3.3. Experimental designs for optimization
Experimental designs allow to experimentally study the
influence of several variables with a limited number of
experiments. Statistical analysis of results will allow to know
which variables have a significant influence, and to correlate
desired response with variables by polynomial equations. In
Fig. 3 an example of experimental design is shown, and in Fig. 4
there is an example of response surface.
Not many papers present optimization of nano-emulsion
preparation by experimental designs, and most of them deal about
pharmaceutical formulations for self-emulsification [27,58–61].
In Ref. [27] experimental design was used to determine the
influence of two qualitative independent variables: type of oil and
type of lipophilic emulsifier. The other four references correspond
to the same research group. In Refs. [58,59] the incorporation of
retinol to a self nanoemulsifying formulation is studied, being
oil, surfactant and cosurfactant amounts in the formulation the
three independent variables, and mean droplet size, turbidity, and
dissolution rate at 10 and 30 min, the four response variables
studied. Response equations are presented, and system is optimized
for dissolution rate at 30 min using the other three
responses as restrictions. In Ref. [60] the surface response
technology explained in a more detailed way and six response
variables are analyzed. In Ref. [61], authors apply the same
methodology to evaluate ultrasonic technique in characterization
of nano-emulsions.