Implantable Medical Systems Research Articles

A Novel Method of Wireless Micro Energy Transmission Based on MEMS Micro Coil.

Based on current implantable devices, a battery's rigidity and large size makes it prone to immune rejection and wound incisions. Additionally, it is limited by its finite lifespan, which hinders long-term usage. These limitations greatly restrict the development of implantable medical device systems towards miniaturization and minimally invasive approaches. Consequently, obtaining high-fidelity and stable biological signals from the target tissue area of the organism remains challenging. Therefore, there is a need to develop wireless power transmission technology. In this paper, we propose a wireless micro energy transfer method based on MEMS micro coils for charging implantable devices. Through simulation calculations, we first investigate the influence of coaxial distance, horizontal displacement, and rotation angle between the MEMS micro coil and the transmitting coil on power transmission. Subsequently, we utilize micro nanofabrication technology to create a MEMS micro spiral copper coil with a line width, thickness, and spacing of 50 µm and a total of five turns. Finally, we conduct wireless power transmission tests on the coil. The results show that, when the transmitting coil and the receiving coil are 10 mm apart and the operating frequency is 100 kHz, the power of the wireless power transmission system reaches 45 µW. This power level is sufficient to meet the power supply requirements of implantable pacemakers. Therefore, this technology holds great potential for applications in the field of wireless power transmission for implantable medical devices, including pacemakers and brain neurostimulators.

Ultrasound vibration energy harvesting from a rotary-type piezoelectric ultrasonic actuator

Ultrasound vibrations, which are abundant in our everyday environment, have long been widely used in industrial applications and medical therapeutics. While there have massive number of studies on harvesting the low-frequency vibration energy to power the low-powered electronic devices, there are few literatures on the ultrasound vibration energy harvesting. In order to validate the feasibility of ultrasound vibration energy harvesting, this article takes a rotary-type piezoelectric ultrasound actuator (PUA) as the research object, a new PZT ring with appropriate zoning and polarization is bonded onto its elastomer top surface to harvest the vibration energy induced by the ultrasound waves. The manufacturing process and operating mechanism of the modified PUA are firstly introduced. Then, the electromechanical coupled model is derived based on the equivalent circuit method, and the dynamic and energetic characteristics of the ultrasound vibration energy harvesting under three excitation modes (i.e., two standing waves and one traveling wave excitations) are theoretically studied. The experimental results testify the theoretical values, and the feasibility of ultrasound vibration energy harvesting is also validated by experiments and an application example. When the PUA is excited by traveling ultrasound wave with amplitude 67 V and frequency 35.1 kHz, the maximum harvested power of each sector of the new PZT ring and λ/4 sector of the bottom PZT ring reach 58 mW and 82.4 mW, respectively, which fully meet the power supplying requirements of low-powered electronic products and implantable medical systems.

Simultaneous Wireless Power and Data Transfer: Methods to Design Robust Medical Implants for Gastrointestinal Tract

Implantable medical systems for long-term monitoring of bioelectrical activity of the gastrointestinal (GI) tract, known as slow waves, and for treating GI dysmotility and functional disorders through electrical stimulation pulses have emerged over the recent years. These implants construct a bidirectional interface between the clinician and the patient&#x0027;s GI tract, to record and monitor slow waves and to provide electrical therapies. Because of the limited battery life of the implants, wireless power transfer (WPT) is a fundamental requirement to conduct studies and provide treatments for an extended period. Furthermore, the WPT link provides the opportunity to establish near-field data communication over the same link. Currently, there are three main wireless power and data transfer (WPDT) approaches for GI tract implants consisting of resonant inductive, ultrasonic, and capacitive couplings. Each approach provides a tradeoff based on the size of the implant, depth of implantation <i>in vivo</i>, the amount of power received by the implant, and the WPT efficiency. In this review, we present the theory and an overview of the major research works accomplished for each of the aforementioned WPT approaches. In particular, this paper focuses on simultaneous WPDT for systems implanted in the GI tract, while fluctuations of the wireless link efficiency and reliability due to body movements and stomach motility are investigated, and techniques are introduced to improve the WPDT fidelity.

Overview of Wireless Implantable Energy Supply and Communication Technology

With the development of integrated circuits and microelectronics, integrated and miniaturized implantable medical devices are increasingly used in modern medical technologies, e.g., cardiac pacemakers, vasodilators, and cochlear implants. However, the normal operation of these devices is inseparable from the availability of sufficient energy supply and the bidirectional transmission of internal and external signals. Due to the limitation of the working environment of sensors, there is only a small space for most implanted electronic devices, which is a challenge faced by existing technology. In this paper, current wireless implantable energy supply and communication technologies are reviewed to determine the best available technologies, thereby providing a reference for method selection in designing implantable medical systems.

