Circuitry for a remotely powered bio-implantable gastric electrical stimulation system

Power to bio-implantable devices is usually supplied through a battery implanted with the system or through wires extending to an outside power source. The latter case with wires protruding out of the body can be unaesthetic in appearance and can cause infection. In this research, we consider an alternative way to power a bio-implantable microsystem. It involves using rechargeable lithium batteries. Here, power is delivered remotely to charge implanted battery or batteries. This approach avoids periodic surgery necessary for battery replacement. It also does not tie a person to an external power source at all times. This improves patient’s quality of life. The present work involves design and fabrication of signal conditioning circuit for a remotely rechargeable, bio-implantable, Battery-powered Electrical Stimulation System (BESS). A rechargeable lithium ion battery with a voltage of 3.7 V powers the proposed circuit. The desired output, which goes directly to the electrodes, is a series of 10 V, 15 mA pulses with a duty cycle of 4.5 %. A second rechargeable lithium ion battery serves as back-up. A lithium ion charging chip is included which is connected to the designed IC through a logic interface. The two batteries work in tandem i.e. when one battery powers the IC the other gets recharged and vice versa thereby providing an uninterruptible output. The IC uses a series of charge pumps to get the required boost in voltage. The IC also includes voltage detector circuits to detect battery voltages, voltage regulator, pulse generator circuits, logic circuits and necessary switches. Individual subsystems of the IC were designed, simulated and fabricated using standard CMOS technology. Individual subsystem circuits were found to work satisfactorily except for the charge pump. A revised design is now under fabrication. The microsystem utilizes a hybrid approach. Experiments done with a bench-top circuit model to simulate the proposed IC showed that a 3 V battery with a capacity of 190 mAh could power the IC for 15 hrs and needed 4 hrs for recharging

A Wireless, High-Voltage Compliant, and Energy-Efficient Visual Intracortical Microstimulator

