# Incorporation of UV Filters into Oil-in-Water Emulsions--Release and Permeability Characteristics
## 3 Results and Discussion
### Release and Permeation of UV Filters from Oil-in-Water Emulsions  
As it was proved that the formulations were stable, and their particle size distributions were similar to each other, the release and permeation studies of avobenzene and octyl methoxycinnamate from o/w emulsions were carried out. [PERSON] et al. suggested that the initial stage of percutaneous absorption of the active compound is related to its release from the formulation [49]. Consequently, in the first step, the release studies of UV filters from emulsions through the cellulose membrane were performed. The UV spectra of each sunscreen agent (Figure 5) were registered to determine the wavelength corresponding to the maximum absorbance characteristic for both the compounds in the receptor fluid selected for the release studies. The maximum absorbance (\(\lambda_{\text{max}}\)) of avobenzene was recorded at 265 nm and 361 nm, which corresponds to the keto and enol forms, respectively [50]. In \begin{table}
\begin{tabular}{c c c c c c} \hline
**Emulsion** & **E** & **E\({}_{\text{95\%Avo}}\)** & **E\({}_{\text{25\%Avo}}\)** & **E\({}_{\text{0.5\%OMC}}\)** & **E\({}_{\text{25\%OMC}}\)** \\ \hline D [3,2] & 1.570 \(\pm\) 0.008 μm & 1.620 \(\pm\) 0.014 μm & 1.300 \(\pm\) 0.001 μm & 1.790 \(\pm\) 0.001 μm & 1.640 \(\pm\) 0.016 μm \\ \hline d(0.1) & 0.671 \(\pm\) 0.002 μm & 0.716 \(\pm\) 0.001 μm & 0.652 \(\pm\) 0.002 μm & 0.983 \(\pm\) 0.001 μm & 0.696 \(\pm\) 0.026 μm \\ \hline d(0.5) & 1.850 \(\pm\) 0.011 μm & 1.780 \(\pm\) 0.023 μm & 1.370 \(\pm\) 0.006 μm & 1.850 \(\pm\) 0.001 μm & 1.890 \(\pm\) 0.203 μm \\ \hline d(0.9) & 33.000 \(\pm\) 0.153 μm & 30.300 \(\pm\) 1.535 μm & 16.500 \(\pm\) 1.170 μm & 9.340 \(\pm\) 0.045 μm & 31.300 \(\pm\) 1.077 μm \\ \hline  & \multicolumn{4}{c}{Ultrasound treatment} \\ \hline D [3,2] & 1.400 \(\pm\) 0.088 μm & 1.350 \(\pm\) 0.083 μm & 1.190 \(\pm\) 0.082 μm & 1.660 \(\pm\) 0.016 μm & 1.310 \(\pm\) 0.108 μm \\ \hline d(0.1) & 0.630 \(\pm\) 0.021 μm & 0.641 \(\pm\) 0.026 μm & 0.614 \(\pm\) 0.019 μm & 0.946 \(\pm\) 0.007 μm & 0.617 \(\pm\) 0.036 μm \\ \hline d(0.5) & 1.570 \(\pm\) 0.145 μm & 1.370 \(\pm\) 0.097 μm & 1.250 \(\pm\) 0.076 μm & 1.730 \(\pm\) 0.024 μm & 1.400 \(\pm\) 0.206 μm \\ \hline d(0.9) & 26.400 \(\pm\) 2.533 μm & 19.400 \(\pm\) 2.146 μm & 14.300 \(\pm\) 1.543 μm & 7.280 \(\pm\) 0.446 μm & 24.200 \(\pm\) 1.720 μm \\ \hline \end{tabular}
\end{table} 
Table 4: Parameters determined based on the particle size distribution measurements of emulsions with and without UV filters. Figure 3: Particle size distributions of topical formulations measured without (**A**) and with the use of ultrasounds (**B**). turn, in OMC, the benzene ring is substituted with 2-ethylhexyll propenoate ester group, acting as an electron acceptor, and methoxyl group in the para position is playing the role of an electron donor [51]. Therefore, the extended delocalization of electrons occurs in the OMC molecule. The \(\lambda_{\text{max}}\) for OMC was registered at 311 nm. The octyl methoxycinnamate protects against UVB, while avobenzene is a UVA sunscreen agent (Figure 5). Figure 4: Optical microscope images of emulsions without (**A**) and with sunscreen agents: E\({}_{0.5\%\text{AVO}}\) (B), E\({}_{2\%\text{AVO}}\) (C), E\({}_{0.5\%\text{OMC}}\) (D), E\({}_{2\%\text{OMC}}\) (E). Figure 5: UV spectra of avobenzene and octyl methoxycinnamate in receptor fluid (mixture of ethanol and phosphate buffer of pH 5.8). The release studies of the UV filters from the emulsions were performed through a cellulose membrane. The results are presented in Figure 6A. The amount of UV filters released after 48 h from the same type of emulsion decreased in the following order E\({}_{2\%\text{OMC}}>\) E\({}_{0.5\%\text{OMC}}>\) E\({}_{2\%\text{Avo}}>\) E\({}_{0.5\%\text{Avo}}\). It was also observed that the diffusion of the UV filters from the formulation to the receptor fluid depended on their concentration. With the increase in Avo/OMC concentration in the emulsion, a higher amount of UV filter was liberated to the receiving medium.