In vitro investigations of a pH- and ionic-strength-responsive polyelectrolytic hydrogel using a piezoresistive microsensor

Volker Schulz; Margarita Guenther; Gerald U. Gerlach; Jules J. Magda; Prashant Tathireddy; Loren Rieth; Florian Solzbacher

doi:10.1117/12.816478

6 April 2009 In vitro investigations of a pH- and ionic-strength-responsive polyelectrolytic hydrogel using a piezoresistive microsensor

Volker Schulz, Margarita Guenther, Gerald U. Gerlach, Jules J. Magda, Prashant Tathireddy, Loren Rieth, Florian Solzbacher

Author Affiliations +

Proceedings Volume 7287, Electroactive Polymer Actuators and Devices (EAPAD) 2009; 728712 (2009) https://doi.org/10.1117/12.816478
Event: SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring, 2009, San Diego, California, United States

Abstract

Environmentally responsive or smart hydrogels show a volume phase transition due to changes of external stimuli such as pH or ionic strength of an ambient solution. Thus, they are able to convert reversibly chemical energy into mechanical energy and therefore they are suitable as sensitive material to be integrated in biochemical microsensors and MEMS devices. In this work, micro fabricated silicon pressure sensor chips with integrated piezoresistors were used as transducers for the conversion of mechanical work into an appropriate electrical output signal due to the deflection of a thin silicon bending plate. Within this work two different sensor designs have been studied. The biocompatible poly(hydroxypropyl methacrylate-N,N-dimethylaminoethyl methacrylate-tetra-ethyleneglycol dimethacrylate) (HPMADMA- TEGDMA) was used as an environmental-sensitive element in piezoresistive biochemical sensors. This polyelectrolytic hydrogel shows a very sharp volume phase transition at pH values below about 7.4 which is in the range of the physiological pH. The sensor's characteristic response was measured in-vitro for changes in pH of PBS buffer solution at fixed ionic strength. The experimental data was applied to the Hill equation and the sensor sensitivity as a function of pH was calculated out of it. The time-dependent sensor response was measured for small changes in pH, whereas different time constants have been observed. The same sensor principal was used for sensing the ionic strength. The time-dependent electrical output signal of both sensors was measured for variations in ionic strength at fixed pH value using PBS buffer solution. Both sensor types showed an asymmetric swelling behavior between the swelling and the deswelling cycle as well as different time constants, which was attributed to the different nature of mechanical hydrogel confinement inside the sensor.

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Volker Schulz, Margarita Guenther, Gerald U. Gerlach, Jules J. Magda, Prashant Tathireddy, Loren Rieth, and Florian Solzbacher "In vitro investigations of a pH- and ionic-strength-responsive polyelectrolytic hydrogel using a piezoresistive microsensor", Proc. SPIE 7287, Electroactive Polymer Actuators and Devices (EAPAD) 2009, 728712 (6 April 2009); https://doi.org/10.1117/12.816478

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