Urea
THE INS AND OUTS OF YOUR SKIN Emma Sparr Physical Chemistry Lund University
The skin - A Responding Barrier Membrane
stratum corneum (10–20 µm)
Water CO2
O2
Temperature pH 5.5
Moisturizers, Drugs etc
pH 7.4
The skin - A Responding Barrier Membrane
stratum corneum (10–20 µm)
Water
Water flux across stratum corneum versus RH (Blank et al J Invest Dermatol 1984)
RESPONDING MEMBRANE Protects from evaporation!
Responding membranes? Non-responding membrane
Responding membranes? Non-responding membrane
Responding membrane
The skin - A Responding Barrier Membrane
stratum corneum (10–20 µm)
Water
Water flux across stratum corneum versus RH (Blank et al J Invest Dermatol 1984)
RESPONDING MEMBRANE Protects from evaporation!
Water
The skin - A Responding Barrier Membrane
askin0.9 Pskin “high” SC more permeable
Stratum Corneum n=N n=N-1
”Brick & Mortar” Corneocytes in a lipid matrix
n=2
n=1
Lipid Stacked lipid bilayers
Mortar...
Scale indicator = 250 Å = 250*10-10 m
[Swartzendruber et al., J. Invest. Dermatolgy1989]
Small size domains Domain Mosaic Model (B Forslind 1994) Atomic force microscopy (AFM) on model mixtures of skin lipids
1×1 µm
(Sparr, Eriksson, Bouwstra, Ekelund., Langmuir, 2001; Ekelund, Eriksson, Sparr, BBA, 2000)
Questions • Why do we not evaporate during a dry day? • How can we understand skin occlusion? • What can “moisturizers” do to dry skin?
APPROACH Coupling between structure & transport • Model membranes
• Theoretical model
• Stratum corneum
n=N n=N-1
n=2
n=1
(Sparr, Åberg, Nilsson, Wennerström, Soft Matter 2009)
Responding membranes
Responding membranes Water
Responding membranes Water Membrane Respond to Water Gradient • Inhomogeneous swelling
Responding membranes Water Membrane Respond to Water Gradient • Inhomogeneous swelling Isothermal sorption calorimetry
sc
corneocytes lipids
|Silva, Topgaard, Kocherbitov, Pais, Sousa, Sparr, BBA 2007]
Responding membranes Water Membrane Response to Water Gradient • Inhomogeneous swelling • Phase transitions dehydration e.g. phospholipids, ceramides
Responding membranes Water Membrane Response to Water Gradient • Inhomogeneous swelling • Phase transitions Extracted skin lipids, NMR FID 35 °C
40 °C
(Silva, Topgaard, Sparr, Manuscript)
Transport in responding membranes Constant gradient in model susbtance (ex nicotine) Vary water gradient
(Sparr & Wennerström, Biophys. J. 2001)
Transport in responding membranes Constant gradient in model susbtance (ex nicotine) Vary water gradient
The water gradient regulate the barrier properties (compare skin occlusion) (Sparr & Wennerström, Biophys. J. 2001)
Water flux as a function of RH
Exp. data for stratum corneum (Blank et al J Invest Dermatol 1984)
Why do we not evaporate on a dry day? Water flux vs water gradient
6
Water flux (× 10
4
mol m-2 s-1)
Water flux (× 10 mol m-2 s-1)
RH (%) Model calculations
(Sparr & Wennerström, Biophys. J. 2001)
Exp. data for stratum corneum (Blank et al J Invest Dermatol 1984)
Responding membranes • The skin: a membrane that is exposed to several different gradients and different environments (not equilibrium!) • Stratum corneum behave as a responding membrane Cannot be described by a simple permeability but depends on the external conditions (eg hydration) • The membrane barrier properties can be regulated by an external gradient- “Switch”
Questions • Why do we not evaporate during a dry day? • How can we understand skin occlusion? • What can “moisturizers” do to dry skin?
dehydration
Fluid membranes More permeable Swell in water More flexible / elastic
Solid membranes “Impermeable” Minor swelling in water Less flexible / elastic
MOISTERIZERS & LIPID MEMBRANES dehydration
Fluid membranes More permeable Swell in water More flexible / elastic
Solid membranes “Impermeable” Minor swelling in water Less flexible / elastic
Add moisterizer; Urea or Glycerol What happens?
