sonication time was introduced as a key factor to reduce vesicle size and polidispersity. The final model was validated by performing four experiments. The optimised formulation showed a vesicle size of 181.6±3.1 nm, a PDI of 0.160±0.015, a zeta potential of 12.31±0.97 mV and a gelation time of 16 s. This approach allowed efficient and precise development of the final formulation from nanovesicles to gel.