In Vitro UV Testing—Robot vs. Human Spreading for Repeatable, Reproducible Results

Oct 1, 2013 | Contact Author | By: Sébastien Miksa, Dominique Lutz and Céline Guy, HelioScreen Labs
Your message has been sent.
(click to close)
Contact the Author
Save
This item has been saved to your library.
View My Library
(click to close)
Save to My Library
Title: In Vitro UV Testing—Robot vs. Human Spreading for Repeatable, Reproducible Results
In vitro SPFx automated spreadingx repeatabilityx reproducibilityx sunscreenx
  • Article
  • Media
  • Keywords/Abstract
  • Related Material

Keywords: In vitro SPF | automated spreading | repeatability | reproducibility | sunscreen

Abstract: Repeatability and reproducibility are crucial to validate any test method. In order to master these criteria, the authors developed an automated spreading device and compared it with human spreading. Application of the device in eight laboratories and using 36 sunscreens revealed great improvements via automated spreading, ensuring good intra- and inter-laboratory variability.

View citation for this article

S Miksa, Lutz and Guy, In Vitro UV Testing—Robot vs. Human Spreading for Repeatable, Reproducible Results, Cosm & Toil 128(10) 742 (2013)

Market Data

  • Awareness among consumers about the harmful effects of UV boosted sun care sales by 6.5% in 2012 in the United States.
  • Sun care marketers are diversifying their product offerings; a common trend emerging is to include tint.
  • Although spray-on sun care products are popular, there are rising concerns associated with the inhalation of nanoparticles.
view full article

Excerpt Only This is a shortened version or summary of the article you requested. To view the complete article, please log in or create an account. Registration is Free!

Editor’s note: This is the third article in a four-part series considering the effects of test variables on SPF results. The final article, to appear in the November 2013 issue, will consider the effects of pressure on SPF results.

Sun protection factor (SPF) is one of the most used indicators for the classification of protection levels afforded by sunscreen products against sunburn, mainly due to harmful UVB radiation (290–320 nm solar spectrum range)—and recent studies, it should be noted, have shown the importance of protection against UVA (320 nm–400 nm). SPF has historically been evaluated by in vivo methods, but in recent years, for ethical, economical and practical reasons, in vitro evaluations are being used more and more. These methods are recognized worldwide, although with significant disparity in results between, and sometimes even within, laboratories. Further, results from in vitro methods must correlate in vivo, which is challenging mainly due to the biological endpoints of tests being subject-dependant.

One advantage of in vitro methods is that, in theory, they should at the very least provide the same measurement with optimized intra- and inter-laboratory protocols. However, most would agree that this is not currently demonstrated. Indeed, in vitro methods are based on the assessment of UV transmittance through a thin film of sunscreen sample spread onto a roughened substrate, and these measurements are not yet well-controlled.

Recently validated in vitro methods have been proposed and accepted worldwide by the International Organization for Standardization (ISO) and Cosmetics Europe, formerly Colipa, but they still rely upon an in vivo value. Others use a ratio within the absorbance curve, such as the critical wavelength, as proposed by Cosmetics Europe in the European Union. The U.S. Food and Drug Administration (FDA) requires both in vivo and in vitro methods.

Unfortunately, despite all the hard work, in vitro methods for SPF assessment are still not validated due to the high variability between measurements and disparity within laboratories—even when applying a precise protocol. There is also a major problem in validating any modifications or improvements to in vitro methods, which stir continuous debates. Therefore, the reliability and reproducibility of in vitro results are key to approval and correlation—or at least to sort out reasons for no correlation—and to at last realize a reliable harmonized method. While it seems logical to consider repeatability and reproducibility as a prior condition, many studies are solely focused in vivo/in vitro correlation. Clearly, even in the case of good correlations, it is not enough if similar results between laboratories are not found.

Previous work demonstrates that several parameters must be strictly controlled in order to improve reproducibility; parameters include the amount of product applied, spreading protocol, topography properties of the substrate, and transmittance analyzer used. More recent work has identified never before-considered parameters that improve repeatability and reproducibility; i.e., pressure control during the spreading step and substrate surface temperature control throughout the application process. Until now, in vitro methods have been based on manual spreading, but it is well-known that mastering all parameters is difficult. Even when applying strict protocol, it is nearly impossible for different laboratories to produce the same results for some products.

