Phase II: Product realization and heuristics update
Starting from a generic basic skin moisturizing cream, identified as
K0-N1, which solves the problem specified in Table 2 at a minimum cost,
specific changes were made to comply with different attributes for the
two evaluated references (Samples 1 and 2). For this, additional
heuristics from Table 3 were included in the algorithm as restrictions
that allowed searching for feasible alternatives, which increased or
reduced the level of the aimed attribute. The resulting formulations are
presented in Table E-1 of the Supplementary material.
From the results obtained in the consumer assessment phase for Sample 1,
ease of absorption, freshness, and residues were the most important
attributes by the composite index. Due to the high interaction between
these attributes (see Table 5), and the fact that the base formulation
left more white residues than the Sample 1 (Figure 3), the first change
made to the algorithm was to implement one of the actions to reduce the
white residues by adding up to 2% low HLB emulsifier (see Table 3). A
series of experiments were performed to understand how each change
affected the emulsion properties, especially the white residues after
product application on skin and the product viscosity. Each one of these
alternatives was generated using the optimization problem specified in
Table 2. The name of the formulations was given according to the
following parameters: The first letter indicates if the product is a
cream (K) or a lotion (L), while the number corresponds either to the
base case (0) or to the samples 1 or 2. The following parts also contain
letters and numbers. The letter corresponds to the aimed attribute(s) -
R for “Residues”, G for “Greasiness/oiliness”, V for “Thickness”
and N if no attribute is aimed. The numbers correspond to a counter of
the alternatives at this stage.
- Formulation K1-R1 is essentially K0-N1 + 1% Glyceryl Stearate
(replaces water). This could be considered a classical corrective
action and is only chosen here to compare with a more systematic
approach to solve the problem.
- Formulation K1-R2 includes 1% Glyceryl Stearate but compensates with
the addition of other emollients to keep the minimal surfactant/oil
ratio (1:4). The restriction HLB=RLHB is imposed as before in Eq. 5.
- Formulation K1-R3 includes 1% of a low HLB surfactant with the
restriction in Eq. 6.
- Formulation K1-G1 is made ignoring the importance of indices
attributes of the previous section and only taking into account the
high value given to the greasiness. This could be considered as an
approach to generate a less greasy alternative formulation, based on
the consumer assessment, but disregarding the importance and
interactions of the attributes. To have a less greasy alternative, the
maximal value of γ was allowed to be 2.2 instead of 2.4, and K0-N1
left considerably more residues than Sample 2, as it can be observed in
Figure 3.
For the case of Sample 2, the starting point was set to be Formulation
K1-R3, as in this case residues are the most important attribute too
(0.34 in the composite index; see Table 6), and from the previous
example, it was known that K0-N1 left considerably more residues than
Sample 2, as it can be observed in Figure 3. The next action targeted
the thickness, as there was no reliable action to correct and easily
evaluate the change of the freshness attribute. Two different actions
were taken, to observe the results of each change.
- Formulation K2-R3-V1, which comes from the choice of the surfactants,
preferring those having oleyl (Polysorbate 80) instead of stearyl
groups (Polysorbate 60), as mentioned in Table 3.
- Formulation L2-R3-V1, which considers the same modifications and the
viscosity parameters for lotions too.