Characterizing Roughness: A New Substrate to Measure SPF

Sep 1, 2009 | Contact Author | By: M. Pissavini, S. Marguerie, A. Dehais, L. Ferrero and L. Zastrow, Coty-Lancaster International
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Title: Characterizing Roughness: A New Substrate to Measure SPF
SPFx PPDx PMMA substratex roughness parameterx control chartx
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Keywords: SPF | PPD | PMMA substrate | roughness parameter | control chart

Abstract: Here, the authors describe a variable that affects the results of SPF testing in vitro—the roughness parameter—and investigate this variable using standard and molded poly(methyl methacrylate) (PMMA) substrates. They conclude that use of a molded substrate, along with the described control chart, improves the reproducibility of in vitro SPF test results.

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In vitro testing for the determination of sun protection is essential for the cosmetics industry. It is fast, relatively inexpensive, and can be used routinely. However, until 2006, only in vivo methods were subject to recommendations or regulations. Since then, organizations such as the Agence Française de Securité Sanitaire des Produits de Santé (AFSSAPS), Colipa and the International Organization for Standardization (ISO) have proposed the development of in vitro methods to replace in vivo methods.

Standard in vitro tests are based on diffuse transmission spectroscopy, wherein a thin film of sunscreen is applied to a suitable UV-transparent substrate, then UV radiation is transmitted through the film and measured by a spectrophotometer equipped with an integrating sphere. Several authors have used the SPF in vitro method and shown a fair correlation with in vivo values;1-4 however, controversy surrounding the results underlines a weakness in the existing in vitro method: a lack of control over the parameters that influence the results. Interestingly, better correlations were obtained when strict control was exercised over variables including the validation equipment and amount of product used, as well as its evenness of application.5-8 Among these important variables is the roughness of the test substrate, which until now, had not yet been fully detailed.

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Table 1. Percentage of transmission

 Table 1. Percentage of transmission 

Table 2. Sa values and in vitro SPF

 Table 2. Sa values and in vitro SPF 

Table 3. Comparison of the roughness

 Table 3. Comparison of the roughness 

Table 4. Mean values and % of the coefficient of variation

 Table 4. Mean values and % of the coefficient of variation (

Table 5. Mean values and % CV of the different roughness

 Table 5. Mean values and % CV of the different roughness 

Table 6. Control charts of the molded PMMA plates

 Table 6. Control charts of the molded PMMA plates

Pissavini Topography Parameters

Topography Parameters

Figure 1. Depiction of the topographic properties

 Figure 1. Depiction of the topographic properties

Figure 2. Influence of roughness homogeneity on the SPF variance

 Figure 2. Influence of roughness homogeneity on the SPF variance

Figure 3. Principal component analysis of sand-blasted and molded roughness parameters

 Figure 3. Principal component analysis of sand-blasted and molded roughness parameters

Pissavini Roughness footnotes

 a The Altisurf 500 lab workstation is an apparatus from Altimet, France.

b The Mountain Altimap microtopography software module is a product of Digital Surf, Besançon, France.
c Helioplates [INCI: Polymethylmethacrylate (PMMA)] is a product of Helioscreen, Creil, France. 
d Helioplates HD6 [INCI: Polymethylmethacrylate (PMMA)] is a product of Helioscreen, Creil, France. 
e The Labsphere UV-1000 S Transmittance analyzer is a device from Labsphere, North Sutten, NH, USA.

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