Browsing by Subject "Electrode"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Creation and In Vivo evaluation of a porous electrode for pacing in a coronary vein: an assessment of the potential for improved electrical performance and chronic stability of coronary venous pacing leads.
    (2009-05) Koop, Brendan Early
    In this work, a porous electrode was fabricated and evaluated in a chronic animal study on a coronary venous pacing lead in order to assess its potential for mitigating chronic lead dislodgements and reducing the characteristic rise in pacing thresholds after implant, both of which being important issues that impact safety and efficacy of implanted cardiac resynchronization therapy systems. Eight test leads were assembled with a porous tip electrode with an average pore size of approximately 30 micrometers, created via a novel fabrication method, and eight control leads were assembled with a standard solid tip electrode design. Both groups were created without steroid-eluting collars and without a capacitive coating on the tip electrodes in order to isolate the affects of electrode porosity. Leads were implanted in canines, and electrical data and x-rays of lead position were taken regularly throughout the 60-day study. Tissue histology was performed for each lead. Significantly lower (p<0.05) mean rise in pacing threshold after implant was observed at day 3 and day 21 for the test group leads (with porous electrodes) as compared to the control group leads. Despite the higher surface area of the porous tip electrodes, pacing impedance was not statistically different between the groups throughout the study, a result likely due to decreased chronic inflammatory response at the surface of porous electrodes. The test group had no lead retractions after day 3 as determined by inspection of x-ray radiographs, while 3-6 (of 8) control group leads retracted after day 3, a result likely due to anchoring of the lead tip due to observed tissue growth into porous electrodes. Mean fibrous capsule thickness at pre-defined measurement points on the tip electrode was not statistically different between the groups, which correlates with the nearly equal mean pacing thresholds for the groups at day 60. The lack of lead retractions for the test groups leads after day 3 is a promising result which should be investigated further, along with investigations of lead extraction force and further electrical data evaluations, using larger sample sizes and more challenging implant conditions.
  • Thumbnail Image
    Item
    The utilization of templated porous electrodes in electrochemical applications
    (2013-09) Fierke, Melissa Ann
    The unifying theme within this work is three-dimensionally ordered macroporous (3DOM) carbon. This material consists of an ordered array of pores surrounded by a skeleton of amorphous carbon with nanometer-scale dimensions. 3DOM carbon offers several advantages that make it ideal for use in electrochemical applications. It has a high surface area, an interconnected pore structure, it is electrically conductive and chemically inert, the surface chemistry can be modified and characterized using slight modifications of well-established techniques, and robust monoliths can be produced. Here, 3DOM carbon was utilized in three distinct electrochemical applications. A three-dimensional interpenetrating lithium ion battery with a 3DOM carbon anode and a mixed vanadia/ruthenia cathode was investigated. Optimization of the synthesis of the polymeric separator layer and the ruthenia component of the cathode were carried out. The synthesis conditions and post-synthesis treatment greatly affect the degree of ruthenia deposition within the porous structure and the extent of hydration of the product. An ion-selective electrode system with 3DOM carbon as the solid contact was developed. 3DOM carbon was covered with an ionophore-based sensing membrane, allowing for selective detection of K+ or Ag+. This system exhibited very low detection limits (4.3 ppt for Ag+), unprecedented electrode stability, and little-to-no response to common interferents (such as carbon dioxide and light). The reasons for this excellent performance were investigated using a variety of characterization methods (with an emphasis on electrochemical techniques). The high surface area and low concentration of surface functional groups on 3DOM carbon are important factors. A receptor-based sensor for explosives detection was also developed. The pore walls of 3DOM carbon were modified with a receptor for 2,4-dinitrotoluene (DNT) using a series of chemical and electrochemical modification steps. Only 3DOM carbon that had been modified with the receptor exhibited a response to the presence of DNT. This selective detection of DNT was also possible in the presence of interfering molecules. However, the high capacitance of the 3DOM carbon led to poor limits when using cyclic voltammetry as the detection method. When square wave voltammetry was used, which eliminates the capacitive currents, much improved detection limits (10 μM) were achieved.