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Flexible electrode arrays are a crucial technology for neural interfaces. In this thesis, the continued development of a flexible based electrode array is discussed. Two types of strain relief are introduced into the leads to allow the base to deform like the spinal cord in a repeatable manner. The resulting sandwich and embedded lead configurations were characterized using a tensile tester. In addition, the base material was characterized after exposure to physiological solutions and a sterilization protocol. Results show that the sandwich lead configuration had properties that were better matched to those of the spinal cord tissue. Parametric finite element modelling was also performed to identify the effect of the base modulus after varying several properties associated with the base. The results of the modelling would help in the long term manufacturing of these flexible based electrode arrays.
The brain is a massively-interconnected and constantly-evolving network of specialized circuits; a systematic understanding of the circuits requires a probe-tissue interface that can record and modulate brain activities at diverse spatial and temporal scales. Implanted electrodes provide a unique approach to decipher brain circuitry by allowing for time-resolved electrical detection of individual neuron activity. However, conventional intracortical recordings are often sparse, and importantly, unstable over long term. These pose limitations on their scientific and clinical applications. Through the use of less-rigid polymer materials and the ten-to-a-hundred fold reduction on probe size, the flexibility of a neural probe can be improved by four orders of magnitude, which results in a friendly probe-tissue interfaces, long-term recording performance, and greater potential for scaling up in implantation density. Here we present our progress on the development of a novel neural recording platform including 1. A stable neural interface named nanoelectronic threads (NETs) which demonstrated long-term stable recording over four months, seamless chronic probe-tissue integration and easy compatibility with optical imaging. 2. A facile implantation method to apply the flexible NETs in scalable, reliable neural recording in rodent brain. 3. A dense and high-bandwidth NET platform towards volumetric mapping and large-scale distributed recordings in the neocortex and subcortical structures, and 4. A low-cost and versatile multifunctional neural probe platform to achieve optogenetic stimulation and controlled drug infusion with simultaneous, spatially resolved neural recording. These capabilities will drive new long-term studies of brain circuits across different spatiotemporal dimensions and modalities
Neuroprostheses allow the possibility of restoring lost sensory and motor function by directly interfacing with the nervous system. The multi-electrode array serves as a key component of the neural interface system that allows the recoding from and stimulation of the nervous system. Three neural electrode systems were developed in this work (1) Three dimensional bulk micromachined electrode array (2) Silicon-SU8 neural electrode with embedded microchannels for drug and growth factor delivery (3) A flexible SU-8 neural electrode with simultaneous fluidic delivery and electrical stimulation and recording capabilities. A three dimensional electrode array that depend only MEMS processes was developed to improve on several key fabrication steps involved in the manufacturing of the current state of the art intraneural electrodes which rely heavily on non-IC processes. A silicon and SU-8 neural probe with an embedded fluidic channel is developed to deliver growth factors and drugs that would mitigate the cellular responses that have limited the chronic implementation of current multielectrode arrays. In addition to delivering drugs and growth factors, a flexible SU-8 based neural probe with fluidic and electrical capabilities was developed to further extend the longevity of neural electrodes by reducing the tissue/electrode mechanical mismatch of traditional silicon based neural electrodes.
This book provides a comprehensive reference to major neural interfacing technologies used to transmit signals between the physical world and the nervous system for repairing, restoring and even augmenting body functions. The authors discuss the classic approaches for neural interfacing, the major challenges encountered, and recent, emerging techniques to mitigate these challenges for better chronic performances. Readers will benefit from this book’s unprecedented scope and depth of coverage on the technology of neural interfaces, the most critical component in any type of neural prostheses. Provides comprehensive coverage of major neural interfacing technologies; Reviews and discusses both classic and latest, emerging topics; Includes classification of technologies to provide an easy grasp of research and trends in the field.
This book describes the design, fabrication and evaluation of a polymer-based neural interface for a cochlear electrode array, reviewed in terms of fabrication process, functionality, and reliability. Polymer-based devices have attracted attention in the neural prosthetic field due to their flexibility and compatibility with micro-fabrication process. A liquid crystal polymer (LCP) is an inert, highly water-resistant polymer suitable for the encapsulation of electronic components and as a substrate material for fabricating neural interfaces. The author has designed, fabricated, and evaluated an LCP-based cochlear electrode array for an improved polymer-based cochlear implant. The thesis deals with 3 key topics: atraumatic deep insertion, tripolar stimulation, and long-term reliability. Atraumatic insertion of the intracochlear electrode and resulting preservation of residual hearing have become essential in state–of-the-art cochlear implantation. A novel tapered design of an LCP-based cochlear electrode array is presented to meet such goals. For high-density and pitch-recognizable cochlear implant, channel interaction should be avoided. Local tripolar stimulation using multi-layered electrode sites are shown to achieve highly focused electrical stimulation. This thesis addresses another vital issue in the polymer-based neural implants: the long-term reliability issue. After suggesting a new method of forming mechanical interlocking to improve polymer-metal adhesion, the author performs accelerating aging tests to verify the method’s efficacy. The aforementioned three topics have been thoroughly examined through various in vitro and in vivo studies. Verification foresees the development of LCP-based cochlear electrode array for an atraumatic deep insertion, advanced stimulation, and long-term clinical implant.