Lipid dehydration in the presence of urea 20
hydration Lβ’
Lα
nw/nl
15
10
5
0 0
20
40
60
RH (%)
80
100
Sorption microbalance + X-ray scattering (SAXS, WAXS)
Lipid dehydration in the presence of urea 20
hydration Lβ’
Lα
nw/nl
15
+urea
10
1 % urea
5
0 % urea 0 0
20
40
60
RH (%)
80
100
FLUID MEMBRANE PRESENT AT LOWER RH
Lipid dehydration in the presence of urea / glycerol
T (°C)
Lipid in water
40
30
20 85
90
95
100
RH (%)
Lipid dehydration in the presence of urea / glycerol T (°C) 40
T (°C) 40
30
Pure lipid
with urea 20 85
30
90
T (°C)
9 5
100 RH (%)
40 20 85
90
95
100 RH (%) 30
20
85
90
95
100 RH (%)
MOISTERIZERS & LIPID MEMBRANES dehydration
Fluid membranes More permeable Swell in water More flexible / elastic
Solid membranes “Impermeable” Minor swelling in water Less flexible / elastic
Add moisterizer; Urea or Glycerol
MOISTERIZERS & LIPID MEMBRANES • In the presence of urea or glycerol – the properties of the fully hydrated system is retained also under dehydration • Urea and glycerol “protects” the fluid membrane structure under dehydration • “Moisturizing” properties: fluid membranes that are also able to swell in water
CONCLUSIONS • The stratum corneum is a clear non-equilibrium system - Many parallel transport processes • Stratum corneum behave as a responding membrane Cannot be described by a simple permeability but depends on the external conditions (eg hydration) • Switch: The responding membrane barrier properties can be regulated by an external gradient • “Moisturizers” like urea or glycerol can “protect” the fluid membrane structure under dehydration
Acknowledgements Christoffer Åberg (Physical Chemistry, Lund) Fatima Costa-Balogh (Physical Chemistry, Lund; Dept Pharmacy, Coimbra) Stephane Douzane (Physical Chemistry, Lund; ESPCI, Paris) Håkan Wennerström (Physical Chemistry, Lund) Johan Engblom (Malmö University) Lars Wadsö (Building Materials, Lund) Claudia Silva (Dept Pharmacy, Coimbra) Daniel Topgaard (Physical Chemistry 1, Lund) Vitaly Kocherbitov (Malmö University)
Craaford foundation
Water profile of skin
No hydration
SC
Viable epidermis
Caspers et. el. J. Raman Spectrosc. 31, 813–818 (2000)
After 45 min hydration with wet bandage In vivo determination of water concentration profiles in human skin by depth-scanning confocal Raman microspectrometry
How does small polar molecules, like urea or glycerol, protect lipid membranes against osmotic stress? dehydration Urea or Glycerol Model system: DMPC, urea (or glycerol) , water Techniques: Calorimetry, X-ray scattering (SAXS+WAXS), MAS NMR, Sorption microbalance
Lipid dehydration in the presence of urea DSC DMPC, in excess water-urea Phase diagram 40 % urea
86.0 %RH
T (°C)
Endothermic
40
30 % urea
90.5 %RH
20 % urea
94.1 %RH
no urea 30
10 % urea
97.2 %RH
5 % urea
98.6 %RH
0 % urea 15
100 %RH 20
25
with urea 20 85
90
95
30
o
Temperature ( C)
(Costa-Balogh, Wennerström, Wadsö, Sparr, J. Phys. Chem. 2006)
100
RH (%)
Lipid dehydration in the presence of urea Urea - A polar molecule with low vapor pressure • Urea “replaces” water in an almost ideal way Retains the properties of the fully hydrated system • Urea “protects” the liquid crystalline phase upon dehydration
T (°C) 40
no urea 30
with urea 20 85
90
95
100
RH (%)
CONCLUSIONS • The stratum corneum is a clear non-equilibrium system - Many parallel transport processes • The membrane barrier properties can be regulated by an external gradient - Switch - A possible explanation for non-linear transport behavior in stratum corneum • Transport of water and CO2 across the bilayer membrane can give rise to a pH gradient • Urea can “replace” water and “protect” the fluid structures possible mechanism also for skin care products and urea naturally present in the stratum corneum.
