Electronic and Ionic Neural Interfaces for Neural Prostheses

Luke Theogarajan, Massachusetts Institute of Technology

Friday, February 15, 2008, 3:30pm

Spanos Auditorium

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This seminar is part of the Jones Seminars on Science, Technology, and Society series

Retinal Prostheses are being developed around the world in hopes of restoring useful vision for patients suffering from certain types of diseases like Age Related Macular Degeneration and retinitis pigmentosa. This talk will examine two approaches to developing such a retinal prosthesis. The first is an electrically based retinal prosthesis and the second is a novel bio-ionic neural interface. The central component of an electrical retinal prosthesis is a wirelessly powered and driven stimulator chip. In this talk we will discuss the design of a 15-channel, low-power, fully implantable stimulator chip. The chip is powered wirelessly and receives wireless commands. The chip features a CMOS only ASK detector, a single-differential converter based on a novel feedback loop, a low-power adaptive bandwidth DLL and 15 programmable current sources that can be controlled via four commands. Electrode interfaces are not the most ideal neural interface and suffer from some drawbacks that prevent the use of large numbers of electrodes. This is especially crucial for a retinal prosthesis since a viable prosthesis requires electrodes above a thousand to be useful. Some of the methods that alleviate some of these issues will be discussed. An alternative to electrical stimulation is chemical stimulation though a common issue with chemical stimulation is the issue of replenishing the stimulating species. The use of ionic gradients, specifically K+ ions as an alternative chemical stimulation method will be examined in this talk. The key advantage being that the required ions can readily be sequestered from the background extracellular fluid. Results from in-vitro stimulation of rabbit retina show that modest increases in K+ ion concentration are sufficient to elicit a neural response. Following this I will present some of the ideas that I have been pursuing to build a neural prosthetic device using ionic stimulation.

About the Speaker

Luke Theogarajan received his bachelor's in Electronics and Telecommunications engineering from the Manipal Institute of Technology, India in 1994. He got his M.S. from Arizona State University in 1996. In 1996 he joined Intel Corporation where he worked on various aspects of the Pentium 4 Microprocessor and Intel's next generation network processor. In the fall of 2001 he left Intel to pursue a Ph.D. at MIT in the area of bioelectronics. He received his Ph.D. in May 2007 from MIT for the work he did on the electronic and ionic neural interfaces. He is currently a post-doctoral associate with Prof. Marc Baldo at MIT working on adapting inkjet printing technology as a platform to study chemically based neural stimulation. His research interests include combining the processing power of electronics with the versatility of synthetic chemistry to develop neural prosthetic devices and developing simple synthetic mimics of biological function to gain a deeper physical understanding of biological phenomena. He has published both in the field of electrical engineering and polymer chemistry and holds 5 patents.