Amputation is a life-changing event that results in a drastic reduction in quality of life including extreme loss of function and severe mental, emotional and physical pain. In order to mitigate these negative outcomes, there is great interest in the design of ‘advanced/robotic’ prosthetics that cosmetically and functionally mimic the lost limb. While the robotics side of advanced prosthetics has seen many advances recently, they still provide only a fraction of the natural limbs’ functionality. At the heart of the issue is the interface between the robotic limb and the individual that needs significant development. Amputees retain significant function in their nerves post-amputation, which offers a unique opportunity to interface with the peripheral nerve. Here we evaluate a relatively new approach to peripheral nerve interfacing by using microchannels, which hold the intrinsic ability to record larger neural signals from nerves than previously developed peripheral nerve interfaces. We first demonstrate that microchannel scaffolds are well suited for chronic integration with amputated nerves and promote highly organized nerve regeneration. We then demonstrate the ability to record neural signals, specifically action potentials, using microchannels permanently integrated with electrodes after chronic implantation in a terminal study. Together these studies suggest that microchannels are well suited for chronic implantation and stable peripheral nerve interfacing. As a next step toward clinical translation, we developed fully-integrated high electrode count microchannel interfacing technology capable of functioning while implanted in awake and freely moving animal models as needed for pre-clinical evaluation. Importantly, fabrication techniques were developed that apply to a broad range of flexible devices/sensors benefiting from flexible interconnects, surface mount device (SMD) integration, and/or operation in aqueous environments. Examples include diabetic glucose sensors, flexible skin based health monitors, and the burgeoning flexible wearable technology industry. Finally, we successfully utilized the fully integrated microchannel interfaces to record action potentials in the challenging awake and freely moving animal model validating the microchannel approach for peripheral nerve interfacing. In the end, the findings of these studies help direct and give significant credence to future technology development enabling eventual clinical application of microchannels for peripheral nerve interfacing.

The aim of my Ph.D. thesis is to summarize my research on the development of multimateiral multifunctional fibers for bio-related application, mainly in the fields of neural interfacing and bioimpedance sensing. Understanding the cytoarchitecture and wiring of the brain requires improved methods to record and stimulate large groups of neurons with cellular specificity. This requires the development of improved miniaturized neural interfaces that integrate into brain tissue without altering its properties. Despite the advancement of the existing neural interface technologies such as microwires, silicon-based multielectrode arrays, and electrode arrays with flexible substrates, the physical properties of these devices limit their access to one, small brain region with single implantation. Beyond neural interfacing, extracting molecular information is crucial for understanding many neurological diseases and disorders. The most adapted methods are fast scan cyclic voltammetry and microdialysis. However, both have some limitations such as offline sensing or lack of selectivity. Furthermore, by concentrating optical fields at the nanoscale, plasmonic nanostructures can serve as optical nanoantennas to achieve ultrasensitive bio-/chemical sensing. But due to the limitation of the sensing mechanism, it is hard to perform the plasmonic sensing in live animals. Moreover, the relatively poor electrical performance of the electrode materials that can be utilized in the thermal drawing process limits the function of the fiber in other types of biomedical application, such as deep brain stimulation and electrochemical sensing. For example, the large inherent electrical resistance of the electrode material will significantly interference the electrical impedance result while the main purpose of this kind of study is to explore the frequency-dependent electrical properties of the tested subjects. To overcome above difficulties This thesis introduces broad application of multimaterial multiplexed fibers in biomedical areas. I first describe the development and application of spatially expandable multifunctional fiber-based probes for mapping and modulating brain activities across distant regions in the deep brain (Chapter 2). Secondly, I present the flexible nano-optoelectrodes integrated multifunctional fiber probes that can have hybrid optical-electrical sensing multimodalities, including optical refractive-index sensing, surface-enhanced Raman spectroscopy, and electrophysiological recording (Chapter 3). Thirdly, I demonstrate that hollow multifunctional fibers enable in-line impedimetric sensing of bioink composition and exhibit selectivity for real-time classification of cell type, viability, and state of differentiation during bioprinting (Chapter 4). The same device allows for local delivery of immune checkpoint blockade antibodies and for monitoring of clinical outcomes by tumor impedance measurement over the course of weeks with the photodynamic therapy option to enhance anti-tumor immunity and prolong intratumoral drug retention (Chapter 5). An overview future work has been summarized (Chapter 6). / Doctor of Philosophy / Electrode technology has played an indispensable role in neuroscience community since the first employment of insulated tungsten wire in cat brain in 1950s. The electrophysiological signal acquired from or the electrical current delivered to the brain tissue using the implanted electrode, has permitted us to understand the functional networks in the brain and treat neurological diseases. Over the past decades, significant progress has been made in developing miniaturized electrical neural interfaces. The development of optogenetics involving genetically-modified neurons that express light-sensitive proteins (opsins) has provided a powerful tool for modulating the neuronal activity to be switched on or off using light at a particular wavelength. Leveraging the thermal drawing process (TDP) from optical fiber industry for producing conventional silica fibers, multifunctional fiber-based neural probes have recently been developed, allowing for simultaneous optical stimulation, electrical recording, and drug delivery in vivo. However, the interfacing sites in these fiber-based neural probes have been restricted to a single location (at the fiber tip) so far, making the broad application of these probes unfeasible. Beyond neural interfacing, extracting molecular information is crucial for understanding many neurological diseases and disorders. The most adapted methods are fast scan cyclic voltammetry and microdialysis. However, both have some limitations such as offline sensing or lack of selectivity. Furthermore, by concentrating optical fields at the nanoscale, plasmonic nanostructures can serve as optical nanoantennas to achieve ultrasensitive bio-/chemical sensing. But due to the limitation of the sensing mechanism, it is hard to perform the plasmonic sensing in live animals. To overcome these limitations, we first developed a platform that provides three-dimensional coverage of brain tissue through multifunctional polymer fiber-based neural probes capable of interfacing simultaneously with neurons in multiple sites (Chapter 2). In a later study, we demonstrate that conductive nanoantenna arrays can be integrated with microelectrodes on the tip of multifunctional fiber probes as nano-optoelectrodes to enable optical bio-/chemical spectroscopy as well as to improve electrophysiology recording (Chapter 3). Besides, inspired by a convergence fiber drawing method, we have also managed to incorporate copper wires inside multifunctional fibers with a hollow channel in the center, in favor of high electrical conductivity. This technology developed here holds great promise for electrochemical impedance sensing of the tested media without the interference from the utilized electrodes' high resistance. Hence, by exploiting the functional fibers and the superior electrical performance, the copper-electrode-based fiber has been used for in vitro bioink bioimpedance sensing during 3D printing process (Chapter 4) and in vivo tumor impedance monitoring and drug delivery (Chapter 5). In summary, my research produces unique platforms for fundamental research studies as well as the readily translational application for human subjects. Given the scalable, straightforward, and versatile fabrication method, the multifunctional fibers delivered by our team would pave the way for new engineered tools for broad biomedical community.

