A PHOTOACOUSTIC HYDRATION STUDY OF HUMAN STRATUM CORNEUM

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A PHOTOACOUSTIC HYDRATION STUDY OF HUMAN STRATUM CORNEUM

K. Giese, K. Kölmel

To cite this version:

K. Giese, K. Kölmel. A PHOTOACOUSTIC HYDRATION STUDY OF HUMAN STRA- TUM CORNEUM. Journal de Physique Colloques, 1983, 44 (C6), pp.C6-373-C6-378.

�10.1051/jphyscol:1983661�. �jpa-00223220�

JOURNAL DE PHYSIQUE

Colloque C6, suppl6rnent au nD1O, T o m e 44, octobre 1983 page C 6 - 373

A

PHOTOACOUSTIC HYDRATION STUDY OF HUMAN STRATUM CORNEUM

K. Giese a n d K. ~ o l m e l *

i n s t i t u t Yiir 1Yedizinische Physik und Riophysik der U n i v e r s i t t i t , Gd'ttingen, 17.9. C.

*Universitdts-HautkZinik, W t t i n g e i z , 17. R. C .

hGsum6

-

^Dans c e t t e c o m m u n i c a t i o n l e s v a r i a t i o n s d u s i g n a l p h o t o a c o u s t i q u e dQ

a

l a c o u c h e c o r n 6 e n n e d ' u n o e i l humain e n f o n c t i o n d e s o n t a u x d ' h y d r a t a t i o n s o n t d i s c u t e e s e n t e r m e s d e v a r i a t i o n s d e p a r a m s t r e s t h e r m i q u e s e t o p t i q u e s .

A b s t r a c t

-

I n t h i s p a p e r t h e v a r i a t i o n o f t h e p h o t o a c o u s t i c s i g n a l o f human s t r a t u m corneum w i t h w a t e r c o n t e n t i s d i s - c u s s e d i n t e r m s o f v a r i a t i o n s o f t h e r m a l a n d o p t i c a l p a r a - meters.

The s t r a t u m corneum f o r m e s t h e o u t e r m o s t l a y e r o f t h e human e p i d e r m i s . A p a r t f r o m s p e c i a l l o c a l i s a t i o n s i t s t h i c k n e s s i s a b o u t 1 2

urn

[ I ] . The s t r a t u m corneum p l a y s a f u n d a m e n t a l r o l e b o t h a s a r e s e r v o i r a n d a b a r r i e r i n t h e r e g u l a t i o n o f w a t e r b a l a n c e o f t h e body. P h o t o a c o u s t i c s p e c t r o s c o p y , w h i c h a l l o w s t h e d e t e r m i n a t i o n o f o p t i c a l a n d t h e r m a l p a r a m e t e r s o f a s a m p l e , seems t o b e o n e o f t h e most d e p t h s e n s i t i v e means f o r t h e i n v e s t i g a t i o n o f t h e h y d r a t i o n p r o p e r t i e s o f t h e h o r n y l a y e r .

W e h a v e p e r f o r m e d p h o t o a c o u s t i c i n v i t r o m e a s u r e m e n t s o n s a m p l e s o f human s t r a t u m c o r n e u n w i t h i n t h e p r o t e i n a b s o r p t i o n b a n d a r o u n d h = 2 8 0 nm a t c h o p p i n g f r e q u e n c i e s b e t w e e n 1 0 a n d 1 0 0 0 H z . A s a l r e a d y shown by o t h e r a u t h o r s [ 2

-

^{S j ,} t h e p h o t o a c o u s t i c s i g n a l s t r o n g l y d e - p e n d s o n t h e w a t e r c o n t e n t o f t h e s a m p l e s . W h i l e t h e s e a u t h o r s , how- e v e r , assumed t h i s d e p e n d e n c e t o r e f l e c t o n l y v a r i a t i o n s o f t h e r m a l p a r a m e t e r s , e s p e c i a l l y t h e t h e r m a l i n e r t i a K = K ~ C a n d t h e t h e r m a l d i f f u s i v i t y a = K / ~ C , t h e e x t e n s i v e e x p e r i m e n t a l d a t a a v a i l a b l e now show t h a t a d d i t i o n a l l y t h e o p t i c a l a b s o r p t i o n c o e f f i c i e n t B i s c h a n g e d d u e t o t h e s w e l l i n g o f t h e s a m p l e s w i t h i n c r e a s i n g w a t e r c o n t e n t . The s a m p l e s w e r e o p t i c a l l y a n d t h e r m a l l y t h i c k s a m p l e s o f e x c i s e d p l a n t a r corneum and t h i n l a y e r s o f s t r a t u m corneum o f t h e f o r e a r n , o b t a i n e d by s k i n s u r f a c e b i o p s y w i t h c y a n o a c r y l a t a d h e s i v e . The e v a - l u a t i o n o f e l e c t r o n p h o t o m i c r o g r a p h s shows t h a t t h e l a t t e r method y i e l d s s a m p l e s , t h e t h i c k n e s s o f which i s a b o u t 2

