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Efficacy Methodology and Assessment of Cosmetics
R. Randall Wickett University of Cincinnati College of Pharmacy
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Outline of Topics Non-invasive measurements of skin function
Transepidermal Water Loss Electrical Measurements Mechanical Measurements Skin Color Surface Analysis Protocols for Efficacy Assessment Moisturizer Efficacy Cleanser Mildness Anti-aging products
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Utility of Non-invasive Bioengineering Measurements
Why not just rely on visual grading? Grading is not “objective” Grading is not “reproducible” at an exact level. Agreement within ± 0.5 grades units is considered very good. Bioengineering Tools can give additional information. For instance visual grades will not necessarily tell you if skin is more or less elastic or if the skin barrier is perturbed. Bioengineering measurements can be used to support claims and for guiding the product development process Training and experience are required to obtain valid and reproducible bioengineering measurements
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Ronald Marks, M.D. One of the “Godfathers” of bioengineering measurement on skin Organized the first symposium on noninvasive methods and the skin in 1976 and founded ISBS
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Albert M. Kligman, M.D. A fool with a tool is still a fool
Another Godfather of Skin Bioengineering – first talked about the possibility of admitting a “blind person” as a dermatology resident. A fool with a tool is still a fool
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General Considerations for non-invasive measurements on skin
There are no published standard protocols similar to ASTM (American Society for Testing Materials) “Guidances” are published by EEMCO (European group on Efficacy Measurements of COsmetics and other topical products) for various categories of methods
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General Recommendations for instrumental measurements on Skin
Some control of testing environment is necessary to prevent sweating Normally 20 ± 1 C, 30-45% RH Subjects should equilibrate 30 minutes if possible Subjects should avoid drinking hot coffee or tea or eating for at least 1 hour prior to measurement Subjects should avoid uncontrolled use of cosmetic products on the measurement sites for at least 1 week prior to measurement Subjects with any obvious skin disease, tattoos or injury in the treatment area will be excluded.
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Transepidermal Water Loss
Water transport through the skin by passive diffusion Rate is 5-10 g/m2/hr in healthy skin Increases with surfactant damage Used to measure occlusion by products Used extensively in barrier disruption and repair studies Panelists must not be sweating. Equilibrate 30 min. at ~21C RH<50%
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The Dermalab Evaporimeter
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The C+K devices Corneometer probe Cutometer probe TEWA Meter probe
Sebumeter
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The operating principle of open chamber TEWL devices
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Forearm Controlled Application Test (FCAT)
Lather wetted bar for 6 seconds with Masselin towel Transfer lather to site and wash for 10 seconds Leave lather in place 90 seconds Rinse for 20 seconds Repeat 4X daily for one week
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Forearm washing
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Washing and rinsing
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Forearm wash test bars Bar 1 mild syndet + oatmeal
Bar 4 Soap pure soap Bar 5 Soap + humectant
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Measuring TEWL after a forearm wash test
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TEWL: Forearm wash test
RR Wickett, Forearm wash testing of mild soap bars containing colloidal oatmeal, Canadian Chemical News, 49(1), (1997).
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Redness grade versus TEWL: Forearm Wash Test
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Electrical Measurements of Skin
Skin lipids have a low dielectric constant, water has a high dielectric constant. When skin is hydrated conductance and capacitance (reactance) increase and impedance decreases. Used to estimate water content of stratum corneum.
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The NOVA DPM
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The Skicon
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Correlation with dry skin grades
Dry skin is lacking in moisture. Several studies have shown that electrical measurements correlate with dry skin grades as expected Morrison and Scala correlated Correlated Corneometer and Skicon readings to flaking grades on dry hands scores that developed as subjects washed their hands for 1 minute five times a day for 4 days. We also have data on correlation of readings of all three instruments to dry skin grades on the legs.
