Injectable Sensors Based on Passive Rectification of Volume-Conducted Currents.

Shahid Malik,Quim Castellvi,Aracelys Garcia-Moreno,Marc Tudela-Pi,Antoni Ivorra,Laura Becerra-Fajardo,Maryam Shojaei Baghini

doi:10.1109/tbcas.2020.3002326

Abstract

Sensing implants that can be deployed by catheterization or by injection are preferable over implants requiring invasive surgery. However, present powering methods for active implants and present interrogation methods for passive implants require bulky parts within the implants that hinder the development of such minimally invasive devices. In this article, we propose a novel approach that potentially enables the development of passive sensing systems overcoming the limitations of previous implantable sensing systems in terms of miniaturization. In this approach implants are shaped as thread-like devices suitable for implantation by injection. Their basic structure consists of a thin elongated body with two electrodes at opposite ends and a simple and small circuit made up of a diode, a capacitor and a resistor. The interrogation method to obtain measurements from the implants consists in applying innocuous bursts of high frequency (≥1MHz) alternating current that reach the implants by volume conduction and in capturing and processing the voltage signals that the implants produce after the bursts. As proof-of-concept, and for illustrating how to put in practice this novel approach, here we describe the development and characterization of a system for measuring the conductivity of tissues surrounding the implant. We also describe the implementation and the in vitro validation of a 0.95mm-thick, flexible injectable implant made of off-the-shelf components. For conductivities ranging from about 0.2 to 0.8S/m, when compared to a commercial conductivity meter, the accuracy of the implemented system was about ±10%.

Highlights

IntroductionI MPLANTABLE sensing systems are mainly motivated by the need to monitor clinically relevant magnitudes directly in the body regions where the physiologically relevant events take place [1]
I MPLANTABLE sensing systems are mainly motivated by the need to monitor clinically relevant magnitudes directly in the body regions where the physiologically relevant events take place [1].Some implantable sensing systems are already used in clinical practice
In a preceding study in which we propose the use of volume conduction to power active implants, we lengthy discuss the implications of these two restrictions on the permissible characteristics of the applied alternating currents [14]

Summary

Introduction

I MPLANTABLE sensing systems are mainly motivated by the need to monitor clinically relevant magnitudes directly in the body regions where the physiologically relevant events take place [1]. Some implantable sensing systems are already used in clinical practice. The number of commercially available systems is very small in contrast with the breath of academic research in the field of implantable sensors [1]. Among those factors is invasiveness: systems that require highly invasive surgeries to implant the devices are unlikely to be adopted if less invasive, or non-invasive, solutions exist; even if those solutions are sub-optimal regarding their performance [5]

Methods

Results

Discussion

Conclusion