Remote Powering and Communication of Implantable Biosensors Through Inductive Link

Nowadays there is an increasing interest in the field of implantable biosensors. The possibility of real-time monitoring of the human body from inside paves the way to a large number of applications and offers wide opportunities for the future. Within this scenario, the i-IronIC project aims to develop an implantable, low cost, health-care device for real-time monitoring of human metabolites. The contribution of this research work to the i-IronIC project consists of the design and realization of a complete platform to provide power, data communication and remote control to the implantable biosensor. High wearability of the transmitting unit, low invasivity of the implanted electronics, integration of the power management module within the sensor, and a reliable communication protocol with portable devices are the key points of this platform. The power is transmitted to the implanted sensor by exploiting an inductive link. Simulations have been performed to check the effects of several variables on the link performance. These simulations have finally confirmed the possibility to operate in the low megahertz range, where tissue absorption is minimum, even if a miniaturized receiving inductor is used. A wearable patch has been designed to transmit power through the body tissues by driving an external inductor. The same inductive link is used to achieve bidirectional data communication with the implanted device. The patch, named IronIC, is powered by lithium-ion polymer batteries and can be remotely controlled by means of a dedicated Android application running on smartphones and tablets. Long-range communication between the patch and portable devices is performed by means of Bluetooth protocol. Different typologies of receiving inductors have been designed to minimize the size of the implantable device and reduce the discomfort of the patience. Multi-layer, printed spiral inductors and microfabricated spiral inductors have been designed, fabricated and tested. Both the approaches involve a sensibly smaller size, as compared to classic “pancake” inductors used for remote powering. Furthermore, the second solution enables the realization of the receiving inductor directly on the silicon substrate hosting the sensor, thus involving a further miniaturization of the implanted device. An integrated power module has been designed and fabricated in 0.18 μm CMOS technology to perform power management and data communication with the external patch. The circuit, to be merged with the sensor readout circuit, consists of an half-wave voltage rectifier, a low-dropout regulator, an amplitude demodulator and a load modulator. The module receives the power from the implanted inductor and provides a stable voltage to the sensor readout circuit. Finally, the amplitude demodulator and the load modulator enable short-range communication with the patch

Modeling of Printed Spiral Inductors for Remote Powering of Implantable Biosensors

Fully implantable biosensors require small size to be minimally invasive. To avoid embedded batteries, power can be supplied by means of printed spiral inductors located on the skin, close to the implanted devices. Reliable models are required to optimize the design of such inductors. In this paper, a RLC model to describe the electrical properties of printed spiral inductors is proposed. The model is based on the geometrical and physical characteristics of the inductors. The accuracy of the model is finally compared with the experimental measurements

Optimal Frequencies for Inductive Powering of Fully Implantable Biosensors for Chronic and Elderly Patients

The paper aims at exploring advantages and drawbacks of using high-frequency inductive links to transmit power wirelessly to implanted biosensors. A system with an external transmitting coil located into a skin patch and a receiving coil embedded into a fully implanted biosensor is simulated. The effects of the geometry of the coils on the optimal working frequencies and on the power gain have been analyzed. For applications dedicated to elderly and chronic patients, attention has been posed to the effects on link efficiency of different implantation sites and possible misalignments between the coils

IronIC Patch: A Wearable Device for the Remote Powering and Connectivity of Implantable Systems

A wearable device to power implanted sensors by means of an inductive link is presented. The system, having size 69 × 40 mm2, is designed to be embedded into a skin patch and located over the implantation area. The system can transfer up to 15 mW within 6 mm in air. Tested with a 17 mm thick beef sirloin placed between the inductors, the device is able to deliver up to 1.17 mW. Downlink communication with the implanted sensors is performed at 100 kbps by using amplitude modulation. Uplink communication is performed at 66.6 kbps by using load modulation. Long range communication between the system and remote devices is enabled by a bluetooth module. The system is powered by two rechargeable lithium-ion polymer batteries and has an autonomy of 10 h in stand-by mode and about 1.5 h in transmitting mode

A Study of Multi-Layer Spiral Inductors for Remote Powering of Implantable Sensors

An approach based on multi-layer spiral inductors to remotely power implantable sensors is investigated. As compared to single-layer inductors having the same area, multi-layer printed inductors enable a higher efficiency (up to 35% higher) and voltage gain (almost one order of magnitude higher). A system conceived to be embedded into a skin patch is designed to verify the performance. The system is able to transmit up to 15 mW over a distance of 6 mm and up to 1.17 mW where a 17 mm beef sirloin is placed between the inductors. Furthermore, the system performs downlink communication (up to 100 kbps) and uplink communication based on the backscattering technique (up to 66.6 kbps). Long-range communication is achieved by means of a bluetooth module

