- Email: [email protected]
A study on the deswelling behaviour of a thermo-responsive hydrogel prepared by radiation polymerization
Radiat. Phys. Chem. Vol. 42, Nos 4—6, PP. 959—962, 1993
Printed in Great Britain. All rights reserved
0146-5724/93 $6.00 + 0.00 Copyright © 1993 Pergamon Press Ltd
A STUDY ON THE DESWELLING BEHAVIOUR OF A THERNO-RESPONSIVE HYDROGEL PREPARED BY RADIATION POLYMERIZATION
2, Ma Zueteh~- and M. Kumakura2 Ding Zhong1i~-, YOSHIDA ‘Shanghai Applied radiation Institute, Shanghai University of Science and Technology, Jia Ding, Shanghai 201800, China 2Takasaki Radiation Chemistry Research Institute, Japan Atomic Energy Research Institute, Takasaki, Gunma, Japan
ABSTRACT A new kind of thermo-responsive hydrogel, poly(methacryloyl-DL.alanie methyl ester), was synthesized by means of radiation polymerization. The swelling and desweHing were reversible.The deswelling kinetics changes with the variation of temperature. It was found that a rigid membrane was formed during deswlling at 40 °C . In the case of deswelling at 20 °C , no skin was found. The hydrogel deswelled uniformly.
KEYWORDS Thermo-responsive hydrogel; radiation polymerization; swelling.
INTRODUCTION Thermo-resporisive hydrogels have found many applications in drug delivery system [1], thermo- feedback control reaction 121 and solvents extraction from solutions [3j because of their excellent properties of reversible swelling and deswelling. So far, most of the researches focused on N-isopropylacryloylamide. To develop new kinds of materials, we have synthesized amino acid contained polymer, poty(methacryloyl-DLalanine methyl ester) and its copolymers, by means of radiation polymerization. The polymer was found to be possess of thermo- responsive swelling and deswelling property. It was found that there were different ways of deswelling at the temperature of 20 °Cand 40 °C . A skin was formed on the surface of hydorgel deswelled at 40 °C and no akin could be found on the hydrogel deswelled at 20 °C
EXPERIMENTAL Synthesis Mixtures of monomer (methacryloyl-DL-alanine methyl ester), comonmers and crosslinking agents (Polyetylene glycol dimethacrylate) were charged into test tubes with diameter of 8mm and irradiated by ‘~ — ray. from a cobalt 60 source at a dose rate of 10 kGy/h for 3 hr. at 50 °C with nitrogen gas protection. The polymers were subsequently extracted by immersing in ethanol for 5 days to remove unreacted chemicals and water to replace the ethanol in the polymers. Swelling and deswelling Swelling ratio of polymers was measured gravimetrically. The swelling ratio was defined as C(%) = (W — Wo)/Wo x 100, where W is the weight of the sample after swelling at desired temperature for 24 hours and Wo is the weight of sample. In the measurement of deswelling, the samples saturate swollen at 0 °Cwere put into water bath of 20 °C or 40 °C , where the samples began to desweli. The weights of the samples were recorded at varying deswelling time.
959
960
DING ZHONGLI et a!.
Sample preparation for SEM observation To study deswelling kinetics, the samples were swollen to saturation at 0 00 before deswellung. Samples deswelled at a constant temperature water bath for desired time were taken out and immediatly put into dry ice-ethanol mixture for one mm. and freeze dryed. The dry samples were golden tinted. Then SEM observations were made.
RESULTS AND DISCUSSION To observe the difference of deswelling at different temperature, the gels saturate swollen at 0 00 were put into 20 00 and 40 00 water bathes, respectively. The result shown in Fig.! tells the remarkable difference. About 80% of water was extruded out of the gals within one hour when deswelled at 40 00 . It took about 24 hours for the gels deswelled at 20 00 to drive out 75% of water. To finde the causes, we investigated process of deswelling by microscopy. Pictures taken during deswelling were shown in Fig.2. Gel swelled at 0 ~C was transparent (a). It changed to white immediately after immersing into water bath of 40 00 (b) and then bubbles appeared on its surface (c). A membrane is clearly shown in picture (d) which was taken in 1580 miii.. SEM (scanning electron microscopy) observation gives the micros view on this interesting membrane as shown in Fig.3. The control sample (a) was full of pores either inside and surface. The pores still were visible on the surface of the gel deswelled 15 mm.. A rigid membrane was present on the surface of the gel which had undergone 45 mm. deswelling. The embrane grow thicker from 2.6 ~m (at 45 miii.) to 78 ~im (at 180 miii.). Fig.4 shows the deswelling process of 20 00 There were pores on the surface of the gel even after 180 miii. deswelling though the sizes of that were decreased. The shrinkage force of the gel is much stronger at 40 00 than that at 20 00 . It is due to having less equilibrium swelling ratio at 40 00 . In the case of deswellung at 40 00 , surface layer of the gel shrinked very quickly and water provisions from inside of the gel was not enough to compensate the water lose of surface layer because of its low diffuse speed. This surface layer was finaly changed into a rigid membrane which blocked the water to diffuse out in great amount. The deswellung, therefore, became slower. En contrast, the surface layer of a gel deswelled at 20 ~c shrunked slowly. It, hence, acquired sufficient water supply from inside of the gel to leak out. In this case, membrane could not be formed.