Neural electrodes enable the recording and stimulation of bioelectrical activity in the nervous system. This technology provides neuroscientists with the means to probe the functionality of neural circuitry in both health and disease. In addition, neural electrodes can deliver therapeutic stimulation for the relief of debilitating symptoms associated with neurological disorders such as Parkinson's disease and may serve as the basis for the restoration of sensory perception through peripheral nerve and brain regions after disease or injury. Lastly, microscale neural electrodes recording signals associated with volitional movement in paralyzed individuals can be decoded for controlling external devices and prosthetic limbs or driving the stimulation of paralyzed muscles for functional movements. In spite of the promise of neural electrodes for a range of applications, chronic performance remains a goal for long-term basic science studies, as well as clinical applications. New perspectives and opportunities from fields including tissue biomechanics, materials science, and biological mechanisms of inflammation and neurodegeneration are critical to advances in neural electrode technology. This Special Issue will address the state-of-the-art knowledge and emerging opportunities for the development and demonstration of advanced neural electrodes.
Nerve stimulation technology utilizing electricity, magnetism, light, and ultrasound has found extensive applications in biotechnology and medical fields. Neurostimulation devices serve as the crucial interface between biological tissue and the external environment, posing a bottleneck in the advancement of neurostimulation technology. Ensuring safety and stability is essential for their future applications. Traditional rigid devices often elicit significant immune responses due to the mechanical mismatch between their materials and biological tissues. Consequently, there is a growing demand for flexible nerve stimulation devices that offer enhanced treatment efficacy while minimizing irritation to the human body. This review provides a comprehensive summary of the historical development and recent advancements in flexible devices utilizing four neurostimulation techniques: electrical stimulation, magnetic stimulation, optic stimulation, and ultrasonic stimulation. It highlights their potential for high biocompatibility, low power consumption, wireless operation, and superior stability. The aim is to offer valuable insights and guidance for the future development and application of flexible neurostimulation devices.
THIN-FILM NEURAL INTERFACES FOR BRAIN-COMPUTER INTERFACE AND ELECTRORETINOGRAPHY APPLICATIONS Sanitta Thongpang Under the supervision of Associate Professor Justin C. Williams At the University of Wisconsin-Madison The brain, and more precisely the central nervous system (CNS), is an extremely complex organ responsible for controlling essential sensorimotor functions of the human body. These functions rely on nerves running all-throughout the organism, transporting the sensory information from the body towards the CNS and the motor information from the CNS to the muscles. However, when severed, these functions can be durably lost, provoking paralysis and significant loss of quality of life. Neuroprosthesis is a promising approach to allow the patient to regain some of the quality of life lost through the control of a computer directly from measuring brain activity. Unfortunately, current methods are either too invasive, risk a decrease of performance over time and require extreme precision to place (i.e. single-unit electrode) or non-invasive but imprecise and limited (e.g. electroencephalogram). Electrocorticogram interfaces (ECoG and micro-ECoG) have been developed to measure brain activity as close as possible to the neurons while minimizing invasivity and long-term effects. These are placed on between the cortex and the cranium and allow good improvements in signal quality and spatial resolution. Here, I present the improved electrode designs and fabrication methods for reliable micro-ECoG electrode arrays using flexible insulating materials such as polyimide and parylene C. Furthermore, we characterize the long-term effect of chronic implantation of the device both on the electrical and material properties as well as the biological response of the brain of the micro-ECoG arrays. In addition, leveraging recent developments in optogenetics, two-way neural interface devices were developed. By integrating these methods with cranial window imaging techniques, I demonstrated that very powerful tools for optimizing micro-ECoG electrode arrays, as well as answering fundamental biological question on the function of the brain, can be developed. Finally, the flexible thin-film bio-MEMS fabrication methods demonstrated were readily expanded to many other applications such as electroretinogram (ERG) recording.