# Incorporation of UV Filters into Oil-in-Water Emulsions--Release and Permeability Characteristics
## 4 Conclusions  
In this report, an efficient preparation procedure for novel oil-in-water emulsions, containing various concentrations of two commonly used chemical filters, avobenzene and octyl methoxycinnamate, was presented. The important aspect was the in vitro permeation experiments through different membranes, which are recently of great interests due to the ban on animal testing for cosmetics. The development of an appropriate methodology to evaluate UV filter penetration will be beneficial for both pharmaceutical and cosmetic industries. The obtained topical formulations did not show phase separation in the centrifuge test performed directly after obtaining and after 35 days of storage at room temperature, regardless of composition. The use of multiple light scattering methods allowed to observe changes in the stability index values. It was established that emulsions with the addition of avobenzene are characterized by the highest stability. The topical formulations show  
Figure 6: The release profile of avobenzene and octyl methoxycinnamate from emulsions through the cellulose membrane (**A**), and cumulative amount of UV filters permeated through the Strat-M membrane (**B**). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Zero Order** & **First Order** & **Higuchi Model** &
\begin{tabular}{c} **Hixson–Crowell** \\ **Model** \\ \end{tabular} & **Korsmeyer–Peppas Model** \\ \cline{2-6}  & **Model** & **Model** & **Correlation Co-Efficient (R2)** & & **n** \\ \hline E\({}_{0.5\%\text{ Avo}}\) & 0.889 & 0.898 & 0.949 & 0.895 & 0.964 & 0.575 \\ E\({}_{2\%\text{Avo}}\) & 0.968 & 0.966 & 0.907 & 0.961 & 0.970 & 0.824 \\ E\({}_{0.5\%\text{OMC}}\) & 0.880 & 0.878 & 0.877 & 0.879 & 0.931 & 0.989 \\ E\({}_{2\%\text{OMC}}\) & 0.959 & 0.962 & 0.931 & 0.961 & 0.968 & 0.978 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Kinetic models used to describe the release of UV filters from oil-in-water emulsions through cellulose membrane. a pH in the range of 6.02-6.11, which is acceptable for cosmetic products. There were no significant differences in the size of the emulsion particles after the introduction of the selected sunscreen agent. Due to the growing awareness of the harmful effects caused by UV filters on the skin, release and permeation tests of avobenzene and octyl methoxycinnamate, from the obtained emulsions to receptor fluids at pH 5.8, were carried out. In the assays, cellulose and Strat-M membranes, simulating human skin, were applied. It was found that octyl methoxycinnamate diffuses more easily through the cellulose membrane compared to avobenzene, and the release profiles correspond to the Korsmeyer-Peppas kinetic model. The permeation of the UV filters via the Strat-M membrane occurs to a small extent, which means that they will remain on the skin surface after application. The results obtained support the safety of the formulations containing avobenzene and octyl methoxycinnamate as sunscreen agents providing effective protection against UV radiation. The UV filter lipophilicity mostly affects both the release and permeation through the skin. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13137674/s1](https://www.mdpi.com/article/10.3390/app13137674/s1)]([https://www.mdpi.com/article/10.3390/app13137674/s1](https://www.mdpi.com/article/10.3390/app13137674/s1)), Figure S1. Particle size distributions of formulations E, E\({}_{0.5\%\text{Avo}}\), E\({}_{2\%\text{Avo}}\), E\({}_{0.5\%\text{OMC}}\), E\({}_{2\%\text{OMC}}\) after ultrasound treatment; Figure S2. Diagrams of droplet size of formulations E, E\({}_{0.5\%\text{Avo}}\), E\({}_{2\%\text{Avo}}\), E\({}_{0.5\%\text{OMC}}\), E\({}_{2\%\text{OMC}}\). Conceptualization, A.O. and J.G. ; methodology, A.O. ; validation, A.O. and J.G. ; investigation, A.O. ; data curation, A.O. and J.G. ; writing--original draft preparation, A.O. ; writing--review and editing, J.G. ; visualization, A.O. and J.G. ; supervision, J.G. ; project administration, A.O.