1. Intracortical Microelectrodes
Feyza Dündar
Spring 2012-Chem 442
“shaped a little like a loaf of french country bread, our brain is a crowded chemistry lab, bustling with nonstop neural conversations.” — Diane Ackerman

2. OUTLINE A bit of History Introduction Materials Microwires
Silicon micromachined microelectrodes
Stimuli-responsive polymer nanocomposites
Biocompatibility
State of art and Comparison
Conclusion

3. A Bıt of History 1791 ---- “animal electricity” on frog by Galvani
1930’s ---- invention of microelectrode by Ida Henrietta Hyde
implantation of an array of 80 electrodes .

4. Intracortical Microelectrodes
Introduction
Intracortical Microelectrodes
Brain’s cortex is the main portion regulating the memory, thinking, language, social behavior etc.
Parkinson’s disease, stroke and spinal chord injuries
Intracortical microelectrodes have the ability to record brain activity
Initial modulus of at least 4 GPa is required
Various types of intracortical microelectrodes

5. Introduction
If microelectrodes are used in humans, three points arise.
1. The special human safety and tissue biocompatibility issue
2. The neurosurgical technical concern
3. The stability and quality of recording
electrode sharpness, shape, size, and insertion speed
recording site area, spacing, configuration, and charge injection capabilities

6. MATERIALS Microwires The first chronic recording electrodes
Stainless steel or tungsten
Insulated with teflon or polyimide
A hole in the skull
A. B. Schwartz, Cortical Neural Prosthetics, Annu. Rev. Neurosci, 2004,

7. Silicon Microelectrodes
MATERIALS
Silicon Microelectrodes
Michigan probe
Iridium is deposited
Planar
4 parallel shank -- a microsilicon ribbon cable
15 μm thick and 50 to 100 μm wide
semiflexible ribbon cable -- the probes to “float” in the brain
D. R. Kipke, Rio J. Vetter, J. C. Williams, J. F. Hetke Silicon-Substrate Intracortical Microelectrode Arrays for Long-Term Recording of Neuronal Spike Activity in Cerebral Cortex,
IEEE Trans. Rehab. Eng, 11, 2, 2003,

8. Silicon Microelectrodes
MATERIALS
Silicon Microelectrodes
Utah probe
solid block of silicon
10 × 10 array of needles on a 4 × 4–mm square
lengths range from 1.0 to 1.5 mm
platinum-plated tips
implantation --- with a special high-speed device
large number of recording sites
A. B. Schwartz, Cortical Neural Prosthetics, Annu. Rev. Neurosci, 2004,

9. MATERIALS The important surgical and biological problem is;
stiffness difference between brain tissue and typical electrode material
Sea cucumber is a marine animal with a leathery skin
They have the ability to rapidly and reversibly alter the stiffness of their inner dermis
Modulus can be altered from 5 MPa to 50 MPa

10. Stimuli-responsive polymer nanocomposites
MATERIALS
Stimuli-responsive polymer nanocomposites
mimicking the sea cucumber dermis
poly(vinyl acetate) and cellulose nanowhisker
3 mm long shaft, 125 μm wide with a thickness of 53 μm
Initial modulus: ~5GPa, reducing its modulus to 12 MPa
without assitive device
less foreign body reactions
J. R. Capadona, K. Shanmuganathan,1 D. J. Tyler, S. J. Rowan, C. Weder1, Stimuli-Responsive Polymer Nanocomposites Inspired by the Sea Cucumber Dermis, Science 319, 1370, 2008.

11. BIOCOMPATIBILITY When the microelectrode is inserted; acute response
stimulating nearby microglia and astrocytes
proliferation of a glial scar
loss of neurons
diminishes the ability the record
Possible chemical and biological modifications;
hyaluranic acid, peptides, sugars
hydrogels, polymers, carbon nanotubes
C. Marin, E. Fernández, Biocompatibility of intracortical microelectrodes: current status and future prospects, Frontiers in Neuroengineering, 3, 2010.

12. STATE OF THE ART
M. P. Ward, P. Rajdev, C. Ellison, P. P. Irazoqui, Toward a comparison of microelectrodes for acute and chronic recordings, B R A I N R E S E A R C H , , –

13. PROPERTIES
M. P. Ward, P. Rajdev, C. Ellison, P. P. Irazoqui, Toward a comparison of microelectrodes for acute and chronic recordings, B R A I N R E S E A R C H , , –

14. APPLICATIONS
M. P. Ward, P. Rajdev, C. Ellison, P. P. Irazoqui, Toward a comparison of microelectrodes for acute and chronic recordings, B R A I N R E S E A R C H , , –

15. COMPARISON
M. P. Ward, P. Rajdev, C. Ellison, P. P. Irazoqui, Toward a comparison of microelectrodes for acute and chronic recordings, B R A I N R E S E A R C H , , –

16. CONCLUSIONS
Most of the current designs are based on mechanical considerations that minimize tissue, material selections that minimize the observed foreign body response, and design features that are necessary to record from or stimulate many small populations of neurons.
Each electrode investigated has its key strengths and weaknesses.
Selection of a microelectrode for use with a chronically implantable medical device today will depend heavily on implant location, duration, and the desired recording and/or stimulation characteristics.

17. There is no scientific study more vital to man than the study of his own brain. Our entire view of the universe depends on it. (Francis H.C. Crick)
THANK YOU… :)