-

5 pm. By r e p e a t i n g t h e s t r i p p i n g p r o c e d u r e a t t h e same s i t e , it i s p o s s i b l e t o l e v e l down t h e s t r a t u m corneum s t e p by s t e p a n d t o i n v e s t i g a t e t h e h y d r a t i o n p r o - p e r t i e s i n d e p e n d e n c e o n d e p t h .

Theory

A s a model f o r t h e c y a n o a c r y l a t s t r i p p i n g s we c o n s i d e r a n a r r a n g e m e n t w i t h p l a n e p a r a l l e l i n t e r f a c e s b e t w e e n g a s , s t r a t u m corneum ( S C ) , a d - h e s i v e ( A ) a n d s u p p o r t ( S ) . The t h i n h o r n y l a y e r i s assumed t o b e ho- mogeneous. I f e n e r g y i s a b s o r b e d w i t h i n t h i s l a y e r f r o m a s i n u s o i d a l l y c h o p p e d i n c i d e n t l i g h t beam, t h e o s c i l l a t o r y t e m p e r a t u r e a t t h e i n t e r - f a c e g a s / s t r a t u m corneum i s g i v e n by [ 6 ] :

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983661

JOURNAL DE PHYSIQUE

Here d i s t h e t h i c k n e s s of t h e horny l a y e r , o = and Z = l / m t h e p r o p a g a t i o n c o e f f i c i e n t and t h e i m ~ e d a n c e o f t h e t h e r m a l waves i n t h e s t r a t u m corneum, r e s p e c t i v e l y , w t h e a n g u l a r f r e q u e n c y o f t h e l i g h t modulation and j t h e i m a g i n a r y u n i t . I. d e n o t e s t h e mean i n t e n - s i t y of t h e chopped l i g h t .

The r e f l e c t i o n c o e f f i c i e n t ,

w i t h

t a k e s i n t o a c c o u n t t h e r e f l e c t i o n of t h e r m a l waves a t t h e i n t e r f a c e s s t r a t u m corneum/adhesive and a d h e s i v e / s u p p o r t . D i s t h e t h i c k n e s s o f t h e a d h e s i v e , a~ t h e p r o p a g a t i o n c o e f f i c i e n t and ZA t h e impedance o f t h e t h e r m a l waves i n t h i s l a y e r and ZS t h e t h e r m a l wave impedance of t h e s u p p o r t .

With r e s p e c t t o t h e s t r a t u m corneum t h e a d h e s i v e i s a weakly a b s o r b i n g m a t e r i a l w i t h s i m i l a r t h e r m a l p r o p e r t i e s ( l / P A = 215 bm a t

X

= 280 nm, a A = 10-3 cm2/s and KA = 2

.

c a 1 2 / c m 4 s o ~ 2 ) . The t h i c k n e s s , D , o f t h e a d h e s i v e l a y e r i s a b o u t 40 pm. The samples a r e s u p p o r t e d on b r a s s c y l i n d e r s , which a t low UV-wavelengths o n l y weakly r e f l e c t l i g h t . The s u p p o r t may be c o n s i d e r e d a s a p h o t o a c o u s t i c a l l y s a t u r a t e d a b s o r b e r o f l a r g e t h e r m a l i n e r t i a ( K S = 0.2 ca12/cm4soc2). Compared t o t h e photo- a c o u s t i c s i g n a l of t h e s t r a t u m corneum t h e s i g n a l s caused by t h e ab- s o r p t i o n o f l i g h t i n t h e a d h e s i v e l a y e r and i n t h e s u p p o r t i n g e n e r a l a r e s m a l l and have t o be r e g a r d e d o n l y a t low chopping f r e q u e n c i e s . The e x p e r i m e n t a l p h o t o a c o u s t i c s p e c t r a p r e s e n t e d below a r e normalized t o t h e spectrum of a t h e r m a l l y t h i c k sample o f carbon b l a c k (KCB = 2 1

o - ~

ca12/cm4soC2)

