Development of a Cellulose Acetate Membrane and a Module for

5 Development of a Cellulose Acetate Membrane and a Module for Hemofiltration M . K A I , K . ISHII, Z. H O N D A , and H . T S U G A Y A Daicel Chemical Industries, Ltd., 1 Teppo-cho, Sakai-shi 590, Japan

Downloaded by UNIV OF AUCKLAND on May 3, 2015 | http://pubs.acs.org Publication Date: May 27, 1981 | doi: 10.1021/bk-1981-0154.ch005

M . M A E K A W A , T. K I S H I M O T O , and S. Y A M A G A M I Osaka City University Medical School, 1-5-7 Asahi-machi, Abeno-ku, Osaka-shi 545 Japan

Since Henderson opened the gate t o the clinical a p p l i c a t i o n of ultrafiltration t o r e n a l failure as an alternative to hemodialysis and p e r i t o n e a l dialysis, the ultrafiltration o f blood, hemofiltration, has been i n c r e a s i n g l y attracting both clinical and pathological interest. I n the course of h e m o f i l t r a t i o n s t u d i e s , it has been amply confirmed that t h i s new therapy is effective f o r treatment o f hemodialysis-difficulties p a t i e n t s who a r e not compatible w i t h hemodialysis due t o s e r i o u s syndrome. Various s t u d i e s are being under way concerning the mechanistic differences between h e m o f i l t r a t i o n and hemodialysis. In hemodialysis the t r a n s p o r t of plasma s o l u t e s through membrane is c o n t r o l l e d by c o n c e n t r a t i o n gradient and diffusion coefficient. Since diffusion coefficient decreases w i t h molecular weight, the whole blood clearance (the amount o f removed s o l u t e in u n i t time d i v i d e d by the s o l u t e c o n c e n t r a t i o n in the blood) sharply diminishes w i t h molecular weight as illustrated in Figure 1 (1). I n h e m o f i l t r a t i o n , on the other hand, removal of s o l u t e s is almost independent o f molecular weight up t o the c u t o f f molecu l a r weight o f the membrane. This d i f f e r e n c e in the clearance f o r s o l u t e s l a r g e r than uric a c i d is r e l a t e d t o the f a c t that hemofiltration i s effective f o r hemodialysis-difficulties patients. For h e m o f i l t r a t i o n t o be effective, the total amount o f blood wat e r t o be ultrafiltered i n one treatment is 20 t o 23 liters depending on p a t i e n t s ' c o n d i t i o n s . To complete each treatment i n f i v e hours, h e m o f i l t e r , UF module f o r h e m o f i l t r a t i o n , i s r e q u i r e d to permeate 66 t o 77 ml/min of water. None of h e m o f i l t e r s so f a r in use meet this requirement. D a i c e l and Osaka C i t y U n i v e r s i t y Medical School s t a r t e d a joint study t o develop a practically more f e a s i b l e h e m o f i l t e r . The r e q u i r e d p r o p e r t i e s f o r a new hem o f i l t e r are s p e c i f i e d i n Table 1. I t is t o be noted i n Table 1 that UFR, ultrafiltration r a t e , i s not l e s s than 70 ml/min.

0097-6156/81/0154-0045$05.00/0 © 1981 American Chemical Society

In Synthetic Membranes: Volume II; Turbak, A.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

SYNTHETIC MEMBRANES:

46

Table 1

USES

REQUIRED PROPERTIES FOR A NEW HEMOFILTER

UFR

>70 ml/min

Transmembrane Pressure

£300 mmHg/cm

Permeation, of which molecular weight i s :


H F AND U F

2

if

5xlO

k

100% 2

Additive Solution (%)


10

Cyclohexanone (%)

Water (%)

7

3

2.3

1.06

2.2

Cyclohexanone/ water (-)

Water flux (-)

Permeation (-)

20

15

5

3.0

0.80

6.5

30

20

10

2.0

0.34

3.3

I t i s remarkable i n Table IV, that water f l u x decreases w i t h i n crease i n water. T h i s means the water f l u x promoting e f f e c t o f water as the o n l y nonsolvent f o r c e l l u l o s e a c e t a t e contained i n the c a s t i n g dope was suppressed by the c o e x i s t e n c e of p a r t i a l l y water s o l u b l e s o l v e n t , cyclohexanone. Increase of water i n the c a s t i n g dope a c c e l e r a t e s phase sep a r a t i o n i n the e a r l y stage of g e l a t i o n and i n c r e a s e s the number of and decreases the s i z e of p r e c i p i t a t i n g polymer cores. A cer t a i n amount of water, t h e r e f o r e , i s necessary to o b t a i n a f i n e l y pored membrane w i t h low s o l u t e p e r m e a b i l i t y ( 4 ) . T h i s e x p l a i n s why the minimum permeation v a l u e f o r 10% a d d i t i v e i s more than twice those f o r 20 to 30% a d d i t i v e s . A t the same time, however, the nascent polymer cores seem to r a p i d l y l o s e f l e x i b i l i t y r e s u l t i n g i n the f i x a t i o n of the membrane m a t r i x at a r e l a t i v e l y e a r l y stage of g e l a t i o n and thus g i v i n g a broad pore s i z e d i s t r i b u t i o n . The nascent membrane m a t r i x , however, i s l i k e l y to keep f l e x i b i l i t y to the r e l a t i v e l y l a t e stage of g e l a t i o n by the exi s t e n c e o f cyclohexanone, a p o r t i o n of which may be l e f t p a r t i t i o n e d to the p r e c i p i t a t e d polymer phase due to i t s l i m i t e d s o l u b i l i t y i n water. Thus, enhanced polymer f l e x i b i l i t y a c c e l e r a t e s the polymer network to c o n t r a c t so as to make i n t e r s t i c e s o r pores narrow enough to r e j e c t the passage of ovalbumine. I n crease i n water content, t h e r e f o r e , r e q u i r e s the augmentation o f cyclohexanone and the both i n g r e d i e n t s work s y n e r g i s t i c a l l y . However, i f the cyclohexancne content exceeds a c e r t a i n l e v e l , i . e . , 1.5 times of water, e x c e s s i v e c o n t r a c t i o n of h i g h l y s o l v ated polymer networks occurs l e a d i n g to c o l l a p s e of the i n t e r s t i c e s . A t the same time, t h i s c o n t r a c t i o n of nascent membrane m a t r i x would cause the f o r m a t i o n of some s p e c i f i c chasms or v o i d and make them l a r g e enough to pass ovalbumine f r e e l y . In subs t r a t e where polymer c o n c e n t r a t i o n i s c o n s i d e r a b l y lower than that o f s k i n l a y e r , tendency to c o n t r a c t i o n of polymer network n e c e s s a r i l y y i e l d s numbers of l a r g e s i z e d v o i d s , and hence, r e -


SYNTHETIC MEMBRANES:


54

H F AND U F

USES

Figure 7.

Membrane cross-section for cyclohexanone content of 32 wt % of additive solution

Figure 8.




KAI E T A L .

Hemofiltration

Figure 9. Membrane cross-section for cyclohexanone content of 50 wt % of additive solution

Figure 10. Membrane cross-section for cyclohexanone content of 60 wt % of additive solution



SYNTHETIC M E M B R A N E S :

Figure 11.

H F AND U F

USES


3.5 3.0

x

2.5

j

2.0

5 X o

1

5

£

5

1.0

D O.JT_J_L_

• • •i 10

0.5 1 3 5 7 IMMERSION TIME UPSE(

Development of a Cellulose Acetate Membrane and a Module for

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