Recent Advances on Implantable Wireless Sensor Networks

Implantable electronic devices are undergoing a miniaturization age, becoming more efficient and yet more powerful as well. Biomedical sensors are used to monitor a multitude of physiological parameters, such as glucose levels, blood pressure and neural activity. A group of sensors working together in the human body is the main component of a body area network, which is a wireless sensor network applied to the human body. In this chapter, applications of wireless biomedical sensors are presented, along with state-of-the-art communication and powering mechanisms of these devices. Furthermore, recent integration methods that allow the sensors to become smaller and more suitable for implantation are summarized. For individual sensors to become a body area network (BAN), they must form a network and work together. Issues that must be addressed when developing these networks are detailed and, finally, mobility methods for implanted sensors are presented

Antennas and wireless power transfer to small biomedical brain implants

Peer reviewe

An Implantable Low Pressure, Low Drift, Dual BioPressure Sensor and In-Vivo Calibration Methods Thereof

The human body’s intracranial pressure (ICP) is a critical component in sustaining healthy blood flow to the brain while allowing adequate volume for brain tissue within the rigid structures of the cranium. Disruptions in the body’s autoregulation of intracranial pressure are often caused by hemorrhage, tumors, edema, or excess cerebral spinal fluid resulting in treatments that are estimated to globally cost up to approximately five billion dollars annually. A critical element in the contemporary management of acute head injury, intracranial hemorrhage, stroke, or other conditions resulting in intracranial hypertension, is the real-time monitoring of ICP. Currently, such mainstream clinical monitoring can only take place short-term within an acute care hospital. The monitoring is prone to measurement drift and is comprised of externally tethered pressure sensors that are temporarily implanted into the brain, thus carrying a significant risk of infection. To date, reliable, low drift, completely internalized, long-term ICP monitoring devices remain elusive. The successful development of such a device would not only be safer and more reliable in the short-term but would expand the use of ICP monitoring for the management of chronic intracranial hypertension and enable further clinical research into these disorders. The research herein reviews the current challenges of existing ICP monitoring systems, develops a new novel sensing technology, and evaluates the same for potentially facilitating long-term implantable ICP sensing. Based upon the findings of this research, this dissertation proposes and evaluates a dual matched-die piezo-resistive strain sensing device, with a novel in-vivo calibration system and method thereof, for application to long-term implantable ICP sensing

Inductively Powered Implantable System with Far-field Data Transmitter for an Intracranial Pressure Monitoring Application: Design and Performance Validation

Monitoring of the intracranial pressure (ICP) is an essential activity for many brain diseases and injuries. For an adult, ICP value is between 7 mmHg to 15 mmHg . However, for a critically ill patient, the ICP should be maintained below 20 mmHg. Therefore, continuous monitoring of ICP is a life-saving activity. Several invasive and non-invasive methods have been proposed for monitoring of the ICP. However, invasive methods cannot be used for continuous monitoring of the ICP due to the risk of infection. Moreover, non-invasive methods lack in accuracy.Therefore, many researchers reported battery-powered or fully passive implantable systems. However, a battery-powered implant has limited life and large size. On the other hand, in a fully passive implant the readout distance is relatively small in comparison with a battery-powered implant due to its zero-power operation.In contrast, this work presents the development of an inductively powered implantable system equipped with a data transmission unit for an ICP monitoring application. The developed system has three main parts: an implant or in-body unit, an on-body unit and an off-body unit. The on-body unit powers the implant through inductive near-field link. After the activation, the implant, consists of a piezoresistive pressure sensor and a data transmission unit, transmits the pressure signal at the industrial, scientific, and medical radio (ISM) band of 2.45 GHz. The off-body unit receives the transmitted signal from the implant and estimates the pressure value.The simulation and the measurement results of both near-filed and far-field links are presented. After the development of the system, the pressue readout measurement results have been presented in the air, water and in a setting mimicking the human head dielectric properties. For biocompatibility, the implant is coated with biocompatible adhesive silicone. The effect of coating on both wireless links has also been studied.Finally, this work also presents the effect of misalignment between the inductively coupled antennas on the pressure readout accuracy of the developed ICP monitoring system and discusses the solution to overcome this impact. The thesis also presents the response of the developed ICP monitoring system with the change in the temperature

Beyond Tissue replacement: The Emerging role of smart implants in healthcare

Smart implants are increasingly used to treat various diseases, track patient status, and restore tissue and organ function. These devices support internal organs, actively stimulate nerves, and monitor essential functions. With continuous monitoring or stimulation, patient observation quality and subsequent treatment can be improved. Additionally, using biodegradable and entirely excreted implant materials eliminates the need for surgical removal, providing a patient-friendly solution. In this review, we classify smart implants and discuss the latest prototypes, materials, and technologies employed in their creation. Our focus lies in exploring medical devices beyond replacing an organ or tissue and incorporating new functionality through sensors and electronic circuits. We also examine the advantages, opportunities, and challenges of creating implantable devices that preserve all critical functions. By presenting an in-depth overview of the current state-of-the-art smart implants, we shed light on persistent issues and limitations while discussing potential avenues for future advancements in materials used for these devices

