23 Development of Subcutaneous-Type Glucose Sensors for Implantable or Portable Artificial Pancreas Fundamentals and Applications of Chemical Sensors Downloaded from pubs.acs.org by UNIV OF MASSACHUSETTS AMHERST on 08/10/18. For personal use only.
1
1
1
1
2
Kaname Ito , Shoichiro Ikeda , Kaori Asai , Hirotoshi Naruse , Kunitoshi Ohkura , Hidehito Ichihashi , Hideo Kamei , and Tatsuhei Kondo 2
2
2
1
Department of Applied Chemistry, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466, Japan Department of Surgery, Nagoya University, School of Medicine, Tsurumai-cho, Showa-ku, Nagoya 466, Japan
2
Most subcutaneous-type glucose sensors developed to date have been based upon oxygen type enzyme electrodes. A new glucose sensor developed may be characterized by the glucose semipermeable menbrane covered on the enzyme electrodes. The sensor which was prepared from an oxygen permeable PMSP (poly (1-trimethylsilyl-1-propyne)) membrane and a glucose semipermeable AC (acetyl cellulose) membrane, rapidly responded to glucose levels up to 500 mg/dl without the effect of oxygen tension in the range of 5 to 21 %. This sensor appears to hold promise for artificial pancreas applications. The c l o s e d - l o o p type a r t i f i c i a l pancreas (specifically 3-cell), which c o n s i s t s o f an a u t o m a t i c c o n t i n u o u s monitor o f blood g l u c o s e l e v e l (BGL) and an a u t o m a t i c i n j e c t o r o f i n s u l i n which are c o u p l e d w i t h feed-back system, has g r e a t p o t e n t i a l f o r p r e v e n t i o n o f d i a b e t i c c o m p l i c a t i o n such as m i c r o - a n g i o p a t h i e s ( l ) . A large-scale closedl o o p type a r t i f i c i a l pancreas f o r b e d s i d e use has a l r e a d y been developed and i s c l i n i c a l l y used a t some l a b o r a t o r i e s and h o s p i t a l s (2-4). However, t h i s d e v i c e i s l i m i t e d t o o n l y bedside u s e . On the o t h e r hand, the open-loop type a r t i f i c i a l pancreas which c o n s i s t s o f o n l y a i n s u l i n i n j e c t i n g pump w i t h o u t an a u t o m a t i c c o n t i n u o u s monitor o f BGL, has been developed and i s going t o be clinically u s e d ( 5 - 7 ) . T h i s system, however, c a n n o t c o m p l e t e l y c o n t r o l BGL as w e l l as the bare pancreas i n a normal body and o f t e n causes lower BGL(8-9). In o r d e r t o p r o v i d e f o r t h e complete therapy of d i a b e t i c p a t i e n t s , an i m p l a n t a b l e o r p o r t a b l e c l o s e d - l o o p type a r t i f i c i a l pancreas must be developed. The key f a c t o r i n the development o f such system i s development o f a s m a l l - s i z e g l u c o s e sensor which i s a b l e t o measure d i r e c t l y up t o 500-700 mg/dl o f BGL i n a b l o o d stream o r i n a body f l u i d . About t e n y e a r s ago, Bessman e t a l ( 1 0 ) , U n i v e r s i t y o f Southern C a l i f o r n i a , developed a g l u c o s e sensor o f enzyme e l e c t r o d e type w i t h g l u c o s e o x i d a s e (G0X) f o r an a r t i f i c i a l pancreas. T h i s sensor had 0097-6156/86/0309-O373$06.00/0 © 1986 American Chemical Society
374
FUNDAMENTALS AND APPLICATIONS OF CHEMICAL SENSORS
