Smart Hydrogels Designed for use in Microfabricated Sensor Arrays
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Smart Hydrogels Designed for use in Microfabricated Sensor Arrays Jeffrey S. Bates1, Seung Hei Cho2, Prashant Tathireddy3, Loren W. Rieth3 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. 3 Department of Electrical and Computer Engineering, University of Utah, 50 Central Campus Drive, Room 3280, Salt Lake City, UT 84112 U.S.A. ABSTRACT Hydrogels are considered smart materials because they respond to environmental stimuli. Sensors that monitor the body’s pH levels would be helpful for doctors to determine the severity of a patient’s condition, especially if they exhibit signs of shock. The motivation of this project is to create a biomedical device that can be worn sublingually or implanted into the body to help doctors with diagnosing a patient’s condition. The magnitude of the swelling/deswelling behavior can be measured by placing a sample of the hydrogel in a piezoresistive sensor. The degree of swelling/deswelling is directly proportional to the change in pH of the aqueous solution it is placed in. In this study, a variety of compositions of pH responsive hydrogels were designed and tested to determine the response time and magnitude for use in both macro and micro sensor arrays. This pressure sensor has been designed for use with thinner gels than have been used in the past. The results for swelling time and magnitude were compared to determine the effect of the thickness of the hydrogel samples on the swelling/deswelling kinetics of the material in order to find the appropriate composition, thickness and device that will yield the desired response rate and sensitivity. INTRODUCTION Hydrogels have proven their ability to respond to changes in the local environment [1-6]. 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 respond to small changes in pH and other analyte concentrations in solution. Some researchers have proposed utilizing hydrogel based sensors in implantable devices [7-14]. There are others who have focused on hydrogel-based sensors for use in measuring changes in systemic pH changes in the human body [9-11]. A hydrogel sample of the same composition was tested under pH and ionic strength conditions to determine the response time and magnitude to changes in the analyte concentration. The gel was tested to determine the sensitivity to small changes in pH as well as the cross-sensitivity response to other analytes that may be present under systemic physiological conditions. EXPERIMENTAL METHODS Materials The following monomers were used as received from Sigma Aldrich: 2-hydroxyethyl methacrylate (HEMA), dimethylaminoethyl methacrylate (DMA), tetraethylene glycol
dimethacrylate, 2,2-dimethoxy-2-phenylacetophenone (DMPAP), ethylene glyc
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