33 research outputs found
Advances in Scalable Implantable Systems for Neurostimulation Using Networked ASICs
Neurostimulation is a known method for restoring
lost functions to neurologically impaired patients. This paper
describes recent advances in scalable implantable stimulation
systems using networked application specific integrated circuits
(ASICs). It discusses how they can meet the ever-growing
demand for high-density neural interfacing and long-term
reliability. A detailed design example of an implantable
(inductively linked) scalable stimulation system for restoring
lower limb functions in paraplegics after spinal cord injury is
presented. It comprises a central hub implanted at the costal
margin and multiple Active Books which provide the interface for
stimulating nerve roots in the cauda equina. A 16-channel
stimulation system using four Active Books is demonstrated. Each
Active Book has an embedded ASIC, which is responsible for
initiating stimulus current to the electrodes. It also ensures device
safety by monitoring temperature, humidity, and peak electrode
voltage during stimulation. The implant hub was implemented
using a microcontroller-based circuit. The ASIC in the Active
Book was fabricated using XFABโs 0.6-ยตm high-voltage CMOS
process. The stimulation system does not require an accurate
reference clock in the implant. Measured results are provided
Wireless networks of injectable microelectronic stimulators based on rectification of volume conducted high frequency currents
Objective. To develop and in vivo demonstrate threadlike wireless implantable neuromuscular
microstimulators that are digitally addressable. Approach. These devices perform, through its two
electrodes, electronic rectification of innocuous high frequency current bursts delivered by volume
conduction via epidermal textile electrodes. By avoiding the need of large components to obtain
electrical energy, this approach allows the development of thin devices that can be intramuscularly
implanted by minimally invasive procedures such as injection. For compliance with electrical safety
standards, this approach requires a minimum distance, in the order of millimeters or a very few
centimeters, between the implant electrodes. Additionally, the devices must cause minimal
mechanical damage to tissues, avoid dislocation and be adequate for long-term implantation.
Considering these requirements, the implants were conceived as tubular and flexible devices with
two electrodes at opposite ends and, at the middle section, a hermetic metallic capsule housing the
electronics. Main results. The developed implants have a submillimetric diameter (0.97 mm
diameter, 35 mm length) and consist of a microcircuit, which contains a single custom-developed
integrated circuit, housed within a titanium capsule (0.7 mm diameter, 6.5 mm length), and two
platinumโiridium coils that form two electrodes (3 mm length) located at opposite ends of a
silicone body. These neuromuscular stimulators are addressable, allowing to establish a network of
microstimulators that can be controlled independently. Their operation was demonstrated in an
acute study by injecting a few of them in the hind limb of anesthetized rabbits and inducing
controlled and independent contractions. Significance. These results show the feasibility of
manufacturing threadlike wireless addressable neuromuscular stimulators by using fabrication
techniques and materials well established for chronic electronic implants. Although long-term
operation still must be demonstrated, the obtained results pave the way to the clinical development
of advanced motor neuroprostheses formed by dense networks of such wireless devices.European Research Council (ERC) 724244ICREA under the ICREA Academia programm
Wireless integrated circuit for 100-channel charge-balanced neural stimulation
Journal ArticleThe authors present the design of an integrated circuit for wireless neural stimulation, along with benchtop and in-vivo experimental results. The chip has the ability to drive 100 individual stimulation electrodes with constant-current pulses of varying amplitude, duration, interphasic delay, and repetition rate. The stimulation is performed by using a biphasic (cathodic and anodic) current source, injecting and retracting charge from the nervous system. Wireless communication and power are delivered over a 2.765-MHz inductive link. Only three off-chip components are needed to operate the stimulator: a 10-nF capacitor to aid in power-supply regulation, a small capacitor (100 pF) for tuning the coil to resonance, and a coil for power and command reception. The chip was fabricated in a commercially available 0.6- m 2P3M BiCMOS process. The chip was able to activate motor fibers to produce muscle twitches via a Utah Slanted Electrode Array implanted in cat sciatic nerve, and to activate sensory fibers to recruit evoked potentials in somatosensory cortex
VLSI Circuits for Bidirectional Neural Interfaces
Medical devices that deliver electrical stimulation to neural tissue are important clinical tools that can augment or replace pharmacological therapies. The success of such devices has led to an explosion of interest in the field, termed neuromodulation, with a diverse set of disorders being targeted for device-based treatment. Nevertheless, a large degree of uncertainty surrounds how and why these devices are effective. This uncertainty limits the ability to optimize therapy and gives rise to deleterious side effects. An emerging approach to improve neuromodulation efficacy and to better understand its mechanisms is to record bioelectric activity during stimulation. Understanding how stimulation affects electrophysiology can provide insights into disease, and also provides a feedback signal to autonomously tune stimulation parameters to improve efficacy or decrease side-effects. The aims of this work were taken up to advance the state-of-the-art in neuro-interface technology to enable closed-loop neuromodulation therapies.
Long term monitoring of neuronal activity in awake and behaving subjects can provide critical insights into brain dynamics that can inform system-level design of closed-loop neuromodulation systems. Thus, first we designed a system that wirelessly telemetered electrocorticography signals from awake-behaving rats. We hypothesized that such a system could be useful for detecting sporadic but clinically relevant electrophysiological events. In an 18-hour, overnight recording, seizure activity was detected in a pre-clinical rodent model of global ischemic brain injury.
We subsequently turned to the design of neurostimulation circuits. Three critical features of neurostimulation devices are safety, programmability, and specificity. We conceived and implemented a neurostimulator architecture that utilizes a compact on-chip circuit for charge balancing (safety), digital-to-analog converter calibration (programmability) and current steering (specificity). Charge balancing accuracy was measured at better than 0.3%, the digital-to-analog converters achieved 8-bit resolution, and physiological effects of current steering stimulation were demonstrated in an anesthetized rat.
Lastly, to implement a bidirectional neural interface, both the recording and stimulation circuits were fabricated on a single chip. In doing so, we implemented a low noise, ultra-low power recording front end with a high dynamic range. The recording circuits achieved a signal-to-noise ratio of 58 dB and a spurious-free dynamic range of better than 70 dB, while consuming 5.5 ฮผW per channel. We demonstrated bidirectional operation of the chip by recording cardiac modulation induced through vagus nerve stimulation, and demonstrated closed-loop control of cardiac rhythm
A Closed-Loop Deep Brain Stimulation Device With a Logarithmic Pipeline ADC.
