48 ANTI-AGEING
Methods Adhesion of particulate matter after product application in vitro A standardized test method was developed to evaluate pollutant adhesion of particulate matter after product application on a substrate. SiO2
dust particles, classified
as PM10, were used as the test pollutant. The products tested were a gel cream base formulation, base formulation with 5% second skin film former, and base formulation with 5% conventional macrowax technology comprised of the same composition. Each test product was applied uniformly
onto polymethyl methacrylate (PMMA) substrates and allowed to dry at 38°C overnight. Subsequently, the pre-treated substrates were exposed to a petri dish containing SiO2
Dust adhesion level = Remaining Dust Applied Dust x 100%
dust material, shaken for 30
seconds, then removed. The remaining dust material was measured to evaluate the dust adhesion level. The experiment was repeated six times on different areas of the PMMA substrate and results were averaged.
Permeability test simulating penetration of chemical pollutants in vitro A test setup4
method (e.g. Skin PAMPA)5
similar to the above-described was used. The
plates have a history of use in skin penetration studies and the set-up is based on a similar principle as that of Franz cell studies. They consist of a donor chamber (for product application), an artificial membrane (mimicking the stratum corneum) and a receptor chamber (representing the viable skin). In this experimental set-up, the test product
was applied to individual wells of the donor plate and left to dry. The products tested were water, the base formulation, base formulation with 5% second skin film former, and base formulation with 5% benchmark. The donor plates were then placed onto the acceptor plates containing the acceptor medium. The model pollutant, a fluorescein-based
fluorescent dye, was applied to the donor chambers. After an incubation time of 15 minutes, the penetration of the fluorescent dye into the acceptor plate was measured via spectrometric analyses. The concentrations of the dye found in the acceptor medium were compared to those of the untreated control which served as reference for 100% penetration.
Removability of particulate matter after product application in vivo Tests were conducted on the volar forearm of volunteers. Arms were gently cleaned with an ethanol-soaked tissue and, after drying, the test sample was applied to the test areas. One area was not treated with a product but was otherwise subjected to the same test procedure and then used as a reference (untreated). Test products were a formulation with 5% second skin film former and a formulation incorporating the same ingredients using a conventional emulsion technology. After a ten-minute drying time, the model
pollutant was applied to the test area via a standardized blast of air. Activated charcoal was
PERSONAL CARE January 2023
40% 35% 30% 25% 20% 15% 10% 5% 0%
33% 33% 22% 27%
Base formula
Base + 2nd
Film Former
used as a model pollutant and was applied via a closed system to ensure inhalation exposure was avoided. Thereafter, 500 mL of room temperature
water (22°C) or lukewarm water (36°C) was gently and evenly poured over the test site. Photographs of the test areas were taken under controlled light conditions after each step. Image analyses were used to evaluate the amounts of particles adhering to the skin by determining changes to the mean skin lightness. The results allowed conclusions to be drawn about a specific product’s ability to improve the removability of particle pollutants.
Results Reduction in the adhesion of pollutant particles Silica dust (SiO2
) particles (<10 µm) were used
as a model pollutant to evaluate the effects of different products on pollutant adhesion. Figure 1 shows the dust adhesion level of a formulation with and without the second skin film former compared to the same base formulation with conventional macrowax technology.
Skin
Base + Macrowax Figure 1: Dust adhesion level of PM 10 SiO2 on substrates treated with test product Incorporating 5% second skin film former to
the formula gave a 33% reduction in adhered dust particles compared to the control without it. In contrast, the base formula with 5% of a macrowax dispersion composed of the same ingredients, only showed a slight reduction in dust adhesion level over the control base formula.
The second skin film former supports the
anti-adhesion of pollutant particles by reducing the amount of particulate matter adhering to the skin.
Decrease in the penetration of harmful substances To test for chemical penetration, permeability membranes were treated with a known amount of test product and the penetration rate of a model pollutant was measured (Figure 2). The membranes treated with base formulation and base formulation with 5% benchmark gave a chemical penetration rate close to that of water, 94% and 91%, respectively. This indicates the base formulation with and without the
120% 100% 805 60% 40% 20% 0%
100% 94% 58% 91%
Water
Formulation
Base
Base + 2nd
Film Former
Skin
benchmark Figure 2: Chemical penetration rates of a fluorescent dye through a membrane treated with test product
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Base +
Penetration rate (%) Better protection
Dust adhesion level
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