Acknowledgements Christoffer Åberg (Physical Chemistry 1, Lund) Fatima Costa-Balogh (Physical Chemistry 1, Lund; Dept Pharmacy, Coimbra) Cécile Pairin (Physical Chemistry 1, Lund; ENSCP Paris) Lars Wadsö (Building Materials, Lund) Håkan Wennerström (Physical Chemistry 1, Lund)
Stratum corneum lipids Sorption calorimetry
SC lipids sc Δhw corneocytes Δµw lipids • Swelling of both lipids and corneocytes • Exothermic transitions in SC lipids at 91-94 %RH (Silva, Topgaard, Kocherbitov, Pais, Sousa, Sparr, BBA 2007)
MODEL SYSTEM Phospholipid (DMPC) and urea • The overall phase behavior is hardly affected by the presence of urea • Urea replaces the water in an almost ideal way
Replace water by urea lamellar repeat distance
(Costa-Balogh, Wennerström, Wadsö, Sparr (2006) J Phys Chem B)
Lipid dehydration in the presence of urea 20
20 % urea hydration Lβ’
15
+urea
10 % urea
Lα
1 % urea 10
0 % urea 5
0 0
20
40
60
80
100
Urea “protects” liquid crystalline (Lα) phase upon dehydration Sorptionthe microbalance + X-ray scattering (SAXS, WAXS) (Costa-Balogh, Wennerström, Wadsö, Sparr, J. Phys. Chem. 2006)
Cell membrane
Stratum corneum
LIPID MEMBRANE
Alveolar membrane
Drug delivery system
Temperature-induced transition DMPC in excess urea-water solution
20 % urea 20 C 25 C
20 C 25 C Tm Lβ’
Lα
• The overall phase behavior is hardly affected by the presence of urea • The weakening of hydrophobic interactions caused by urea is by far not sufficient to solubilize / disturb the lamellar phases (compare protein denaturation)
The skin - A Responding Barrier Membrane
stratum corneum (10–20 µm)
Water CO2
O2
Temperature pH 5.5
Moisturizers, Drugs etc
pH 7.4
The skin - A Responding Barrier Membrane
stratum corneum (10–20 µm)
Water
Water flux across stratum corneum versus RH (Blank et al J Invest Dermatol 1984)
RESPONDING MEMBRANE Protects from evaporation!
Responding membranes? Non-responding membrane
Responding membranes? Non-responding membrane
Responding membrane
The skin - A Responding Barrier Membrane
stratum corneum (10–20 µm)
Water
Water flux across stratum corneum versus RH (Blank et al J Invest Dermatol 1984)
RESPONDING MEMBRANE Protects from evaporation!
Water
The skin - A Responding Barrier Membrane
askin0.9 Pskin “high” SC more permeable
Stratum Corneum n=N n=N-1
”Brick & Mortar” Corneocytes in a lipid matrix
n=2
n=1
Lipid Stacked lipid bilayers
Mortar...
Scale indicator = 250 Å = 250*10-10 m
[Swartzendruber et al., J. Invest. Dermatolgy1989]
Small size domains Domain Mosaic Model (B Forslind 1994) Atomic force microscopy (AFM) on model mixtures of skin lipids
1×1 µm
(Sparr, Eriksson, Bouwstra, Ekelund., Langmuir, 2001; Ekelund, Eriksson, Sparr, BBA, 2000)
Questions • Why do we not evaporate during a dry day? • How can we understand skin occlusion? • What can “moisturizers” do to dry skin?
