Fully-Implantable Self-Contained Dual-Channel Electrical Recording and Directivity-Enhanced Optical Stimulation System on a Chip

This thesis presents an integrated system-on-a-chip (SoC), designed, fabricated, and characterized for conducting simultaneous dual-channel optogenetic stimulation and electrophysiological recording. An inductive coil as well as power management circuits are also integrated on the chip, enabling wireless power reception, hence, allowing full implantation. The optical stimulation channels host a novel LED driver circuit that can generate currents up to 10mA with a minimum required headroom voltage reported in the literature, resulting in a superior power efficiency compared to the state of the art. The output current in each channel can be programmed to have an arbitrary waveform with digitally-controlled magnitude and timing. The final design is fabricated as a 34 mm2 microchip using a CMOS 130nm technology and characterized both in terms of electrical and optical performance. A pair of custom-designed inkjet-printed micro-lenses are also fabricated and placed on top of the LEDs. The lenses are optimized to enhance the light directivity of optical stimulation, resulting in significant improvements in terms of spatial resolution, power consumption (30.5x reduction), and safety aspects (temperature increase of <0.1c) of the device

Design, Fabrication, and Validation of a Highly Miniaturized Wirelessly Powered Neural Implant

We have recently witnessed an explosion in the number of neurons that can be recorded and/or stimulated simultaneously during neurophysiological experiments. Experiments have progressed from recording or stimulation with a single electrode to Micro-Electrode Array (MEA) such as the Utah Array. These MEAs can be instrumented with current drivers, neural amplifiers, digitizers and wireless communication links. The broad interest in these MEAs suggests that there is a need for large scale neural recording and stimulation. The ultimate goal is to coordinate the recordings and stimulation of potentially thousands of neurons from many brain areas. Unfortunately, current state-of-the-art MEAs are limited by their scalability and long-term stability because of their physical size and rigid configuration. Furthermore, some applications prioritize a distributed neural interface over one that offers high resolution. Examples of biomedical applications that necessitate an interface with neurons from many sites in the brain include: i) understanding and treating neurological disorders that affect distributed locations throughout the CNS; ii) revolutionizing our understanding of the brain by studying the correlations between neural networks from different regions of the brain and the mechanisms of cognitive functions; and iii) covering larger area in the sensorimotor cortex of amputees to more accurately control robotic prosthetic limbs or better evoke a sense of touch. One solution to make large scale, fully specifiable, electrical stimulation and recording possible, is to disconnect the electrodes from the base, so that they can be arbitrarily placed, using a syringe, freely in the nervous system. To overcome the challenges of system miniaturization, we propose the “microbead”, an ultra-small neural stimulating implant, that is currently implemented in a 130nm CMOS technology with the following characteristics: 200 μm × 200 μm × 80 μm size; optimized wireless powering, all micro-electronics on single chip; and integrated electrodes and coil. The stimulating microbead is validated in a sciatic nerve by generating leg movements. A recording microbead is also investigated with following characteristics: wireless powering using steerable phased coil array, miniaturized front-end, and backscattering telemetry. These microbeads could eventually replace the rigid arrays that are currently the state-of-the-art in electrophysiology set-ups

Biointegrated and wirelessly powered implantable brain devices: a review

Implantable neural interfacing devices have added significantly to neural engineering by introducing the low-frequency oscillations of small populations of neurons known as local field potential as well as high-frequency action potentials of individual neurons. Regardless of the astounding progression as of late, conventional neural modulating system is still incapable to achieve the desired chronic in vivo implantation. The real constraint emerges from mechanical and physical diffierences between implants and brain tissue that initiates an inflammatory reaction and glial scar formation that reduces the recording and stimulation quality. Furthermore, traditional strategies consisting of rigid and tethered neural devices cause substantial tissue damage and impede the natural behaviour of an animal, thus hindering chronic in vivo measurements. Therefore, enabling fully implantable neural devices, requires biocompatibility, wireless power/data capability, biointegration using thin and flexible electronics, and chronic recording properties. This paper reviews biocompatibility and design approaches for developing biointegrated and wirelessly powered implantable neural devices in animals aimed at long-term neural interfacing and outlines current challenges toward developing the next generation of implantable neural devices

A Fully Implantable Opto-Electro Closed-Loop Neural Interface for Motor Neuron Disease Studies

This paper presents a fully implantable closed-loop device for use in freely moving rodents to investigate new treatments for motor neuron disease. The 0.18 µm CMOS integrated circuit comprises 4 stimulators, each featuring 16 channels for optical and electrical stimulation using arbitrary current waveforms at frequencies from 1.5 Hz to 50 kHz, and a bandwidth programmable front-end for neural recording. The implant uses a Qi wireless inductive link which can deliver >100 mW power at a maximum distance of 2 cm for a freely moving rodent. A backup rechargeable battery can support 10 mA continuous stimulation currents for 2.5 hours in the absence of an inductive power link. The implant is controlled by a graphic user interface with broad programmable parameters via a Bluetooth low energy bidirectional data telemetry link. The encapsulated implant is 40 mm × 20 mm × 10 mm. Measured results are presented showing the electrical performance of the electronics and the packaging method

