USC Viterbi School of Engineering USC Keck School of Medicine National Science Foundation

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Biomimetic MicroElectronic Systems
Engineering Research Center
University of Southern California

1450 San Pablo Street
DVRC - 130
Los Angeles, CA 90033

T. 323-442-6786
F. 323-442-6790

BMES Research Testbeds

The range of BMES research efforts are all focused on the same goal of developing three implantable microelectronic devices for three applications - treatment of retinal degenerative diseases, treatment of neurologic disorders like dimentia, and pricise one-to-one communication and control of cellular function and activities.

We employ a systems engineering approach by first devleoping and understanding core areas of science, engineering and medicine.  We then leverage this knowledge to create new Enabling Technologies.  Enabling Technologies are assembled into larger Working Systems that are then validatedin through application in one of the following Testbeds.  Please click on the following to learn more about each Testbed.

Retinal Prosthesis Testbed
Cortical Prosthesis Testbed
Cellular Prosthesis Testbed




Retinal Prosthesis Testbed


Led by James D. Weiland, Ph.D.

The overall goal of this test-bed is to develop a retinal prosthetic system, designed to provide useful vision to millions of blind world-wide.  From psychophysical testing in sighted volunteers by our group and others, 1,000 electrodes in the central 6 mm diameter area of the human retina could allow large print reading and adequate face recognition vision as well as a 20 degree visual field. Consisting of several subsystems, the retinal prosthesis will be initially divided between implanted and external components. External components will include a camera, image processing unit and bi-directional telemetry. Implanted components will include bi-directional telemetry, hermetically packaged electronics, and a multi-channel electrode array. The implanted electronics will perform power recovery, management of data reception and transmission, digital processing, and analog output of stimulus current.

The figure above shows an intraocular retinal prosthesis will use an external system (visual capture/processing unit not shown other than the camera unit) to capture and process image data and transmit the information to an implanted unit. The implanted unit would decode the data and stimulate the retina with a pattern of electrical impulses to produce a perception.
 
We have obtained important results about stimulus parameters and percepts from 6 subjects implanted with out Model 1 retinal implant which has a 4x4 electrode array.  This informaion directs the design of a higher resolution retinal prosthesis, which is being devleopedi n colaboration with the Technology Thrusts and our corporate partner - Second Sight Medical Products, Inc.  Specific achievementate in the first three years include demonstration of an integrated interconnect scheme and a prototype 1000 channel electrode array design.  We have invented a closed loop power control system, and a 1000-channel stimulator chip has been designed and submitted for fabrication.  We have implemented real-time image processing algorithms on multiple platforms and have begun to integrate these systems with data telemetry.  Finally, we have implanted prototype systems in cadaveric pig adn dog eyes.  This includes image acquisition components to demonstrate surgical biocompatibility and mechnaical fit.

Fundamental research projects in retinal prosthesis physiology are an essential element of our system integration plan.  For example, we have developed a novel method for measuring retinal response to electrical stimulation by using a custom build gene gun.  This device propels nanometer siz particles (coated with flourescent indicators) into live retinal cells.  We also have constructed multielectrode arrays with a layout similar to the proposed stimulating array.  This will allow us to study stimulating channel intereactions in isolated retina.  Another isolated retina study involves analysis of the retinal response to natural images and the decomposition of that response into Volterra kernels.  Such an alaysis will lead to a further understanding of the system response of the retina and will allow us to create biomimetic stimulation strategies.  From a biocompatibility standpoint, we have begun to study the response of retinal cells to electrical stimulation both in isolated cultured cells and in intact animal models.  These studies will establish safe limits for electrical stimulation in the retina.  Finally, we have begun to study mechanical properties of the retina and other eye tissues.  Our past experience with chronic implantation suggests that the mechanical damage to the retina is a signficant concern for long-term implants.  However, detailed knowledge of the mechanical properties of eye tissues is lacking, making it difficult to design electrode arrays whose mechanical properties complement the retina.  Thus, a study into the fundamental mechanical properties of eye tiissues is needed to better design the electrode array.  In summary, we have fundamental research proejcts in retinal electrophysiology, retinal neuropathology, and biomaterials that will provide a scientific basis for the retinal prosthesis systems design.

For more information, please visit 
http://artificialretina.energy.gov


 

Cortical Prosthesis Testbed


Schematic for replacing a hippocampal brain regionwith a microelectronic prosthetic device.

The goal of the Cortical Testbed is to restore higher cognitive functions that are lost as a result of damage (stroke, head trauma, epilepsy) or degenerative disease (dementia, Alzheimer’s disease). Specifically, we are focusing on loss of long-term memory formation which is supported by the hippocampus and surrounding limbic cortical brain regions. Unlike the first 2 testbeds, this testbed does not have a prototype device in clinical trials and is thus further from a clinical application. However, our group has made significant progress and this testbed has the added benefit of contributing to the overall effort of neuralprosthesis. Achieving a neural prosthesis in this case requires replacing damaged hippocampus with biomimetic devices that (1) perform the same signal processing functions (biologically realistic, nonlinear input/output transformations) of the damaged neurons, and that (2) bi-directionally communicate with the afferents and efferents of the damaged hippocampal circuits to functionally “by-pass” the lost/dysfunctional brain area(s). During the past three years, we have successfully demonstrated a “proof-of-principle” of this approach using a hippocampal slice preparation. Specifically, we have shown that we can replace one portion of the multi-component circuit of the in vitro hippocampus with a VLSI-based model that accurately predicts the nonlinear dynamics of that component, and as a consequence, restores hippocampal system function. Completing this “proof-of-principle” allowed us to develop the fundamental strategy and tools to achieve a hippocampal prosthesis at a single circuit level. Already during the past year 3 and this year 4, we are building on these accomplishments to develop a multi-circuit, systems level solution for a prosthesis. This device is designed for the behaving rat, i.e., designing and fabricating novel penetrating electrode arrays that conform to the cytoarchitecture of the three-dimensional hippocampus, recording the propagation of electrophysiological activity of hippocampal neurons during learning and memory functions of the behaving animal, developing a multi-input/multi-output model that captures the essential nonlinear dynamics of the hippocampal system, implementing that model in VLSI, and integrating the components of this neural prosthetic system to restore memory function in an animal with hippocampal damage. In the process of development, we have also identified a more near-term application for the cortical testbed. We plan to explore extending the approach described above to the control of hippocampus-generated epileptiform activity, i.e., pharmacologically or electrically suppressing an epileptic focus, and then by-passing that suppressed brain region with a biomimetic model to maintain cognitive function.

To learn more about this project, visit the Neural Prosthesis Website.



Cellular Prosthesis Testbed