APPROACH Coupling between structure & transport • Model membranes
• Theoretical model
• Stratum corneum
n=N n=N-1
n=2
n=1
(Sparr, Åberg, Nilsson, Wennerström, Soft Matter 2009)
Responding membranes
Responding membranes Water
Responding membranes Water Membrane Respond to Water Gradient • Inhomogeneous swelling
Responding membranes Water Membrane Respond to Water Gradient • Inhomogeneous swelling Isothermal sorption calorimetry
sc
corneocytes lipids
|Silva, Topgaard, Kocherbitov, Pais, Sousa, Sparr, BBA 2007]
Responding membranes Water Membrane Response to Water Gradient • Inhomogeneous swelling • Phase transitions dehydration e.g. phospholipids, ceramides
Responding membranes Water Membrane Response to Water Gradient • Inhomogeneous swelling • Phase transitions Extracted skin lipids, NMR FID 35 °C
40 °C
(Silva, Topgaard, Sparr, Manuscript)
Transport in responding membranes Constant gradient in model susbtance (ex nicotine) Vary water gradient
(Sparr & Wennerström, Biophys. J. 2001)
Transport in responding membranes Constant gradient in model susbtance (ex nicotine) Vary water gradient
The water gradient regulate the barrier properties (compare skin occlusion) (Sparr & Wennerström, Biophys. J. 2001)
Water flux as a function of RH
Exp. data for stratum corneum (Blank et al J Invest Dermatol 1984)
Why do we not evaporate on a dry day? Water flux vs water gradient
6
Water flux (× 10
4
mol m-2 s-1)
Water flux (× 10 mol m-2 s-1)
RH (%) Model calculations
(Sparr & Wennerström, Biophys. J. 2001)
Exp. data for stratum corneum (Blank et al J Invest Dermatol 1984)
Responding membranes • The skin: a membrane that is exposed to several different gradients and different environments (not equilibrium!) • Stratum corneum behave as a responding membrane Cannot be described by a simple permeability but depends on the external conditions (eg hydration) • The membrane barrier properties can be regulated by an external gradient- “Switch”
Questions • Why do we not evaporate during a dry day? • How can we understand skin occlusion? • What can “moisturizers” do to dry skin?
dehydration
Fluid membranes More permeable Swell in water More flexible / elastic
Solid membranes “Impermeable” Minor swelling in water Less flexible / elastic
MOISTERIZERS & LIPID MEMBRANES dehydration
Fluid membranes More permeable Swell in water More flexible / elastic
Solid membranes “Impermeable” Minor swelling in water Less flexible / elastic
Add moisterizer; Urea or Glycerol What happens?
Lipid dehydration in the presence of urea 20
hydration Lβ’
Lα
nw/nl
15
10
5
0 0
20
40
60
RH (%)
80
100
Sorption microbalance + X-ray scattering (SAXS, WAXS)
Lipid dehydration in the presence of urea 20
hydration Lβ’
Lα
nw/nl
15
+urea
10
1 % urea
5
0 % urea 0 0
20
40
60
RH (%)
80
100
FLUID MEMBRANE PRESENT AT LOWER RH
Lipid dehydration in the presence of urea / glycerol
T (°C)
Lipid in water
40
30
20 85
90
95
100
RH (%)
Lipid dehydration in the presence of urea / glycerol T (°C) 40
T (°C) 40
30
Pure lipid
with urea 20 85
30
90
T (°C)
9 5
100 RH (%)
40 20 85
90
95
100 RH (%) 30
20
85
90
95
100 RH (%)
MOISTERIZERS & LIPID MEMBRANES dehydration
Fluid membranes More permeable Swell in water More flexible / elastic
Solid membranes “Impermeable” Minor swelling in water Less flexible / elastic
Add moisterizer; Urea or Glycerol
MOISTERIZERS & LIPID MEMBRANES • In the presence of urea or glycerol – the properties of the fully hydrated system is retained also under dehydration • Urea and glycerol “protects” the fluid membrane structure under dehydration • “Moisturizing” properties: fluid membranes that are also able to swell in water
CONCLUSIONS • The stratum corneum is a clear non-equilibrium system - Many parallel transport processes • Stratum corneum behave as a responding membrane Cannot be described by a simple permeability but depends on the external conditions (eg hydration) • Switch: The responding membrane barrier properties can be regulated by an external gradient • “Moisturizers” like urea or glycerol can “protect” the fluid membrane structure under dehydration