t h e l i m i t a t i o n t h a t t h e measurable g l u c o s e l e v e l was up t o c a . 150 mg/dl, a t maximum. Shichiri et a l ( l l ) (Osaka U n i v e r s i t y i n Japan) has developed the micro needle type g l u c o s e s e n s o r , which c o n s i s t e d o f a hydrogen p e r o x i d e e l e c t r o d e and a GOX enzyme i m m o b i l i z e d l a y e r . The sensor was clinically used, but i t had t o be renewed a f t e r a few days because o f a g r a d u a l d e c l i n e i n i t s o u t p u t . In t h e p r e v i o u s p a p e r s ( 1 2 , 1 3 ) , we r e p o r t e d on t h e v e s s e l a c c e s s type, i . e . t u b u l a r type, glucose sensor. I t c o n s i s t e d of a glucose e l e c t r o d e system w i t h a GOX enzyme i m m o b i l i z e d Nylon membrane and a g l u c o s e semipermeable membrane, and a r e f e r e n c e oxygen e l e c t r o d e system. The sensor c o u l d d i r e c t l y measure up t o 700 mg/dl o f BGL i n an a r t e r i a l b l o o d stream when i t was p l a c e d i n t o an e x t e r n a l A-V shunt. T h i s s e n s o r , however, has some problems such as thrombus d u r i n g in vivo t e s t i n g without h e p a r i n and c l i n i c a l complexity a s s o c i a t e d w i t h i m p l a n t i n g t h e sensor i n a blood stream. I n t h e p r e s e n t paper, t h e r e f o r e , we have m o d i f i e d t h e shape and the performance o f t h e g l u c o s e sensor t o measure t h e g l u c o s e l e v e l i n the subcutaneous t i s s u e . Experimental Preperation of sensors. The subcutaneous type g l u c o s e s e n s o r s developed a r e e s s e n t i a l l y an oxygen type enzyme e l e c t r o d e as w e l l a s the t u b u l a r type sensors p r e v i o u s l y r e p o r t e d ( 1 2 , 1 3 ) . F i g u r e 1 shows a schematic diagram o f an oxygen e l e c t r o d e system and epoxy r e s i n p a r t s used t o c o n s t r u c t t h i s type o f g l u c o s e s e n s o r . The cathode i s a 0.5 mm diameter P t w i r e s e a l e d w i t h a g l a s s tube, and t h e anode i s a 0.5 mm diameter Ag w i r e . These e l e c t r o d e s were s e t i n s i d e and o u t s i d e o f epoxy r e s i n r i n g , r e s p e c t i v e l y , and i t was s e t i n an epoxy r e s i n s o c k e t . The oxygen s e n s i n g p r o p e r t i e s o f such e l e c t r o d e systems were measured a t f i r s t . The r e p r o d u c i b i l i t y o f t h e output c u r r e n t v e r s u s oxygen t e n s i o n i s shown i n F i g u r e 2. The c o e f f i c i e n t o f c o r r e l a t i o n was 0.987 u s i n g e i g h t e e n d a t a p o i n t s . One p a i r o f oxygen e l e c t r o d e s w i t h s i m i l a r p r o p e r t i e s and t h e epoxy r e s i n p a r t s a s shown i n F i g u r e 1 were assembled and a subcutaneous type g l u c o s e sensor a s shown i n F i g u r e 3 was prepared by the f o l l o w i n g p r o c e s s . I n i t i a l l y , both e l e c t r o d e systems were f i l l e d w i t h normal s a l i n e s o l u t i o n i n c l u d i n g g e l a t i n . I n t h e case o f t h e g l u c o s e e l e c t r o d e system, an oxygen permeable T e f l o n FEP membrane, a GOX enzyme i m m o b i l i z e d Nylon membrane and a g l u c o s e semipermeable membrane were s e t up on t h e e l e c t r o d e system and were f i x e d by a waterproof Kapton t a p e . W h i l e t h e r e f e r e n c e oxygen e l e c t r o d e system was prepared by a s i m i l a r manner a s t h e g l u c o s e e l e c t r o d e system, except t h a t a bare Nylon membrane was used i n p l a c e o f an enzyme i m m o b i l i z e d membrane. Measurement. The measurement apparatus f o r t h e in vitro t e s t o f t h i s sensor i s shown i n F i g u r e 4. The sensor was dipped i n t o t h e f l a s k c o n t a i n i n g 100 ml o f phosphate b u f f e r e d s a l i n e s o l u t i o n , pH 7.4, and t h e output was measured w i t h r e s p e c t t o s t e p w i s e changed g l u c o s e c o n c e n t r a t i o n s o f 0 t o 2000 mg/dl under t h e oxygen t e n s i o n s of 5 t o 21%, which prepared by m i x i n g a i r and N2 g a s .