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Correlation between Flake Grade and Corneometer CM 820 values
Morrison and Scala(1996) J. Toxicol-Cut.& Ocular Toxicol, 15:
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Skicon versus mean flaking grade
Morrison and Scala(1996) J. Toxicol-Cut.& Ocular Toxicol, 15:
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Grading scale for dry skin, half grades are allowed
Description No scaling 1.0 Slight powdery appearance and occasional patches of small scales widely distributed 2.0 Small scales in combination with a few larger scales, slight roughness, whitish appearance 3.0 Small and large scales uniformly distributed, definite roughness and possible a few superficial cracks 4.0 Dominated by large scale, rough, redness present and eczematous changes F Li, MO Visscher, E Conroy and RR Wickett, J. Cosmet. Sci. 52, (2001).
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Scatter plot of Skicon reading versus Dry Skin Grade
R. R. Wickett and F. Li Unpublished Data
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Average values versus dry skin grades Skicon and Corneometer
R. R. Wickett and F. Li Unpublished Data
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Average values versus dry skin grades NOVA meter
R. R. Wickett and F. Li Unpublished Data
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Brancaleon et al. correlated Skicon readings with ATR-FTIR measurements of water in the SC. “Our attempt to link the hydration measured with ATR-FTIR to the hydration measured with the Skicon hygrometer shows a high degree of correlation. This is not unexpected as both instruments record superficial hydration.”
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Correlations among instrumental measurements
F. Li, et. Al J. Cosmet. Sci. 52, 13-22(2001).
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Correlations between instruments
Clarys et. al. Fluhr et. al. Our work* NOVA vs Skicon NOVA vs. CM Skicon vs. CM Clarys, P., et al Skin Res Technol, 5, 14(1999). Fluhr, J. W., et al Skin Res. and Technol., 5, 171 (1999). Li, F. et al J. Cosmet Sci 52, (2001)
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Electrical measurements and moisturizer claims
For more than 20 years electrical measurements made within 30 minutes to a few hours of treatment have been used to substantiate claims of moisturizing efficacy. We have reported that measurements made at one hour predicted moisturizing in a two week test for formulations containing glycerin from 0 to 15% concentration. (Li et al J Cosmetic Science, January 2001)
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Effect of moisturizers on DPM (Formulations from ~ 1990)
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Correlation Test One hour Test: 9 subjects Two week test: 20 subjects
Goal determine the correlation between one hour device readings and effects on skin grades in a dry skin test: One hour Test: 9 subjects Two week test: 20 subjects subjects were female, between the ages of 18 and 57 and in good general health with no known skin diseases. Products contained 0, 5, 10 and 15% Glycerin in identical base Each subject used each of the 4 products on their legs
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DEVICE PREDICTION CAPABILITY: SKICON
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Regression equations of one week skin grade versus one hour electrical measurements
Device Regression equation R-square p NOVA G = x 0.92 0.04 SKICON G = x 0.97 0.02 CM 825 G = x+ 0.76 0.84 0.08 We do not consider the difference between instruments to be meaningful.
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Conclusion Single point or short term electrical measurements have been shown to be predictive of long term moisturization for simple formulations using on Glycerin as a moisturizer. F Li, MO Visscher, E Conroy and RR Wickett, J. Cosmet. Sci. 52, (2001).
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Mechanical Properties of Skin
There are two fundamental ways to measure the mechanical properties of an object Apply a known strain and measure the stress Apply a known stress and measure the strain Most skin instruments use the second approach
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The Cutometer 575
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The Cutometer probe An optical system is used to measure the height that the skin rises into the probe
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The optical system of the Cutometer
Picture courtesy of Courage + Khazaka GmbH
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The Cutometer 575 probe
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Cutometer curves
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Cutometer Parameters UE is the elastic deformation of the skin due to the application of stress (vacuum or torque) by the instrument; UV is the viscoelastic creep occurring after the elastic deformation; UF is the total extensibility of the skin; UR is the elastic deformation recovery due to stress removal; UA is the total deformation recovery at the end of the stress-off period; R is the amount of deformation not recovered by the end of the stress-off period
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Cutometer curves
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An illustration of the Cutometer curve and analysis (from C+K)
See RR Wickett, Stretching the Skin Surface Cosmetics and Toiletries 116(3), 47-54(2001) for details of Cutometer and DTM analysis
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Ratio Parameters UA/UF is the overall elasticity of the skin including creep and creep recovery; UR/UE is the pure elasticity ignoring viscoelastic creep; UV/UE is the ratio of viscoelastic to elastic extension called the viscoelastic ratio; UR/UF is the ratio of elastic recovery to total deformation.