Acknowledgements Christoffer Åberg (Physical Chemistry, Lund) Fatima Costa-Balogh (Physical Chemistry, Lund; Dept Pharmacy, Coimbra) Stephane Douzane (Physical Chemistry, Lund; ESPCI, Paris) Håkan Wennerström (Physical Chemistry, Lund) Johan Engblom (Malmö University) Lars Wadsö (Building Materials, Lund) Claudia Silva (Dept Pharmacy, Coimbra) Daniel Topgaard (Physical Chemistry 1, Lund) Vitaly Kocherbitov (Malmö University)
Craaford foundation
Water profile of skin
No hydration
SC
Viable epidermis
Caspers et. el. J. Raman Spectrosc. 31, 813–818 (2000)
After 45 min hydration with wet bandage In vivo determination of water concentration profiles in human skin by depth-scanning confocal Raman microspectrometry
How does small polar molecules, like urea or glycerol, protect lipid membranes against osmotic stress? dehydration Urea or Glycerol Model system: DMPC, urea (or glycerol) , water Techniques: Calorimetry, X-ray scattering (SAXS+WAXS), MAS NMR, Sorption microbalance
Lipid dehydration in the presence of urea DSC DMPC, in excess water-urea Phase diagram 40 % urea
86.0 %RH
T (°C)
Endothermic
40
30 % urea
90.5 %RH
20 % urea
94.1 %RH
no urea 30
10 % urea
97.2 %RH
5 % urea
98.6 %RH
0 % urea 15
100 %RH 20
25
with urea 20 85
90
95
30
o
Temperature ( C)
(Costa-Balogh, Wennerström, Wadsö, Sparr, J. Phys. Chem. 2006)
100
RH (%)
Lipid dehydration in the presence of urea Urea - A polar molecule with low vapor pressure • Urea “replaces” water in an almost ideal way Retains the properties of the fully hydrated system • Urea “protects” the liquid crystalline phase upon dehydration
T (°C) 40
no urea 30
with urea 20 85
90
95
100
RH (%)
CONCLUSIONS • The stratum corneum is a clear non-equilibrium system - Many parallel transport processes • The membrane barrier properties can be regulated by an external gradient - Switch - A possible explanation for non-linear transport behavior in stratum corneum • Transport of water and CO2 across the bilayer membrane can give rise to a pH gradient • Urea can “replace” water and “protect” the fluid structures possible mechanism also for skin care products and urea naturally present in the stratum corneum.
Acknowledgements Christoffer Åberg (Physical Chemistry 1, Lund) Fatima Costa-Balogh (Physical Chemistry 1, Lund; Dept Pharmacy, Coimbra) Cécile Pairin (Physical Chemistry 1, Lund; ENSCP Paris) Lars Wadsö (Building Materials, Lund) Håkan Wennerström (Physical Chemistry 1, Lund)
Stratum corneum lipids Sorption calorimetry
SC lipids sc Δhw corneocytes Δµw lipids • Swelling of both lipids and corneocytes • Exothermic transitions in SC lipids at 91-94 %RH (Silva, Topgaard, Kocherbitov, Pais, Sousa, Sparr, BBA 2007)
MODEL SYSTEM Phospholipid (DMPC) and urea • The overall phase behavior is hardly affected by the presence of urea • Urea replaces the water in an almost ideal way
Replace water by urea lamellar repeat distance
(Costa-Balogh, Wennerström, Wadsö, Sparr (2006) J Phys Chem B)
Lipid dehydration in the presence of urea 20
20 % urea hydration Lβ’
15
+urea
10 % urea
Lα
1 % urea 10
0 % urea 5
0 0
20
40
60
80
100
Urea “protects” liquid crystalline (Lα) phase upon dehydration Sorptionthe microbalance + X-ray scattering (SAXS, WAXS) (Costa-Balogh, Wennerström, Wadsö, Sparr, J. Phys. Chem. 2006)
Cell membrane
Stratum corneum
LIPID MEMBRANE
Alveolar membrane
Drug delivery system
Temperature-induced transition DMPC in excess urea-water solution
20 % urea 20 C 25 C
20 C 25 C Tm Lβ’
Lα
• The overall phase behavior is hardly affected by the presence of urea • The weakening of hydrophobic interactions caused by urea is by far not sufficient to solubilize / disturb the lamellar phases (compare protein denaturation)