Ultrasound-Induced Wireless Energy Harvesting: From Materials Strategies to Functional Applications.

Wireless energy harvesting represents an emerging technology that can be integrated into a variety of systems for biomedical, physical, and chemical functions. The miniaturization and ease of implementation are the main challenges for the development of wireless energy harvesting systems. Unlike most reported wireless energy harvesting technologies represented by electromagnetic coupling, the new generation of ultrasound-induced wireless energy harvesting (UWEH) that use propagating ultrasound waves to carry the available energy provides a strategy with higher resolution, deeper penetration, and more security, especially in nanodevices and implantable medical systems where a long-term stable power is required. Recently, advances in nanotechnologies, microelectronics, and biomedical systems are revolutionizing UWEH. In this article, an overview of recent developments in UWEH technologies that use a variety of material strategies and system designs based on the piezoelectric and capacitive energy harvesting mechanisms is provided. Practical applications are also presented, including wireless power for bio-implantable devices, direct cell/tissue electrical stimulations, wireless recording and communication in nervous systems, ultrasonic modulated drug delivery, self-powered acoustic sensors, and ultrasound-induced piezoelectric catalysis. Finally, perspectives and opportunities are also highlighted.

A Low Contact Impedance Medical Flexible Electrode Based on a Pyramid Array Micro-Structure.

Flexible electrodes are extensively used to detect signals in electrocardiography, electroencephalography, electro-ophthalmography, and electromyography, among others. These electrodes can also be used in wearable and implantable medical systems. The collected signals directly affect doctors’ diagnoses of patient etiology and are closely associated with patients’ life safety. Electrodes with low contact impedance can acquire good quality signals. Herein, we established a method of arraying pyramidal microstructures on polydimethylsiloxane (PDMS) substrates to increase the contact area of electrodes, and a parylene transitional layer is coated between PDMS substrates and metal membranes to enhance the bonding force, finally reducing the impedance of flexible electrodes. Experimental results demonstrated that the proposed methods were effective. The contact area of the fabricated electrode increased by 18.15% per unit area, and the contact impedance at 20 Hz to 1 kHz scanning frequency ranged from 23 to 8 kΩ, which was always smaller than that of a commercial electrode. Overall, these results indicated the excellent performance of the fabricated electrode given its low contact impedance and good biocompatibility. This study can also serve as a reference for further electrode research and application in wearable and implantable medical systems.

Voltage-Boosted Current-Mode Wireless Power Receiver for Directly Charging a Low-Voltage Battery in Implantable Medical Systems

In this paper, a resonant current-mode receiver is studied to charge low-voltage batteries wirelessly for supplying medical implantable systems. To increase efficiency, the root-mean-square (rms) current in the LC tank of the receiver (RX) is reduced by using a voltage-boosted current-mode (VBCM) receiver. This receiver combines the conventional current-mode receiver with a switched-capacitor converter to boost the voltage instantaneously at the switching node ( $V_{X}$ ) of coil. Owing to the suggested technique, the receiver directly charges a low-voltage battery while maintaining a small rms current without using a complex voltage regulator. The receiver achieves an efficiency as high as 84.7% with a 1.1 V battery while operating at the resonant frequency ( $f_{{\text{reso}}}$ ) of 6.78 MHz. The power delivered to the output ( $P_{O}$ ) is in the range from 1.5 to 50 mW. The VBCM receiver was fabricated by 180 nm CMOS technology with a total active area of 0.22 mm2.

Raney-platinum thin film electrodes for the catalysis of glucose in abiotically catalyzed micro-glucose fuel cells

Fuel cells capable of synthetic glucose catalysis have revolved around the implementation of abiotic catalysts that require extreme acid and alkaline environments. These are not compatible with implantable medical sensor systems, and hence, there is a need to develop abiotic catalysts that operate at neutral pH. This paper presents structural and electrochemical characteristics of a nanoporous electrode designed for abiotic glucose oxidation in the presence of oxygen in neutral physiological media. The electrode was fabricated by annealing e-beam deposited thin films of platinum (Pt) and nickel (Ni) into a Pt–Ni alloy on a silicon substrate. The porous nature of the alloy enhances electrochemical properties by increasing the real surface area ~ 500 times compared to the geometric surface area of as-prepared multilayer thin films. This was reflected in the exchange current density of the electrode annealed at 800 °C being twice that of the electrode annealed at 650 °C. The cell voltage increase, due to the addition of dissolved physiological oxygen of 2 ppm, was about 100 ± 8 mV under a load current density of 2 µA cm−2. After running for 72 h in a physiological saline solution with 5 mM glucose, the increase in the electrode potential was only 23 µV h−1. These results suggest that the nanoporous Pt–Ni alloy anode offers an improved catalytic stability with time and should be a viable candidate for use in abiotic catalyzed glucose fuel cell systems operating under physiological conditions.