Excerpt Only This is a shortened version or summary of the article you requested. To view the complete article, please log in or create an account. Registration is Free!

 

Close

Table 1. In vitro SPF results according to manual and automated spreading

To estimate proper reproducibility from each operator, a double-blind test was performed for two products tested three times (see Table 1, blue and orange).

Table 3. Results of coefficient of variation; intra-operator and automated spreading comparison

Table 3. Results of coefficient of variation; intra-operator and automated spreading comparison

Figure 2 and Table 3 clearly demonstrate that automated spreading varied less than the manual spreading.

Table 2. Explanation of statistical parameters (for all box and whisker plots shown)

Table 2. Explanation of statistical parameters (for all box and  whisker plots shown)

Several statistical parameters were displayed together, explained in Table 2, according to the CV studied.

Figure 1. Automated spreading by means of robotic arma

Figure 1. Automated spreading by means of robotic arm<sup>a</sup>

Automated spreading was performed by means of a device specifically developed for this purpose by the authors’ laboratory.

Figure 2. Box and whisker plots of CV variability intra-operator and automated spreading

Figure 2. Box and whisker plots of CV variability intra-operator and automated spreading

Figure 2 and Table 3 clearly demonstrate that automated spreading varied less than the manual spreading.

Figure 3. In vitro SPF results of first triplicate blind tests.

Figure 3. In vitro SPF results of first triplicate blind tests.

Concerning the two triplicate blind tests, the in vitro SPFs were slightly more reproducible when applied by the same operator, which shows that even if an operator mastered his/her spreading, while there would be repeatability, there would be differences between several laboratories (see Figures 3 and 4).

Figure 4. In vitro SPF results of second triplicate blind tests.

Figure 4. In vitro SPF results of second triplicate blind tests.

Concerning the two triplicate blind tests, the in vitro SPFs were slightly more reproducible when applied by the same operator, which shows that even if an operator mastered his/her spreading, while there would be repeatability, there would be differences between several laboratories (see Figures 3 and 4).

Figure 5. Box plots of in vitro SPF variability according to manual spreading

Figure 5. Box plots of in vitro SPF variability according to manual spreading

Thus, Figures 5 and 6 show box plots for each operator, manual and automated, and in vitro SPF values for each product.

Figure 6. Box plots of in vitro SPF variability according to automated spreading

Figure 6. Box plots of in vitro SPF variability according to automated spreading

Thus, Figures 5 and 6 show box plots for each operator, manual and automated, and in vitro SPF values for each product.

Figure 7. Repeatability and reproducibility comparison from ANOVA Gage R&R results

Figure 7. Repeatability and reproducibility comparison from ANOVA Gage R&R results

As shown in Figures 5–8, a clear improvement was observed when using automated spreading; all the products exhibited a drastic reduction of in vitro SPF variation.

Figure 8. Principal component analysis of in vitro SPF from different laboratories and automated spreading

Figure 8. Principal component analysis of in vitro SPF from different laboratories and automated spreading

As shown in Figures 5–8, a clear improvement was observed when using automated spreading; all the products exhibited a drastic reduction of in vitro SPF variation.

Footnotes (CT1310 Miksa)

a The HD-SPREADMASTER device, Helioplate HD6 PMMA plates and b HD-THERMASTER appliance are manufactured by HelioScreen.
c The Altisurf 500 lab workstation is manufactured by Altimet.
d The Labsphere UV-2000S transmittance analyzer and
e Ultraviolet Transmittance Analyzer Performance Validation Standards are manufactured and created by Labsphere Inc.
f Helioplate HD0 PMMA plates are manufactured by HelioScreen.

Next image >

 
 

Close

It's Free...

Register or Log in to get full access to this content

Registration includes:

  • Access to all premium content
  • One click ingredient sample requests
  • Save articles in the My Library tool

Create an Account or Log In