Biofuel Cells and Inductive Powering as Energy Harvesting Techniques for Implantable Sensors

In order to increase the power autonomy of implantable sensors, energy harvesters can aid and, in certain cases, substitute implantable batteries. The paper describes two promising techniques among the approaches presented in literature: biofuel cells and inductive powering. For both tech- niques, key points and drawbacks are illustrated, together with a summary of the solutions pre- sented in literature. Potential methods to enhance the performance of biofuel cells by means of nanostructured materials are presented and discussed

Energy Harvesting and Remote Powering for Implantable Biosensors

The paper reviews some popular techniques to harvest energy for implantable biosensors. For each technique, the advantages and drawbacks are discussed. Emphasis is placed to the inductive links, able to deliver power wirelessly through the biological tissues and to enable a bidirectional data communication with the implanted sensors. Finally, high frequency inductive links are described, focusing also on the power absorbed by the tissues

Integrated biosensors for cell culture monitoring

Biosensors for endogenous compounds, such as glucose and lactate, are applied to monitor cell cultures. Cells can be cultivated for several purposes, such as understanding and modeling some biological mechanisms, the development of new drugs and therapies, and in the field of regenerative medicine. We have realized a self-contained monitoring system with remote readout. Metabolite detection is based on oxidases immobilized onto carbon nanotubes. We calibrate the system for glucose and lactate detection in phosphate buffer solution. A hw/sw architecture records the signal generated by the biosensor and transmits it to a remote station by means of a Bluetooth module. We have validated two biosensors for metabolic monitoring in culture medium and we detect lactate production in neuroblastoma cells after 72 h of cultivation. The integrated system proposed in the present work opens new opportunities towards the development of novel tools for cell analysis

New Approaches for Carbon Nanotubes-Based Biosensors and Their Application to Cell Culture Monitoring

Amperometric biosensors are complex systems and they require a combination of technologies for their development. The aim of the present work is to propose a new approach in order to develop nanostructured biosensors for the real-time detection of multiple metabolites in cell culture flasks. The fabrication of five Au working electrodes onto silicon substrate is achieved with CMOS compatible microtechnology. Each working electrode presents an area of 0.25 mm2 , so structuration with carbon nanotubes and specific functionalization are carried out by using spotting technology, originally developed for microarrays and DNA printing. The electrodes are characterized by cyclic voltammetry and compared with commercially available screen-printed electrodes. Measurements are carried out under flow conditions, so a simple fluidic system is developed to guarantee a continuous flow next to the electrodes. The working electrodes are functionalized with different enzymes and calibrated for the real-time detection of glucose, lactate, and glutamate. Finally, some tests are performed on surnatant conditioned medium sampled from neuroblastoma cells (NG-108 cell line) to detect glucose and lactate concentration after 72 hours of cultivation. The developed biosensor for real-time and online detection of multiple metabolites shows very promising results towards circuits and systems for cell culture monitoring

A Self-Contained System With CNTs-Based Biosensors for Cell Culture Monitoring

Biosensors have been applied to disparate fields, especially for endogenous compounds such as glucose and lactate. The main areas of application are certainly related to medical and diagnostic purposes. However, metabolic monitoring can be also of interest in cell analysis. Cells can be cultivated for several purposes, such as understanding and modeling some biological mechanisms, the development of new drugs and therapies, or in the field of regenerative medicine. All the aforementioned applications require a thorough knowledge of the biological system under study. In this paper, we propose the development of a self-contained system based on electrochemical biosensors for cell culture monitoring. The detection is based on oxidases immobilized onto carbon nanotubes. We also develop an architecture to record the signal generated by the biosensor and transmit it to a remote station by means of a Bluetooth module. We calibrate the system for glucose and lactate detection in phosphate buffer solution. We achieve a sensitivity of 55.5 µA/mMcm-2and a detection limit of 2 µM for glucose, as well as a sensitivity of 25.0 µA/mMcm-2 and a detection limit of 11 µM for lactate. We finally validate the two biosensors for metabolic monitoring in culture medium and we detect lactate production in neuroblastoma cells after 72 h of cultivation. The integrated system proposed in the present work opens new opportunities towards the development of novel tools for cell analysis