Browsing by Author "Deku, Felix"
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Item Amorphous Silicon Carbide Ultramicroelectrode Arrays for Neural Stimulation and Recording(2018-10-22) Deku, Felix; Cohen, Yarden; Joshi-Imre, Alexandra; Kanneganti, Aswini; Gardner, Timothy J.; Cogan, Stuart F.; 0000-0002-4915-1200 (Deku, F)); 0000-0002-8149-6954 (Cohen, Y); Deku, Felix; Cohen, Yarden; Joshi-Imre, Alexandra; Kanneganti, Aswini; Cogan, Stuart F.OBJECTIVE: Foreign body response to indwelling cortical microelectrodes limits the reliability of neural stimulation and recording, particularly for extended chronic applications in behaving animals. The extent to which this response compromises the chronic stability of neural devices depends on many factors including the materials used in the electrode construction, the size, and geometry of the indwelling structure. Here, we report on the development of microelectrode arrays (MEAs) based on amorphous silicon carbide (a-SiC).; APPROACH: This technology utilizes a-SiC for its chronic stability and employs semiconductor manufacturing processes to create MEAs with small shank dimensions. The a-SiC films were deposited by plasma enhanced chemical vapor deposition and patterned by thin-film photolithographic techniques. To improve stimulation and recording capabilities with small contact areas, we investigated low impedance coatings on the electrode sites. The assembled devices were characterized in phosphate buffered saline for their electrochemical properties.; MAIN RESULTS: MEAs utilizing a-SiC as both the primary structural element and encapsulation were fabricated successfully. These a-SiC MEAs had 16 penetrating shanks. Each shank has a cross-sectional area less than 60 m² and electrode sites with a geometric surface area varying from 20 to 200 m². Electrode coatings of TiN and SIROF reduced 1 kHz electrode impedance to less than 100 kΩ from ~2.8 MΩ for 100 m² Au electrode sites and increased the charge injection capacities to values greater than 3 mC cm⁻². Finally, we demonstrated functionality by recording neural activity from basal ganglia nucleus of Zebra Finches and motor cortex of rat.; SIGNIFICANCE: The a-SiC MEAs provide a significant advancement in the development of microelectrodes that over the years has relied on silicon platforms for device manufacture. These flexible a-SiC MEAs have the potential for decreased tissue damage and reduced foreign body response. The technique is promising and has potential for clinical translation and large scale manufacturing.Item Development of Amorphous Silicon Carbide Ultramicroelectrode Arrays for Neural Stimulation and Recording(2018-12) Deku, Felix; 0000-0002-4915-1200 (Deku, F); Cogan, StuartInterest in restoring lost function using neuro-prosthetic devices and treating neurological disorders or neurodegenerative diseases through electrical stimulation of neural activity has increased in recent years. For example, implantable cortical neural interfaces allow investigation of sensorimotor learning, and control of both natural and prosthetic limbs through recording of volitional intent and stimulation of neural activity. However, these interfaces decline rapidly in performance over chronic timescales. Foreign body response is believed to limit their recording and stimulation reliability. The resulting glial scar isolates the indwelling microelectrodes from healthy neuronal cells. The consequence is recording from large populations of weak neural signals and the requirement for high current amplitudes to deliver the necessary charge for neural activation. Recently, carbon fiber microelectrodes with small cross-sectional dimensions (below 10 µm) have been shown to reduce insertion damage to neurons and microvasculature, minimize adverse tissue reaction, and provide stable neural recording over chronic timescales. Despite these achievements, the development of carbon fiber MEAs faces the issue of micro-assembly, micromanipulation, and the general lack of control of the geometric surface area (GSA) of the active sites. This dissertation addresses these issues by developing ultrathin cellular or sub-cellular scale microelectrode arrays (MEAs) based on amorphous silicon carbide. Amorphous silicon carbide (a-SiC) deposited by plasma enhanced chemical vapor deposition has similar mechanical properties to carbon fiber but is amenable to thin-film microfabrication methods, thus permitting a wide variety of designs, control of GSA, and batch fabrication of microelectrode arrays. Challenges associated with residual stress control in the a-SiC and those associated with metal patterning needs to be addressed to use the a-SiC in ultrathin MEA designs. Also, implantation strategies for ultrathin MEA shanks and the burden of using small contact sites for electrochemical measurement, electrical stimulation and electrophysiology need to be addressed. In this dissertation, microelectrode arrays based on a-SiC were fabricated, characterized for their electrochemical properties in a saline model of the interstitial fluid, and evaluated functionally in songbird and rat brain. We describe stress engineering in the multilayered structure to regulate the curvature of the a-SiC MEAs. Engineering