,

a p h o t o a c o u s t i c a l l y s a t u r a t e d a b s o r b e r , t h e s u r f a c e t e m p e r a t u r e of which i s g i v e n by

I f t h e measurements a r e performed w i t h i n an a d e q u a t e f r e q u e n c y r a n g e , t h e f i t t i n g o f t h e t h e o r e t i c a l dependence on chopping f r e q u e n c y , eqn.

( I ) , t o t h e e x p e r i m e n t a l c u r v e s a l l o w s t h e d e t e r m i n a t i o n o f t h r e e sample p a r a m e t e r s : ( 1 ) t h e c h a r a c t e r i s t i c chopping f r e q u e n c y , f o = a p 2 / n 1 a t which t h e t h e r m a l d i f f u s i o n l e n g t h i s e q u a l t o t h e o p t i c a l a b s o r p t i o n l e n g t h , ( 2 ) t h e t h e r m a l i n e r t i a K and, i f c y a n o a c r y l a t s t r i p p i n g s a r e i n v e s t i g a t e d , ( 3 ) t h e p r o d u c t o f o p t i c a l a b s o r p t i o n c o e f f i c i e n t and sample t h i c k n e s s , Bd.

Experimental r e s u l t s

The dual-beam p h o t o a c o u s t i c s p e c t r o m e t e r employed f o r t h e measurements h a s been d e s c r i b e d p r e v i o u s l y i71. The F i g u r e s 1 and 2 show r e s u l t s a s o b t a i n e d w i t h an o p t i c a l l y and t h e r m a l l y t h i c k sample o f p l a n t a r c o r -

neum. By i n c r e a s i n g t h e wavelength from 280 t o 320 nm, t h e o p t i c a l ab- s o r p t i o n c o e f f i c i e n t , p, d e c r e a s e s by a f a c t o r of a b o u t 10, s o t h a t t h e c h a r a c t e r i s t i c f r e q u e n c y i s s h i f t e d t o lower f r e q u e n c i e s by a f a c - t o r o f a b o u t 100. Assuming t h e t h e r m a l d i f f u s i v i t y o f d r y s k i n t o be 7 10-4 cm2/s 18

I ,

t h e o p t i c a l a b s o r p t i o n l e n g t h a t 280 nm i s 4 b m , which i s comparable t o t h e t h i c k n e s s of t h e c y a n o a c r y l a t s t r i p p i n g s . By h y d r a t i o n o f t h e sample t h e t h e r m a l i n e r t i a i n c r e a s e s by a f a c t o r of a b o u t 2 and approaches t h a t of w a t e r . S i m u l t a n e o u s l y , t h e c h a r a c t e - r i s t i c f r e q u e n c y d e c r e a s e s , i n d e p e n d e n t l y of t h e o p t i c a l wavelength, by a f a c t o r o f a b o u t 6 . A s b o t h t h e t h e r m a l c o n d u c t i v i t y , K , and t h e h e a t c a p a c i t y p e r u n i t volume, pC, i n c r e a s e w i t h i n c r e a s i n g w a t e r con- t e n t 12, 9 1 , t h e t h e r m a l d i f f u s i v i t y s h o u l d be l e s s i n f l u e n c e d t h a n t h e t h e r m a l i n e r t i a . C o r r e s p o n d i n g l y , t h e s t r o n g d e c r e a s e of t h e cha- r a c t e r i s t i c f r e q u e n c y s h o u l d be mainly due t o an d e c r e a s e of t h e o p t i - c a l a b s o r p t i o n c o e f f i c i e n t . We b e l i e v e t h a t t h i s dependence i s con- n e c t e d w i t h t h e s t r o n g s w e l l i n g o f t h e h y d r a t e d s t r a t u m corneum.

