Material Science Seminar

Daniel R. MerrillDirector of Applications Engineering
Alfred E. Mann Foundation for Scientific ResearchSanta Clarita, CA 91355 Increased Electrode Impedance as a Mechanism of Recording Instability Abstract The mechanisms underlying performance degradation of chronically implanted silicon microelectrode arrays in the central nervous system (CNS) remain unclear. One proposed mechanism is increased electrical impedance due to the foreign body reaction at the electrode-brain tissue interface. In this seminar I will first discuss some of the technical issues of impedance measurement including procedural issues that are often poorly understood and implemented. Next I will present experimental work directed towards understanding the failure mechanisms of chronically implanted devices. Several components of the foreign body response were evaluated to determine whether their presence correlates with increased electrical impedance that may be a factor in loss of device performance. Iridium oxide microelectrode recording arrays were electrically characterized in vitro in the presence of saline, culture media with 10% fetal bovine serum (FBS), and coated with various CNS cell types isolated from young Sprague-Dawley rats. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were performed using a three-electrode system. Microelectrodes coated with various cell types known to participate in the foreign body response caused a significant increase in impedance immediately after seeding on the order of 50%, and this value remained constant or gradually increased for up to several weeks. These findings indicate that the attachment of various molecular and cellular species likely contribute to increases in electrical impedance following implantation in brain tissue, but do not appear sufficient to hinder recording performance. These data further suggest that designers may consider incorporation of adherent cells on implanted microelectrodes to promote integration, improve tissue response or deliver therapeutic agents to adjacent tissue. I will lastly present preliminary results of in vivo impedance measurements using a novel tool for characterizing temporal changes at the electrode-brain tissue interface. September 1st, 20062:30-3:50 PM(Refreshments will be served at 2:15 PM)SLH 102**All first year materials science majors are required to attend**

Location: John Stauffer Science Lecture Hall (SLH) - 102

Audiences: Everyone Is Invited

Contact: Petra Pearce