Browsing by Author "Joshi-Imre, Alexandra"
Now showing 1 - 4 of 4
- Results Per Page
- Sort Options
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 Electrical Properties of Thiol-ene-Based Shape Memory Polymers Intended For Flexible Electronics(MDPI AG, 2019-05-17) Frewin, Christopher L.; Ecker, Melanie; Joshi-Imre, Alexandra; Kamgue, Jonathan; Waddell, Jeanneane; Danda, Vindhya Reddy; Stiller, Alison M.; Voit, Walter E.; Pancrazio, Joseph J.; 0000-0002-0603-6683 (Ecker, M); 0000-0002-4271-1623 (Joshi-Imre, A); 0000-0003-0135-0531 (Voit, WE); 0000-0001-8276-3690 (Pancrazio, JJ); Frewin, Christopher L.; Ecker, Melanie; Joshi-Imre, Alexandra; Kamgue, Jonathan; Waddell, Jeanneane; Danda, Vindhya Reddy; Stiller, Alison M.; Voit, Walter E.; Pancrazio, Joseph J.Thiol-ene/acrylate-based shape memory polymers (SMPs) with tunable mechanical and thermomechanical properties are promising substrate materials for flexible electronics applications. These UV-curable polymer compositions can easily be polymerized onto pre-fabricated electronic components and can be molded into desired geometries to provide a shape-changing behavior or a tunable softness. Alternatively, SMPs may be prepared as a flat substrate, and electronic circuitry may be built directly on top by thin film processing technologies. Whichever way the final structure is produced, the operation of electronic circuits will be influenced by the electrical and mechanical properties of the underlying (and sometimes also encapsulating) SMP substrate. Here, we present electronic properties, such as permittivity and resistivity of a typical SMP composition that has a low glass transition temperature (between 40 and 60 °C dependent on the curing process) in different thermomechanical states of polymer. We fabricated parallel plate capacitors from a previously reported SMP composition (fully softening (FS)-SMP) using two different curing processes, and then we determined the electrical properties of relative permittivity and resistivity below and above the glass transition temperature. Our data shows that the curing process influenced the electrical permittivity, but not the electrical resistivity. Corona-Kelvin metrology evaluated the quality of the surface of FS-SMP spun on the wafer. Overall, FS-SMP demonstrates resistivity appropriate for use as an insulating material. © 2019 by the authors.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 Stability of Softening Neural Interfaces With a-SIC Thin Film Interlayer(2021-12-01T06:00:00.000Z) Duran Martinez, Adriana C; Voit, Walter E.; Cogan, Stuart F.; Hsu, Julia; Di Prima, Matthew; Joshi-Imre, Alexandra; Prasad, ShaliniNeural interfaces are implantable devices that enable communication between a computer and nervous tissue to read, write and block neural activity within targeted nerves. To improve the chronic use of neural interfaces, the materials used to develop them have been evolving with time, leading to softer and thinner layers of the involved materials to minimize the foreign body response from the body caused by the implanted device. Recently, researchers have studied many biocompatible polymers that promise to extend the lifetime of neural interfaces. An emerging materials class of interest, softening polymers (SPs), has performance advantages (while stiff and rigid) similar to Parylene-C and Polyimide during fabrication, handling, and insertion, but after softening (e.g. once implanted into the body), this class of polymers demonstrates enhanced conformability. This dissertation work (1) describes the flexibility and performance as an insulator of thiol-ene based softening polymers, (2) details a fabrication process of SP-based devices integrating amorphous silicon carbide (a-SiC) as an encapsulation layer and (3) elucidates structure-property-processing relationships of a-SiC SP neural interfaces via long-term electrical stability after accelerated aging and cyclic bending for future use in chronic animal studies.