Surface Structures of Cosmetic Standard Poly Methyl Methacrylate UV Evaluation Plates and their Influence on the <i>in vitro</i> Evaluation of UV Protection Abilities of Cosmetic Sunscreens

Abstract

for the Broad-spectrum approval by US FDA s Final Sunscreen Rule 10 , roughened cosmetic standard poly methyl methacrylate PMMA UV evaluation plates are used 11 13. In our previous studies, it was shown that spontaneous pattern formation by viscous fingering 14 18 on the sunscreen layer during the process of its application onto a flat Abstract: Cosmetic standard poly methyl methacrylate (PMMA) UV evaluation plates, i.e., roughened PMMA plates, are used in the EU and the US for the in vitro evaluation of UV protection abilities of sunscreen, such as in vitro UVA-PF and critical wavelength for the Broad-spectrum approval. In our previous studies, inhomogeneity in the thickness of a pseudo-sunscreen layer applied on a flat quartz plate was observed to alter UV transmission. Thus, the surface roughness of the standard plates should have a significant influence on the in vitro evaluation. In the present study, we have analyzed the surface structures of three cosmetic standard PMMA UV evaluation plates: Helioplates HD6 (Sa = 6 µm) and ISO plates (Ra = 2 and 5 µm). A decamethylcyclopentasiloxane and 2-propanol-mixed solvent solution of acrylsilicone resin was prepared, and the solution was added dropwise onto the plates. After the evaporation of the solvents, the plates were cut and the cross section was analyzed using SEM-EDS. The distribution of silicon atoms at the cross-section suggested that the maximum depth of penetrating of acrylsilicone resin was larger than Ra for all the standard plates, and the surface structure was significantly different for each standard plate. In addition, cracks into which the acrylsilicone resin deeply penetrated were observed on the surface of some plates. Clear-solution-type pseudo-sunscreen samples in which UV absorbers and acrylsilicone resin were dissolved were deposited on the standard roughened PMMA plates. It was observed that the addition of acrylsilicone resin drastically changed the net UV transmission. The degree to which the hollows of the roughened surface were filled with the pseudo-sunscreen samples determined the variation of UV transmittance.

Factors to control the alignment of surface‐treated titanium dioxide powders to maximize performance of sunscreens

“…The finding that integrated UV‐B absorbance clearly increased with increasing the flatness of the sample deposited layer in this study is well in accordance with the results of our previous study. On the other hand, UV intensity was found to decrease upon passing through the plate having roughened surface mostly due to the diffuse reflection at the surface [30]. In this study, an increase in the value of integrated UV‐A absorbance accompanied by decreasing the flatness of the deposited layer was observed in some cases.…”

“…Titanium dioxide is known to absorb UV-B since its valence band possesses many densely packed electron states [22][23][24][25][26]. Significant contribution of the spatial homogeneity of UV absorbers in the sunscreen layer for the enhancement of UV shielding ability was verified by the combination of theoretical calculation and experimental analysis in our previous study [27][28][29][30]. The finding that integrated UV-B absorbance clearly increased with increasing the flatness of the sample deposited layer in this study is well in accordance with the results of our previous study.…”

<i>In vitro</i> Evaluation Method of UV Protecting Ability of Sunscreens: Clarifying and Overcoming Problems to Develop New Method

“…All plates are square of one side of 5 cm. Surface roughness of three types of plates were analyzed, and its influence on the in vitro evaluation of UV protecting ability of sunscreens was studied 51) . Acrylsilicone resin was dissolved in a mixed solvent of iso-propanol and decamethylcyclopentasiloxane, and the solution thus obtained was slowly dropwised on HD6, ISO2 and ISO5 plate.…”

“…The roughened cosmetic standard PMMA UV evaluation plates should be used for the in vitro evaluation of UVA-PF by ISO 24443 18) and critical wavelength for the Broad Spectrum approval by US FDA s Final Sunscreen Rule 19) . We have studied the influence of surface roughness of the cosmetic standard PMMA UV evaluation plate on the value of in vitro UV protecting ability 51) , since it surely affects the spatial inhomogeneity in applied sunscreen layer.…”

Oil Thickening with Organoclay Enhances the Ultraviolet Absorption Ability of Sunscreen on a Skin-mimicking Substrate

“…The application amount and application method are defined in all SPF test methods. Therefore, parameters protection ability of sunscreen products is strongly influenced by the extent to which the sunscreen flows into the grooves 16 . Furthermore, oil-in-water vehicles with low viscosity, owing to the absence of water-soluble thickeners such as xanthan gum, have a negative effect on the SPF values 17,18 .…”