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Issues with mechanical measurements
What part of the skin are we measuring? General principle: to measure the stratum corneum use the smallest feasible deformation To measure the dermis use a larger deformation Interpretation of data For moisturization we can look increased Ue and Ur reflecting increased elasticity. Many anti-aging treatments claim “firmness” but there is no engineering definition of firmness
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Extensibility of shoulder skin v. age Cutometer Uf 6 mm diameter probe
Smalls LK, Wickett RR, Visscher M, Effect of Dermal Thickness, Tissue Composition, and Body Site on Skin Biomechanical Properties, Skin Research and Technology, (2006) Lola Kelly Smalls Ph.D. dissertation University of Cincinnati
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Effect of vacuum level on Cutometer sensitivity to 1 week of treatment with a moisturizer with limited efficacy Parameter Pre-treat Post-Treat P-value NOVA DPM 98.8 116.2 0.001 Ue (200) 0.036 0.048 0.02 Ue (500) 0.068 0.079 0.46 Uv (200) 0.015 0.024 0.07 Uv (500) 0.025 0.029 0.60 Ur (200) 0.026 0.039 0.03 Ur (500) 0.050 0.061 0.26 Wickett, RR (2001) Cosmetics and Toiletries 116, 47-54
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D’Squames® are an easy way in investigate skin scaling and flaking
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They can be graded visually or analyzed by computer
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The computer can calculate the Desquamation index (D.I.)
A = percent area covered by scales Tn = percentage of scale at each thickness level n = thickness level 1 to 5 Schatz, et al. J. Soc Cosmet. Chem. 44, 53-63, 1993
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Warrier(1996) et al J. Soc. Cosmet. Chem. 47, 229-240
We found blacks to have higher visual dryness scores than whites, especially on legs Warrier(1996) et al J. Soc. Cosmet. Chem. 47,
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Warrier(1996) et al J. Soc. Cosmet. Chem. 47, 229-240
D.I. showed the opposite Warrier(1996) et al J. Soc. Cosmet. Chem. 47,
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The Minolta Chromameter
Color is measured on the L* a* b* scale. L* = white 0 to 100 a* = red – green 60 to –60 b* = blue – yellow –60 to 60
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Using the Chromameter
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The color wheel
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The color solid
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Minolta a* in forearm wash test
RR Wickett, Canadian Chemical News, 49(1), (1997).
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Correlation between a* and erythema grade in the FCAT
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Chromameter L values for various ethnic groups
Alaluf et al (2002) Pigment Cell Res.
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Analysis of skin surface texture Silicone replicas are most commonly used
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Obtaining a replica from the peri-orbital (crows foot) area
Photo courtesy of Ken Marenus
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Image analysis can quantify wrinkle depth by the shadow principle
Corcuff et. Al. JSCC (1983)
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Replicas of young and old forearm skin montage
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Replicas from the “crows foot” area of the eye
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Crow’s foot wrinkle depth versus age
Corcuff et. Al. JSCC (1983)
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Visiometer Replicas are died blue
Light transmission is measured to determine the depth of the lines
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Visiometer
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Microrelief of the skin determined by the visiometer
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Fringe Projection (PRIMOS)
Phase Shifting Rapid In vivo Measurement of Skin Digital micromirror device used to project fringe pattern on the skin surface CCD camera records image Shifting of the fringe patterns by surface contour allows 3D imaging
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Primos measurement on the face
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Distortion of fringes by wrinkles
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Grey scale coded 3D image
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Line profile from the Primos
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The VISIA imaging system by Canfield allows for capture of high quality images of the face using different types of light Image analysis can be performed to pick out hyperpigmented spots and other features of photoaging
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Image of face with spots highlighted
Photo courtesy of Greg Hillebrand, used with permission
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Moisturizer Testing Regression and “mini” regression tests
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Regression testing of moisturizers
The ‘Gold Standard’ test of moisturizer efficacy Three weeks of treatment followed by two weeks of regression The goal is to separate out the visual effects of the product and show only the real effect on skin physiology Better moisturizers will be better in the regression phase Kligman, Cosmetics and Toiletries April Rogers et al JAAD (1989)
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Regression test with Petrolatum
Kligman, Cosmetics and Toiletries April
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Regression test with “Cosmetic” and “Therapeutic” Moisturizers
From Rawlings et al Derm Ther (2004)
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Pretreatment The ‘mini’ regression test: One or two week treatment phase, one week to a few days regression. By comparing products on the same panelist and using instruments better sensitivity can be achieved with fewer subjects and a shorter treatment time.