Integrated Electronics for Wireless Imaging Microsystems with CMUT Arrays

Integration of transducer arrays with interface electronics in the form of single-chip CMUT-on-CMOS has emerged into the field of medical ultrasound imaging and is transforming this field. It has already been used in several commercial products such as handheld full-body imagers and it is being implemented by commercial and academic groups for Intravascular Ultrasound and Intracardiac Echocardiography. However, large attenuation of ultrasonic waves transmitted through the skull has prevented ultrasound imaging of the brain. This research is a prime step toward implantable wireless microsystems that use ultrasound to image the brain by bypassing the skull. These microsystems offer autonomous scanning (beam steering and focusing) of the brain and transferring data out of the brain for further processing and image reconstruction. The objective of the presented research is to develop building blocks of an integrated electronics architecture for CMUT based wireless ultrasound imaging systems while providing a fundamental study on interfacing CMUT arrays with their associated integrated electronics in terms of electrical power transfer and acoustic reflection which would potentially lead to more efficient and high-performance systems. A fully wireless architecture for ultrasound imaging is demonstrated for the first time. An on-chip programmable transmit (TX) beamformer enables phased array focusing and steering of ultrasound waves in the transmit mode while its on-chip bandpass noise shaping digitizer followed by an ultra-wideband (UWB) uplink transmitter minimizes the effect of path loss on the transmitted image data out of the brain. A single-chip application-specific integrated circuit (ASIC) is de- signed to realize the wireless architecture and interface with array elements, each of which includes a transceiver (TRX) front-end with a high-voltage (HV) pulser, a high-voltage T/R switch, and a low-noise amplifier (LNA). Novel design techniques are implemented in the system to enhance the performance of its building blocks. Apart from imaging capability, the implantable wireless microsystems can include a pressure sensing readout to measure intracranial pressure. To do so, a power-efficient readout for pressure sensing is presented. It uses pseudo-pseudo differential readout topology to cut down the static power consumption of the sensor for further power savings in wireless microsystems. In addition, the effect of matching and electrical termination on CMUT array elements is explored leading to new interface structures to improve bandwidth and sensitivity of CMUT arrays in different operation regions. Comprehensive analysis, modeling, and simulation methodologies are presented for further investigation.Ph.D

A Fully Implantable, Miniaturized RFID Platform for Neurosurgical Biomedical Devices

Hydrocephalus occurs when excessive quantities of cerebrospinal fluid (CSF) accumulate in the ventricles. Current treatment of the condition involves implanting a ventricular shunt, composed of an inflow catheter originating at the site of the obstructed ventricle, a valve, and an outflow catheter that drains the excess fluid into the peritoneal cavity where it can be safely reabsorbed or excreted. This method of treatment is crude and subject to many complications including, but not limited to, infection, blockage, and over-draining. Therefore, the flow of CSF out of the ventricles and into the abdomen must be carefully monitored. Unfortunately, there is currently no effective and non-invasive means of doing so. Here we present the design and partial integration of a prototype for a wireless, fully implantable, miniaturized RFID-based device for monitoring and recording the functional state of a ventricular shunt. The purpose of this device is to provide a minimally-invasive and robust method for digitally interrogating shunt function. Such a platform would, ideally, allow for real-time, wireless monitoring which will serve to inform the patient and their care providers of abnormalities in shunt performance and allow them to take the appropriate measures before further complications can occur

Miniaturized Piezo Force Sensor for a Medical Catheter and Implantable Device

Real-time monitoring of intrabody pressures can benefit from the use of miniaturized force sensors during surgical interventions or for the recovery period thereafter. Herein, we present a force sensor made of poly(vinylidene fluoride)-co-trifluoroethylene (P(VDF-TrFE)) with a simple fabrication process that has been integrated into the tip of a medical catheter for intraluminal pressure monitoring, as well as into an implantable device with a power consumption of 180 μW obtained by the near-field communication (NFC) interface to monitor the arterial pulse at the subcutaneous level (≤1 cm). The pressure range supported by the sensor is below 40 kPa, with a signal responsivity of 0.63 μV/Pa and a mean lifetime expectancy of 400 000 loading cycles inside physiological conditions (12 kPa). The proposed sensor has been tested experimentally with synthetic anatomical models for the lungs (bronchoscopy) and subcutaneous tissue, as well as directly above the human carotid and radial arteries. Information about these pressure levels can provide insights about tissue homeostasis inside the body as fluid dynamics are altered in some health conditions affecting the hemodynamic and endocrine body systems, whereas for surgical interventions, precise control and estimation of the pressure exerted by a catheter over the internal walls are necessary to avoid endothelium injuries that lead to bleeding, liquid extravasation, or flow alteration associated with atheroma formation