Hair Hydration Measurements Using Opto-thermal Radiometry and AquaFlux

aFaculty of ESBE, London South Bank University, 103 Borough Road, London SE1 0AA, UK

bBiox Systems Ltd, 103 Borough Road, London SE1 0AA, UK

Perry Xiaoab and RE Imhofb

Opto-Thermal Transient Emission Radiometry (OTTER)

Pulsed Laser ExcitationPulsed Laser Excitation Infrared Emission SignalInfrared Emission Signal

SampleSample

tt tt

9.5µm9.5µm13.1µm13.1µm

Heat

AirAir

Thermal diffusivity, D (m2s-1)

Absorption coefficient to excitation light, (m-1)

Absorption coefficient to emission light, (m-1)

Layer structure

Opto-Thermal Skin Measurements

Opto-Thermal Delayed Thermal Wave (DTW) Measurements

Opto-thermal delay time t=L2/(D)

L : Epidermis thickness

D: Epidermis thermal diffusivity

SkinSkin

Stratum Stratum

CorneumCorneum

EpidermisEpidermis

DermisDermis

Heat absorbed byHeat absorbed by

melanin &melanin &

HaemoglobinHaemoglobin

LL

OPO Laser

420 ~ 590nm

Thermal Delayed Signal

AirAirTime /ms

Inte

ns

ity

/a

rb A

C

B

Time /ms

Inte

ns

ity

/a

rb A

C

B

Opto-Thermal Skin Measurements

Infrared Infrared Emission SignalEmission Signal

Er:YAG 2.94µmEr:YAG 2.94µm

Stratum Stratum CorneumCorneum

EpidermisEpidermis

DermisDermis

Heat absorbed byHeat absorbed bywaterwater

AirAir

SkinSkin

S t Ae erfc tt( ) //

Opto-Thermal Skin Measurements

Stratum CorneumStratum Corneum EpidermisEpidermis

HydrationHydration HydrationHydration

Stratum CorneumStratum Corneum EpidermisEpidermis airair

HH00

HH00

HH11

LL

S t A

W t

Wt

Wte erfc

t

Wt

t

Wt

( )( )

( )(

/)

/

2

2 1

1

2 1 2 132 1

S t A e erfc tt( ) ( / )/

1 2/ D 1 0

2/ D W wD

Uniform Model Gradient ModelUniform Model Gradient Model

Opto-Thermal Skin Measurements

1 2 3 4 5 6 7 8 9 10 11 12a

b

c0

0.2

0.4

0.6

0.8

1

1.2

1.4

Surface Lifetime

/ms

Row

1.2-1.4

1-1.2

0.8-1

0.6-0.8

0.4-0.6

0.2-0.4

0-0.2Wrist

Elbow

1 2 3 4 5 6 7 8 9 10 11 12a

b

c0

200

400

600

800

1000

1200

1400

1600

Effective Gradient

/s-1

Row

1400-1600

1200-1400

1000-1200

800-1000

600-800

400-600

200-400

0-200Wrist

Elbow

12

34

56

78

910

1112

a

b

c

0

10

20

30

40

50

60

70

Th

ick

ne

ss

/µ

m

Row

60-70

50-60

40-50

30-40

20-30

10-20

0-10

Elbow

Wrist

Opto-Thermal Measurements

0 0.2 0.4 0.6 0.8 1

0.2

0.4

0.6

0.8

1

S t

t

S t t / m

Z te z z t dz

e z t dz

z

z( )

( , )

( , )

0

0

Opto-Thermal Measurements

S t Ae erfc tt( ) //

Traditional Least-Squares Fitting Segmented Least-Squares Fitting

Opto-Thermal Measurements

( )z

S t( )

Z tt

e erfc t

t

t( )

22

Time

Depth

1

1

0

Transform Function

( )( )

zt D

1

Opto-Thermal Hair Measurements

Opto-Thermal Hair Measurements

Opto-Thermal Hair Measurements

Opto-Thermal Hair Measurements

Opto-Thermal Hair Measurements

Condenser TEWL Method -AquaFlux

Condenser based, Closed-Chamber TEWL Measurements Technology

Condenser-7.65 °C

RH and Temperature Sensors

Sample

Ice

TEWL – Trans - Epidermal Water LossTOWL – Trans - Onychial Water Loss

TEWL and TOWL Measurements

TEWLV

ambambskinV

JJ

TRHTHBfJ

),,,,( 0

Stratum CorneumStratum Corneum EpidermiEpidermiss

HydrationHydration

airair

HH00

HH11

LL

WW

Jv JTEWL

z

HDJTEWL

Hair Desorption

Hair Desorption

Hair Desorption

Hair Desorption

Conclusions

•The results show that OTTER can be used to measure the water concentration and water diffusion within hair samples. OTTER signals can reflect the layered structure of hair, the water concentration depth profiles show that within hair water might not distributed uniformly. Hair samples appeared to be able to absorb a lot of water during 10 minutes soaking, and to hold on most of it during the next 20 minutes period.

•AquaFlux can be used for measuring the water holding capability of ex-vivo hair samples through natural desorption process. The results show that different hairs have quite different desorption processes which are likely indicating different water holding capabilities. By fitting the desorption curves with suitable mathematical models we can also extract the water diffusion coefficients of hair.

Acknowledgements

We thank London South Bank University and EPSRC for the financial support.