An integrated bidirectional multi-channel opto-electro arbitrary waveform stimulator for treating motor neurone disease

This paper presents a prototype integrated bidirectional stimulator ASIC capable of mixed opto-electro stimulation and electrophysiological signal recording. The development is part of the research into a fully implantable device for treating motor neurone disease using optogenetics and stem cell technology. The ASIC consists of 4 stimulator units, each featuring 16-channel optical and electrical stimulation using arbitrary current waveforms with an amplitude up to 16 mA and a frequency from 1.5 Hz to 50 kHz, and a recording front-end with a programmable bandwidth of 1 Hz to 4 kHz, and a programmable amplifier gain up to 74 dB. The ASIC was implemented in a 0.18μm CMOS technology. Simulated performance in stimulation and recording is presented

Bidirectional Neural Interface Circuits with On-Chip Stimulation Artifact Reduction Schemes

Bidirectional neural interfaces are tools designed to “communicate” with the brain via recording and modulation of neuronal activity. The bidirectional interface systems have been adopted for many applications. Neuroscientists employ them to map neuronal circuits through precise stimulation and recording. Medical doctors deploy them as adaptable medical devices which control therapeutic stimulation parameters based on monitoring real-time neural activity. Brain-machine-interface (BMI) researchers use neural interfaces to bypass the nervous system and directly control neuroprosthetics or brain-computer-interface (BCI) spellers. In bidirectional interfaces, the implantable transducers as well as the corresponding electronic circuits and systems face several challenges. A high channel count, low power consumption, and reduced system size are desirable for potential chronic deployment and wider applicability. Moreover, a neural interface designed for robust closed-loop operation requires the mitigation of stimulation artifacts which corrupt the recorded signals. This dissertation introduces several techniques targeting low power consumption, small size, and reduction of stimulation artifacts. These techniques are implemented for extracellular electrophysiological recording and two stimulation modalities: direct current stimulation for closed-loop control of seizure detection/quench and optical stimulation for optogenetic studies. While the two modalities differ in their mechanisms, hardware implementation, and applications, they share many crucial system-level challenges. The first method aims at solving the critical issue of stimulation artifacts saturating the preamplifier in the recording front-end. To prevent saturation, a novel mixed-signal stimulation artifact cancellation circuit is devised to subtract the artifact before amplification and maintain the standard input range of a power-hungry preamplifier. Additional novel techniques have been also implemented to lower the noise and power consumption. A common average referencing (CAR) front-end circuit eliminates the cross-channel common mode noise by averaging and subtracting it in analog domain. A range-adapting SAR ADC saves additional power by eliminating unnecessary conversion cycles when the input signal is small. Measurements of an integrated circuit (IC) prototype demonstrate the attenuation of stimulation artifacts by up to 42 dB and cross-channel noise suppression by up to 39.8 dB. The power consumption per channel is maintained at 330 nW, while the area per channel is only 0.17 mm2. The second system implements a compact headstage for closed-loop optogenetic stimulation and electrophysiological recording. This design targets a miniaturized form factor, high channel count, and high-precision stimulation control suitable for rodent in-vivo optogenetic studies. Monolithically integrated optoelectrodes (which include 12 µLEDs for optical stimulation and 12 electrical recording sites) are combined with an off-the-shelf recording IC and a custom-designed high-precision LED driver. 32 recording and 12 stimulation channels can be individually accessed and controlled on a small headstage with dimensions of 2.16 x 2.38 x 0.35 cm and mass of 1.9 g. A third system prototype improves the optogenetic headstage prototype by furthering system integration and improving power efficiency facilitating wireless operation. The custom application-specific integrated circuit (ASIC) combines recording and stimulation channels with a power management unit, allowing the system to be powered by an ultra-light Li-ion battery. Additionally, the µLED drivers include a high-resolution arbitrary waveform generation mode for shaping of µLED current pulses to preemptively reduce artifacts. A prototype IC occupies 7.66 mm2, consumes 3.04 mW under typical operating conditions, and the optical pulse shaping scheme can attenuate stimulation artifacts by up to 3x with a Gaussian-rise pulse rise time under 1 ms.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147674/1/mendrela_1.pd

Intra-Body Communications for Nervous System Applications: Current Technologies and Future Directions

The Internet of Medical Things (IoMT) paradigm will enable next generation healthcare by enhancing human abilities, supporting continuous body monitoring and restoring lost physiological functions due to serious impairments. This paper presents intra-body communication solutions that interconnect implantable devices for application to the nervous system, challenging the specific features of the complex intra-body scenario. The presented approaches include both speculative and implementative methods, ranging from neural signal transmission to testbeds, to be applied to specific neural diseases therapies. Also future directions in this research area are considered to overcome the existing technical challenges mainly associated with miniaturization, power supply, and multi-scale communications.Comment: https://www.sciencedirect.com/science/article/pii/S138912862300163