Design and Implementation of a Passive Neurostimulator with Wireless Resonance-Coupled Power Delivery and Demonstration on Frog Sciatic Nerve and Gastrocnemius Muscle

The thesis presented has four goals: to perform a comprehensive literature review on current neurostimulator technology; to outline the current issues with the state-of-the-art; to provide a neurostimulator design that solves these issues, and to characterize the design and demonstrate its neurostimulation features. The literature review describes the physiology of a neuron, and then proceeds to outline neural interfaces and neurostimulators. The neurostimulator design process is then outlined and current requirements in the field are described. The novel neurostimulator circuit that implements a solution that has wireless capability, passive control, and small size is outlined and characterized. The circuit is demonstrated to operate wirelessly with a resonance-coupled multi-channel implementation, and is shown powering LEDs. The circuit was then fabricated in a miniature implementation which utilized a 10 x 20 x 3 mm&179 antenna, and occupied a volume approximating 1 cm&179. This miniature circuit is used to stimulate frog sciatic nerve and gastrocnemius muscle in vitro. These demonstrations and characterization show the device is capable of neurostimulation, can operate wirelessly, is controlled passively, and can be implemented in a small size, thus solving the aforementioned neurostimulator requirements. Further work in this area is focused on developing an extensive characterization of the device and the wireless power delivery system, optimizing the circuit design, and performing in vivo experiments with restoration of motor control in injured animals. This device shows promise to provide a comprehensive solution to many application-specific problems in neurostimulation, and be a modular addition to larger neural interface systems

Wireless tools for neuromodulation

Epilepsy is a spectrum of diseases characterized by recurrent seizures. It is estimated that 50 million individuals worldwide are affected and 30% of cases are medically refractory or drug resistant. Vagus nerve stimulation (VNS) and deep brain stimulation (DBS) are the only FDA approved device based therapies. Neither therapy offers complete seizure freedom in a majority of users. Novel methodologies are needed to better understand mechanisms and chronic nature of epilepsy. Most tools for neuromodulation in rodents are tethered. The few wireless devices use batteries or are inductively powered. The tether restricts movement, limits behavioral tests, and increases the risk of infection. Batteries are large and heavy with a limited lifetime. Inductive powering suffers from rapid efficiency drops due to alignment mismatches and increased distances. Miniature wireless tools that offer behavioral freedom, data acquisition, and stimulation are needed. This dissertation presents a platform of electrical, optical and radiofrequency (RF) technologies for device based neuromodulation. The platform can be configured with features including: two channels differential recording, one channel electrical stimulation, and one channel optical stimulation. Typical device operation consumes less than 4 mW. The analog front end has a bandwidth of 0.7 Hz - 1 kHz and a gain of 60 dB, and the constant current driver provides biphasic electrical stimulation. For use with optogenetics, the deep brain optical stimulation module provides 27 mW/mm2 of blue light (473 nm) with 21.01 mA. Pairing of stimulating and recording technologies allows closed-loop operation. A wireless powering cage is designed using the resonantly coupled filter energy transfer (RCFET) methodology. RF energy is coupled through magnetic resonance. The cage has a PTE ranging from 1.8-6.28% for a volume of 11 x 11 x 11 in3. This is sufficient to chronically house subjects. The technologies are validated through various in vivo preparations. The tools are designed to study epilepsy, SUDEP, and urinary incontinence but can be configured for other studies. The broad application of these technologies can enable the scientific community to better study chronic diseases and closed-loop therapies

Ultra-low-power circuits and systems for wearable and implantable medical devices

Thesis (Ph. D.)--Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 219-231).Advances in circuits, sensors, and energy storage elements have opened up many new possibilities in the health industry. In the area of wearable devices, the miniaturization of electronics has spurred the rapid development of wearable vital signs, activity, and fitness monitors. Maximizing the time between battery recharge places stringent requirements on power consumption by the device. For implantable devices, the situation is exacerbated by the fact that energy storage capacity is limited by volume constraints, and frequent battery replacement via surgery is undesirable. In this case, the design of energy-efficient circuits and systems becomes even more crucial. This thesis explores the design of energy-efficient circuits and systems for two medical applications. The first half of the thesis focuses on the design and implementation of an ultra-low-power, mixed-signal front-end for a wearable ECG monitor in a 0.18pm CMOS process. A mixed-signal architecture together with analog circuit optimizations enable ultra-low-voltage operation at 0.6V which provides power savings through voltage scaling, and ensures compatibility with state-of-the-art DSPs. The fully-integrated front-end consumes just 2.9[mu]W, which is two orders of magnitude lower than commercially available parts. The second half of this thesis focuses on ultra-low-power system design and energy-efficient neural stimulation for a proof-of-concept fully-implantable cochlear implant. First, implantable acoustic sensing is demonstrated by sensing the motion of a human cadaveric middle ear with a piezoelectric sensor. Second, alternate energy-efficient electrical stimulation waveforms are investigated to reduce neural stimulation power when compared to the conventional rectangular waveform. The energy-optimal waveform is analyzed using a computational nerve fiber model, and validated with in-vivo ECAP recordings in the auditory nerve of two cats and with psychophysical tests in two human cochlear implant users. Preliminary human subject testing shows that charge and energy savings of 20-30% and 15-35% respectively are possible with alternative waveforms. A system-on-chip comprising the sensor interface, reconfigurable sound processor, and arbitrary-waveform neural stimulator is implemented in a 0.18[mu]m high-voltage CMOS process to demonstrate the feasibility of this system. The sensor interface and sound processor consume just 12[mu]W of power, representing just 2% of the overall system power which is dominated by stimulation. As a result, the energy savings from using alternative stimulation waveforms transfer directly to the system.by Marcus Yip.Ph.D