Time Interval and Continuous Testing of Stimuli Responsive Hydrogels
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Time Interval and Continuous Testing of Stimuli Responsive Hydrogels Jeffrey S. Bates1 and Jules J. Magda2 1 Department of Materials Science and Engineering, University of Utah, 122 Central Campus Drive, Room 304, Salt Lake City, UT 84112, U.S.A. 2 Department of Chemical Engineering, University of Utah, 50 Central Campus Drive, Room 3290, Salt Lake City, UT 84112 U.S.A.
ABSTRACT Researchers have investigated hydrogels as potential materials for biological monitoring. Hydrogel compositions have been designed to respond to changes in temperature, pH, glucose concentration and ionic strength concentration. Hydrogels designed to respond to changes in environmental conditions have demonstrated their ability to respond via a swelling or shrinking action. This swelling behavior can be exploited using a variety of signal transduction methods. While this technology shows promise, the degradation of hydrogel materials has not yet been characterized with respect to the shelf life of hydrogel samples or to their use in continuous testing. A series of experiments were performed to test hydrogels stored for extended periods of time then subjected to oscillatory testing, and the results have been analyzed to determine whether hydrogels can be used for extended periods of time for biological sensing applications. INTRODUCTION Hydrogels have proven their ability to respond to changes in the local environment [16]. While the results obtained by many researchers highlight the promising nature of hydrogels in biomedical sensors, work has yet to be done to demonstrate the ability of hydrogels to maintain a response after being stored for an extended period of time, and to demonstrate the ability to maintain a strong stimuli response after repeated cycles. Some researchers have proposed utilizing hydrogel based sensors in implantable devices [7]. If this technology is to work, it is important to understand the duration and stability of the stimuli response. This will determine the life of a hydrogel based sensor and the time frame in which the device will become ineffective and need to be replaced. Furthermore, devices may not be used as soon as the hydrogel has been synthesized. Therefore it is also important to understand how long a device may remain in storage before it loses its effectiveness. In this project, a hydrogel with a 2-hydroxyethyl methacrylate backbone was studied to determine the ability of the hydrogel to respond after extended periods of time in ambient conditions. The time intervals for this study were at zero, nine and at eighteen months. The data gathered in this project will be useful in determining storage duration and conditions for maintaining a strong stimuli response of the hydrogel. The research presented here also addresses the operational stability of the hydrogel. This will help researchers determine the length in which a hydrogel-based chemomechanical sensor may be used in medical and other biological applications without losing sensitivity to changes in environmental conditions. Chemomechanical sensors
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