Injectable Sensors Based on Passive Rectification of Volume-Conducted Currents

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 threadlike 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 (≥1 MHz) 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 0.95 mm-thick, flexible injectable implant made of off-the-shelf components. For conductivities ranging from about 0.2 to 0.8 S/m, when compared to a commercial conductivity meter, the accuracy of the implemented system was about ±10%.

Wireless networks of injectable microelectronic stimulators based on rectification of volume conducted high frequency currents

“…As previously demonstrated in [30,41–43], volume conduction can be electrically modeled using a two-port impedance network that characterizes coupling between the external system and the implanted device. Here, such modeling approach was tried for further confirmation of its validity.…”

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

“…The external unit must include a switching mechanism to avoid short-circuiting the decaying voltage signal volumeconducted from the implant in-between bursts. In [10] two antiparallel switching diodes connected in series to the external electrodes are proposed. This mechanism allows the flow of the HF current bursts delivered by the external generator, but blocks the small decaying voltages coming from the implant in-between bursts.…”

“…In [10] we described the development and characterization of a system for measuring the conductivity of tissues surrounding a 0.95 mm-thick, passive, flexible and injectable implant. Here we report the development and in vitro evaluation of a novel temperature sensing system based on the same passive sensing method to obtain ultrathin and flexible sensors that could be used for in situ temperature monitoring.…”

Injectable, dispersible polysulfone‐polysulfone core‐shell particles for optical oxygen sensing

“…In biomedical applications, injection of the sensing platform eliminates the need for more complex surgical implantations that can introduce additional complications and longer recovery times. [1][2][3] Luminescent oxygen sensors provide a robust sensor platform that can identify hypoxic areas. 4 In some cancer treatments, poorly oxygenated areas typically resist traditional chemotherapy and radiation and are associated with an increased likelihood of metastasis.…”

“…In biomedical applications, injection of the sensing platform eliminates the need for more complex surgical implantations that can introduce additional complications and longer recovery times 1–3 . Luminescent oxygen sensors provide a robust sensor platform that can identify hypoxic areas 4 .…”