A s i t c a n be s e e n from F i g . 2 , t h e p h o t o a c o u s t i c s i g n a l o f p l a n t a r corneum i s most s e n s i t i v e t o a change i n w a t e r c o n t e n t a t h i g h f r e -

0.2

1

^{I I} I

0.01 0.1

-

1 ^frequency k H z 10

F i g . 1

-

Frequency dependence o f t h e PA-signal of an o p t i c a l l y and t h e r m a l l y t h i c k sample o f d r y p l a n t a r corneum.

I I I I

0.01 0.1

-

1 ^frequency kHz 10

F i g . 2

-

The PA-signal of h y d r a t e d p l a n t a r corneum r e l a t i v t o t h e s i g - n a l o f t h e d r y sample (100 % r e l a t i v e h u m i d i t y environment f o r 24 h )

JOURNAL DE PHYSIQUE

q u e n c i e s , where b e s i d e s t h e i n c r e a s e o f t h e t h e r m a l i n e r t i a , which a t low f r e q u e n c i e s y i e l d s t h e o n l y c o n t r i b u t i o n , t h e d e c r e a s e of t h e cha- r a c t e r i s t i c f r e q u e n c y becomes e f f e c t i v e . I t may be emphasized t h a t t h i s dependence on chopping f r e q u e n c y i s u n d e r s t a n d a b l e a s t h e photo- a c o u s t i c b e h a v i o u r o f a homogeneous sample. I n g e n e r a l one c a n n o t de- duce a v a r i a t i o n o f t h e r m a l p a r a m e t e r s w i t h d e p t h from t h i s experimen- t a l f i n d i n g , a s it r e c e n t l y h a s been done by o t h e r a u t h o r s / 5 1 .

P l a n t a r corneum samples of d i f f e r e n t d o n o r s y i e l d v e r y s i m i l a r photo- a c o u s t i c s p e c t r a . L a r g e r d i f f e r e n c e s , which t o a c e r t a i n d e g r e e a r e r e p r o d u c i b l e , a r e o b t a i n e d w i t h c y a n o a c r y l a t s t r i p p i n g s . The a n a l y s i s of e x p e r i m e n t a l d a t a shows t h a t t h i s s p r e a d i s m a i n l y due t o d i f f e r e n - c e s i n t h e r m a l i n e r t i a and t h i c k n e s s o f t h e horny l a y e r s s t r i p p e d o f f . With r e s p e c t t o t h e o p t i c a l p r o p e r t i e s , t h e h o r n y l a y e r of t h e f o r e a r m and t h e p l a n t a r corneum a r e s i m i l a r . The c h a r a c t e r i s t i c f r e q u e n c y of d r y samples a t 280 nm i s a b o u t 1 kHz and h y d r a t i o n r e d u c e s t h i s v a l u e by a f a c t o r of a b o u t 6 .

F i g u r e 3 shows s p e c t r a o f a sequence of d r y s a m p l e s , s t r i p p e d o f f one a f t e r t h e o t h e r from one s i t e o f t h e f o r e a r m . The o u t e r m o s t l a y e r i s d e n o t e d a s N r . 1 . The s i g n a l a m p l i t u d e o b t a i n e d w i t h t h i s l a y e r i s a b o u t t w i c e t h e a m p l i t u d e o b s e r v e d w i t h p l a n t a r corneum s a m p l e s . By i n v e s t i g a t i o n of samples o f a group of 30 donors we found 3 s u b j e c t s , t h e o u t e r m o s t l a y e r of s t r a t u m corneum of which showed such l a r g e pho- t o a c o u s t i c s i g n a l s . A s t h e r e s u l t o f t h e c u r v e f i t t i n g we o b t a i n e d f o r t h e s t r i p p i n g s 1 t o 4 t h e t h e r m a l i n e r t i a r e l a t i v e t o t h a t o f w a t e r t o be q i v e n by K / K W = 0.1, 0.15, 0.3 and 0 . 5 , r e s p e c t i v e l y (Kbv = 1 . 4

-

^10-3

c a l /cm4soc2). With most o f t h e d o n o r s t h e d r y s t r i p p i n g s y i e l d v a l u e s i n t h e r a n g e 0.3 < K / K W < 0.5.

