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

Beyond solid-state lighting: Miniaturization, hybrid integration, and applications og GaN nano- and micro-LEDs

Gallium Nitride (GaN) light-emitting-diode (LED) technology has been the revolution in modern lighting. In the last decade, a huge global market of efficient, long-lasting and ubiquitous white light sources has developed around the inception of the Nobel-price-winning blue GaN LEDs. Today GaN optoelectronics is developing beyond lighting, leading to new and innovative devices, e.g. for micro-displays, being the core technology for future augmented reality and visualization, as well as point light sources for optical excitation in communications, imaging, and sensing. This explosion of applications is driven by two main directions: the ability to produce very small GaN LEDs (microLEDs and nanoLEDs) with high efficiency and across large areas, in combination with the possibility to merge optoelectronic-grade GaN microLEDs with silicon microelectronics in a fully hybrid approach. GaN LED technology today is even spreading into the realm of display technology, which has been occupied by organic LED (OLED) and liquid crystal display (LCD) for decades. In this review, the technological transition towards GaN micro- and nanodevices beyond lighting is discussed including an up-to-date overview on the state of the art

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

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

Outan: An On-Head System for Driving micro-LED Arrays Implanted in Freely Moving Mice

In the intact brain, neural activity can be recorded using sensing electrodes and manipulated using light stimulation. Silicon probes with integrated electrodes and micro-LEDs enable the detection and control of neural activity using a single implanted device. Miniaturized solutions for recordings from small freely moving animals are commercially available, but stimulation is driven by large, stationary current sources. We designed and fabricated a current source chip and integrated it into a headstage PCB that weighs 1.37 g. The proposed system provides 10-bit resolution current control for 32 channels, driving micro-LEDs with up to 4.6 V and sourcing up to 0.9 mA at a refresh rate of 5 kHz per channel. When calibrated against a micro-LED probe, the system allows linear control of light output power, up to 10 micro-W per micro-LED. To demonstrate the capabilities of the system, synthetic sequences of neural spiking activity were produced by driving multiple micro-LEDs implanted in the hippocampal CA1 area of a freely moving mouse. The high spatial, temporal, and amplitude resolution of the system provides a rich variety of stimulation patterns. Combined with commercially available sampling headstages, the system provides an easy to use back-end, fully utilizing the bi-directional potential of integrated opto-electronic arrays.Comment: 11 pages, 9 figure

Technological challenges in the development of optogenetic closed-loop therapy approaches in epilepsy and related network disorders of the brain

Epilepsy is a chronic, neurological disorder affecting millions of people every year. The current available pharmacological and surgical treatments are lacking in overall efficacy and cause side-effects like cognitive impairment, depression, tremor, abnormal liver and kidney function. In recent years, the application of optogenetic implants have shown promise to target aberrant neuronal circuits in epilepsy with the advantage of both high spatial and temporal resolution and high cell-specificity, a feature that could tackle both the efficacy and side-effect problems in epilepsy treatment. Optrodes consist of electrodes to record local field potentials and an optical component to modulate neurons via activation of opsin expressed by these neurons. The goal of optogenetics in epilepsy is to interrupt seizure activity in its earliest state, providing a so-called closed-loop therapeutic intervention. The chronic implantation in vivo poses specific demands for the engineering of therapeutic optrodes. Enzymatic degradation and glial encapsulation of implants may compromise long-term recording and sufficient illumination of the opsin-expressing neural tissue. Engineering efforts for optimal optrode design have to be directed towards limitation of the foreign body reaction by reducing the implant’s elastic modulus and overall size, while still providing stable long-term recording and large-area illumination, and guaranteeing successful intracerebral implantation. This paper presents an overview of the challenges and recent advances in the field of electrode design, neural-tissue illumination, and neural-probe implantation, with the goal of identifying a suitable candidate to be incorporated in a therapeutic approach for long-term treatment of epilepsy patients

