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Investigation of electrochemical properties and performance of stimulation/sensing electrodes for pacemaker applications
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

People suffering from certain types of arrhythmia may benefit from the implantation of a cardiac pacemaker. Pacemakers artificially stimulate the heart by applying short electrical pulses to the cardiac tissue to restore and maintain a steady heart rhythm. By adjusting the pulse delivery rate the heart is stimulated to beat at desired pace. The stimulation pulses are transferred from the pacemaker to the heart via an electrode, which is implanted into the cardiac tissue. Additionally, the electrode must also sense the cardiac response and transfer those signals back to the electronics in the pacemaker for processing. The communication between the electrode and the tissue takes place on the electrode/electrolyte (tissue) interface. This interface serves as the contact point where the electronic current in the electrode is converted to ionic currents capable to operate in the body. The stimulation/sensing signals are transferred across the interface via three electrochemical mechanisms: i) non-faradaic charging/discharging of the electrochemical double layer, ii) reversible and iii) irreversible faradaic reactions. It is necessary to study the contribution of each mechanism to the total charge transferred to evaluate the pacing/sensing performance of the pacemaker electrode.

In this thesis, the electrochemical properties and performance of stimulation/sensing electrodes for pacemaker applications have been investigated by electrochemical impedance spectroscopy, cyclic voltammetry and transient electrochemical techniques. All measurements were performed in synthetic body fluid with buffer capacity. Complementary surface analysis was performed with scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy.

The results reveal different interfacial behaviour and stability for electrode materials such as Pt, TiN, porous carbon, conducting oxides (RuO2 and IrO2 and mixed oxides) and porous Nb2O5 oxide. The influence of the charge/discharge rate on the electrode characteristics also has been evaluated. Although the rough and porous electrodes provide a high interfacial capacitance, the maximum capacitance cannot be fully employed at high charge/discharge rates because only a small part of the effective surface area is accessible. The benefit of pseudo-capacitive material properties on charge delivery was observed. However, these materials suffer similar limitations at high charge/discharge rate and, hence, are only utilising the surface bound pseudo-capacitive sites. Porous Nb2O5 electrodes were investigated to study the performance of capacitor electrodes. These electrodes predominantly deliver the charge via reversible non-faradaic mechanisms and hence do not produce irreversible by-products. They can deliver very high potential pulses while maintaining high impedance and, thus, charge lost by faradaic currents are kept low. By producing Nb oxide by plasma electrolysis oxidation a porous surface structure is obtained which has the potential to provide a biocompatible interface for cell adherence and growth.

This thesis covers a multidisciplinary area. In an attempt to connect diverse fields, such as electrophysiology, materials science and electrochemistry, the first chapters have been attributed to explaining fundamental aspects of the respective fields. This thesis also reviews the current opinion of pacing and sensing theory, with special focus on some areas where detailed explanation is needed for the fundamental nature of electrostimulation/sensing.

Place, publisher, year, edition, pages
Stockholm: KTH , 2005. , vii, 119 p.
Keyword [en]
Physical chemistry, pacemaker electrode, interfacial property, biomaterial, electrostimulation charge transfer mechanism, electrochemical impedance spectroscopy, transient processes, plasma electrolysis anodisation, porous niobium oxide, ruthenium oxide, nano-porous carbon, iridium oxide, titanium nitride, platinum, surface roughness, porous electrode, pacing impedance, electrode polarisation
Keyword [sv]
Fysikalisk kemi
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-176ISBN: 91-7283-994-5 (print)OAI: oai:DiVA.org:kth-176DiVA: diva2:7750
Public defence
2005-04-29, Kollegiesalen, Administrationsbyggnaden, Valhallavägen 79, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20101014Available from: 2005-04-25 Created: 2005-04-25 Last updated: 2012-03-14Bibliographically approved
List of papers
1. Investigation of Interfacial Capacitance of Pt, Ti and TiN Coated Electrodes by Electrochemical Impedance Spectroscopy
Open this publication in new window or tab >>Investigation of Interfacial Capacitance of Pt, Ti and TiN Coated Electrodes by Electrochemical Impedance Spectroscopy
2002 (English)In: Biomolecular Engineering, ISSN 1389-0344, E-ISSN 1878-559X, Vol. 19, no 2-6, 67-71 p.Article in journal (Refereed) Published
Abstract [en]

Electrochemical processes at the electrode-electrolyte (body fluid) interface are of ultimate importance for stimulating/sensing electrode function. A high electrode surface area is desirable for safe stimulation through double-layer charging and discharging. Pt and Pt-Ir alloys have been the most common electrode materials. The use of TiN coating as the surface layer on the electrode has found increasing interest because of its metal-like conductivity, excellent mechanical and chemical properties, and the fact that it can be deposited with a high surface area. In this work, electrochemical impedance spectroscopy (EIS), which is a sensitive and non-destructive technique and widely used for characterization of electrical properties of electrode-electrolyte interfaces, was applied to investigate pure Pt and Ti, and TiN coated electrodes exposed to a phosphate-buffered-saline (PBS) solution. Platinized Pt and Ti were also studied for comparison. The capacitance value of the electrodes in PBS was obtained through quantitative analysis of the EIS spectra. The results reveal that the capacitance of the TiN coated electrodes with a rough surface is several hundreds times higher than that of a smooth Pt surface. Platinization of Ti can also increase the capacitance to the same extent as platina. EIS has been shown to be a powerful technique for characterization of stimulating/sensing electrodes.

