## 3 Results and Discussion
### Characterization of the Nanoparticles Containing Zinc Complexes
#### 3.2.5 Evaluation of the Creams  
In order to obtain stable creams, it is necessary to use emulsifying agents, whose main role is to reduce the interfacial tension between the oily and the aqueous phases. For the preparation of the creams, the non-ionic emulsifiers Tween 80 (as an emulsifier in the aqueous phase) and Span 80 (as an emulsifier in the oily phase) were used since they are not irritating to the skin, are not easily influenced by pH and are non-toxic. When formulating the new cream, we aimed to use minimal amounts of synthetic emulsifiers and natural products with the role of co-emulsionsiers or viscosity modifying agents. Chitosan and gelatine favorably influence the stability of the emulsion by forming a polymer network (gel framework) that increases the viscosity of the emulsion by decreasing the mobility of oil droplets, thus preventing the destabilization of the emulsion. Also, both the gelatine as well as the chitosan form protective films around the oil phase droplets, preventing, through electrostatic repulsion and by steric hindrances, the flocculation and/or the coalescence of the oily phase droplets. Glycerol acts as a humectant in skin hydration and as an emollient. Figure 4: DR UV-visible spectra of VLSENP and ZnNP samples. Beeswax gives consistency, stability and texture to the creams. Olive oil was used as an emollient and as a non-polar solvent for beeswax. Microscopic Analysis of the Creams  
The microscopic photos accomplished after 6 h from the preparation of the creams (Figure 5) show that semisolid emulsions contain a high number of small droplets with a relatively uniform distribution of the particle size, indicating that the prepared creams have a very good stability. Organoleptic Characteristics and Physical-Chemical Properties of the Creams  
The organoleptic characteristics, pH, viscosities and spreading diameters values of the creams are shown in Table 3.  
From the evaluations carried out after 1, 3, 6, 9 and 12 months, no changes inthe organoleptic characteristics were found in the case of the samples containing ZnNPs (Figure 6). For sample S1, which does not contain nanoparticles, phase separation occurred after 6 months of storage (Figure 6a), while for sample S2,whichcontains VLSENP phases, separation was noticed after 9 months of storage at room temperature (Figure 6b). Additionally, in the case of samples S1 and S2, the appearance of some mold colonies after 9 months and, respectively, 12 months from the preparation of creams was noticed. The samples that contain the ZnNPs (samples S3-S6) did not exhibit any change intheri properties, although the containers wherein these creams have been kept were opened many times for taking of the samples required for the determination of viscosity, spreading diameters and pH. This fact proves once more the antimicrobial activity of the cream formulations that  
Figure 6: Images regarding the stability of the creams: (**a**) after 9 months from their preparation; (**b**) after 12 months from their preparation. contain ZnNPs. The pH of the creams that contain ZnNPs ranged from 4.96 to 5.25 and did not significantly change over the storage time (over the period of 12 months wherein they were analysed). The pH values of the obtained creams fall within the pH range of the skin that, according to the most recent studies, varies from 4.1 to 5.8 [9; 22; 41]. The viscosity of the creams that contain ZnNPs (samples S3-S6) slightly increased with the increase of the zinc complexes amount added into the cream due to the intensification of the interactions between the hydrophobic components of the emulsion through van der Waals dispersion forces. The values obtained for viscosity (comprised between 13.75 Pa\(\cdot\)s and 16.50 Pa\(\cdot\)s) and for the spreading diameters (comprised between 5.23 cm and 5.75 cm) showed that the obtained creams can be easily spread on the surface of the skin. The skin irritation test confirmed that the obtained creams did not produce any irritation, redness, or signs of erythema after being applied to volunteers.