SENSORY ANALYSIS OF A CHITOSAN GEL NANOFORMULATION 303 applied on the skin by the volunteers during 1 min, controlling the rate by a metronome (120 beats per min). The samples were presented in pairs and the volunteers answered about the difference between formulations regarding specifi c attributes (discriminative analysis) and about their general preference (affective analysis). All volunteers analyzed three pairs of samples identifi ed with three-letter random codes. For the samples that ap- peared more than one time, in different pair of samples, the code was different for avoid- ing identifi cation of the sample by the volunteer. The sensory study was characterized as discriminative and affective and it was performed in two distinct phases. Each phase was composed of 60 volunteers analyzing distinct pairs of samples. The attributes analyzed in both phases were: spreadability, oiliness, immedi- ate and residual stickiness, fi lm formation, homogeneity of the fi lm, and preference. Phase I sensory study: Chitosan gel versus hydroxyethyl cellulose gel. The sample pairs analyzed were the following: CH versus HEC, CH-NC versus HEC-NC, and CH versus CH-NC. The fi rst two pairs aimed to identify differences between the chitosan and hydroxylethyl cellulose gels containing or not containing nanocapsules, for the mentioned attributes. The preference between such formulations was analyzed, without relating the preference to any attribute. The last pair (CH vs. CH-NC) aimed to observe the differences that were brought to the formulation due to the incorporation of nanocapsules in the chitosan hy- drogel, the focus of this study. The preference of the volunteers was determined also for this pair of sample. Phase II sensory study: Chitosan gel versus optimized chitosan gel. The sample pairs analyzed were the following: CH versus CH-OPT, CH-NC versus CH-NC-OPT, and CH-OPT versus CH-NC-OPT. The fi rst two pairs aimed to identify differences between the chitosan and optimized chitosan gels containing or not containing nanocapsules, for the men- tioned attributes. The preference between such formulations was analyzed, without relating the preference to any attribute. The last pair (CH-OPT vs. CH-NC-OPT) aimed to observe the differences that were brought to the formulation due to the incorporation of nanocapsules in the optimized chitosan hydrogel. The preference of the volunteers was determined also for this pair of sample. Statistical analysis. The statistical analysis of the characterization properties were per- formed by Student’s t-test, while the statistical difference of the sensory studies was de- termined through the χ2 test (proportions test). In both cases, differences were considered signifi cant for α = 0.05. RESULTS AND DISCUSSION CHARACTERIZATION OF HYDROGELS All hydrogels presented slightly different aspects. The hydrogels containing nanocap- sules presented opacity due to the nanocapsule aqueous suspension, while the hydrogels without nanocapsules presented transparency, in except for the optimized chitosan hydro- gel, which presented some opacity due to the adjuvants addition. The pH values were around 4.5 for chitosan hydrogels (CH = 4.32 ± 0.21, CH-NC = 4.31 ± 0.16, CH-OPT = 4.50 ± 0.18, CH-NC-OPT = 4.42 ± 0.15) due to lactic acid used for chitosan solubiliza- tion and chains entanglement, in a way that neither the addition of adjuvants (silicone

JOURNAL OF COSMETIC SCIENCE 304 and PCA-Na) nor the addition of nanocapsules led to signifi cant changes in the pH val- ues. The hydroxyethyl cellulose gels presented pH values around 6.5 (HEC = 6.68 ± 0.27, HEC-NC = 6.77 ± 0.13) and no differences were observed when the nanocapsules were added, as well. The values were considered suitable for skin application due to slight acidity of the stratum corneum (24). Regarding the presence of nanocapsules in the hydrogels, CH-NC, HEC-NC, and CH- NC-OPT, it was observed, through analysis of the volume (Figure 1A) and number (%) (Figure 1B) distribution of particles sizes, that the nanocapsules are present in the gels, showing similar size when compared to the nanocapsule aqueous suspension. The pres- ence of a micrometric peak in HEC-NC gel only appears when the volume of the particles are considered, disappearing when taking into consideration the number of the particles. This micrometric peak could be related to the HEC microdomains. TEM photomicro- graphs (Figure 2) confi rmed that the nanocapsules were not damaged due to incorpora- tion in the hydrogel formulations and that similar size is observed comparing both techniques for determination of particles sizes. These results demonstrate the applicabil- ity of the proposed hydrogels as suitable vehicles for polymeric nanocapsules. The hydrogels were submitted to rheological analysis aiming to verify the viscosity of the products. Since non-Newtonian fl uids present viscosity dependent on the shear rate, rhe- ological profi les were obtained (shear stress vs. shear rate, Figure 3). When fi tting such data by the Ostwald fl ow model of pseudoplasticity, the determination coeffi cients were above 0.99 for all hydrogels, indicating that the model is suitable for the data obtained. Figure 1. (A) Volume percentage and (B) number percentage distribution of particles sizes (CH: chitosan gel, HEC: hydroxyethyl cellulose gel, NC: nanocapsules, OPT: optimized hydrogels).