Smart Hydrogel Ultrasound Resonators for Biomedical Sensing Applications

Smart hydrogels that react by a volume change to the presence (or absence) of analytes of biomedical relevance in their environment can be used as potentially biocompatible and versatile transducer component materials for sensing applications. While many different formulations for these hydrophilic stimuli-responsive polymeric materials are available in the literature, the challenge lies in the reliable detection of their volume-phase transition. We recently developed a novel read-out mechanism for smart hydrogel-based sensing that is realized by structuring the smart hydrogel into micromechanical resonators with resonance frequencies in the medical ultrasound range. These resonator structures are then queried remotely via the application of medical ultrasound imaging. Any change to the hydrogels’ swelling state also influences the resonance spectrum of the resonators and thus will result in altered absorption characteristics of the structures when exposed to ultrasound waves. Extracting this information from reflected ultrasound pulses enables a measurement of the swelling state of the hydrogel and, given a suitable smart hydrogel, the analyte-of-interest concentration in the environment of the hydrogel. The remote sensing principle and the widespread use of ultrasound in a medical context makes this approach well-tailored towards biomedical applications such as implantable analyte concentration monitoring devices for healthcare. In this presentation we will discuss our recent in vitro and in vivo results that are based on the described sensing principle with glucose as the target analyte. For this an acrylamide-based smart hydrogel using 3-acrylamidophenylboronic acid as analyte sensing moiety was employed. In these proof-of-principle in vitro experiments, the sensor was verified and characterized using commercially available medical ultrasound equipment. In the follow-up acute in vivo experiments, we then demonstrated that the hydrogel resonators could be implanted and maintain their functionality for glucose sensing. Additionally, we will briefly touch on the theory behind the measurements as well as the fabrication of smart hydrogel resonator structures and discuss other potential applications for this platform technology.<br/>The authors declare the following competing financial interests managed through the University of Utah's Conflict of Interest Management: Florian Solzbacher declares a financial interest in Blackrock Microsystems, LLC and Sentiomed, Inc. Jules J. Magda declares a financial interest in Applied Biosensors, LLC.