A Batteryless Energy Harvesting Storage System for Implantable Medical Devices Demonstrated In Situ

We report a wireless energy harvesting and telemetry storage system in 180 nm CMOS technology, demonstrated in situ in rat carcass. The implantable device has dimensions 13 mm × 15 mm and stores 87.5 mJ, providing a self-powering time of 8.5 s transmitting through tissue. We utilize an all-solid-state flexible supercapacitor of breakdown voltage 0.8 V and capacitance 400 mF to harvest incoming wireless power, followed by a boost converter CMOS that drives an active wireless transmitter at 1.5 V at 2.4 GHz in the industrial, scientific, and medical (ISM) band. The DC/DC converter component and switching frequency selection were guided by genetic algorithm analysis and use digital feedback to control the pulse width modulation (PWM), which slowly modifies the duty cycle to control output voltage fluctuations. This implantable medical device system presents the roadmap for batteryless energy harvesting in vivo and in clinical environments, exhibiting the highest operating storage density of 450 μJ/mm2 reported to date.

TiN/Al2O3 Interface Study through ALD Process Modulations

Integration and miniaturization of highly reliable electronic devices are the basis of advanced technologies used for the manufacturing of implantable medical systems such as pacemakers or neuronal stimulators. Among these components, passive devices and more particularly capacitors have a key role in signal filtering and power energy management. In this context, the capacitance density improvement is a way to enable smaller components, thus increasing the final device miniaturization. Currently, Murata Integrated Passive Solutions is running in production a technology called “PICS™” enabling the 3D structuring of the silicon substrate that dramatically enhances its specific area (i.e. capacitance density) when combined with highly reliable low-k dielectric stacks such as silicon dioxide/nitride/dioxide (ONO). In order to significantly increase the capacitance density, two points are critical: first the 3D structures need to evolve toward a more aggressive template with a higher aspect ratio, so as to increase much more the dielectric specific area. The second point is the change of dielectric toward materials with higher dielectric constant such as Al2O3 or HfO2. Atomic Layer Deposition (ALD) technique is a key requirement here, as it is a method enabling conformal deposition of various materials, dielectrics or conductors, such as TiN, on high aspect ratio structures. In parallel of the integration and the optimization of such materials within 3D structures, planar ALD based Metal/Insulator(s)/Metal (MIM) capacitors need to be studied to serve as a reference point. The aim of our investigations is to link the electrical properties of MIM capacitors with the parameters applied during a batch ALD process such as temperature, pulse and purge times, with the support of physico-chemical characterizations (X-ray Photoelectron Spectrometry (XPS), Secondary Ion Mass Spectrometry (SIMS), Scanning Transmission Electron Microscopy (STEM)…). We will focus on the dielectric/electrode interfaces analysis through leakage current mechanism modeling and interpretations. Especially, the amount of O3 used in the Al2O3 deposition process has an important impact on the electrical properties of the MIM by impacting both TiN/Al2O3 interfaces in different ways. An optimization of the O3 dose is proposed.

Trusted Authority Assisted Three‐Factor Authentication and Key Agreement Protocol for the Implantable Medical System

The application of implantable medical devices (IMDs), which solves the problems of geographical distance limitation and real‐time health monitoring that plague patients and doctors, has caused great repercussions in the medical community. Despite the great potential of wide application, it also brings some security and privacy issues, such as the leakage of health data and unauthorized access to IMDs. Although a number of authentication and key agreement (AKA) schemes have been developed, we find that some subtle attacks still remain to be addressed. Then we propose an improved AKA scheme which achieves strong security features including user anonymity and known key security. It is formally proved to be secure under the Real‐or‐Random model. Moreover, a comprehensive security analysis shows that our scheme can resist various attacks and satisfy the desired requirements. Finally, the performance analysis shows the superiority of our protocol which is suitable for the implantable medical system.

