A 3D-Capable, Flexible, Hybrid µECoG Optrode
-
1
Otto-von-Guericke University of Magdeburg, Institute of Micro and Sensor Systems, Germany
-
2
Leibniz Institute for Neurobiology Magdeburg, Department Systems Physiology, Germany
-
3
Leibniz Institute for Neurobiology Magdeburgt, Department Systems Physiology, Germany
-
4
Otto-von-Guericke-University Magdeburg, Institute of Micro and Sensor Systems, Germany
-
5
Otto von Guericke University Magdeburg, Institute of Micro and Sensor Systems, Germany
-
6
Otto-von-Guerricke-University Magdeburg, Institute of Micro and Sensor Systems, Germany
I. MOTIVATION
Extracellular recordings at the mesoscopic scale are of great interdisciplinary interest for basic and clinical neuroscience as well as for brain-machine-interfaces [1-3]. Recent developments in the field of optogenetics have created a demand for advanced engineering tools to not only record neuronal activity, but stimulate it using light [4-5].
II. MATERIALS AND METHODS
Here we present a 3D-capable µECoG optrode array for simultaneous electrophysiological recording and optical stimulation in rodents. The array is based on a polyimide substrate (PI-2611, HD MicroSystems) embedding sputtered metallic traces and electrodes. The metal layer is lithographically patterned in a lift-off process to form a 450 nm thick chromium/gold/platinum thin film and encompasses 32 electrode sites (Fig. A) with their respective connecting traces and contact landing pads (Fig. D). The resulting array has a thickness of only 8.5 µm, which makes it optically near transparent and highly flexible. Electrode sites are 50 µm in diameter and were manufactured with spacings from 250 µm to 1 mm. On the backside of the array, 50 µm thick SMD µLEDs (190 x 190 µm², C470UT190-0314-31, Cree) are mounted, delivering distinct optical stimulation (Fig. F, G, I-K). The LEDs are hermetically sealed by a 2 µm and pinhole free CVD deposited parylene C coating by Specialty Coating Systems (SCS).
To contact the electrode array onto a PCB harboring a fine-pitch connector, flip-chip bonding and vapor phase soldering was used (Figure B-D, K). The LEDs were contacted via aerosol jet direct writing (Optomec AJ 300 system).
III. RESULTS
The resulting electrode array is distinguished by typical impedances of 225.8 ± 5.2 kΩ at 1 kHz, sufficient for neural recordings. We successfully tested it in gerbil (Meriones unguiculatus) and rat (Rattus norvegicus, Fig. L-O). Sample traces from gerbil visual cortex are shown in Figure R. Owing to its low thickness, the array was sufficiently transparent (transmittance: 93% at 470 nm measured with TE Cooled CCD spectroscope, Edmund Optics) to allow optogenetic stimulation from the rear-mounted LEDs (Figure Q), and thus effectively forming a read-write neural interface. As apparent in Figure R, stimulation artifacts accompany LED switching.
Over the course of a two-month chronic implantation in rats, we found no signs of neural degeneration around the polymer or electrode structures (Figure O).
IV. DISCUSSION
We successfully developed a thin-film optrode array for application in rodent cortex. It was able to record ongoing LFP in gerbil and rat cortex and emit 10 mW of blue light for optogenetic stimulation. Currently, the optogenetic response is difficult to isolate from the capacitive stimulation artifact, which we plan to reduce further through charge balanced drivers, co-axial shielding and signal processing.
V. CONCLUSION
A highly flexible µECoG optrode array based on a PI sandwich structure and rear-mounted SMD LEDs was developed. The array is able to record and stimulate at the mesoscopic scale in rodent neocortex, while simultaneous recording and stimulation is still limited by stimulation artifacts.
REFERENCES
[1] M. E. J. Obien, K. Deligkaris, T. Bullmann, D. J. Bakkum, and U. Frey, “Revealing neuronal function through microelectrode array recordings,” Frontiers in Neuroscience, vol. 8, pp. 1-30, Jan. 2015.
