In vivo Monitoring of Glucose using Ultrasound-induced Resonance in Implantable Smart Hydrogel Microstructures

Abstract A novel glucose sensor is presented that uses smart hydrogels as a biocompatible implantable sensing element, which completely eliminates the need for any implanted electronics and uses an external conventional medical-grade ultrasound transducer for readout. The readout mechanism makes use of resonance absorption of ultrasound waves in glucose-sensitive hydrogels. Changes in in vivo glucose concentration in the interstitial tissue lead to swelling and de-swelling of the gels which in turn lead to changes in resonance behavior. The hydrogels are designed and shaped such as to exhibit specific mechanical resonance frequencies while remaining sonolucent to other frequencies. Thus, they allow conventional and continued ultrasound imaging, while yielding a sensing signal at specific frequencies that is correlated with glucose concentration. The resonance frequencies can be tuned by changing the shape and mechanical properties of the gel structures, such as to allow for multiple, co-located implanted hydrogels with different sensing characteristics or targets to be employed and read out, without interference, using the same ultrasound transducer, by simply toggling frequencies. The fact that there is no need for any implantable electronics, also opens the path towards future use of biodegradable hydrogels, thus creating a platform that allows injection of sensors that do not need to be retrieved when they reach the end of their useful lifespan.