challenges associated with process controls to produce penetrating probes of reduced cross-sectional shank dimensions are discussed. We have developed implantation strategies to insert ultrathin a-SiC MEAs into rat motor cortex. We show that a minimum a-SiC thickness of 6 µm is required to insert 2 mm long a-SiC MEAs shanks into rat cortex without the need for insertion guides or temporary support structures. Below this thickness, we demonstrate that a-SiC MEAs will require temporary support structures such as polyethylene glycol or in situ designs that increases the critical buckling load of the implanted shanks. With the reduced shank dimensions, the electrode sites on the a-SiC MEA are small with high electrode impedance and low charge injection properties. We investigated low impedance coatings such as titanium nitride, sputtered iridium oxide and electrodeposited iridium oxide films as a means of improving the electrochemical performance for neural stimulation and recording. We show that cathodal charge injection capacities greater than 17 mC/cm2 can be achieved with the coated ultramicroelectrode site with appropriate biasing.Item Electrodeposited Iridium Oxide on Carbon Fiber Ultramicroelectrodes for Neural Recording and Stimulation(Electrochemical Society Inc.) Deku, Felix; Joshi-Imre, Alexandra; Mertiri, A.; Gardner, T. J.; Cogan, Stuart F.; 0000-0002-4915-1200 (Deku, F); 43420545 (Cogan, SF); Deku, Felix; Joshi-Imre, Alexandra; Cogan, Stuart F.Host encapsulation decreases the ability of chronically implanted microelectrodes to record or stimulate neural activity. The degree of foreign body response is thought to depend strongly on the cross-sectional dimensions of the electrode shaft penetrating neural tissue. Microelectrodes with cellular or sub-cellular scale shaft cross-sectional dimensions, such as carbon fiber ultramicroelectrodes have been previously demonstrated to elicit minimal tissue response, but their small geometric surface area results in high electrode impedances for neural recording, and reduced charge injection capacity during current pulsing for neural stimulation. We investigated electrodeposited iridium oxide films (EIROF) on carbon fiber ultramicroelectrodes as a means of enhancing the charge injection capacity and reducing electrode impedance. EIROF coatings reduced the electrode impedance measured at 1 kHz by a factor of 10 and improved charge storage and charge injection capacities. The maximum charge injection capacity was also strongly dependent on the interpulse bias and pulse width, and reflected a potential-dependent EIROF impedance. The charge injection capacity of the EIROF-coated carbon fiber ultramicroelectrodes measured in an inorganic buffered saline model of interstitial fluid exceeded 17 mC/cm2 with appropriate biasing, allowing charge-injection at levels well above reported charge/phase thresholds for intraneural microstimulation.Item Thinking Small: Progress on Microscale Neurostimulation Technology(Wiley, 2018-10-22) Pancrazio, Joseph J.; Deku, Felix; Ghazavi, Atefeh; Stiller, Allison M.; Rihani, Rashed; Frewin, Christopher L.; Varner, Victor D.; Gardner, Timothy J.; Cogan, Stuart F.; 0000 0000 2895 2047 (Cogan, SF); 43420545 (Cogan, SF); Pancrazio, Joseph J.; Deku, Felix; Ghazavi, Atefeh; Stiller, Allison M.; Rihani, Rashed; Frewin, Christopher L.; Varner, Victor D.; Gardner, Timothy J.; Cogan, Stuart F.Objectives: Neural stimulation is well-accepted as an effective therapy for a wide range of neurological disorders. While the scale of clinical devices is relatively large, translational, and pilot clinical applications are underway for microelectrode-based systems. Microelectrodes have the advantage of stimulating a relatively small tissue volume which may improve selectivity of therapeutic stimuli. Current microelectrode technology is associated with chronic tissue response which limits utility of these devices for neural recording and stimulation. One approach for addressing the tissue response problem may be to reduce physical dimensions of the device. "Thinking small" is a trend for the electronics industry, and for implantable neural interfaces, the result may be a device that can evade the foreign body response. Materials and Methods: This review paper surveys our current understanding pertaining to the relationship between implant size and tissue response and the state-of-the-art in ultrasmall microelectrodes. A comprehensive literature search was performed using PubMed, Web of Science (Clarivate Analytics), and Google Scholar. Results: The literature review shows recent efforts to create microelectrodes that are extremely thin appear to reduce or even eliminate the chronic tissue response. With high charge capacity coatings, ultramicroelectrodes fabricated from emerging polymers, and amorphous silicon carbide appear promising for neurostimulation applications. Conclusion: We envision the emergence of robust and manufacturable ultramicroelectrodes that leverage advanced materials where the small cross-sectional geometry enables compliance within tissue. Nevertheless, future testing under in vivo conditions is particularly important for assessing the stability of thin film devices under chronic stimulation.