Keyword
Effective surface area, Electrochemical impedance spectroscopy, Interfacial capacitance, Platinization, Stimulating/sensing electrodes, TiN coating
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5060 (URN)10.1016/S1389-0344(02)00013-8 (DOI)000178266800007 ()
Note
QC 20100920Available from: 2005-04-25 Created: 2005-04-25 Last updated: 2017-12-05Bibliographically approved
2. Investigation of Pt, Ti, TiN and Nano-porous Carbon Electrodes for Implantable Cardioverter-Defibrillator Applications
Open this publication in new window or tab >>Investigation of Pt, Ti, TiN and Nano-porous Carbon Electrodes for Implantable Cardioverter-Defibrillator Applications
2004 (English)In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 49, no 22-23, 4011-4020 p.Article in journal (Refereed) Published
Abstract [en]

 The electrochemical behavior and stability of Pt, Ti, TiN, and nano-porous carbon for implantable cardioverter-defibrillator (ICD) electrode application were investigated in a phosphate buffered saline solution. The electrochemical interfacial proper-ties were examined by electrochemical impedance spectroscopy, and the potential and current response during ICD shock pulses were recorded by a digital oscilloscope. Changes in surface composition and structure were investigated using X-ray photoelectron spectroscopy and environmental scanning electron microscopy. When exposed to anodic 700 V shock pulses with duration of 10 ms, only Pt was stable, nano-porous carbon electrode was slightly attacked, whereas Ti and TiN electrodes suffered severe degradation. Upon cathodic shock pulsing, all the materials were stable, but Ti and TiN electrodes with a smooth surface showed evidence of hydrogen adsorption. Porous and rough electrodes produced less gas evolution compared to a smooth surfaces, due to a higher amount of charge transferred through non-Faradaic processes. The reason for this could be higher interfacial capacity due to the large surface area.

Keyword
Electrical shock pulse, Electrochemical degradation, Implantable cardioverter-defibrillator, Nano-porous carbon, Rough TiN
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5061 (URN)10.1016/j.electacta.2003.11.040 (DOI)000222818100043 ()2-s2.0-3042751098 (Scopus ID)
Note
QC 20100920 QC 20110916. 54th Annual ISE Meeting. Sao Pedro, BRAZIL. SEP 01-05, 2003Available from: 2005-04-25 Created: 2005-04-25 Last updated: 2017-12-05Bibliographically approved
3. Investigation of Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications I:  Pt, Ti, and TiN coated electrodes
Open this publication in new window or tab >>Investigation of Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications I:  Pt, Ti, and TiN coated electrodes
2005 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, no 2, J7-J15 p.Article in journal (Refereed) Published
Abstract [en]

The electrochemical behavior, interfacial properties, and stability of Pt, Ti, smooth and rough TiN electrodes for pacemaker applications were investigated in a phosphate-buffered saline solution, by electrochemical impedance spectroscopy and cyclic voltammetry (CV), as well as surface analysis using scanning electron microscopy and X-ray photoelectron spectroscopy. The influence of surface roughness on charge-transfer characteristics was examined under fast cyclic potential sweeps. The stability of the electrodes was investigated by simulated aging through large numbers of CV cycles between -3 to 1 V vs. open-circuit potential. The results show that these electrodes exhibit different electrochemical behavior, and surface roughness plays an important role. Although the rough-surfaced TiN provides a high interfacial capacitance, the maximum capacitance cannot be fully utilized at high CV sweep rates, because part of the effective surface area is inaccessible. As the sweep rate increases, the current-potential response becomes linear (ohmic) due to the pore-like rough surface. Upon accelerated aging, changes in surface composition and structure occurred to different extents on the electrode materials. Pt and the rough TiN electrodes were stable, whereas Ti and the smooth TiN electrodes were affected, mainly by oxidation of Ti and nitride, but also by H adsorption on Ti.