Determining Threshold Distance Providing Less Interference for Wireless Medical Implant Communication Systems in Coexisting Environments under Shadow Fading Conditions

Important interference problems will be able to be encountered especially close areas to the hospitals where wireless implantable medical systems' communication traffic occurs heavily in near future. It is possible that these interferences could cause wireless implant devices to malfunction and harmful effects on patients. In this study, it is proposed to determine threshold distance in order to get less interference for wireless implantable medical systems under shadow fading conditions where MICS band and MetAids band users coexist intensely simultaneously. In this method, threshold power according to the \cite{FCC} is pulled down by adding extra distance margin in order to minimize the interference effects to the MICS systems using confidence interval calculations. Because received signal strength just below the monitoring threshold power according to the \cite{FCC} brings about much more interferences for the MICS systems even if listen-before-talk technique is applied.

3-D Hetero-Integration Technologies for Multifunctional Convergence Systems

Since CMOS device scaling has stalled, three-dimensional (3-D) integration allows extending Moore's law to ever high density, higher functionality, higher performance, and more diversed materials and devices to be integrated with lower cost. 3-D integration has many benefits such as increased multi-functionality, increased performance, increased data bandwidth, reduced power, small form factor, reduced packaging volume, because it vertically stacks multiple materials, technologies, and functional components such as processor, memory, sensors, logic, analog, and power ICs into one stacked chip. Anticipated applications start with memory, handheld devices, and high-performance computers and especially extend to multifunctional convengence systems such as cloud networking for internet of things, exascale computing for big data server, electrical vehicle system for future automotive, radioactivity safety system, energy harvesting system and, wireless implantable medical system by flexible heterogeneous integrations involving CMOS, MEMS, sensors and photonic circuits. However, heterogeneous integration of different functional devices has many technical challenges owing to various types of size, thickness, and substrate of different functional devices, because they were fabricated by different technologies. This paper describes new 3-D heterogeneous integration technologies of chip self-assembling stacking and 3-D heterogeneous opto-electronics integration, backside TSV fabrication developed by Tohoku University for multifunctional convergence systems. The paper introduce a high speed sensing, highly parallel processing image sensor system comprising a 3-D stacked image sensor with extremely fast signal sensing and processing speed and a 3-D stacked microprocessor with a self-test and self-repair function for autonomous driving assist fabricated by 3-D heterogeneous integration technologies.

A 65nm CMOS low-power MedRadio-band integer-N cascaded phase-locked loop for implantable medical systems.

This paper presents a low-power MedRadio-band integer-N phase-locked Loop (PLL) system which is composed of two charge-pump PLLs cascade connected. The PLL provides the operation clock and local carrier signals for an implantable medical electronic system. In addition, to avoid the off-chip crystal oscillator, the 13.56 MHz Industrial, Scientific and Medical (ISM) band signal from the wireless power transmission system is adopted as the input reference signal for the PLL. Ring-based voltage controlled oscillators (VCOs) with current control units are adopted to reduce chip area and power dissipation. The proposed cascaded PLL system is designed and implemented in TSMC 65-nm CMOS technology. The measured jitter for 216.96 MHz signal is 12.23 ps and the phase noise is -65.9 dBc/Hz at 100 kHz frequency offset under 402.926 MHz carrier frequency. The measured power dissipations are 66 μW in the first PLL and 195 μW in the whole system under 1-V supply voltage. The chip area is 0.1088 mm(2) and no off-chip component is required which is suitable for the integration of the implantable medical electronic system.

Advances in Microelectronics for Implantable Medical Devices

Implantable medical devices provide therapy to treat numerous health conditions as well as monitoring and diagnosis. Over the years, the development of these devices has seen remarkable progress thanks to tremendous advances in microelectronics, electrode technology, packaging and signal processing techniques. Many of today’s implantable devices use wireless technology to supply power and provide communication. There are many challenges when creating an implantable device. Issues such as reliable and fast bidirectional data communication, efficient power delivery to the implantable circuits, low noise and low power for the recording part of the system, and delivery of safe stimulation to avoid tissue and electrode damage are some of the challenges faced by the microelectronics circuit designer. This paper provides a review of advances in microelectronics over the last decade or so for implantable medical devices and systems. The focus is on neural recording and stimulation circuits suitable for fabrication in modern silicon process technologies and biotelemetry methods for power and data transfer, with particular emphasis on methods employing radio frequency inductive coupling. The paper concludes by highlighting some of the issues that will drive future research in the field.

