18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis by Raman spectroscopy
PROTECTION AGAINST
MICROORGANISMS,
CHEMICALS,
ALLERGENS,
POLLUTANTS,…
Gerwin Puppels, Claudio Nico, Johanna de Sterke, Paul Pudney,* Peter Caspers*Unilever Research Port Sunlight, UK
Analysis of skin penetration / permeation
18 Sept 2019, OEESC, Dublin
Outline
18 Sept 2019, OEESC, Dublin
Raman spectroscopy & in vivo skin analysis
Non-invasive analysis of the penetration of topically applied materials
Quantification Concentration (mg/cm3)
Total uptake (mg/cm2)
Flux (mg/cm2.h)
Example: retinol
Applications
molecular composition of the skin - spatially resolved
SC
living
epidermis
25%
70%
H2O
penetration
of topically
applied
materials
UV, season
nmf
age, body site, response to challenges, ….
Raman spectroscopy & in vivo skin analysis
18 Sept 2019, OEESC, Dublin
O C O O C O
Raman spectroscopy & in vivo skin analysis
18 Sept 2019, OEESC, Dublin
500 1000 1500 2000
lactate
blood
glycogen
Fatty acid
cholesterol
RNA
DNA
elastin
collagen
Dcm-1
20 mm
Proteins
DNA
Sugars
Lipids
RNA
Raman spectroscopy & in vivo skin analysis
18 Sept 2019, OEESC, Dublin
Interpretation of spectra
Raman spectrum of stratum corneum
Signal contributions of:
Proteins
amino acids
sweat constituents
lipids
water
Raman spectroscopy & in vivo skin analysis
18 Sept 2019, OEESC, Dublin
in vivo skin
400 600 800 1000 1200 1400 1600 1800
Inte
nsi
ty
Raman shift, cm-1
fit-result
residual
Raman spectroscopy & in vivo skin analysis
18 Sept 2019, OEESC, Dublin
skin
window
laser
dermis
SC
epidermis
500 1000 1500
distance to skin
surface
co
nce
ntr
ation
skin surface
Raman spectroscopy & in vivo skin analysis
18 Sept 2019, OEESC, Dublin
Raman spectroscopy & in vivo skin analysis
18 Sept 2019, OEESC, Dublin
0 20 40 60 80 100 120 140 160 180 2000
10
20
30
40
50
60
70
80
depth (micron)
wat
er (
mas
s-%
)
Raman spectroscopy & in vivo skin analysis
18 Sept 2019, OEESC, Dublin
skin characterization
• skin typing
• age related effects
• seasonal effects
• skin conditions
• skin lesions
Topically applied products
penetration & permeation of:•drugs
•personal care actives •perfumes (fragrances)
•chemicals
Raman spectroscopy & in vivo skin analysis
SC ED
0 10 20 30
productconcentration
Distance to skin surface (μm)
product
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
in vivo skin
400 600 800 1000 1200 1400 1600 1800
Inte
nsi
ty
Raman shift, cm-1
fit-result
residual
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
skin
400 600 800 1000 1200 1400 1600 1800
Inte
nsi
ty
Raman shift, cm-1
fit-result
residual
SC EDproduct
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
RA ~ ρA
~ Ilaser
~ f(Ω,V)
• RA: intensity of the Raman signal of a compound A [photons/s]
• gA: concentration of compound A in the measurement volume V [kg/m3]
• Ilaser: laser light intensity [J/s]
• V: measurement volume [m3]
• Ω: measurement configuration
• kA: proportionality constant (property of compound A)
RA = kA . Ilaser . f(Ω,V) . gA
= CA(Ilaser,Ω,V) . ρA
homogeneous medium: compound A in solution
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
z
Skin: an inhomogeneous medium
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
z
The skin is an inhomogeneous medium
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
Quantification of skin penetration of products
z
The skin is an inhomogeneous medium
•RA
RB= CA/B .
gAgB
gA = RA
RB
.1
CA/B. gB
• gprotein,skin(z)
the protein concentration in the skin can be estimated from water concentration profiles in the skin
Quantification of skin penetration of products
Eliminating unknowns
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
z 0 20 40 60 80 100 120 140 160 180 2000
10
20
30
40
50
60
70
80
Distance z to skin surface (µm)
wat
er (
mas
s-%
)
sc epidermis dermis
• mass-fractionwater,skin = 0.25 - 0.65 (SC)
• mass-fractionwater,skin = 0.65 - 0.70 (epidermis)
• mass-fractionwater,skin = 0.70 – 0.75 (dermis)
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
z 0 20 40 60 80 100 120 140 160 180 2000
10
20
30
40
50
60
70
80
Distance z to skin surface (µm)
dry
mas
s (m
ass-
%)
sc epidermis dermis
density dry SC = 1.15 g/cm3
60% protein;
15% lipids;
20 - 30% natural moisturizing factor
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
Quantification of skin penetration of products
z
• ρA(z) = RA(z)
Rprotein(z).
1CA/protein
. ρprotein,skin(z)
1.RA(z)
Rprotein(z): from skin Raman spectra
2. CA/protein : from calibration experiments
3. ρprotein,skin(z) : from water concentration profiles
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
Proportionality constants Cmaterial:solvent
Cmaterial:solvent = (Rmaterial / Rsolvent) / (mmaterial / msolvent)
Cretinol:protein = Cretinol:ethanol . Cethanol:water / Cprotein:water
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
• 0.3% retinol in 70% ethanol – 30% PG
• Volar forearm
• 70 ml on skin area of 4 x 4 cm2
• 10 min
distance to skin surface (mm)
con
cen
trat
ion
(m
g /
cm3)
0 5 10 15 20 250
2
44
6
8
10
12
amo
un
t in
SC
(m
g /
cm2)
1
2
3
4
5
6
7
8
0
time (h)
1 2 3 4 5 6
Flux: 0.6 mg/cm2.h
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
distance to skin surface (mm)
con
cen
trat
ion
(m
g /
cm3)
0 5 10 15 20 25
amo
un
t in
SC
(m
g /
cm2)
50
100
150
200
250
300
0
time (h)
1 2 3 4 5 6
Flux: 8 mg/cm2.h
50
100
150
200
250
300
0
350
400
18 Sept 2019, OEESC, Dublin
Skin penetration of chemicals: quantitative in vivo analysis
• retinol
• max. retinol concentration in SC ≃ retinol concentration in formulation after evaporation of ethanol
• 40% of applied dose detected in the skin
• After 6 hrs: 75% skin
• propylene glycol
• 16% of applied dose detected in the skin
• After 6 hrs: 20% skin
Skin penetration of chemicals: quantitative in vivo analysis
Skin penetration of topically applied materials
• In vivo Raman spectroscopy can provide• Qualitative information
• Did a material penetrate into the skin?
• How far into the skin?
• How fast?
• How long does it stay in the skin?
• Semi-quantitative information
• Comparison of efficiency of delivery of an active for different formulations.
• Comparison of delivery for different application times
• …
• Quantitative information
• How much penetrated into the skin (µg.cm-2)?
• What is the flux into the skin (µg/s-1.cm-2)?
18 Sept 2019, OEESC, Dublin