This dissertation is a summary of the research on integrated closed-loop deep brain stimulation for treatment of Parkinsonโs disease. Parkinson's disease is a progressive disorder of the central nervous system affecting more than three million people in the United States. Deep Brain Stimulation (DBS) is one of the most effective treatments of Parkinsonโs symptoms. DBS excites the Subthalamic Nucleus (STN) with a high frequency electrical signal. The proposed device is a single-chip closed-loop DBS (CDBS) system. Closed-loop feedback of sensed neural activity promises better control and optimization of stimulation parameters than with open-loop devices.
Thanks to a novel architecture, the prototype system incorporates more functionality yet consumes less power and area compared to other systems. Eight front-end low-noise neural amplifiers (LNAs) are multiplexed to a single high-dynamic-range logarithmic, pipeline analog-to-digital converter (ADC). To save area and power consumption, a high dynamic-range log ADC is used, making analog automatic gain control unnecessary. The redundant 1.5b architecture relaxes the requirements for the comparator accuracy and comparator reference voltage accuracy. Instead of an analog filter, an on-chip digital filter separates the low frequency neural field potential signal from the neural spike energy. An on-chip controller generates stimulation patterns to control the 64 on-chip current-steering DACs. The 64 DACs are formed as a cascade of a single shared 2-bit coarse current DAC and 64 individual bi-directional 4-bit fine DACs. The coarse/fine configuration saves die area since the MSB devices tend to be large.
Real-time neural activity was recorded with the prototype device connected to microprobes that were chronically implanted in two Long Evans rats. The recorded in-vivo signal clearly shows neural spikes of 10.2 dB signal-to-noise ratio (SNR) as well as a periodic artifact from neural stimulation. The recorded neural information has been analyzed with single unit sorting and principal component analysis (PCA). The PCA scattering plots from multi-layers of cortex represent diverse information from either single or multiple neural sources. The single-unit neural sorting analysis along with PCA verifies the feasibility of the implantable CDBS device for to in-vivo neural recording interface applications.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/60733/1/milaca_1.pd
์์ ์ด์ํ ์๊ฐ ๋ณด์ฒ ์์คํ ์ ์ํ ์ฐ๊ตฌ
ํ์๋
ผ๋ฌธ(๋ฐ์ฌ)--์์ธ๋ํ๊ต ๋ํ์ :๊ณต๊ณผ๋ํ ์ ๊ธฐยท์ ๋ณด๊ณตํ๋ถ,2020. 2. ๊น์ฑ์ค.A visual prosthetic system typically consists of a neural stimulator, which is a surgically implantable device for electrical stimulation intended to restore the partial vision of blind patients, and peripheral external devices including an image sensor, a controller, and a processor. Although several visual prosthetic systems, such as retinal prostheses or retinal implants, have already been commercialized, there are still many issues on them (e.g., substrate materials for implantable units, electrode configurations, the use of external hardware, power supply and data transmission methods, design and fabrication approaches, etc.) to be dealt with for an improved visual prosthetic system. In this dissertation, a totally implantable visual prosthetic system is suggested with four motivations, which are thought to be important, as in the following: 1) simple fabrication of implantable parts, such as micro-sized electrodes and a case, for a neural stimulator based on polymer without semiconductor techniques, 2) multi-polar stimulation for virtual channel generation to overcome a limited number of physical electrodes in a confined space, 3) a new image acquisition strategy using an implantable camera, and 4) power supply as well as data transmission to a neural stimulator without hindering patients various activities.
First, polymer materials have been widely used to develop various implantable devices for visual prosthetic systems because of their outstanding advantages including flexibility and applicability to microfabrication, compared with metal, silicon, or ceramic. Most polymer-based implantable devices have been fabricated by the semiconductor technology based on metal deposition and photolithography. This technology provides high accuracy and precision for metal patterning on a polymer substrate. However, the technology is also complicated and time-consuming as it requires masks for photolithography and vacuum for metal deposition as well as huge fabrication facilities. This is the reason why biocompatible cyclic olefin polymer (COP) with low water absorption (<0.01 %) and high light transmission (92 %) was chosen as a new substrate material of an implantable device in this study. Based on COP, simple fabrication process of an implantable device was developed without masks, vacuum, and huge fabrication facilities. COP is characterized by strong adhesion to gold and high ultraviolet (UV) transparency as well. Because of such adhesion and UV transparency, a gold thin film can be thermally laminated on a COP substrate with no adhesion layer and micromachined by a UV laser without damaging the substrate. Using the developed COP-based process, a depth-type microprobe was fabricated first, and its electrochemical and mechanical properties as well as functionality were evaluated by impedance measurements, buckling tests, and in vivo neural signal recording, respectively. Furthermore, the long-term reliability of COP encapsulation formed by the developed process was estimated through leakage current measurements during accelerated aging in saline solution, to show the feasibility of the encapsulation using COP as well.
Second, even if stimulation electrodes become sufficiently small, it is demanding to arrange them for precise
stimulation on individual neurons due to electrical crosstalk, which is the spatial superposition of electric fields generated by simultaneous stimuli. Hence, an adequate spacing between adjacent electrodes is required, and this causes a limited number of physical electrodes in a confined space such as in the brain or in the retina. To overcome this limitation, many researchers have proposed stimulation strategies using virtual channels, which are intermediate areas with large magnitudes of electric fields between physical electrodes. Such virtual channels can be created by multi-polar stimulation that can combine stimuli output from two or more electrodes at the same time. To produce more delicate stimulation patterns using virtual channels herein, penta-polar stimulation with a grid-shaped arrangement of electrodes was leveraged specially to generate them in two dimensions. This penta-polar stimulation was realized using a custom-designed integrated circuit with five different current sources and surface-type electrodes fabricated by the developed COP-based process. The effectiveness of the penta-polar stimulation was firstly evaluated by focusing electric fields in comparison to mono-polar stimulation. In addition, the distribution of electric fields changed by the penta-polar stimulation, which indicated virtual channel generation, was estimated in accordance with an amplitude ratio between stimuli of the two adjacent electrodes and a distance from them, through both finite element analysis and in vitro evaluation.
Third, an implantable camera is herein proposed as a new image acquisition approach capturing real-time images while implanted in the eye, to construct a totally implantable visual prosthetic system. This implantable camera has distinct advantages in that it can provide blind patients with benefits to perform several ordinary activities, such as sleep, shower, or running, while focusing on objects in accordance with natural eye movements. These advantages are impossible to be achieved using a wearing unit such as a glasses-mounted camera used in a conventional partially implantable visual prosthetic system. Moreover, the implantable camera also has a merit of garnering a variety of image information using the complete structure of a camera, compared with a micro-photodiode array of a retinal implant. To fulfill these advantageous features, after having been coated with a biocompatible epoxy to prevent moisture penetration and sealed using a medical-grade silicone elastomer to gain biocompatibility as well as flexibility, the implantable camera was fabricated enough to be inserted into the eye. Its operation was assessed by wireless image acquisition that displayed a processed black and white image. In addition, to estimate reliable wireless communication ranges of the implantable camera in the body, signal-to-noise ratio measurements were conducted while it was covered by an 8-mm-thick biological medium that mimicked an in vivo environment.