By h y d r a t i o n t h e p h o t o a c o u s t i c s i g n a l o f t h e s t r i p p i n g s d e c r e a s e s ( F i - g u r e 4 ) . From t h e a n a l y s i s o f t h e c u r v e s t h e t h e r m a l i n e r t i a of t h e h y d r a t e d samples came o u t t o be a b o u t t h a t of w a t e r . To u n d e r s t a n d t h e d i f f e r e n t shape of c u r v e 1 i n F i g u r e 4 one h a s t o know t h a t w i t h t h i s s t r i p p i n g a r a t h e r t h i c k h o r n y l a y e r was removed (Bd

=

2 ) , whereas

w i t h t h e s u b s e q u e n t s t r i p p i n g s much t h i n n e r l a y e r s were o b t a i n e d (Bd : 0 . 5 ) . I t c a n be deduced from t h e t h e o r e t i c a l d e s c r i p t i o n of t h e s i g n a l , eqn. (1 )

,

t h a t f o r a t h i c k sample an i n c r e a s e of t h e t h e r m a l i n e r t i a y i e l d s a uniform l o w e r i n g of t h e s i g n a l a m p l i t u d e . A g a i n s t t h i s , w i t h

0.01 0.1 1 k H z 10

-

^frequency

F i g . 3

-

Frequency dependence o f t h e PA-signal of a sequence o f d r y c y a n o a c r y l a t s t r i p p i n g s from one s i t e o f t h e f o r e a r m -(A = 280 nm).

01 I I 1

0.01 0.1 1 k H z 10

-

^frequency

F i g . 4

-

The PA-signal o f t h e h y d r a t e d s t r i p p i n g s ( 1 0 0 % r e l a t i v e humi- d i t y environment f o r 2 4 h ) r e l a t i v e t o t h e s i g n a l of t h e d r y samples

( A = 2 8 0 nm).

0.1 I I I \ I

T

t

0.01 0.03 0.1

-

0.3 ^frequency kHz 1

F i g . 5

-

Frequency dependence o f t h e PA-signal of a 30 pm t h i c k adhe- s i v e l a y e r s u p p o r t e d on a b r a s s c y l i n d e r .

t h i n samples t h e s i g n a l s e n s i t i v e l y depends on such a change o n l y a t h i g h e r f r e q u e n c i e s .

The f i g u r e 5 shows t h e p h o t o a c o u s t i c spectrum of a n a d h e s i v e l a y e r s u p p o r t e d on a b r a s s c y l i n d e r . A s one c a n s e e , t h e s i g n a l i s s m a l l e r t h a n t h a t of t h e horny l a y e r by a b o u t one o r d e r o f magnitude. By f i t - t i n g t h e o r e t i c a l s p e c t r a t o t h e e x p e r i m e n t a l d a t a o b t a i n e d by t h e s t r i p p i n g method we r e g a r d t h i s s i g n a l by u s e of t h e d a t a mentioned above.

Conclusion

To summarize, t h e d a t a p r e s e n t e d i n t h i s l e t t e r show (11 t h a t a quan- t i t a t i v e d e s c r i p t i o n o f t h e p h o t o a c o u s t i c s p e c t r a of s t r a t u m corneum r e q u i r e s t h e o p t i c a l a b s o r p t i o n c o e f f i c i e n t t o be assumed a s a guan-

JOURNAL DE PHYSIQUE

t i t y t h a t depends on t h e w a t e r c o n t e n t of t h e sample; ( 2 ) t h e s t r i p - p i n g method a l l o w s t h e d e t e r m i n a t i o n o f o p t i c a l and t h e r m a l p r o p e r t i e s of s t r a t u m corneum i n dependence on d e p t h . Because of t h e s i m p l i c i t y o f g e t t i n g s t r a t u m corneum samples o f d i f f e r e n t s i t e s of t h e human bo- dy, it seems t o be a v a l u a b l e method i n d e r m a t o l o g i c a l p h o t o a c o u s t i c s .

Acknowledgements

F i n a n c i a l s u p p o r t by t h e Deutsche Forschungsgemeinschaft i s g r a t e f u l l y acknowledged.

R e f e r e n c e s

[ I ] Anderson, R. L . and J . M . C a s s i d y , V a r i a t i o n s i n p h y s i c a l dimen- s i o n s and chemical composition of human s t r a t u m corneum, J.

I n v e s t . Dermatol.

3

(1973) 30

-

32

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