This work details CMOS, bio-inspired, bio-compatible circuits which were used as synapses between an artificial neuron and a living neuron and between two living neurons. An intracellular signal from a living neuron was amplified, an integrate-and-fire neuron was used as a simple processing element to detect the spikes, and an artificial synapse was used to send outputs to another living neuron. The key structure is an electronic synapse which is based around a floating-gate pFET. The charge on the floating-gate is analogous to the synaptic weight and can be modified. This modification can be viewed as similar to long-term potentiation and long-term depression. The modification can either be programmed (supervised learning) or can adapt to the inputs (unsupervised learning). Since the technology to change the floating-gate weight has greatly improved, these weights can be set quickly and accurately. Intrinsic floating-gate learning rules were explored and the ability to change the synaptic weight was shown.

Neuro-engineering is an emerging multi-disciplinary domain which investigates the electrophysiological activities of the nervous system. It provides procedures and techniques to explore, analyze and characterize the functions of the different components comprising the nervous system. Neuro-engineering is not limited to research applications; it is employed in developing unconventional therapeutic techniques for treating different neurological disorders and restoring lost sensory or motor functions. Microelectrodes are principal elements in functional electric stimulation (FES) systems used in electrophysiological procedures. They are used in establishing an interface with the individual neurons or in clusters to record activities and communications, as well as modulate neuron behaviour through stimulation. Microelectrode technologies progressed through several modifications and innovations to improve their functionality and usability. However, conventional electrode technologies are open to further development, and advancement in microelectrodes technology will progressively meliorate the neuro-interfacing and electrotherapeutic techniques. This research introduced design methodology and fabrication processes for intra-cortical microelectrodes capable of befitting a wide range of design requirements and applications. The design process was employed in developing and implementing an ensemble of intra-cortical microelectrodes customized for different neuro-interfacing applications. The proposed designs presented several innovations and novelties. The research addressed practical considerations including assembly and interconnection to external circuitry. The research was concluded by exhibiting the Waterloo Array which is a high channel count flexible 3-D neuro-interfacing array. Finally, the dissertation was concluded by demonstrating the characterization, in vitro and acute in vivo testing results of the Waterloo Array. The implemented electrodes were tested and benchmarked against commercial equivalents and the results manifested improvement in the electrode performance compared to conventional electrodes. Electrode testing and evaluation were conducted in the Krembil Neuroscience Centre Research Lab (Toronto Western Hospital), and the Neurosciences & Mental Health Research Institute (the Sick Kids hospital). The research results and outcomes are currently being employed in developing chronic intra-cortical and electrocorticography (ECoG) electrode arrays for the epilepsy research and rodents nervous system investigations. The introduced electrode technologies will be used to develop customized designs for the clinical research labs collaborating with CIRFE Lab.