Lastly, external hardware attached on the body has been generally used in conventional visual prosthetic systems to stably deliver power and data to implanted units and to acquire image signals outside the body. However, there are common problems caused by this external hardware, including functional failure due to external damages, unavailability during sleep, in the shower, or while running or swimming, and cosmetic issues. Especially, an external coil for power and data transmission in a conventional visual prosthetic system is connected to a controller and processor through a wire, which makes the coil more vulnerable to the problems. To solve this issue, a totally implantable neural stimulation system controlled by a handheld remote controller is presented. This handheld remote controller can control a totally implantable stimulator powered by a rechargeable battery through low-power but relatively long-range ZigBee wireless communication. Moreover, two more functions can be performed by the handheld controller for expanded applications; one is percutaneous stimulation, and the other is inductive charging of the rechargeable battery. Additionally, simple switches on the handheld controller enable users to modulate parameters of stimuli like a gamepad. These handheld and user-friendly interfaces can make it easy to use the controller under various circumstances. The functionality of the controller was evaluated in vivo, through percutaneous stimulation and remote control especially for avian navigation, as well as in vitro. Results of both in vivo experiments were compared in order to verify the feasibility of remote control of neural stimulation using the controller.
In conclusion, several discussions on results of this study, including the COP-based simple fabrication process, the penta-polar stimulation, the implantable camera, and the multi-functional handheld remote controller, are addressed. Based on these findings and discussions, how the researches in this thesis can be applied to the realization of a totally implantable visual prosthetic system is elucidated at the end of this dissertation.์๊ฐ ๋ณด์ฒ ์์คํ
์ ์ผ๋ฐ์ ์ผ๋ก ์ค๋ช
ํ์๋ค์ ๋ถ๋ถ ์๋ ฅ์ ์ ๊ธฐ ์๊ทน์ผ๋ก ํ๋ณต์ํค๊ธฐ ์ํ์ฌ ์์ ์ ์ผ๋ก ์ด์๋ ์ ์๋ ์ฅ์น์ธ ์ ๊ฒฝ ์๊ทน๊ธฐ์ ์ด๋ฏธ์ง ์ผ์ ๋๋ ์ปจํธ๋กค๋ฌ, ํ๋ก์ธ์๋ฅผ ํฌํจํ๋ ์ธ๋ถ์ ์ฃผ๋ณ ์ฅ์น๋ค๋ก ๊ตฌ์ฑ๋๋ค. ๋ง๋ง ๋ณด์ฒ ์ฅ์น ๋๋ ๋ง๋ง ์ํ๋ํธ์ ๊ฐ์ด ๋ช๋ช ์๊ฐ ๋ณด์ฒ ์์คํ
์ ์ด๋ฏธ ์์ฉํ ๋์์ง๋ง, ์ฌ์ ํ ๋ ๋์ ์๊ฐ ๋ณด์ฒ ์์คํ
์ ์ํ์ฌ ๋ค๋ค์ ธ์ผ ํ ๋ง์ ์ด์๋ค (์๋ฅผ ๋ค์ด, ์ด์ํ ์ฅ์น์ ๊ธฐํ ๋ฌผ์ง, ์ ๊ทน์ ๋ฐฐ์ด, ์ธ๋ถ ํ๋์จ์ด์ ์ฌ์ฉ, ์ ๋ ฅ ๊ณต๊ธ ๋ฐ ๋ฐ์ดํฐ ์ ์ก ๋ฐฉ๋ฒ, ์ค๊ณ ๋ฐ ์ ์ ๋ฐฉ์ ๋ฑ)์ด ์๋ค. ๋ณธ ํ์๋
ผ๋ฌธ์ ์์ ์ด์ํ ์๊ฐ ๋ณด์ฒ ์์คํ
์ ์ ์ํ๋ฉฐ, ์ด๋ฅผ ์ํ์ฌ ๋ค์๊ณผ ๊ฐ์ด ์ค์ํ๋ค๊ณ ์๊ฐ๋๋ ์ด ๋ค ๊ฐ์ง์ ์ด์๋ค๊ณผ ๊ด๋ จ๋ ์ฐ๊ตฌ ๋ด์ฉ์ ๋ค๋ฃฌ๋ค. 1) ํด๋ฆฌ๋จธ๋ฅผ ๊ธฐ๋ฐ์ผ๋ก ํ ์ ๊ฒฝ ์๊ทน๊ธฐ์ ๋ฏธ์ธ ์ ๊ทน ๋ฐ ํจํค์ง์ ๊ฐ์ ์ด์ ๊ฐ๋ฅํ ๋ถ๋ถ์ ๋ฐ๋์ฒด ๊ธฐ์ ์์ด ๊ฐ๋จํ๊ฒ ์ ์ํ๋ ๋ฐฉ๋ฒ๊ณผ 2) ์ ํ๋ ๊ณต๊ฐ์์ ์ ๊ทน ๊ฐ์์ ๋ฌผ๋ฆฌ์ ์ธ ํ๊ณ๋ฅผ ๊ทน๋ณตํ๊ธฐ ์ํ์ฌ ๊ฐ์ ์ฑ๋์ ํ์ฑํ๋ ๋ค๊ทน์ฑ ์๊ทน ๋ฐฉ์, 3) ์ด์ํ ์นด๋ฉ๋ผ๋ฅผ ์ฌ์ฉํ๋ ์๋ก์ด ์ด๋ฏธ์ง ํ๋ ์ ๋ต, 4) ํ์์ ๋ค์ํ ํ๋์ ๋ฐฉํดํ์ง ์์ผ๋ฉด์ ์ ๊ฒฝ ์๊ทน๊ธฐ์ ์ ๋ ฅ์ ๊ณต๊ธํ๊ณ ๋ฐ์ดํฐ๋ฅผ ์ ์กํ๋ ๋ฐฉ๋ฒ.