CONCLUSION The deswllung kinetics was affected by temperature. Being smooth at 20 °Cthe deswelling was rather fast at 40 00 and a rigid membrane was formed on the surface.
REFERENCES [lj. T. Okano, Y. H. Bea, H. Jacobs and S. W. Kim (1q90). Thermally on.off switching polymers for drug permeation and release. ,LQLcontrolled Release, 11, 255-26~. 121. L. Z. Doug and A. S. Hoffman (1986). Thermally reversible hydrogels. III. Immobilization of enzymes for feedback reactiontrol. J. of Controlled Release, 4, 223-227. [31.R. F. S. F’reitas and E. L. Cussler (1987). Temperature sensitive gels as size selective absobants. ch~m. En~ineerungScj,, ~,
97-103.
8th International Meeting on Radiation Processing
‘~1200
-
ot~2~3.b#~5O6.b7.O
Time
(
hr.)
Fig.l. Deswelling kinetics of copoly(MA—DL—A1&)Me/HPA/9G) (v/v/v) at 20°C (o) and 40°C (D).
Fig.2. ~icroscopypictures of deswelling ~el at 40°c. a. 0 mm. (xlO); b. 0.5 mm. (xlO); c. 6 mm. (x20); d. 1200 mm. (x30).
961
962
DING ZHONGLI et a!.
Inside
Surface
I’
b
..1
.
Fig. 3. SEM pictures of deswelling gel at 40°C a. Control (x400); b. 15 mm. (x400); c. 45 mm. (x1000) and d. 180 mm. (x400). The thickness of membrane in c. is 2.6 tim and d. 78 ~m.
__
-
-
Fig. 4. SEM pictures of deswelling gel at 20°C a. 45 mm. (x130) and b. 180 mm. (xl000).
Printed in Great Britain. All rights reserved
0146-5724/93 $6.00 + 0.00 Copyright © 1993 Pergamon Press Ltd
A STUDY ON THE DESWELLING BEHAVIOUR OF A THERNO-RESPONSIVE HYDROGEL PREPARED BY RADIATION POLYMERIZATION
2, Ma Zueteh~- and M. Kumakura2 Ding Zhong1i~-, YOSHIDA ‘Shanghai Applied radiation Institute, Shanghai University of Science and Technology, Jia Ding, Shanghai 201800, China 2Takasaki Radiation Chemistry Research Institute, Japan Atomic Energy Research Institute, Takasaki, Gunma, Japan
ABSTRACT A new kind of thermo-responsive hydrogel, poly(methacryloyl-DL.alanie methyl ester), was synthesized by means of radiation polymerization. The swelling and desweHing were reversible.The deswelling kinetics changes with the variation of temperature. It was found that a rigid membrane was formed during deswlling at 40 °C . In the case of deswelling at 20 °C , no skin was found. The hydrogel deswelled uniformly.
KEYWORDS Thermo-responsive hydrogel; radiation polymerization; swelling.
INTRODUCTION Thermo-resporisive hydrogels have found many applications in drug delivery system [1], thermo- feedback control reaction 121 and solvents extraction from solutions [3j because of their excellent properties of reversible swelling and deswelling. So far, most of the researches focused on N-isopropylacryloylamide. To develop new kinds of materials, we have synthesized amino acid contained polymer, poty(methacryloyl-DLalanine methyl ester) and its copolymers, by means of radiation polymerization. The polymer was found to be possess of thermo- responsive swelling and deswelling property. It was found that there were different ways of deswelling at the temperature of 20 °Cand 40 °C . A skin was formed on the surface of hydorgel deswelled at 40 °C and no akin could be found on the hydrogel deswelled at 20 °C
EXPERIMENTAL Synthesis Mixtures of monomer (methacryloyl-DL-alanine methyl ester), comonmers and crosslinking agents (Polyetylene glycol dimethacrylate) were charged into test tubes with diameter of 8mm and irradiated by ‘~ — ray. from a cobalt 60 source at a dose rate of 10 kGy/h for 3 hr. at 50 °C with nitrogen gas protection. The polymers were subsequently extracted by immersing in ethanol for 5 days to remove unreacted chemicals and water to replace the ethanol in the polymers. Swelling and deswelling Swelling ratio of polymers was measured gravimetrically. The swelling ratio was defined as C(%) = (W — Wo)/Wo x 100, where W is the weight of the sample after swelling at desired temperature for 24 hours and Wo is the weight of sample. In the measurement of deswelling, the samples saturate swollen at 0 °Cwere put into water bath of 20 °C or 40 °C , where the samples began to desweli. The weights of the samples were recorded at varying deswelling time.