Micro-optics for Opto-genetic Neuro-stimulation with Micro-LED Arrays

The breakthrough discovery of a nanoscale optically gated ion channel protein, Channelrhodopsin 2 (ChR2), in combination with a genetically expressed optically activated ion pump, Halorhodopsin, allowed the direct stimulation and inhibition of individual action potentials with light alone. This thesis describes the development of optics and micro-optics which when used with micro-led array sources, collects and projects light efficiently and uniformly onto such opto-genetically modified specimens. When used with enhanced light gated ion channels and pumps these systems allow us to further our understanding of both brain and visual systems. Micro-LED arrays permit spatio-temporal control of neuron stimulation on sub-millisecond timescales. However, micro-led arrays are disadvantaged by the broad-angular spread of their light emission and their low spatial fill factor. We present the design of macro and micro-optics systems for use with a micro-LED arrays consisting of a matrix of 25μm diameter micro-LEDs with 150 or 80μm centre-to-centre spacing. On one system, the micro-LED array is imaged onto off-the-shelf micro-optics using macro-optics and in the other system; micro-LED array and custom micro-optics are optimised and integrated together. The two systems are designed to improve the fill-factor from 2% to more than 78% by capturing a larger fraction of the LED emission and directing it correctly to the sample plane. This approach allows low fill factor arrays to be used effectively, which in turn has benefits in terms of thermal management and electrical drive from CMOS backplane electronics. These systems were implemented as an independent set that could be connected to a variety of different microscopes available for Patch-clamp and Multi-electrode measurements. As well, the feasibility of an eye prosthesis was tested using virtual reality optics and a fake eye to stimulate ganglion cells and by doing in-vivo stimulation of the genetically modified retina of a mouse.Open Acces

Multifunctional nanostructures for intracellular delivery and sensing in electrogenic cells

In electrophysiology, multielectrode array devices (MEA) are the gold standard for the study of large ensambles of electrogenic cells. In the last decades, thanks to the adoption of nanotechnologies, the study of physiological and pathological conditions of electro-active cells in culture have becomes increasingly accurate. In parallel, studies exploited the integration of nanostructures with delivering capabilities with single-cell specificity and high throughput in biosensing platforms. Delivery and recording have independently led to great advances in neurobiology, however, their integration on a single chip would give complete insights into pathologies development and fundamental advancements in drug screening methods. In this work, we demonstrate how a microfluidic-MEA technology may be used to record both spontaneous and chemically induced activity in vitro. We propose a device that can deliver molecules to only a few chosen cells and detecting the response in cellular activity at multiple sites simultaneously. In addition, will be discussed how the adoption of nanoporous metamaterial in place of nanostructures might lower costs and speed up production. Furthermore, this same material, will be identified for the first time in this work as photoelectrical modulating material for eliciting electrogenic cells firing activity. Specifically, by converting NIR laser pulses into stimulatory currents, plasmonic metamaterials may be employed to induce action potentials. This method enables remote access to optical pacing with precise spatiotemporal control, allowing to be used as a valid alternative of the traditional genetic-based optical stimulation techniques. Therefore, in addition to pharmaceutical applications, these final characteristics may pave the way for a new generation of minimally invasive, cellular type-independent all-optical plasmonic pacemakers and muscle actuators

Multifunctional nanostructures for intracellular delivery and sensing in electrogenic cells