์ฒซ์งธ๋ก, ๊ธ์์ด๋ ์ค๋ฆฌ์ฝ, ์ธ๋ผ๋ฏน์ ๋นํ์ฌ ํด๋ฆฌ๋จธ๋ ์ ์ฐ์ฑ ๋ฐ ๋ฏธ์ธ ์ ์์์ ์ ์ฉ ๊ฐ๋ฅ์ฑ์ ํฌํจํ๋ ๋๋๋ฌ์ง ์ด์ ๋ค์ด ์๊ธฐ ๋๋ฌธ์ ์๊ฐ ๋ณด์ฒ ์์คํ
์ ๊ตฌ์ฑํ๋ ๋ค์ํ ์ด์ ๊ฐ๋ฅํ ๋ถ๋ถ๋ค์ ๋๋ฆฌ ์ด์ฉ๋์๋ค. ๋๋ถ๋ถ์ ํด๋ฆฌ๋จธ ๊ธฐ๋ฐ ์ด์ํ ์ฅ์น๋ค์ ๊ธ์ ์ฆ์ฐฉ๊ณผ ์ฌ์ง ์๊ฐ์ ๊ธฐ๋ฐ์ผ๋ก ํ๋ ๋ฐ๋์ฒด ๊ณต์ ์ผ๋ก ์ ์๋์๋ค. ์ด ๊ณต์ ์ ํด๋ฆฌ๋จธ ๊ธฐํ ์์ ๊ธ์์ ํจํฐ๋ ํ๋ ๋ฐ์ ์์ด์ ๋์ ์ ํ์ฑ๊ณผ ์ ๋ฐ๋๋ฅผ ์ ๊ณตํ๋ค. ํ์ง๋ง ๊ทธ ๊ณต์ ์ ๋ํ, ์ฌ์ง ์๊ฐ์ ์ฐ์ด๋ ๋ง์คํฌ์ ๊ธ์ ์ฆ์ฐฉ์ ์ํ ์ง๊ณต๋ฟ๋ง ์๋๋ผ ์์ฃผ ํฐ ๊ณต์ ์ค๋น๋ฅผ ์๊ตฌํ๊ธฐ ๋๋ฌธ์ ์๊ฐ ์๋ชจ๊ฐ ์ฌํ๊ณ ๋ณต์กํ๋ค. ์ด๋ ๋ณธ ์ฐ๊ตฌ์์ ๋ฎ์ ์๋ถ ํก์ (<0.01 %)์ ๋์ ๋น ํฌ๊ณผ (92 %)๋ฅผ ํน์ง์ผ๋ก ํ๋ ์์ฒด์ ํฉํ ๊ณ ๋ฆฌํ ์ฌ๋ ํ ํด๋ฆฌ๋จธ (cyclic olefin polymer, COP)๊ฐ ์ด์ํ ์ฅ์น๋ฅผ ์ํ ์๋ก์ด ๊ธฐํ ๋ฌผ์ง๋ก์จ ์ ํ๋ ์ด์ ์ด๋ค. COP๋ฅผ ๊ธฐ๋ฐ์ผ๋ก ํ์ฌ, ๋ง์คํฌ์ ์ง๊ณต, ํฐ ๊ณต์ ์ค๋น๊ฐ ํ์ ์์ด ์ด์ ๊ฐ๋ฅํ ์ฅ์น๋ฅผ ๊ฐ๋จํ๊ฒ ์ ์ํ๋ ๊ณต์ ์ด ๊ฐ๋ฐ๋์๋ค. COP๋ ๊ธ๊ณผ์ ๊ฐํ ์ ํฉ๊ณผ ์์ธ์ ์ ๋ํ ๋์ ํฌ๋ช
์ฑ์ ๋ ๋ค๋ฅธ ํน์ง์ผ๋ก ํ๋ค. ์ด์ ๊ฐ์ ์ ํฉ ํน์ฑ๊ณผ ์์ธ์ ํฌ๋ช
์ฑ ๋๋ถ์, ๊ธ๋ฐ์ COP ๊ธฐํ์ ๋ณ๋์ ์ ํฉ์ธต ์์ด ์ด๋ก ์ ํฉ๋ ์ ์์ ๋ฟ๋ง ์๋๋ผ ๊ทธ ๊ธฐํ์ ์์์ ์ฃผ์ง ์์ผ๋ฉด์ ์์ธ์ ๋ ์ด์ ๋ฅผ ํตํ์ฌ ๋ฏธ์ธํ๊ฒ ๊ฐ๊ณต๋ ์ ์๋ค. ๊ฐ๋ฐ๋ COP ๊ธฐ๋ฐ์ ๊ณต์ ์ ์ฒ์์ผ๋ก ์ฌ์ฉํ์ฌ ์นจ์ตํ ๋ฏธ์ธ ํ๋ก๋ธ๊ฐ ์ ์๋์๊ณ , ๊ทธ ์ ๊ธฐํํ์ , ๊ธฐ๊ณ์ ํน์ฑ๊ณผ ๊ธฐ๋ฅ์ฑ์ด ๊ฐ๊ฐ ์ํผ๋์ค ์ธก์ ๊ณผ ๋ฒํด๋ง ํ
์คํธ, ์์ฒด ๋ด ์ ๊ฒฝ์ ํธ ๊ธฐ๋ก์ผ๋ก ํ๊ฐ๋์๋ค. ๊ทธ๋ฆฌ๊ณ COP๋ฅผ ์ฌ์ฉํ ๋ฐ๋ด์ ๊ฐ๋ฅ์ฑ๋ ์์๋ณด๊ธฐ ์ํ์ฌ, ๊ฐ๋ฐ๋ ๊ณต์ ์ ์ฌ์ฉํ์ฌ ํ์ฑ๋ COP ๋ฐ๋ด์ ์ฅ๊ธฐ ์์ ์ฑ์ด ์๋ฆฌ์์ผ์์์์ ๊ฐ์ ๋
ธํ ์ค ๋์ค ์ ๋ฅ ์ธก์ ์ ํตํ์ฌ ์ถ์ ๋์๋ค.