RÉSUMÉ L’objectif général de ce projet de recherche est la conception, la mise en oeuvre et la validation d’une interface sans fil intracorticale implantable en technologie CMOS avancée pour aider les personnes ayant une déficience visuelle. Les défis majeurs de cette recherche sont de répondre à la conformité à haute tension nécessaire à travers l’interface d’électrode-tissu (IET), augmenter la flexibilité dans la microstimulation et la surveillance multicanale, minimiser le budget de puissance pour un dispositif biomédical implantable, réduire la taille de l’implant et améliorer le taux de transmission sans fil des données. Par conséquent, nous présentons dans cette thèse un système de microstimulation intracorticale multi-puce basée sur une nouvelle architecture pour la transmission des données sans fil et le transfert de l’énergie se servant de couplages inductifs et capacitifs. Une première puce, un générateur de stimuli (SG) éconergétique, et une autre qui est un amplificateur de haute impédance se connectant au réseau de microélectrodes de l’étage de sortie. Les 4 canaux de générateurs de stimuli produisent des impulsions rectangulaires, demi-sinus (DS), plateau-sinus (PS) et autres types d’impulsions de courant à haut rendement énergétique. Le SG comporte un contrôleur de faible puissance, des convertisseurs numérique-analogiques (DAC) opérant en mode courant, générateurs multi-forme d’ondes et miroirs de courants alimentés sous 1.2 et 3.3V se servant pour l’interface entre les deux technologies utilisées. Le courant de stimulation du SG varie entre 2.32 et 220μA pour chaque canal. La deuxième puce (pilote de microélectrodes (MED)), une interface entre le SG et de l’arrangement de microélectrodes (MEA), fournit quatre niveaux différents de courant avec la valeur maximale de 400μA par entrée et 100μA par canal de sortie simultanément pour 8 à 16 sites de stimulation à travers les microélectrodes, connectés soit en configuration bipolaire ou monopolaire. Cette étage de sortie est hautement configurable et capable de délivrer une tension élevée pour satisfaire les conditions de l’interface à travers l’impédance de IET par rapport aux systèmes précédemment rapportés. Les valeurs nominales de plus grandes tensions d’alimentation sont de ±10V. La sortie de tension mesurée est conformément 10V/phase (anodique ou cathodique) pour les tensions d’alimentation spécifiées. L’incrémentation de tensions d’alimentation à ±13V permet de produire un courant de stimulation de 220μA par canal de sortie permettant d’élever la tension de sortie jusqu’au 20V par phase. Cet étage de sortie regroupe un commutateur haute tension pour interfacer une matrice des miroirs de courant (3.3V /20V), un registre à décalage de 32-bits à entrée sérielle, sortie parallèle, et un circuit dédié pour bloquer des états interdits.----------ABSTRACT The general objective of this research project is the design, implementation and validation of an implantable wireless intracortical interface in advanced CMOS technology to aid the visually impaired people. The major challenges in this research are to meet the required highvoltage compliance across electrode-tissue interface (ETI), increase lexibility in multichannel microstimulation and monitoring, minimize power budget for an implantable biomedical device, reduce the implant size, and enhance the data rate in wireless transmission. Therefore, we present in this thesis a multi-chip intracortical microstimulation system based on a novel architecture for wireless data and power transmission comprising inductive and capacitive couplings. The first chip is an energy-efficient stimuli generator (SG) and the second one is a highimpedance microelectrode array driver output-stage. The 4-channel stimuli-generator produces rectangular, half-sine (HS), plateau-sine (PS), and other types of energy-efficient current pulse. The SG is featured with low-power controller, current mode source- and sinkdigital- to-analog converters (DACs), multi-waveform generators, and 1.2V/3.3V interface current mirrors. The stimulation current per channel of the SG ranges from 2.32 to 220μA per channel. The second chip (microelectrode driver (MED)), an interface between the SG and the microelectrode array (MEA), supplies four different current levels with the maximum value of 400μA per input and 100μA per output channel. These currents can be delivered simultaneously to 8 to 16 stimulation sites through microelectrodes, connected either in bipolar or monopolar configuration. This output stage is highly-configurable and able to deliver higher compliance voltage across ETI impedance compared to previously reported designs. The nominal values of largest supply voltages are ±10V. The measured output compliance voltage is 10V/phase (anodic or cathodic) for the specified supply voltages. Increment of supply voltages to ±13V allows 220μA stimulation current per output channel enhancing the output compliance voltage up to 20V per phase. This output-stage is featured with a high-voltage switch-matrix, 3.3V/20V current mirrors, an on-chip 32-bit serial-in parallel-out shift register, and the forbidden state logic building blocks. The SG and MED chips have been designed and fabricated in IBM 0.13μm CMOS and Teledyne DALSA 0.8μm 5V/20V CMOS/DMOS technologies with silicon areas occupied by them 1.75 x 1.75mm2 and 4 x 4mm2 respectively. The measured DC power budgets consumed by low-and mid-voltage microchips are 2.56 and 2.1mW consecutively

Design of Integrated Neural/Modular Stimulators

Ph.DDOCTOR OF PHILOSOPH

Walking aids for stroke patients

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN024350 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Doctor of Philosophy

dissertationParalysis can be ameliorated through functional electrical stimulation (FES) of the intact peripheral nerves. The Utah Slanted Electrode Array (USEA) can improve FES systems by providing selective access to many independent motor unit populations.This dissertation includes three studies that expand the role of USEAs in FES applications. The fi rst study leverages the selectivity of the USEA to independently activate the hamstring muscles. Because the di fferent biarticular hamstring muscles can either ex or extend the limb (at the knee or hip), the ability to selectively activate each one independently is required to evoke functional movements such as stance and gait. USEAs implanted in the muscular branch of the sciatic nerve were able to selectively activate each muscle of the hamstring group. Activation of these muscles was graded with increasing stimulus strength, and provided ample dynamic range to allow for fine control of muscle force. The second study demonstrates the ability of the USEA to selectively block neural activity. Upper motor neuron damage can cause hyperre exia and spasticity as well as paralysis. By delivering high-frequency sinusoids through electrodes of the USEA, ber subsets in a nerve were blocked while allowing the remainder of the nerve to function normally. Sinusoids delivered through different electrodes allowed for deactivation of di fferent muscles. The ability to selectively interrupt activity in fiber subpopulations within a nerve will provide new therapeutic options for the positive symptoms of upper motor neuron damage. The fi nal study addresses the practical difficulty of choosing the appropriate stimulus parameters to evoke functional movements. In a USEA-based FES system, the electrodes and stimulus parameters that evoke the desired responses must be identifi ed empirically. USEAs were implanted into three diff erent hind limb nerves, and the response evoked by each electrode was measured noninvasively using 3-D endpoint force. Each electrode was classifi ed as evoking limb flexion or limb extension, and a range of stimulus intensities was identifi ed that evoked a graded force response. Excitation overlap between selected electrode pairs was quantifi ed using the refractory technique. This method will allow for electrode and stimulus parameter selection for use in an FES system using minimal, noninvasive instrumentation

