Computer- aided formulation development - Computer-Aided Applications in Pharmaceutical Technology - page 20

purifi ed water, white petrolatum) and the output neurons were the
measured values of dynamic rheological parameter, tan δ, at different
time intervals. Tan δ could be predicted using a neural network model
and the results have shown a great degree of reliability. Similarly, a neural
network model could be used for prediction of the complex dynamic
viscosity of these semi-solid w/o emulsions (Gašperlin et al., 2000).
Other authors (Kumar et al., 2011) applied the ANN model to optimize
the fatty alcohol concentration in the formulation of an o/w emulsion.
Emulsion was composed of purifi ed water, liquid paraffi n, sodium lauryl
sulfate, and fatty lauryl alcohol. Predictions from ANNs are accurate and
allow quantifi cation of the relative importance of the inputs. Furthermore,
by varying the network topology and parameters, it was possible to
obtain output values (zeta potential, viscosity, conductivity, and particle
size) that were close to experimental values. The ANN model predicted
results and the actual output values were compared. An R 2 value of 0.84
for the model suggested adequate modeling, which is supported by the
correlation coeffi cient value of 0.9445.
Multiple (or double) emulsions are even more complex dispersion
systems, also known as 'emulsions of emulsions'. The most common
multiple emulsions are of the w/o/w type, although, for some specifi c
applications, o/w/o emulsions can also be prepared. Usually, the multiple
emulsions have been produced in a two-step-production process: the fi rst
one for production of the primary emulsion, and the second for production
of the multiple emulsions.
In w/o/w emulsions, oil globules, containing small droplets of water,
are dispersed in an aqueous continuous phase. The advantages of these
types of emulsion systems are relatively high entrapment capacity for
hydrophilic compounds, protection of the encapsulated substances
towards degradation, the ability to introduce incompatible substances
into the same system, and sustained release of active substance. These
characteristics make them potentially interesting for application in
pharmaceutics and cosmetics. However, in practice, signifi cant problems
may arise because of their thermodynamic instability and strong tendency
for coalescence, fl occulation, and creaming. The stability of w/o/w
emulsion may be affected by a number of factors, including the method
of preparation, osmotic balance between the internal and external water
phase, phase volumes ratio, type, and concentration of the emulsifi ers.
In the work of Onuki et al. (2004), formulation optimization of the
w/o/w multiple emulsion incorporating insulin was performed, based on
statistical methods such as the orthogonal experimental design and the
response surface evaluation. As model formulations, 16 types of emulsions

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