๋์งธ๋ก, ์๊ทน ์ ๊ทน์ ํฌ๊ธฐ๊ฐ ์ถฉ๋ถํ ์์์ง๋ค๊ณ ํ๋๋ผ๋, ๋์์ ์ถ๋ ฅ๋๋ ์๊ทน์ ์ํด ํ์ฑ๋๋ ์ ๊ธฐ์ฅ์ ์ค์ฒฉ์ธ ํฌ๋ก์ค ํ ํฌ ๋๋ฌธ์ ๊ฐ๊ฐ์ ์ ๊ฒฝ์ธํฌ๋ฅผ ์ ๋ฐํ๊ฒ ์๊ทนํ๊ธฐ ์ํ์ฌ ์ ๊ทน์ ๋ฐฐ์ดํ๋ ๊ฒ์ ์์ฃผ ์ด๋ ต๋ค. ๋ฐ๋ผ์ ์ธ์ ํ ์ ๊ทน ์ฌ์ด์ ์ ๋นํ ๊ฐ๊ฒฉ์ด ํ์ํ๊ฒ ๋๊ณ , ์ด๋ ํนํ ๋ ๋๋ ๋ง๋ง๊ณผ ๊ฐ์ ์ ํ๋ ๊ณต๊ฐ์์ ์ ๊ทน ๊ฐ์์ ๋ฌผ๋ฆฌ์ ์ธ ํ๊ณ๋ฅผ ์ผ๊ธฐํ๋ค. ์ด ํ๊ณ๋ฅผ ๊ทน๋ณตํ๊ธฐ ์ํ์ฌ, ๋ง์ ์ฐ๊ตฌ์๋ค์ ์ค์ ์ ๊ทน ์ฌ์ด์์ ํฐ ์ ๊ธฐ์ฅ ์ธ๊ธฐ๋ฅผ ๊ฐ๋ ์ค๊ฐ ์์ญ์ ๋ํ๋ด๋ ๊ฐ์ ์ฑ๋์ ์ด์ฉํ ์๊ทน ์ ๋ต์ ์ ์ํ์๋ค. ์ด๋ฌํ ๊ฐ์ ์ฑ๋์ ๋ ์ด์์ ์ ๊ทน์์ ๋์์ ์ถ๋ ฅ๋๋ ์๊ทน ํํ์ ํฉ์น ์ ์๋ ๋ค๊ทน์ฑ ์๊ทน์ ์ํ์ฌ ํ์ฑ์ด ๊ฐ๋ฅํ๋ค. ๋ณธ ์ฐ๊ตฌ์์๋ ๊ฐ์ ์ฑ๋์ ์ด์ฉํ์ฌ ๋ ์ ๊ตํ ์๊ทน ํจํด์ ๋ง๋ค๊ธฐ ์ํ์ฌ, ํนํ 2์ฐจ์์์์ ๊ฐ์ ์ฑ๋์ ์์ฑํ๊ณ ์ ๊ฒฉ์ํ ๋ฐฐ์ด์ ์ ๊ทน๊ณผ ํจ๊ป 5๊ทน์ฑ ์๊ทน์ด ์ฌ์ฉ๋์๋ค. ์ด 5๊ทน์ฑ ์๊ทน์ ๋ค์ฏ ๊ฐ์ ์๋ก ๋ค๋ฅธ ์ ๋ฅ์์ ๊ฐ๋๋ก ๋ง์ถค ์ค๊ณ๋ ์ง์ ํ๋ก์ ๊ฐ๋ฐ๋ COP ๊ธฐ๋ฐ ๊ณต์ ์ผ๋ก ์ ์๋ ํ๋ฉดํ ์ ๊ทน์ ์ฌ์ฉํ์ฌ ๊ตฌํ๋์๋ค. ๋จผ์ , 5๊ทน์ฑ ์๊ทน์ ํจ๊ณผ๋ฅผ ํ์ธํ๊ณ ์ ์ด ์๊ทน์ผ๋ก ์ ๊ธฐ์ฅ์ ํ ๊ณณ์ ๋ ์ง์ค๋ ํํ๋ก ๋ง๋ค ์ ์์์ด ๋จ๊ทน์ฑ ์๊ทน๊ณผ์ ๋น๊ต๋ฅผ ํตํ์ฌ ๊ฒ์ฆ๋์๋ค. ๊ทธ๋ฆฌ๊ณ ์ ํ ์์ ๋ถ์๊ณผ ์์ฒด ์ธ ํ๊ฐ ๋ ๋ชจ๋๋ฅผ ํตํ์ฌ, 5๊ทน์ฑ ์๊ทน์ผ๋ก ์ธํ ๊ฐ์ ์ฑ๋ ํ์ฑ์ ๋ปํ๋ ์ ๊ธฐ์ฅ ๋ถํฌ๊ฐ ์ธ์ ํ ๋ ์ ๊ทน์์ ๋์ค๋ ์๊ทน์ ์งํญ๋น์ ๊ทธ ์ ๊ทน์ผ๋ก๋ถํฐ ๋จ์ด์ง ๊ฑฐ๋ฆฌ์ ๋ฐ๋ผ ๋ณํ๋จ์ด ์ถ์ ๋์๋ค.
์
์งธ๋ก, ๋ณธ ์ฐ๊ตฌ์์๋ ๋์ ์ด์๋ ์ฑ๋ก ์ค์๊ฐ ์ด๋ฏธ์ง๋ฅผ ์ป์์ผ๋ก์จ ์์ ์ด์ํ ์๊ฐ ๋ณด์ฒ ์์คํ
์ ๊ตฌ์ฑํ๋ ์ด์ํ ์นด๋ฉ๋ผ๋ฅผ ์๋ก์ด ์ด๋ฏธ์ง ํ๋ ๋ฐฉ์์ผ๋ก์จ ์ ์ํ๋ค. ์ด ์ด์ํ ์นด๋ฉ๋ผ๋ ์ค๋ช
ํ์๋ค์ด ์์ฐ์ค๋ฌ์ด ๋์ ์์ง์์ ๋ฐ๋ผ์ ๋ฌผ์ฒด๋ฅผ ๋ณผ ์ ์์ผ๋ฉฐ ์ ์ด๋ ์ค์, ๋ฌ๋ฆฌ๊ธฐ์ ๊ฐ์ ์ผ์์ ์ธ ํ๋๋ค์ ๋ฐฉํด ๋ฐ์ง ์๊ณ ์ํํ ์ ์๋๋ก ๋๋๋ค๋ ์ ์์ ๋
ํนํ ์ฅ์ ์ ๊ฐ๋๋ค. ๊ธฐ์กด์ ๋ถ๋ถ ์ด์ํ ์๊ฐ ๋ณด์ฒ ์์คํ
์์ ์ฐ์ด๋ ์๊ฒฝ ๋ถ์ฐฉํ ์นด๋ฉ๋ผ์ ๊ฐ์ ์ฐฉ์ฉ ์ฅ๋น๋ก๋ ์ด๋ฌํ ์ฅ์ ๋ค์ ์ป์ ์ ์๋ค. ๊ฒ๋ค๊ฐ, ์ด์ํ ์นด๋ฉ๋ผ๋ ๋ง๋ง ์ํ๋ํธ์ ๋ฏธ์ธ ํฌํ ๋ค์ด์ค๋ ์ด๋ ์ด์ ๋ฌ๋ฆฌ ์์ ํ ์นด๋ฉ๋ผ ๊ตฌ์กฐ๋ฅผ ์ด์ฉํ์ฌ ๋ค์ํ ์ด๋ฏธ์ง ์ ๋ณด๋ฅผ ํ๋ํ ์ ์๋ค๋ ์ฅ์ ์ ๊ฐ๋๋ค. ์ด๋ฌํ ์ด์ ๋ค์ ๋ฌ์ฑํ๊ธฐ ์ํ์ฌ, ๊ทธ ์ด์ํ ์นด๋ฉ๋ผ๋ ์๋ถ ์นจํฌ๋ฅผ ๋ง๊ณ ์ ์์ฒด์ ํฉํ ์ํญ์๋ก ์ฝํ