Adaptive Closed-Loop Neuromorphic Controller for Use in Respiratory Pacing

Respiratory pacing can treat ventilatory insufficiency through electrical stimulation of the respiratory muscles, or the respective innervating nerves, to induce ventilation. It avoids some of the adverse effects associated with mechanical ventilation such as risk of diaphragm atrophy and lung damage. However, current respiratory pacing systems provide stimulation in an open-loop manner. This often requires users to undergo frequent tuning sessions with trained clinicians if the specified stimulation parameters are unable to induce sufficient ventilation in the presence of time-varying changes in muscle properties, chest biomechanics, and metabolic demand. Lack of adaptation to these changes may lead to complications arising from hyperventilation or hypoventilation. A novel adaptive closed-loop neuromorphic controller for respiratory pacing has been developed to address the need for closed-loop control respiratory pacing capable of responding to changes in metabolic production of CO2, diaphragm muscle health, and biomechanics. A 3-stage processes was utilized to develop the controller. First, an adaptive controller that could follow a preset within-breath volume profile was developed in silico and evaluated in vivo in anesthetized rats with an intact spinal cord or with diaphragm hemiparesis induced by spinal cord hemisection. Second, a neuromorphic computational model was developed to generate a desired trajectory that reflects changes in breath volume and respiratory rate in response to arterial CO2 levels. An enhanced controller capable of generating and matching this model-based desired trajectory was evaluated in silico and in vivo on rats with depressed ventilation and diaphragm hemiparesis. Finally, the enhanced adaptive controller was modified for human-related biomechanics and CO2 dynamics and evaluated in silico under changes of metabolic demand, presence of muscle fatigue, and after randomization of model parameters to reproduce expected between-subject differences. Results showed that the adaptive controller could adapt and modulate stimulation parameters and respiratory rate to follow a desired model-generated breath volume trajectory in response to dynamic arterial CO2 levels. In silico studies aimed at assessing potential for clinical translation showed that an enhanced controller modified for human use could successfully control ventilation to achieve and maintain normocapnic arterial CO2 levels. Overall, these results suggest that use of an adaptive closed-loop controller could lead to improved ventilatory outcomes and quality of life for users of adaptive respiratory pacing

Neurostimulator with Waveforms Inspired by Nature for Wearable Electro-Acupuncture

The work presented here has 3 goals: establish the need for novel neurostimulation waveform solutions through a literature review, develop a neurostimulation pulse generator, and verify the operation of the device for neurostimulation applications. The literature review discusses the importance of stimulation waveforms on the outcomes of neurostimulation, and proposes new directions for neurostimulation research that would help in improving the reproducibility and comparability between studies. The pulse generator circuit is then described that generates signals inspired by the shape of excitatory or inhibitory post-synaptic potentials (EPSP, IPSP). The circuit analytical equations are presented, and the effects of the circuit design components are discussed. The circuit is also analyzed with a capacitive load using a simplified Randles model to represent the electrode-electrolyte interface, and the output is measured in phosphate-buffered saline (PBS) solution as the load with acupuncture needles as electrodes. The circuit is designed to be used in different types of neurostimulators depending on the needs of the application, and to study the effects of varying neurostimulation waveforms. The circuit is used to develop a remote-controlled wearable veterinary electro-acupuncture machine. The device has a small form-factor and 3D printed enclosure, and has a weight of 75 g with leads attached. The device is powered by a 500 mAh lithium polymer battery, and was tested to last 6 hours. The device is tested in an electro-acupuncture animal study on cats performed at the Louisiana State University School of Veterinary Medicine, where it showed expected electro-acupuncture effects. Then, a 2-channel implementation of the device is presented, and tested to show independent output amplitude, frequency, and stimulation duration per channel. Finally, the software and hardware requirements for control of the wearable veterinary electro-acupuncture machine are detailed. The number of output channels is limited to the number of hardware PWM timers available for use. The Arduino software implements PWM control for the output amplitude and frequency. The stimulation duration control is provided using software timers. The communications protocol between the microcontroller board and Android App are described, and communications are performed via Bluetooth