The emergence of organic electronics - a technology that relies on carbon-based semiconductors to deliver devices with unique properties - represents one of the most dramatic developments of the past two decades. A rapidly emerging new direction in the field involves the interface with biology. The "soft" nature of organics offers better mechanical compatibility with tissue than traditional electronic materials, while their natural compatibility with mechanically flexible substrates suits the non-planar form factors often required for implants. More importantly, their ability to conduct ions in addition to electrons and holes opens up a new communication channel with biology. The coupling of electronics with living tissue holds the key to a variety of important life-enhancing technologies. One example is bioelectronic implants that record neural signals and/or electrically stimulate neurons. These devices offer unique opportunities to understand and treat conditions such as hearing and vision loss, epilepsy, brain degenerative diseases, and spinal cord injury.The engineering aspect of the work includes the development of a photolithographic process to integrate the conducting polymer poly(3,4-ethylenedioxythiophene: poly(styrene sulfonate) (PEDOT:PSS) with parylene C supports to make an active device. The technology is used to fabricate electrocorticography (ECoG) probes, high-speed transistors and wearable biosensors. The experimental work explores the fundamentals of communication at the interface between conducting polymers and the brain. It is shown that conducting polymers outperform conventional metallic electrodes for brain signals recording.Organic electrochemical transistors (OECTs) represent a step beyond conducting polymer electrodes. They consist of a conducting polymer channel in contact with an electrolyte. When a gate electrode excites an ionic current in the electrolyte, ions enter the polymer film and change its conductivity. Since a small amount of ions can effectively "block" the transistor channel, these devices offer significant amplification in ion-to-electron transduction. Using the developed technology a high-speed and high-density OECTs array is presented. The dense architecture of the array improves the resolution of the recording from neural networks and the transistors temporal response are 100 μs, significantly faster than the action potential. The experimental transistor responses are fit and modeled in order to optimize the gain of the transistor. Using the model, an OECT with two orders of magnitude higher normalized transconductance per channel width is fabricated as compared to Silicon-based field effect transistors. Furthermore, the OECTs are integrated to a highly conformable ECoG probe. This is the first time that a transistor is used to record brain activities in vivo. It shows a far superior signal-to-noise-ratio (SNR) compare to electrodes. The high SNR of the OECT recordings enables the observation of activities from the surface of the brain that only a perpetrating probe can record. Finally, the application of OECTs for biosensing is explored. The bulk of the currently available biosensors often require complex liquid handling, and thus suffer from problems associated with leakage and contamination. The use of an organic electrochemical transistor for detection of lactate by integration of a room temperature ionic liquid in a gel-format, as a solid-state electrolyte is demonstrated.

Pas de résumé en français seulement en anglais / The emergence of organic electronics – a technology that relies on carbon-based semiconductors to deliver devices with unique properties – represents one of the most dramatic developments of the past two decades. A rapidly emerging new direction in the field involves the interface with biology. The “soft” nature of organics offers better mechanical compatibility with tissue than traditional electronic materials, while their natural compatibility with mechanically flexible substrates suits the non-planar form factors often required for implants. More importantly, their ability to conduct ions in addition to electrons and holes opens up a new communication channel with biology. The coupling of electronics with living tissue holds the key to a variety of important life-enhancing technologies. One example is bioelectronic implants that record neural signals and/or electrically stimulate neurons. These devices offer unique opportunities to understand and treat conditions such as hearing and vision loss, epilepsy, brain degenerative diseases, and spinal cord injury.The engineering aspect of the work includes the development of a photolithographic process to integrate the conducting polymer poly(3,4-ethylenedioxythiophene: poly(styrene sulfonate) (PEDOT:PSS) with parylene C supports to make an active device. The technology is used to fabricate electrocorticography (ECoG) probes, high-speed transistors and wearable biosensors. The experimental work explores the fundamentals of communication at the interface between conducting polymers and the brain. It is shown that conducting polymers outperform conventional metallic electrodes for brain signals recording.Organic electrochemical transistors (OECTs) represent a step beyond conducting polymer electrodes. They consist of a conducting polymer channel in contact with an electrolyte. When a gate electrode excites an ionic current in the electrolyte, ions enter the polymer film and change its conductivity. Since a small amount of ions can effectively “block” the transistor channel, these devices offer significant amplification in ion-to-electron transduction. Using the developed technology a high-speed and high-density OECTs array is presented. The dense architecture of the array improves the resolution of the recording from neural networks and the transistors temporal response are 100 μs, significantly faster than the action potential. The experimental transistor responses are fit and modeled in order to optimize the gain of the transistor. Using the model, an OECT with two orders of magnitude higher normalized transconductance per channel width is fabricated as compared to Silicon-based field effect transistors. Furthermore, the OECTs are integrated to a highly conformable ECoG probe. This is the first time that a transistor is used to record brain activities in vivo. It shows a far superior signal-to-noise-ratio (SNR) compare to electrodes. The high SNR of the OECT recordings enables the observation of activities from the surface of the brain that only a perpetrating probe can record. Finally, the application of OECTs for biosensing is explored. The bulk of the currently available biosensors often require complex liquid handling, and thus suffer from problems associated with leakage and contamination. The use of an organic electrochemical transistor for detection of lactate by integration of a room temperature ionic liquid in a gel-format, as a solid-state electrolyte is demonstrated.