๋์๊ณ ์์ฒด์ ํฉ์ฑ๊ณผ ์ ์ฐ์ฑ์ ์ป๊ธฐ ์ํ์ฌ ์๋ฃ์ฉ ์ค๋ฆฌ์ฝ ์๋ผ์คํ ๋จธ๋ก ๋ฐ๋ด๋ ํ์ ๋์ ์ถฉ๋ถํ ์ฝ์
๋ ์ ์๋ ํํ ๋ฐ ํฌ๊ธฐ๋ก ์ ์๋์๋ค. ์ด ์ฅ์น์ ๋์์ ํ๋ฐฑ์ผ๋ก ์ฒ๋ฆฌ๋ ์ด๋ฏธ์ง๋ฅผ ํ์ํ๋ ๋ฌด์ ์ด๋ฏธ์ง ํ๋์ผ๋ก ์ํ๋์๋ค. ๊ทธ๋ฆฌ๊ณ ๋ชธ ์์์ ์ด์ํ ์นด๋ฉ๋ผ ๊ฐ๋ ์์ ์ ์ธ ํต์ ๊ฑฐ๋ฆฌ๋ฅผ ์ธก์ ํ๊ธฐ ์ํ์ฌ, ์ฅ์น๊ฐ ์์ฒด ๋ด ํ๊ฒฝ์ ๋ชจ์ฌํ๊ธฐ ์ํ 8 mm ๋๊ป์ ์์ฒด ๋ฌผ์ง๋ก ๋ฎ์ธ ์ํ์์ ๊ทธ ์ฅ์น์ ์ ํธ ๋ ์ก์๋น๊ฐ ์ธก์ ๋์๋ค.
๋ง์ง๋ง์ผ๋ก, ๊ธฐ์กด์ ์๊ฐ ๋ณด์ฒ ์์คํ
์์ ๋ชธ์ ๋ถ์ฐฉ๋ ํํ์ ์ธ๋ถ ํ๋์จ์ด๋ ์ด์๋ ์ฅ์น์ ์ ๋ ฅ๊ณผ ๋ฐ์ดํฐ๋ฅผ ์์ ์ ์ผ๋ก ์ ๋ฌํ๊ณ ์ด๋ฏธ์ง ์ ํธ๋ฅผ ์์งํ๊ธฐ ์ํ์ฌ ์ผ๋ฐ์ ์ผ๋ก ์ฌ์ฉ๋์๋ค. ๊ทธ๋ผ์๋ ๋ถ๊ตฌํ๊ณ , ์ด๋ฌํ ํ๋์จ์ด๋ ์ธ๋ถ๋ก๋ถํฐ์ ์์์ผ๋ก ์ธํ ๊ธฐ๋ฅ์ ์ธ ๊ฒฐํจ๊ณผ ์๋ฉด ๋ฐ ์ค์, ๋ฌ๋ฆฌ๊ธฐ, ์์ ํ๋ ์ค ์ด์ฉ ๋ถ๊ฐ๋ฅ์ฑ, ์ธํ์ ์ธ ์ด์ ๋ฑ์ ํฌํจํ๋ ๊ณตํต์ ์ธ ๋ฌธ์ ๋ค์ ์ผ๊ธฐํ๋ค. ์ ๋ ฅ ๋ฐ ๋ฐ์ดํฐ ์ ์ก์ ์ํ ์ธ๋ถ ์ฝ์ผ์ ์๊ฐ ๋ณด์ฒ ์์คํ
์์ ์ปจํธ๋กค๋ฌ์ ํ๋ก์ธ์์ ์ ์ ์ผ๋ก ์ฐ๊ฒฐ๋๊ณ , ์ด๋ฌํ ์ฐ๊ฒฐ์ ๊ทธ ์ฝ์ผ์ด ์์ ์ธ๊ธ๋ ๋ฌธ์ ๋ค์ ํนํ ์ทจ์ฝํ๊ฒ ๋ง๋ ๋ค. ์ด๋ฌํ ์ด์๋ฅผ ํด๊ฒฐํ๊ณ ์, ํด๋์ฉ ๋ฌด์ ์ปจํธ๋กค๋ฌ๋ก ์ ์ด๋๋ ์์ ์ด์ํ ์ ๊ฒฝ ์๊ทน ์์คํ
์ด ์ ์๋๋ค. ์ด ํด๋์ฉ ๋ฌด์ ์ปจํธ๋กค๋ฌ๋ ์ ์ ๋ ฅ์ด์ง๋ง ๋น๊ต์ ์ฅ๊ฑฐ๋ฆฌ ํต์ ์ด ๊ฐ๋ฅํ ์ง๋น (ZigBee) ๋ฌด์ ํต์ ์ ํตํ์ฌ ์ฌ์ถฉ์ ๊ฐ๋ฅํ ๋ฐฐํฐ๋ฆฌ๋ก ๋์ํ๋ ์์ ์ด์ํ ์๊ทน๊ธฐ๋ฅผ ์ ์ดํ ์ ์๋ค. ์ด ์ธ์๋, ์ด ํด๋์ฉ ์ปจํธ๋กค๋ฌ๋ฅผ ์ฌ์ฉํ๋ฉด ํญ๋์ ์์ฉ์ ์ํ ๋ ๊ฐ์ง ๊ธฐ๋ฅ์ ์ถ๊ฐ๋ก ์ํํ ์ ์๋ค. ํ๋๋ ์ ์ ๊ฒฝํผ ์๊ทน์ด๋ฉฐ, ๋ค๋ฅธ ํ๋๋ ์ฌ์ถฉ์ ๊ฐ๋ฅํ ๋ฐฐํฐ๋ฆฌ์ ์ ๋ ์ถฉ์ ๊ธฐ๋ฅ์ด๋ค. ๋ํ, ์ด ํด๋์ฉ ์ปจํธ๋กค๋ฌ์ ๊ฐ๋จํ ์ค์์น๋ฅผ ์ฌ์ฉํ๋ฉด ์ฌ์ฉ์๋ ๊ฒ์ํจ๋์ ๊ฐ์ด ์๊ทน ํ๋ผ๋ฏธํฐ๋ฅผ ์ฝ๊ฒ ์กฐ์ ํ ์ ์๋ค. ์ด๋ฌํ ํด๋ ๊ฐ๋ฅํ๊ณ ์ฌ์ฉ์ ์นํ์ ์ธ ์ธํฐํ์ด์ค๋ฅผ ํตํด ๋ค์ํ ์ํฉ์์ ๊ทธ ์ปจํธ๋กค๋ฌ๋ฅผ ์ฝ๊ฒ ์ฌ์ฉํ ์ ์๋ค. ๊ทธ ์ปจํธ๋กค๋ฌ์ ๊ธฐ๋ฅ์ ์์ฒด ์ธ ํ๊ฐ๋ฟ๋ง ์๋๋ผ ์กฐ๋ฅ์ ์์ง์ ์ ์ด๋ฅผ ์ํ ์ ์ ๊ฒฝํผ ์๊ทน ๋ฐ ์๊ฒฉ ์ ์ด๋ฅผ ํตํด ์์ฒด ๋ด์์๋ ํ๊ฐ๋์๋ค. ๋ํ, ๊ทธ ์ปจํธ๋กค๋ฌ๋ฅผ ์ฌ์ฉํ ์๊ฒฉ ์ ๊ฒฝ ์๊ทน ์ ์ด์ ์ํ ๊ฐ๋ฅ์ฑ์ ๊ฒ์ฆํ๊ธฐ ์ํ์ฌ ๋ ์์ฒด ๋ด ์คํ์ ๊ฒฐ๊ณผ๊ฐ ์๋ก ๋น๊ต๋์๋ค.