Biological studies on in vitro cell cultures are of fundamental importance for investigating cell response to external stimuli, such drugs for specific treatments, or for studying communication between cells. In the electrophysiology field, multielectrode array devices (MEA) are the gold standard for the study of large ensambles of electrogenic cells. Thus, their improvement is a central topic nowadays in neuroscience and cardiology [1]. In the last decades, thanks to the adoption of nanotechnologies, the study of physiological and pathological conditions of electro-active cells in culture have becomes increasingly accurate[2], allowing for monitoring action potentials from many cells simultaneously. In fact, nanoscale biomaterials were able to overcome the limitations of previous technologies, paving the way to the development of platforms for interfacing the electrogenic cells at unprecedented spatiotemporal scales. These devices, together with microfluidics, are starting to be used for drug screening and pharmaceutical drug development since they represent a powerful tool for monitoring cell response when cultures are stimulated by target compounds. Many pharmaceutical agents, however, including various large molecules (enzymes, proteins, antibodies) and even drug-loaded pharmaceutical nanocarriers, need to be delivered intracellularly to exercise their therapeutic action inside the cytoplasm[3]. Nanoscale electrodes offer individual cell access and non-destructive poration of the cellular membrane enabling high capability in the delivery of biomolecules. Among all the techniques, electroporation have proven encouraging potential as alternative to the carrier mediated methods for molecular delivery into cultured cells[4]. In this regard, different groups [5][6][7] exploited the integration of nanostructures with delivering capabilities with single-cell specificity and high throughput in biosensing platforms. These efforts provided powerful tools for advancing applications in therapeutics, diagnostics, and drug discovery, in order to reach an efficient and localized delivery on a chip. Despite these new tactics, there is still a critical need for the development of a functional approach that combines recording capabilities of nanostructured biosensors with intracellular delivery. The device should provide for tight contact between cells and electrode so as to enable highly localized delivery and optimal recording of action potentials in order to attain a high degree of prediction for the disease modeling and drug discovery. This \u201con-chip\u201d approach will help to gain deeper insight in several bio-related studies and analyses, providing a comprehensive knowledge of the entire cellular dynamics when selectively stimulated by the desired bio-molecules. In the first part of this dissertation, a solution will be proposed in order to fill this gap and respond to this need in the biology field. In the first chapter, I will describe briefly the principles of action potentials and how neurons and cardiomyocyte are composed, together with the development of electrophysiology and the advent of multielectrode arrays. In the second chapter, more details about fabrication and cell-electrode system modelling will be explained. In the same chapter, I will explore the development of multielectrode arrays up to the present days, along with the advent of nanotechnologies and the related techniques for improving the previous platforms. The different cell poration techniques will be described in order to reach the best recording capabilities without damaging cells. Electroporation, optoporation and spontaneous poration will be presented and the chosen technique for our application (electroporation) will be reviewed more in detail. In the third chapter, different methodologies for intracellular delivery will be explained, focusing also on the electroporation technique. A small paragraph about the integration of these techniques on chip will be inserted to illustrate the state of the art of these devices. The fourth chapter will explicate in details the Microfluidic multielectrode array idea, the approach used in order to fabricate this novel platform from scratch, the experiments carried out to verify its capabilities and the associated results. In the last paragraph, I will discuss how the proposed platform could became suitable for the day to day uses in research activity by employing nanoporous materials. In fact, big efforts are carried out in order to find appropriate metamaterials as substitutes of the 3D counterparts so as to decrease the cost of device manufacturing that makes them unfitting with research activity. As a novel electrode material, nanoporous metals possess unique properties, such as a low fabrication cost, high plasmonic enhancement and large surface-volume ratio[8]. Nanoporous gold behaves like a metamaterial whose effective dielectric response can be tuned accordingly to the wanted use. These properties make the material suitable for multiple biosensing application, from a high-performance and reliable SERS (surface enhanced raman scattering) substrate [9] to an electrode in CMOS MEAs capable of intracellular recordings[10]. All these properties were explored in the last years, but it could be interesting to further study if the characteristics of this material could make it a good photoelectrical modulating material for eliciting electrogenic cells firing activity. In this way, this technology could be in principle easily implemented on commercial CMOS devices, consenting stimulation and recording at single cell level with high-resolution sensors, opening the way to new methodologies for studying electrogenic cells and tissues. Electrical stimulation of excitable cells is the basis for many implantable devices in cardiac treatment and in neurological studies for treating debilitating neurological syndromes. In order to make the technique less invasive, optical stimulation was widely investigated [11]. The non-genetic photostimulation is starting to make its way in the field since it allows to avoid changing the biological framework by using transient thermal or electrochemical outputs from synthetic materials attached to the target cells[12]. If stimulated with impinging light these materials could inject free charges into the solution resulting in an ionic current at the interface able to eliciting of neurons[13] or cardiomyocyte action potentials. Plasmonic porous materials have all the suitable properties to be considered as an appealing tools for charge injection and consequently for stimulation of electrically active cells [14]. Thus, the second part of this dissertation will exploit the capabilities of these plasmonic metamaterials, placing particular emphasis on the possibility of photoelectrochemical modulation. In particular, in the fifth and last chapter I will describe all the properties and application of the porous material and the mechanism of photoemission. In the experimental paragraphs, the free charge photoemission properties of porous gold will be explored together with plasmonic non-genetic photostimulation of the cardiac cells on commercial CMOS MEAs

Nanotools for Neuroscience and Brain Activity Mapping

Neuroscience is at a crossroads. Great effort is being invested into deciphering specific neural interactions and circuits. At the same time, there exist few general theories or principles that explain brain function. We attribute this disparity, in part, to limitations in current methodologies. Traditional neurophysiological approaches record the activities of one neuron or a few neurons at a time. Neurochemical approaches focus on single neurotransmitters. Yet, there is an increasing realization that neural circuits operate at emergent levels, where the interactions between hundreds or thousands of neurons, utilizing multiple chemical transmitters, generate functional states. Brains function at the nanoscale, so tools to study brains must ultimately operate at this scale, as well. Nanoscience and nanotechnology are poised to provide a rich toolkit of novel methods to explore brain function by enabling simultaneous measurement and manipulation of activity of thousands or even millions of neurons. We and others refer to this goal as the Brain Activity Mapping Project. In this Nano Focus, we discuss how recent developments in nanoscale analysis tools and in the design and synthesis of nanomaterials have generated optical, electrical, and chemical methods that can readily be adapted for use in neuroscience. These approaches represent exciting areas of technical development and research. Moreover, unique opportunities exist for nanoscientists, nanotechnologists, and other physical scientists and engineers to contribute to tackling the challenging problems involved in understanding the fundamentals of brain function