High-gain on-chip antenna using a sapphire substrate for implantable wireless medical systems

This paper presents a high-gain on-chip antenna using a sapphire substrate for implantable wireless medical systems. The antenna model is based on a dipole and the antenna elements are appropriately rolled for impedance matching. The center frequency of the fabricated on-chip antenna was measured as 360 MHz. The return loss was −3.58 dB and the input impedance was 190.5 − j74.7 Ω at 360 MHz. The maximum antenna gain of the fabricated on-chip antenna was −29.2 dBi. The on-chip antenna using a sapphire substrate achieved a 12.9 dB higher gain than that using a silicon substrate and successfully induced signal transmission at a distance of 10 cm with a transmitter chip. The implemented on-chip antenna can improve the power efficiency of implantable wireless medical systems by 95%.

Energy budget of an implantable glucose measurement system

Abstract The theoretical evaluation of an implantable system measuring glucose for diabetes diagnostics and therapy has recently been presented. This work reports on the realisation of the proposed system on a printed circuit board and measurements of its energy budget. It is shown that the system can be run with small 3.2 V batteries for more than six months with an average energy consumption of 0.12 mAh. 1 Introduction Implantable medical systems widely in use, like pacemak-ers, defibrillators and insulin pumps have paved the way to ever more complex applications of implants, e.g. artificial retina, intelligent hip prosthesis etc. [1, 2]. Recently the architecture of an implantable sensor system measuring glucose concentration and temperature in the subcutaneous tissue has been outlined [3]. Here we present the measured power consumption of the system, which is one of the de-cisive parameters of implantable devices governing their operational lifetime. In the first part of this work, the hardware components of the glucose monitor will be de-tailed, while section 2 will describe the application and op-eration scenario. Measurement methods for the energy budget and results will be presented in section 3 and 4, re-spectively. At the end the conclusions and an outlook are given.

Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes

Transparent, elastic conductors are essential components of electronic and optoelectronic devices that facilitate human interaction and biofeedback, such as interactive electronics, implantable medical devices and robotic systems with human-like sensing capabilities. The availability of conducting thin films with these properties could lead to the development of skin-like sensors that stretch reversibly, sense pressure (not just touch), bend into hairpin turns, integrate with collapsible, stretchable and mechanically robust displays and solar cells, and also wrap around non-planar and biological surfaces such as skin and organs, without wrinkling. We report transparent, conducting spray-deposited films of single-walled carbon nanotubes that can be rendered stretchable by applying strain along each axis, and then releasing this strain. This process produces spring-like structures in the nanotubes that accommodate strains of up to 150% and demonstrate conductivities as high as 2,200Scm(-1) in the stretched state. We also use the nanotube films as electrodes in arrays of transparent, stretchable capacitors, which behave as pressure and strain sensors.

Parylene-based implantable Pt-black coated flexible 3-D hemispherical microelectrode arrays for improved neural interfaces

In implantable medical systems, low-impedance electrode-tissue interface is important for maintaining signal quality for recording and effective charge transfer for stimulation. In this paper, we propose a novel hemispherical biocompatible and flexible microelectrode arrays (MEAs) which were fabricated by the process of micro electrical mechanical system (MEMS). Compared with conventional planar microelectrodes, the interface impedance of hemispherical microelectrodes decreased due to their increased surface area. Parylene C thin film with good biocompatibility and flexibility was chemical vapor deposited as packaging material for decreasing nerve tissue damage. Pt-black coatings were electroplated by applying current pulses in H2PtCl6 solution on electrode sites for the further decrease of interface impedance. Moreover, the geometrical and electrical properties of these MEAs were demonstrated by using a scanning electron microscope (SEM) and an electrochemical workstation. Experimental results showed that the interface impedance decreased by about 34% compared with conventional planar microelectrodes, and significantly decreased by 84% with Pt-black coatings on electrode sites compared with those uncoated microelectrodes.

Boolean logic gates based on oxygen-controlled biofuel cell in “one pot”

The present paper is the first report on an enzymatic logic gates system based on oxygen-controlled biofuel cell (BFC). By accepting dual gas-input signals and resulting in the maximum power output changes of the compartmentless BFC with bioanode/biocathode-immobilized enzymes, such system permits AND and XNOR Boolean logic gates readily achieved, reset and interconverted into each other in “one pot”. On the basis of the built-in Boolean XNOR logic, the proof-of-concept oxygen-controlled biocomputing system with miniature BFC operating in serum enabled us to construct a potential self-powered and implantable medical system with the diagnosis aim, which could intellectually make logic decisions that whether the dissolved oxygen content in body fluid is within normal limits or not.