Guo, Liang (郭亮)

(C.V.)

Novel 3-D Microelectrode Geometries on PDMS-Based MEAs

Recently, an emerging demand of intimate interfaces in neuroscience research and neural prosthesis development has stimulated the development of conformable MEAs using compliant materials, such as PDMS, to provide the device capability of conforming to the tissue surface in the pursuit of a uniform and tight contact on the target tissue surface.

We have achieved different 3-D microelectrode geometries on PDMS-based conformable MEAs. Our fabrication method provides PDMS-based MEAs with simply recessed [Fig (i)], conically recessed [Fig (ii)], exponentially recessed [Fig (iv)], or protruded-well [Fig (iii)] microelectrodes at 10 μm resolution. 3-D microelectrode geometry parameters (recess depth, recess slope & profile, and protrusion/planar) can be controlled independently during fabrication.

Exponentially and conically recessed microelectrodes are promising in chronic stimulation applications, such as neural prostheses, for their production of a uniform current density profile during stimulation, which can minimize stimulation-induced tissue burning and electrode corrosion. Protruded-well microelectrodes potentially provide a closer and sealed contact to the target tissue surface, avoiding current leakage during stimulation and thus achieving better stimulation efficiency in both charge delivery and spatial specificity. Please see the publications section for more information.

Multilayer Interconnects on PDMS Substrate

While neuroscience research and neural prosthetics frequently require high-density implementations, all of the PDMS-based MEAs designed so far are implemented with only a single conducting layer, which has significantly limited the integration density and capacity of such MEAs due to the difficulty in wiring a large number of high-density microelectrodes.

We have addressed this issue by implementing multilayer wiring interconnects within PDMS substrate. Our multilayer interconnect technology provides the potential for implementing high-density, high-throughput PDMS-based MEAs with feature size as small as 10 μm and an electrode diameter/electrode center-to-center distance ratio up to 1:2. Please see the publications section for more information.

Integrated Packaging for PDMS-Based MEAs

Packaging for PDMS-based MEAs has long been a great challenge. The traditional methods for connecting the device to external circuitry include (a) clamping on contact pads, (b) gluing wires on contact pads using conductive epoxy/polymer. However, these methods are not so satisfying, because (a) the resulting electrical connections are unreliable and unsustainable; (b) the bonding process is labor intensive; and (c) the contact pads require large size, thus expanding the device size significantly. Therefore, this packaging hurdle has significantly suppressed the otherwise promise of such conformable devices.

We have addressed this issue by implementing multilayer interconnects between PDMS and another substrate, such as glass, silicon, or PCB, which provides better properties for connecting to external circuitry. This newly invented bonding technology is named Via Bonding. Together with the method for making multilayer interconnects within PDMS, this multilayer via-bonding technology provides the potential for directly integrating high-density, high-throughput PDMS-based MEAs with silicon-based ICs to achieve an integrated system solution for neural interfacing. Please see the publications section for more information.

Miniaturized Multichannel Recording and Stimulation System

To provide implantable and miniaturized recording and/or stimulation systems for interfacing with the integratable PDMS-based MEAs, three activities are currently ongoing:

1. Design of a 16-channel miniaturized wireless system with simultaneous recording and stimulation capabilities for dog laryngeal implantation in the pursuit of a prosthesis for unilateral vocal cord paralysis,
2. Design of a 64-channel miniaturized wireless recording system for multichannel surface recording on cat's gastrocnemius muscle in vitro and in vivo,
3. Design of an implantable 16-channel recording and stimulation system directly integrated with a PDMS-based MEA for in vivo interfacing with regenerated peripheral nerve on freely moving rats.

Prosthesis for Unilateral Vocal Cord Paralysis

Unilateral vocal cord paralysis (UVCP) is a common voice disorder found in the practice of Otularyngology, and it is the immobility of one vocal fold because of a dysfunction of the recurrent laryngeal or vagus nerve innervating the larynx. It causes a characteristic breathy voice often accompanied by swallowing disabilty, a weak cough, and the sensation of shortness of breath, because the paralyzed cord or cords remain open, leaving the airway passage and the lungs unprotected, and thus food or liquids can slip into the trachea and lungs.

This collabrative project with Dr. Klein intends to develop a prosthetic therapy that employs recording-triggered muscle surface stimulation to synchronize the performance of the immobile vocal cord with that of the functional cord based on muscle surface recording from the functioning side. We use a frog muscle system for in vitro experiments, and a canine animal model for more advanced in vivo studies. A custom-designed PCB-integrated PDMS-based dual-MEA is used as the muscular interface.

Mutichannel Surface Recording and Stimulation on a Single Muscle

While high-density surface EMG studies reported so far are all conducted on the surface of skin with a multielectrode array covering only a part or one side of the muscle, there have been no reports on high-density epimysial recording.

With our integrated high-density PDMS-based MEA technologies, new perspectives on muscular electrophysiology may be drawn from a whole muscle surface EMG sampling. This collaborative project with Dr. Nichols, thus, involves using a high-density PDMS-based MEA to map the spatiotemporal propagation of electric fields over the entire muscle surface during muscle contraction, with the intent to increase our understanding of the underlying muscle fiber network dynamics and to identify the optimal sites for epimysial stimulation and recording.

Interfacing with Regenerated Peripheral Nerves for Prosthetic Limb Control

Low-Cost MEA for Neural Culture Study

I have been involved in the R&D of Axion Biosystems' Muse platform (64-channel low-cost MEA system) during my 2009 summer internship. Read more here.