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End of treatment End of Regression
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Grove has used 4 day “mini-regression” protocols with grading and conductance measurements on dry legs Products applied to 2x2 cm area by trained staff Conductance measured with Skicon 19 female subjects Two week washout Lotions separated in conductance readings but were not significantly different by skin grade G. Grove et al poster presentation product names removed used with permission
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Rawlings combined visual dryness with Corneometer readings in a 3 day mini regression test
Rawlings et al Derm Ther (2004)
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Testing “Ant-Aging” products
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Clinical Features of Photo-Aging
Lines and Wrinkles Loss of Elasticity Elasticity becomes more anisotropic Appearance of “Age Spots”
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Methods for evaluation of anti-aging products
Clinical grading directly on panelists Grading of high quality clinical photographs Analysis of replicas Mechanical measurements Primos system to analyze wrinkles VISIA System Biopsies to evaluate changes in dermal histology
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Descriptive grading scale for photoaging
Griffiths et. Al. (1992) Arch Dermatol.;128:
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Photographic Grading Scales
There are several different photographic grading scales Griffiths et. Al. (1992) Arch Dermatol.;128: Larnier et. Al. (1994) Brit. J. Dermatol Chung (2003)Photodermatol Photoimmunol Photomed 19: 109–121
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The grading scale by Griffiths et. Al
The grading scale by Griffiths et. Al. is probably the most commonly used.
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The Larnier scale 4 -6
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Chung’s scale with Korean subjects
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Anti-Aging Studies: General Considerations
Anti-aging effects take time to demonstrate. Studies usually run for about 24 weeks and 12 weeks seems to be a minimum. Facial studies are usually monadic. That is each subject tests only one product. Studies on forearms may be done as paired comparisons. Studies must be done double blind. Vehicle (placebo) Effects can be quite large. Moisturizing vehicles will produce noticeable effects on fine wrinkles and avoiding sun will improve grades.
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A reason for not doing split-face studies on anti-aging products
I’ve been part of a 15 year study on sunscreens. Every day I put SPF 30 on one side of my body and nothing on the other side
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Outline for anti-aging test on facial product
60 female subjects with moderate photodamage on the face. Randomized or balanced into two groups of 30, active and vehicle or placebo. Subjects and graders/measurement technicians are blind to the treatment Treatment is to whole face Forearms are also treated for biopsies Measurements made at baseline and after 3 and 6 months of treatment.
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Measurements anti-aging test
Grading. Clinical photographs or VISIA system. Cutometer readings on cheek. Replicas taken from crows foot area of eye for image analysis or PRIMOS measurements made in eye area. Biopsies taken from forearm at baseline and 6 months only for collagen and elastin measurement (this is definitely optional)
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Minimum requirements The test I have described could be called a Cadillac test as it has a lot of options At the minimum grading and clinical photographs should be obtained. Some studies run for only 3-4 months and occasionally they are done split face Pilot studies may be done on photodamage forearms using both male and female subjects and in this case one arm will get vehicle and the other treatment.
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