๊ฒฐ๋ก ์ ์ผ๋ก, COP ๊ธฐ๋ฐ์ ๊ฐ๋จํ ์ ์ ๊ณต์ ๊ณผ 5๊ทน์ฑ ์๊ทน, ์ด์ํ ์นด๋ฉ๋ผ, ํด๋์ฉ ๋ค๊ธฐ๋ฅ ๋ฌด์ ์ปจํธ๋กค๋ฌ๋ฅผ ํฌํจํ๋ ์ฐ๊ตฌ ๊ฒฐ๊ณผ์ ๋ํ ์ฌ๋ฌ ๋
ผ์๊ฐ ์ด๋ฃจ์ด์ง๋ค. ๊ทธ๋ฆฌ๊ณ ์ด๋ฌํ ๊ฒฐ๊ณผ์ ๊ณ ์ฐฐ์ ๊ธฐ์ดํ์ฌ, ๋ณธ ํ์๋
ผ๋ฌธ์ ์ฐ๊ตฌ๊ฐ ์์ ์ด์ํ ์๊ฐ ๋ณด์ฒ ์์คํ
์ ๊ตฌํ์ ์ด๋ป๊ฒ ์ ์ฉ๋ ์ ์๋ ์ง๊ฐ ์ด ๋
ผ๋ฌธ์ ๋์์ ์์ธํ ์ค๋ช
๋๋ค.Abstract ------------------------------------------------------------------ i
Contents ---------------------------------------------------------------- vi
List of Figures ---------------------------------------------------------- xi
List of Tables ----------------------------------------------------------- xx
List of Abbreviations ------------------------------------------------ xxii
Chapter 1. Introduction --------------------------------------------- 1
1.1. Visual Prosthetic System --------------------------------------- 2
1.1.1. Current Issues ------------------------------------------------- 2
1.1.1.1. Substrate Materials ---------------------------------------- 3
1.1.1.2. Electrode Configurations --------------------------------- 5
1.1.1.3. External Hardware ----------------------------------------- 6
1.1.1.4. Other Issues ------------------------------------------------- 7
1.2. Suggested Visual Prosthetic System ------------------------ 8
1.3. Four Motivations ---------------------------------------------- 10
1.4. Proposed Approaches ---------------------------------------- 11
1.4.1. Cyclic Olefin Polymer (COP) ------------------------------ 11
1.4.2. Penta-Polar Stimulation ----------------------------------- 13
1.4.3. Implantable Camera --------------------------------------- 16
1.4.4. Handheld Remote Controller ---------------------------- 18
1.5. Objectives of this Dissertation ------------------------------ 20
Chapter 2. Materials and Methods ----------------------------- 23
2.1. COP-Based Fabrication and Encapsulation -------------- 24
2.1.1. Overview ----------------------------------------------------- 24
2.1.2. Simple Fabrication Process ------------------------------- 24
2.1.3. Depth-Type Microprobe ---------------------------------- 26
2.1.3.1. Design ----------------------------------------------------- 26
2.1.3.2. Characterization ----------------------------------------- 27
2.1.3.3. In Vivo Neural Signal Recording ---------------------- 30
2.1.4. COP Encapsulation ---------------------------------------- 31
2.1.4.1. In Vitro Reliability Test ---------------------------------- 33
2.2. Penta-Polar Stimulation ------------------------------------- 34
2.2.1. Overview ---------------------------------------------------- 34
2.2.2. Design and Fabrication ----------------------------------- 35
2.2.2.1. Integrated Circuit (IC) Design ------------------------- 35
2.2.2.2. Surface-Type Electrode Fabrication ------------------ 38
2.2.3. Evaluations -------------------------------------------------- 39
2.2.3.1. Focused Electric Field Measurement ---------------- 42
2.2.3.2. Steered Electric Field Measurement ----------------- 42
2.3. Implantable Camera ----------------------------------------- 43
2.3.1. Overview ---------------------------------------------------- 43
2.3.2. Design and Fabrication ----------------------------------- 43
2.3.2.1. Circuit Design -------------------------------------------- 43
2.3.2.2. Wireless Communication Program ------------------ 46
2.3.2.3. Epoxy Coating and Elastomer Sealing -------------- 47
2.3.3. Evaluations ------------------------------------------------- 50
2.3.3.1. Wireless Image Acquisition --------------------------- 50
2.3.3.2. Signal-to-Noise Ratio (SNR) Measurement -------- 52
2.4. Multi-Functional Handheld Remote Controller --------- 53
2.4.1. Overview ---------------------------------------------------- 53
2.4.2. Design and Fabrication ----------------------------------- 53
2.4.2.1. Hardware Description ---------------------------------- 53
2.4.2.2. Software Description ----------------------------------- 57
2.4.3. Evaluations -------------------------------------------------- 57
2.4.3.1. In Vitro Evaluation -------------------------------------- 57
2.4.3.2. In Vivo Evaluation --------------------------------------- 59
Chapter 3. Results ------------------------------------------------- 61
3.1. COP-Based Fabrication and Encapsulation ------------- 62
3.1.1. Fabricated Depth-Type Microprobe ------------------- 62
3.1.1.1. Electrochemical Impedance -------------------------- 63
3.1.1.2. Mechanical Characteristics --------------------------- 64
3.1.1.3. In Vivo Neural Signal Recording --------------------- 66
3.1.2. COP Encapsulation --------------------------------------- 68
3.1.2.1. In Vitro Reliability Test --------------------------------- 68
3.2. Penta-Polar Stimulation ------------------------------------ 70
3.2.1. Fabricated IC and Surface-Type Electrodes ---------- 70
3.2.2. Evaluations ------------------------------------------------- 73
3.2.2.1. Focused Electric Field Measurement --------------- 73
3.2.2.2. Steered Electric Field Measurement ---------------- 75
3.3. Implantable Camera ---------------------------------------- 76
3.3.1. Fabricated Implantable Camera ----------------------- 76
3.3.2. Evaluations ------------------------------------------------ 77
3.3.2.1. Wireless Image Acquisition -------------------------- 77
3.3.2.2. SNR Measurement ------------------------------------ 78
3.4. Multi-Functional Handheld Remote Controller ------- 80
3.4.1. Fabricated Remote Controller ------------------------- 80
3.4.2. Evaluations ------------------------------------------------ 81
3.4.2.1. In Vitro Evaluation ------------------------------------ 81
3.4.2.2. In Vivo Evaluation ------------------------------------- 83
Chapter 4. Discussions ------------------------------------------ 86
4.1. COP-Based Fabrication and Encapsulation ------------ 87
4.1.1. Fabrication Process and Fabricated Devices -------- 87
4.1.2. Encapsulation and Optical Transparency ------------ 89
4.2. Penta-Polar Stimulation------------------------------------ 99
4.2.1. Designed IC and Electrode Configurations --------- 99
4.2.2. Virtual Channels in Two Dimensions ---------------- 101