959
960
DING ZHONGLI et a!.
Sample preparation for SEM observation To study deswelling kinetics, the samples were swollen to saturation at 0 00 before deswellung. Samples deswelled at a constant temperature water bath for desired time were taken out and immediatly put into dry ice-ethanol mixture for one mm. and freeze dryed. The dry samples were golden tinted. Then SEM observations were made.
RESULTS AND DISCUSSION To observe the difference of deswelling at different temperature, the gels saturate swollen at 0 00 were put into 20 00 and 40 00 water bathes, respectively. The result shown in Fig.! tells the remarkable difference. About 80% of water was extruded out of the gals within one hour when deswelled at 40 00 . It took about 24 hours for the gels deswelled at 20 00 to drive out 75% of water. To finde the causes, we investigated process of deswelling by microscopy. Pictures taken during deswelling were shown in Fig.2. Gel swelled at 0 ~C was transparent (a). It changed to white immediately after immersing into water bath of 40 00 (b) and then bubbles appeared on its surface (c). A membrane is clearly shown in picture (d) which was taken in 1580 miii.. SEM (scanning electron microscopy) observation gives the micros view on this interesting membrane as shown in Fig.3. The control sample (a) was full of pores either inside and surface. The pores still were visible on the surface of the gel deswelled 15 mm.. A rigid membrane was present on the surface of the gel which had undergone 45 mm. deswelling. The embrane grow thicker from 2.6 ~m (at 45 miii.) to 78 ~im (at 180 miii.). Fig.4 shows the deswelling process of 20 00 There were pores on the surface of the gel even after 180 miii. deswelling though the sizes of that were decreased. The shrinkage force of the gel is much stronger at 40 00 than that at 20 00 . It is due to having less equilibrium swelling ratio at 40 00 . In the case of deswellung at 40 00 , surface layer of the gel shrinked very quickly and water provisions from inside of the gel was not enough to compensate the water lose of surface layer because of its low diffuse speed. This surface layer was finaly changed into a rigid membrane which blocked the water to diffuse out in great amount. The deswellung, therefore, became slower. En contrast, the surface layer of a gel deswelled at 20 ~c shrunked slowly. It, hence, acquired sufficient water supply from inside of the gel to leak out. In this case, membrane could not be formed.
CONCLUSION The deswllung kinetics was affected by temperature. Being smooth at 20 °Cthe deswelling was rather fast at 40 00 and a rigid membrane was formed on the surface.
REFERENCES [lj. T. Okano, Y. H. Bea, H. Jacobs and S. W. Kim (1q90). Thermally on.off switching polymers for drug permeation and release. ,LQLcontrolled Release, 11, 255-26~. 121. L. Z. Doug and A. S. Hoffman (1986). Thermally reversible hydrogels. III. Immobilization of enzymes for feedback reactiontrol. J. of Controlled Release, 4, 223-227. [31.R. F. S. F’reitas and E. L. Cussler (1987). Temperature sensitive gels as size selective absobants. ch~m. En~ineerungScj,, ~,
97-103.
8th International Meeting on Radiation Processing
‘~1200
-
ot~2~3.b#~5O6.b7.O
Time
(
hr.)
Fig.l. Deswelling kinetics of copoly(MA—DL—A1&)Me/HPA/9G) (v/v/v) at 20°C (o) and 40°C (D).
Fig.2. ~icroscopypictures of deswelling ~el at 40°c. a. 0 mm. (xlO); b. 0.5 mm. (xlO); c. 6 mm. (x20); d. 1200 mm. (x30).
961
962
DING ZHONGLI et a!.
Inside
Surface
I’
b
..1
.
Fig. 3. SEM pictures of deswelling gel at 40°C a. Control (x400); b. 15 mm. (x400); c. 45 mm. (x1000) and d. 180 mm. (x400). The thickness of membrane in c. is 2.6 tim and d. 78 ~m.
__
-
-
Fig. 4. SEM pictures of deswelling gel at 20°C a. 45 mm. (x130) and b. 180 mm. (xl000).