ITO ET AL.
Subcutaneous-Type Glucose Sensors
375
Epoxy r e s i n s o c k e t
Epoxy r e s i n p a r t s F i g u r e 1. Schematic diagram of oxygen e l e c t r o d e systems f o r subcutaenous type g l u c o s e s e n s o r s .
Oxygen t e n s i o n
(%)
F i g u r e 2. R e p r o d u c i b i l i t y of output c u r r e n t s v s . oxygen t e n s i o n of oxygen e l e c t r o d e systems.
376
FUNDAMENTALS AND APPLICATIONS OF CHEMICAL SENSORS
Kapton tape Glucose semipermeable membrane Nylon
filter
Enzyme immobillized nylon f i l t e r
O2 permeable membrane
6 mm
EZZÎ 30 mm R e f e r e n c e oxygen e l e c t r o d e system
Glucose electrode
system
F i g u r e 3. S t r u c t u r e o f a subcutaneous type g l u c o s e sensor
— T h e r m o bath Sensor
Magnetic
stirrer
F i g u r e 4. Apparatus f o r in vitro measurement o f dynamic response p r o p e r t i e s o f t h e subcutaneous type g l u c o s e sensor
23.
ITO ET AL.
377
Subcutaneous- Type Glucose Sensors
R e s u l t s and D i s c u s s i o n In vitro tests. The oxygen t e n s i o n i n subcutaneous tissue i s r e p o r t e d t o be about 5 %, and t h e output o f g l u c o s e s e n s o r s i s known to be a f f e c t e d by oxygen t e n s i o n . F i g u r e 5 i l l u s t r a t e s t h e output c u r r e n t s o f t h e g l u c o s e sensor I w i t h r e s p e c t t o t h e s t e p w i s e changed g l u c o s e c o n c e n t r a t i o n s shown i n t h i s f i g u r e , under an oxygen t e n s i o n o f 21, 10 o r 5 %. The sensor I , which i s prepared from t h e g l u c o s e semipermeable T e f l o n FEP membrane w i t h 25 Vim diameter p i n h o l e as shown i n Table 1, has r a p i d response p r o p e r t i e s f o r i n c r e a s i n g and d e c r e a s i n g o f g l u c o s e l e v e l and 95 % response time i s l e s s than 2 min under 21 % oxygen t e n s i o n . At lower oxygen t e n s i o n s such as 10 o r 57o, t h e sensor I has a s m a l l e r o u t p u t c u r r e n t and lower response t i m e s . The c a l i b r a t i o n c u r v e s o f t h e g l u c o s e sensor I a r e shown i n F i g u r e 6 and t h e l i n e a r range o f t h e c u r v e s g r a d u a l l y decrease w i t h d e c r e a s i n g o f t h e oxygen t e n s i o n from 21 t o 5 %. The g l u c o s e o x i d a t i o n r e a c t i o n i n t h e enzyme i m m o b i l i z e d membrane o f t h e g l u c o s e s e n s o r s i s performed according to the following reaction. GOX Glucose + 0
2
+ H 0 2
• Gluconic acid + H 0 2
2
(1)
where GOX i s g l u c o s e o x i d a s e and i s s u f f i c i a n t l y i m m o b i l i z e d on t h e Nylon membrane by c o v a l e n t bonding u s i n g t h e g l u t a r a l d e h y d e method. I f t h e g l u c o s e d i f f u s e d i n t o t h e enzyme membrane i s much l e s s than c o n c e n t r a t i o n o f t h e d i s s o l v e d oxygen i n i t , t h e r e a c t i o n rate becomes t h e f i r s t order with respect t o glucose c o n c e n t r a t i o