Enabling Millimeter Scale Deeply Implanted Glucose Sensors through Ultrasonic Power Transfer and a Novel Glucose Sensing Mechanism

University Of Utah, Salt Lake City UT

Investigators

Abstract

Proposal Title: Enabling Millimeter Scale Deeply Implanted Glucose Sensors through Ultrasonic Power Transfer and a Novel Glucose Sensing Mechanism Proposal Goal: The goal of the proposed project is to enable a new mode for power transfer to and communication with a deeply implanted intraluminal glucose monitor. The current state of the art in integrated circuit and MEMS sensing technologies enables cubic mm size implementations of complex systems for implanted sensors. However, such implementations are never actually realized because the necessary power and communications systems are too large. At very small sizes and large implant depths acoustic energy transfer through human tissue is fundamentally more efficient than either near field electromagnetic (EM) or far field (RF). The long term goal of this research is to create an ultrasonic power and communications platform that will enable unobtrusive long term monitoring of health status through implanted sensing and therapeutic devices. Nontechnical Abstract: The past few decades have seen a dramatic increase in the prevalence of diabetes mellitus and obesity. The chief complications of these chronic diseases are cardiac disease, kidney failure leading to dialysis, retinopathy leading to blindness, and neuropathy and vascular insufficiency leading to amputations. These exert a huge toll, both in financial terms and in human suffering. Our research directly addresses this problem by developing new technologies that will enable long term implantable glucose monitors without the need for transcutaneous wires. This project addresses two fundamental problems with the current state of the art in implantable glucose sensors: lack of a suitable power supply or power transmission mechanism, and the short lifetime and frequent need for re-calibration of glucose oxidase based sensors. As part of this project, the PIs will create an ultrasonic power transmission platform that will allow the glucose sensor (or any highly miniaturized implantable bio-sensor) to be directly powered by ultrasonic energy. At very small sizes and large implant depths acoustic energy transfer through human tissue is fundamentally more efficient than either near field electromagnetic (EM) or far field (RF), the two most common methods of powering implanted sensors. This project will investigate micro-scale acoustic transducer designs and architectures that enable higher power density transmission than either EM or RF transmission through human tissue. To address the second fundamental problem with the state of the art, the PIs will explore a new glucose sensing method using hydrogels with embedded magnetic particles. This method overcomes several limitations that plague current enzymatic continuous glucose sensors and also allows the electronics to be robustly encapsulated as the electronic sensing element does not have to be in direct contact with the hydrogel. Together these advancements promise to enable a vastly improved method of sensing blood glucose and delivering power to any highly miniaturized implantable bio-sensor. Technical Abstract: This research addresses two major challenges that limit the potential of implanted biosensors in general, and glucose monitors in particular. The first is transferring energy at sufficient densities to enable extreme miniaturization. While still more efficient than RF or EM energy transfer, at very small scales, standard ultrasonic transducers rapidly start to lose efficiency due to the interplay between the optimal device thickness, acoustic wavelength, and the frequency dependence of acoustic absorption in tissue. Our guiding hypothesis is that alternative piezoelectric structures will be more efficient at these small sizes. Our work will couple acoustic transmission models, transducer design, and experimental work to empirically determine key interaction effects probing the limits of acoustic power generation at very small scales. Secondly, the research will address a significant issue with glucose sensors, namely that their lifetime is severely limited and they must be frequently re-calibrated because of their reliance on the availability glucose oxidase and oxygen to perform accurate measurements. The PIs will explore a new method using hydrogels with embedded aligned magnetic particles to sense glucose rather than the traditional electrochemical process. These functionalized hydrogels swell in the presence of glucose. The swelling is sensed through the change in inductance value of a miniature coil placed next to the hydrogel. This method not only overcomes several limitations that plague current enzymatic continuous glucose sensors but also allows the electronics to be robustly encapsulated as the sensing coil does not have to be in direct contact with the hydrogel. The sensing coil will be multi-purposed to send data back from the implant in a mm scale system demonstration. Taken together, the three different aspects of this work could provide a basis for fundamentally smaller, longer life implanted sensors.