4.3. Implantable Camera -------------------------------------- 102
4.3.1. Enhanced Reliability by Epoxy Coating ------------- 106
4.4. Multi-Functional Handheld Remote Controller ------ 107
4.4.1. Brief Discussions of the Two Extra Functions ------ 108
4.5. Totally Implantable Visual Prosthetic System --------- 113
Chapter 5. Conclusion ------------------------------------------ 117
References -------------------------------------------------------- 121
Supplements ------------------------------------------------------ 133
๊ตญ๋ฌธ ์ด๋ก ----------------------------------------------------------- 143Docto
Novel methods and circuits for field shaping in deep brain stimulation
Deep Brain Stimulation (DBS) is a clinical tool used to treat various neurological
disorders, including tremor, Parkinsonโs disease (PD) and dystonia. Todayโs routine
use of this therapy is a result of the pioneering work of Benabid and colleagues, who
assessed the benefits of applying high-frequency stimulation to the ventral intermediate
nucleus and reported substantial long-term improvements in PD patients.
Clinical applications of DBS, however, have preceded research and left a number of
challenges to optimise this therapeutic technique in terms of quality, therapy costs
and understanding of its underlying mechanisms. DBS is based on monopolar or
bipolar stimulation techniques, which are characterised by a limited control over the
effects of stimulation and, in particular, over the shape and direction of the electric
field propagating around the electrode. This thesis proposes two approaches
to achieve dynamic electric field control during deep brain stimulation. The first
method is based on the use of current-steering multipolar electrode drive, adopted
to split the stimulation current between 2 or more contacts, in order to shift the
stimulation field to a desired location. The work included the design, development
and testing of an integrated circuit current-steering tripolar current source, developed
in AMS 0.35ฮผm technology. The second method is based on the use of phased
arrays (PAs) in order to create an electromagnetic beam, which can be steered to
a desired location. Computational models have shown the ability to steer and focus
the electromagnetic fields in brain tissue by varying the phase and frequency of
stimulation. Modelling simulations have shown that the use of multipolar electrode
configurations is essential to achieve dynamic control over the shape and area of
tissue stimulated. Configurations with larger number of cathodes allow for several
stimulation patterns, making this stimulation approach beneficial in a clinical environment.
Tests on the performance of the integrated tripolar current source have shown its capability to generate stimulation currents up to 1.86mA, to linearly steer
the stimulation current to one of the anodes and to generate biphasic square and
exponential current pulses, with time constant up to 28ms. In vitro experiments,
carried out to map the electric potential generated by a dynamic tripolar current
source, validated the model results, by showing the ability to shape the potential distribution
around the electrode during stimulation. Finally, models of the behaviour
of PA fields in brain tissue have shown that PAs could be introduced to DBS to allow
for more accurate field steering and shaping in DBS. This thesis presents methods
and implementations to achieve dynamic field shaping in DBS, which can greatly
ameliorate the efficacy of clinical DBS
Enhancing selectivity of minimally invasive peripheral nerve interfaces using combined stimulation and high frequency block: from design to application
The discovery of the excitable property of nerves was a fundamental step forward in our knowledge of the nervous system and our ability to interact with it. As the injection of charge into tissue can drive its artificial activation, devices have been conceived that can serve healthcare by substituting the input or output of the peripheral nervous system when damage or disease has rendered it inaccessible or its action pathological. Applications are far-ranging and transformational as can be attested by the success of neuroprosthetics such as the cochlear implant. However, the bodyโs immune response to invasive implants have prevented the use of more selective interfaces, leading to therapy side-effects and off-target activation. The inherent tradeoff between the selectivity and invasiveness of neural interfaces, and the consequences thereof, is still a defining problem for the field.
More recently, continued research into how nervous tissue responds to stimulation has led to the discovery of High Frequency Alternating Current (HFAC) block as a stimulation method with inhibitory effects for nerve conduction. While leveraging the structure of the peripheral nervous system, this neuromodulation technique could be a key component in efforts to improve the selectivity-invasiveness tradeoff and provide more effective neuroprosthetic therapy while retaining the safety and reliability of minimally invasive neural interfaces.
This thesis describes work investigating the use of HFAC block to improve the selectivity of peripheral nerve interfaces, towards applications such as bladder control or vagus nerve stimulation where selective peripheral nerve interfaces cannot be used, and yet there is an unmet need for more selectivity from stimulation-based therapy. An overview of the underlying neuroanatomy and electrophysiology of the peripheral nervous system combined with a review of existing electrode interfaces and electrochemistry will serve to inform the problem space. Original contributions are the design of a custom multi-channel stimulator able to combine conventional and high frequency stimulation, establishing a suitable experimental platform for ex-vivo electrophysiology of the rat sciatic nerve model for HFAC block, and exploratory experiments to determine the feasibility of using HFAC block in combination with conventional stimulation to enhance the selectivity of minimally-invasive peripheral nerve interfaces.Open Acces