Adjusting Substrate/Product Interfacial Properties to Improve In vivo/In vitro SPF Correlation

Mar 1, 2013 | Contact Author | By: S. Miksa, D. Lutz and J. Ongenaed, HelioScreen Labs; D. Candau, L’Oréal Research & Innovation
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Title: Adjusting Substrate/Product Interfacial Properties to Improve In vivo/In vitro SPF Correlation
in vitro SPFx sunscreen productsx interfacial propertiesx plasma treatmentx
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Keywords: in vitro SPF | sunscreen products | interfacial properties | plasma treatment

Abstract: This work evaluates the impact of a plasma treatment on test substrates to modify their surface energy, to more closely correlate in vitro SPF measurements with in vivo measurements—without chemically altering the test products. The authors chose the level of plasma modification to use on a substrate based on in vivo values; they explain how to choose it regarding specific formulas in a further paper.

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S. Miksa, D. Lutz, J. Ongenaed and D. Candau, Adjusting substrate/product interfacial properties to improve in vivo/in vitro SPF correlation, Cosm & Toil 128(3) 170-181 (Mar 2013)

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Ultraviolet (UV) radiation from sunlight can cause many adverse effects in human skin—particularly in the 290–320 nm UVB range, which is the most harmful. Public concern about skin damage induced by sun exposure also has increased, leading to more specific regulatory requirements as well as controls for sun protection products. Evaluations for the level of UVB protection afforded by sunscreen products are based on in vivo methods. These consist of comparing the UV radiation dose required for the appearance of a biological endpoint, in this case skin redness, with and without protection.

As in most other fields, industrial laboratories and health authorities require that such in vivo methods be substantiated by in vitro methods for ethical, economical and practical reasons. The determination of the in vitro SPF by means of a spectrophotometer was initially described by B.L. Diffey and J. Robson, then modified and improved to evaluate the level of UVB protection brought by the product. In vitro methods typically are based on the assessment of UV transmittance through a thin film of sunscreen sample spread on a roughened substrate. Many studies have been published in which the product quantity, spreading and substrate have been varied to improve the reproducibility and correlation of in vitro SPF evaluations with in vitro methods. Although repeatability can now be made relevant for very specific protocols, correlation with in vivo values is still a challenge for some products. This is clearly because a key parameter has not been considered: the affinity between the plate and the product, owing to the surface properties of the substrate.

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This is an excerpt of an article from GCI Magazine. The full version can be found here.

 

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Table 1. Surface energy determination

Table 1. Surface energy determination

The contact angles of water and diiodo-methane were measured by a drop shape analysis system by placing a 5-µL drop of each on the substrate.

Table 2. Tested sunscreen products

Table 2. Tested sunscreen products

Thirty-four sunscreen products covering various formulations were chosen. For all products, several measurements by different institutes had previously been taken, and in vivo SPF values ranged from 9 to 85.

Table 3. Drop images according to plasma treatment level

Table 3. Drop images according to plasma treatment level

Images of water and diiodo-methane drops according to the level of plasma treatment

Table 5. In vivo/in vitro SPF correlation result levels

Table 5. In vivo/in vitro SPF correlation result levels

Detailed results of linear regression and correlation coefficient; note that in vitro SPFs were generally overestimated.

Figure 1. Angle contact

Figure 1. Angle contact

Angle contact according to plasma treatment level; mean ± SD, three plates

Figure 2. Surface energy

Figure 2. Surface energy

Surface energy according to plasma treatment level; mean ± SD, three plates

Figure 3. Stability of the plasma treatment (first day)

Figure 3. Stability of the plasma treatment (first day)

Stability of the plasma treatment during first day; mean ± SD, 3 plates

Figure 4. Stability of the plasma treatment (per time)

Figure 4. Stability of the plasma treatment (per time)

Stability of the plasma treatment according to time; mean ± SD, 3 plates

Figure 5. In vivo/in vitro SPF correlation

Figure 5. In vivo/in vitro SPF correlation

In vivo/in vitro SPF correlation without plasma treatment

Figure 6. In vivo/in vitro SPF correlation with plasma treatment Level 1

Figure 6. In vivo/in vitro SPF correlation with plasma treatment Level 1

Compared with the results without plasma treatment, a plasma treatment Level 1 (see Figure 6) allows a slightly better correlation coefficient, r = 0.720, and a linear regression of y = 1.155x.

Figure 7. In vivo/in vitro SPF correlation with plasma treatment Level 2

Figure 7. In vivo/in vitro SPF correlation with plasma treatment Level 2

Data with plasma treatment Level 2, with a correlation coefficient r = 0.698, was better than no plasma treatment but slightly worse than Level 1.

Figure 8. In vivo/in vitro SPF correlation with plasma treatment Level 3

Figure 8. In vivo/in vitro SPF correlation with plasma treatment Level 3

From results obtained with a plasma treatment Level 3, the correlation coefficient was improved and reached 0.763 with a linear regression of y = 1.343x.

Figure 9. In vivo/in vitro SPF correlation with adapted plasma treatment

Figure 9. In vivo/in vitro SPF correlation with adapted plasma treatment

Whatever the treatment level, the adapted plasma treatment allows a better correlation coefficient of r = 0.812, compared with the correlation obtained from values issued from untreated substrate.

Footnotes [Miksa 128(3)]

a The Femto LF PCCE control is manufactured by Diener electronic GmbH and Co., KG.
b The Drop Shape Analysis System DSA10 Mk2 is manufactured by KRÜSS GmbH.
c Milli-Q is a device from Merck Millipore.
d Diiodo-methane was obtained from Merck Schuchardt OHG.
e Helioplate HD6 PMMA plates are manufactured by Helioscreen Labs.
f The Labsphere UV-2000S transmittance analyzer is manufactured by Labsphere Inc.
g Ultraviolet Transmittance Analyzer Performance Validation Standards are distributed by Labsphere Inc.
h Helioplate HD0 PMMA plates are manufactured by HelioScreen Labs.

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