3/22: Ke Wang's PhD defense

Ke Wang curlwang at stanford.edu
Tue Mar 14 15:45:12 PST 2006

Dear All,

In case you are interested, I will be giving my PhD dissertation defense
talk next Wednesday.

Ke Wang
Department of Applied Physics
Advisor: Professor James Harris

Title: A Carbon Nanotube Microelectrode Array for Neural Stimulation

Time: 2:00pm, March 22, 2006, Wednesday
      (refreshments will be served from 1:45pm)

Location: CIS-X Auditorium, Room 101

Electrical stimulation of nerve cells is widely employed in neural
prostheses (for hearing, vision, and limb movement restoration),
clinical therapies (treating Parkinson's disease, dystonia and chronic
pain), as well as in basic neuroscience studies. In all these
applications, an implanted microelectrode array transduces electrical
signals to neurons and modulates their behavior. These
stimulating electrodes need to be biocompatible, stable, micro-scaled, and
capable of delivering high current while remaining
electrochemically safe.

This work presents a novel neural interface using multi-walled carbon
nanotubes (CNT) as microelectrodes. We synthesized self-assembled
CNTs by thermal chemical vapor deposition. The CNTs formed pillars of
controllable height projecting orthogonally from the surface.
Using conventional silicon-based micro-fabrication processes, these CNT
ensembles were integrated onto pre-patterned microcircuitry.
The geometry and location of the CNT microelectrodes could be precisely

The electrochemical properties of the CNT microelectrode array were
characterized by cyclic voltammetry, impedance spectroscopy, and
potential transient measurements. Compared to platinum and iridium oxide
neural electrodes, these CNT microelectrodes had a wide
electrochemical operational window, competitive charge injection limit,
and operated capacitively without faradic reactions. These
properties have become increasingly important, as applications in the
central nervous system require a significant reduction in
electrode size. Different surface modification techniques, such as thermal
oxidation, chemical oxidation and non-covalent binding, were
investigated to functionalize the CNT electrodes and the active
interfacial area was considerably increased.

The biocompatibility of CNTs was assessed by in vitro cell culture.
Retinal ganglion cells and hippocampal neurons were cultured on CNT
substrates, and showed comparable viability and neurite outgrowth to
cultures on plastic controls. As a proof of concept, in vitro
stimulation of primary neurons with the CNT microelectrode array was
demonstrated. Neurons could be repeatedly stimulated, indicating
good cell excitability and electrode condition.

In conclusion, a prototype CNT microelectrode array has been developed.
Several critical aspects of CNTs as neural stimulating
electrodes were investigated. The advantageous electrochemical,
mechanical, and chemical properties of CNTs suggest that they are
capable of providing a safer solution for neural stimulation.

Ke Wang
PHD Candidate
Department of Applied Physics, Stanford University

(O): (650)725-5774

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