n . Then, t h e c a l i b r a t i o n c u r v e o f t h e g l u c o s e sensor w i l l show l i n e a r response in t h e range o f t h e c o r r e s p o n d i n g c o n c e n t r a t i o n o f g l u c o s e . T h e r e f o r e , i n o r d e r t o o b t a i n t h e l i n e a r response up t o a h i g h e r g l u c o s e l e v e l , such as 500 mg/dl, t h e g l u c o s e p e r m e a b i l i t y o f the semipermeable membrane, i n t h e case o f lower oxygen t e n s i o n such as 5 %, must be much l e s s than t h a t i n oxygen t e n s i o n o f 21 %. Glucose s e n s o r s H and ΠΓ were prepared from t h e semipermeable membrane o f PMSP, p o l y ( 1 - t r i m e t h y l s i l y l - l - p r o p y n e ) , which has 4 t i m e s t h e oxygen p e r m e a b i l i t y compared w i t h t h a t o f FEP membrane. The response p r o p e r t i e s of sensor IE, u s i n g a PMSP membrane w i t h 25 lim diameter p i n h o l e , were almost s i m i l e r t o t h a t o f t h e sensor I , so t h a t t h e i r c a l i b r a t i o n c u r v e s were not p r e s e n t e d i n t h i s paper. The c a l i b r a t i o n c u r v e s o f sensor ΚΙ , which was prepared u s i n g a PMSP semipermiable membrane w i t h s m a l l e r p i n h o l e (15 Um d i a m e t e r ) than t h a t o f s e n s o r s I and H , i s shown i n F i g u r e 7. The c u r v e s under 5, 10 and 21 % o f oxygen t e n s i o n almost agreed w i t h each o t h e r i n t h e range o f 0 t o 500 mg/dl o f g l u c o s e c o n c e n t r a t i o n and t h e output was h a r d l y a f f e c t e d by oxygen t e n s i o n i n t h e range o f 5 t o 21 %. The c a l i b r a t i o n c u r v e s o f t h e sensor 1/ , which was prepared w i t h a PMSP membrane as an oxygen permeable membrane and an a c e t y l c e l u l o s e ( A C ) membrane as a g l u c o s e semipermeable membrane, were shown in F i g u r e 8. T h i s AC membrane was c a s t by M a n j i k i a n ' s method and t r e a t e d a t a c u r i n g temperature of 85°C. The sensor 1/ i n d i c a t e d a l i n e a r response up t o 500 mg/dl of g l u c o s e c o n c e n t r a t i o n , even under 5 % o f oxygen t e n s i o n , and t h e output c u r r e n t s were h a r d l y a f f e c t e d by oxygen t e n s i o n .
378
FUNDAMENTALS AND APPLICATIONS OF CHEMICAL SENSORS
Glucose c o n c e n t r a t i o n (mg/dl) Ό + 100-* 200 + 300 •> 500 + 700
Time (min.) F i g u r e 5. Dynamic response c u r v e s o f g l u c o s e sensor I under v a r i o u s oxygen t e n s i o n s (%)
F i g u r e 6. C a l i b r a t i o n c u r v e s o f g l u c o s e sensor I h a v i n g g l u c o s e semipermeable FEPp membrane w i t h 25 μ m diameter p i n h o l e .
23.
ITOETAL.
Subcutaneous-Type Glucose Sensors 80 1
—
379 1
Glucose c o n c e n t r a t i o n (mg/dl) F i g u r e 7. C a l i b r a t i o n c u r v e s o f g l u c o s e sensor JE h a v i n g g l u c o s e semipermeable PMSPp( 1 ) membrane w i t h 15 y m diameter p i n h o l e
80
/f //
