Confined Smart Hydrogels for Applications in Chemomechanical Sensors for Physiological Monitoring
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Confined Smart Hydrogels for Applications in Chemomechanical Sensors for Physiological Monitoring Jules J. Magda1, Genyao Lin1, Prashant Tathireddy2, Michael Orthner2, Florian Solzbacher1,2, Volker Schulz3, Margarita Guenther3, and Gerard Gerlach3 : 1Department of Materials Science & Engineering, University of Utah, Salt Lake City, UT 84112, U.S.A 2 Department of Electrical & Computer Engineering, University of Utah, Salt Lake City, UT 84112, U.S.A. 3 Solid-State Electronics Laboratory (IFE), Technische Universität Dresden, Helmholtzstr. 10, 01069 Dresden, Germany
ABSTRACT A “smart” hydrogel is a crosslinked polymer network that reversibly swells and absorbs water in response to an external stimulus such as change in pH or in the concentration of some analyte such as glucose. Microscopically-thin smart hydrogels can be combined with microfabricated piezoresistive pressure transducers to obtain “chemomechanical sensors” that serve as selective and versatile wireless biomedical sensors. Proof-of-concept is shown here using glucose- and pH-responsive hydrogels. INTRODUCTION One of the principal long-term goals of medicine is to couple drug administration with sensors or smart materials to give on-demand delivery of drugs in appropriate amounts.1-5An implanted sensor might be used to signal a patient to inject insulin, or an entire autonomous system might be implanted for in vivo drug delivery. The limiting step in the development of feedback-controlled drug delivery systems is the creation of stable sensors.5 Perhaps the clearest example of this is in the arena of diabetes treatment. Diabetes, defined as the disease in which the body is unable to control blood glucose levels, currently affects over 16 million Americans with an annual growth rate of 15 %.6 In order to control diabetes, there is a great need for a sensor that could be used to measure a patient’s blood glucose concentration continuously twenty four hours a day.7-10 To date this need has not been met, at least on a long-term basis. We believe that hydrogel-based chemomechanical sensors may someday meet this need for a chronically-implantable glucose sensor for the reasons discussed below. However, it should be emphasized that hydrogel-based sensors such as the one considered here are not limited to glucose monitoring. One of the great virtues of smart hydrogels is that they can be tailored to show specific response toward many different analytes, such as cholesterol, lactate, creatine, and various antigens.12,14-15 Outside the body, hydrogel-based sensors might be used to monitor penicillin, alcohols, or toxins for quality control of food processing operations.16 Figure 1 contains a sketch which demonstrates the concept of a chemomechanical sensor. A polymer hydrogel is said to be ‘smart’ or ‘stimuli-responsive’ if it absorbs or desorbs large quantities of water in response to some specific environmental trigger such as change of pH, temperature, or concentration of a specific molecule like glucose.18-20 As shown in Figure 1, our goal is to
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