Bulletin Spring‧Summer Autumn‧Winter 1999

Fig. 1 Polyelectrolyte gel network In fact, familiar gels such as jello and sea cucumbers are all of this type. Their Intelligence Lies i n Phase Transitions Some types of polyelectrolyte gels undergo 'phase transitions', and are extremely useful materials i n medicine and chemical technology. Phase transitions are sudden changes in the properties of a material when the external environment is slightly altered. The classic example is the boiling of water: by just changing the temperature from 99.9...9 °C to 100.0°C, water suddenly becomes steam, expanding 1700-fold. This somewhat trivial observation is the basis of the steam engine, and indeed the industrial revolution. Those polyelectrolyte gels that undergo phase transitions can have sudden changes in volume, ranging from 100 to 500 times of their original size. These transitions are caused by tiny changes i n temperature, solvent composition, salinity, acidity (pH), ionic strength and electric field. For example, the gel called poly(N-isopropylacrylamide) can suddenly swell 100-fold when the temperature is changed by as little as one degree, f r om 32°C to 31°C. It is as if these gels w o u l d pe r f o rm tasks on demand; they are thus sometimes called intelligent gels. Dr. Wu Ch i 's w o r k focusses on these i n t e l l i g e nt p o l y e l e t r o l y t ic ge l s. T h i s impo r t ant projec t w o n competitive f und i ng of $546,000 f r om the Research Grants Council i n 1993. Medi cal Applications Some medication is destroyed i n acidic conditions. They wou l d therefore be rendered useless in the acidic environment of the stomach. Scientists therefore develop a gel wh i ch shrinks m acidic conditions and expands i n alkaline conditions. If the medication is encapsulated in such a gel, it w i l l be t i g h t l y p r o t e c t ed w h e n pa s s i ng through the stomach, however, in the relative alkaline conditions of the intestines, the gel w i l l expand and release the med i c a t i on, w h i c h is t hen absorbed b y the i n t es t i nal walls. A t the Un i vers i ty of Trondheim i n No rway, researchers are wo r k i ng on an even mo r e i n t e r e s t i ng scheme. T h ey use an i n t e l l i g e nt gel t h a t e x p a n ds u p o n t he app l i ca t i on o f an electric f i e l d. I n s u l in is encapsulated i n such a gel, and imp l an t ed into diabetic patients. Then controlled release is achieved by applying an electric field external to the body; needle-pricks are thus spared. Research Objectives and Methodology Currently little is known about the sudden volume change, and its relationship wi th the gel structure. The development of gels wi th specific properties is still based on trial-and- error, which is expensive, time-consuming, and usually unreliable. Therefore the focus of Dr. Wu's research is to obtain a deeper understanding of the transition, which wi ll enable the industrial sector to develop Research 14