[2] J. Ordonez, M. Schuettler, C. Boehler, T. Boretius, and T. Stieglitz, “Thin films and microelectrode arrays for neuroprosthetics,” MRS Bulletin, vol. 37, pp. 590-598, June 2012.
[3] G. Buzsáki, C. A. Anastassiou, and C. Koch, “The origin of extracellular fields and currents – EEG, ECoG, LFP and spikes,” Nature Reviews Neuroscience, vol. 13, pp. 407-420, June 2012.
[4] K. Y. Kwon, H.-M. Lee, M. Ghovanloo, A. Weber, and W. Li, “Design, fabrication, and packaging of an integrated, wirelessly-powerded optrode array for optogenetics application,” Frontiers in Systems Neuroscience, vol. 9, article 69 (pp. 1-12), May 2015.
[5] R. Pashaie, P. Anikeeva, J. H. Lee, R. Prakash, O. Yizhar, M. Prigge, D. Chander, T. J. Richer, and J. Williams, “Optogenetic Brain Interfaces,” IEEE Reviews in Biomedical Engineering, vol. 7, pp. 1-30, April 2014.
FIGURE LEGEND
(A) 3D-capable µECoG-MEA portfolio. (B) 1st generation flip-chip bonding onto customized PCBs with isotropic conductive adhesive (ICA) via pin transfer of H20E-FC, Epotec. (C, D) 2nd generation flip-chip bonding by stencil printing of lead free solder paste SAC305 from Heraeus and a vapor phase soldering process [overall yield 97%]. (E) Impedance spectroscopy measured in 0.9% NaCl for different packaging techniques. (F) Model of optrode backside with surface mounted µLEDs. (G) Aerosol jet (AJ) directly written conductive paths utilizing ultrasonic atomization (US) of silver ink AG25TE from UT Dots for µLEDs contact. Low stress Ag25TE curing is achieved at 200°C for 1 h in nitrogen atmosphere. (H) Characterization of ICA bump printing manufactured by pneumatic AJ deposition of epoxy E8074 from Acura. (I) Optical microscope image of as-fabricated optrode without passivation, whereas EP 601-LV from Polytec is deployed to be the µLED underfiller and µLED top contact is accomplished by US AJ deposition and curing of E8074. (J) Back side contact by US AJ direct writing of E8074 and curing at 200°C for 1 h in vacuum atmosphere. (K) Parylene C passivated optrode: side view. (L-O) In-vivo chronic implantation and long term stability test in rats over a period of two month. (P) Functional demonstration of optrode on agar phantom. (Q) Optogenetic mesoscopic stimulation in a rodent cortex and simultaneous electrophysiological recording using the hybrid µECoG optrode. (R) Ongoing LFP and reaction to optogenetic stimulation in gerbil neocortex.
Acknowledgements
The work has been funded by the Priority Program 1665 of the DFG with the support code “DFG/OH 69/1-1” and by the BMBF in the framework of Forschungscampus STIMULATE with the support code “03FO16102A” as well as by the state of Saxony-Anhalt (sup. code “I 60”).
Keywords:
stimulation,
electrocorticography,
packaging,
MEMS,
optrode
Conference:
MEA Meeting 2016 |
10th International Meeting on Substrate-Integrated Electrode Arrays, Reutlingen, Germany, 28 Jun - 1 Jul, 2016.
Presentation Type:
Poster Presentation
Topic:
MEA Meeting 2016
Citation:
Deckert
M,
Lippert
MT,
Takagaki
K,
Brose
A,
Rathi
S,
Schmidt
B and
Ohl
FW
(2016). A 3D-Capable, Flexible, Hybrid µECoG Optrode.
Front. Neurosci.
Conference Abstract:
MEA Meeting 2016 |
10th International Meeting on Substrate-Integrated Electrode Arrays.
doi: 10.3389/conf.fnins.2016.93.00125
Copyright:
The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers.
They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.
The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.
Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.
For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.
Received:
22 Jun 2016;
Published Online:
24 Jun 2016.
*
Correspondence:
Dr. Martin Deckert, Otto-von-Guericke University of Magdeburg, Institute of Micro and Sensor Systems, Magdeburg, Germany, martin.deckert@ovgu.de