Keyword
Adsorbents, Charge transfer, Computer simulation, Cyclic voltammetry, Electrochemistry, Pacemakers, Surface roughness, Titanium nitride, X ray photoelectron spectroscopy
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5062 (URN)10.1149/1.1842092 (DOI)000227142400074 ()2-s2.0-14744269095 (Scopus ID)
Note
QC 20100920 Available from: 2005-04-25 Created: 2005-04-25 Last updated: 2017-12-05Bibliographically approved
4. Investigation of Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications II: Conducting oxide electrodes
Open this publication in new window or tab >>Investigation of Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications II: Conducting oxide electrodes
2005 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, no 7, J85-J92 p.Article in journal (Refereed) Published
Abstract [en]

The electrochemical behavior, interfacial properties, and stability of RuO2-, IrO2-, (Ru1-xMnx)O-2- and (Ir1-xMnx)O-2-coated electrodes for pacemaker applications were investigated in a phosphate buffered saline solution, by electrochemical impedance spectroscopy and cyclic voltammetry (CV). The psuedocapacitive properties of these conducting oxides and influence of coating roughness and porosity were examined, and accelerated aging of the electrode materials was simulated by fast sweep rate CV cycles between -3 to 1 V vs. Ag/AgCl. Changes in surface composition and structure due to the accelerated aging were investigated using X-ray photoelectron spectroscopy and scanning electron microscopy. The conducting oxides exhibit high interfacial capacitance. At high sweep rates, not all of total capacitance could be utilized due to voltage drop associated with resistance down the pores. Above a certain sweep rate, the charging/discharging mechanism changes from capacitive to resistive character. Showing the best performance among the investigated materials, the RuO2 exhibits capacitive characteristics at sweep rates up to 20 V/s and excellent stability under the accelerated aging. The IrO2 coating was not stable during the cycling. The mixed oxides experience limitations at high sweep rates due to the ohmic effects and some degradation due to the accelerated aging.

Keyword
Aging of materials, Coatings, Cyclic voltammetry, Degradation, Electric conductivity, Electric potential, Electrochemistry, Porosity, Scanning electron microscopy, Spectroscopic analysis, X ray photoelectron spectroscopy
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5063 (URN)10.1149/1.1933372 (DOI)000229859100072 ()2-s2.0-23744517091 (Scopus ID)
Note
QC 20100920Available from: 2005-04-25 Created: 2005-04-25 Last updated: 2017-12-05Bibliographically approved
5. Electrochemical behavior of stimulation/sensing materials for pacemaker electrode applications III: Nanoporous and smooth carbon electrodes
Open this publication in new window or tab >>Electrochemical behavior of stimulation/sensing materials for pacemaker electrode applications III: Nanoporous and smooth carbon electrodes
2005 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, no 9, J110-J116 p.Article in journal (Refereed) Published
Abstract [en]

The electrochemical behavior of nanoporous and smooth carbon electrodes was investigated in a phosphate-buffered saline solution. The interfacial properties were characterized by electrochemical impedance spectroscopy. The influence of charging/discharging rate on the capacitive behavior was investigated by cyclic voltammetry between -3 and 1 V at fast sweep rates. The transient processes taking place at the electrode upon stimulation pulse were also studied by using a pulse generator. For the nanoporous electrode at sufficiently high sweep rates, the charge-transfer characteristics change from capacitive to resistive, due to voltage drop down the pores. Only a small part of total available capacitance of the porous electrode can be utilized at high charging/discharging rates. This is probably the reason for the observed relationship between pacing impedance and geometric electrode surface area. When subjected to stimulation pulses, compared to the smooth electrode, the nanoporous electrode delivers more charge due to lower pacing impedance. At high pulse potentials, some faradaic reaction seems to occur, which is more pronounced on the smooth electrode.

Keyword
Charge transfer, Cyclic voltammetry, Electric impedance, Electrochemistry, Nanostructured materials, Surface chemistry
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5064 (URN)10.1149/1.1972981 (DOI)000231066300080 ()2-s2.0-25844470300 (Scopus ID)
Note
QC 20100913. Tidigare Titel "Investigation of Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications III". Available from: 2005-04-25 Created: 2005-04-25 Last updated: 2017-12-05Bibliographically approved
6. Fabrication of Porous Nb2O5 by Plasma Electrolysis Anodization and Electrochemical Characterization of the Oxide
Open this publication in new window or tab >>Fabrication of Porous Nb2O5 by Plasma Electrolysis Anodization and Electrochemical Characterization of the Oxide
2006 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, no 7, B225-B230 p.Article in journal (Refereed) Published
Abstract [en]

Porous Nb2O5 electrodes were fabricated by applying anodic pulses of 700 V and 10 ms duration to pure Nb in phosphate bufferedsaline solution (PBS), aiming at biomaterial applications. The porosity of the oxide could be controlled by the number of pulses. X-ray photoelectron spectroscopy analysis confirmed the oxide to be Nb2O5. The electrochemical behavior and interfacial propertiesof the porous Nb2O5 were characterized in PBS by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). EIS measurements indicate that the oxide film has a two-layer structure with a compact inner layer and a porousouter layer, and the pores were sealed by precipitates during long-time aging in PBS. The two-layer structure of the oxide film wasobserved by examination of the cross section using scanning electron microscopy in backscatter mode. The CV measurementsreveal that the oxide exhibits an electrochemical “rectifying” property. It is stable over a wide potential range but shows hydrogenuptake upon cathodic polarization below −1 V vs Ag/AgCl.

Place, publisher, year, edition, pages
Electrochemical Society, 2006
Keyword
MICRO-ARC OXIDATION; ANODIC BEHAVIOR; TITANIUM-ALLOYS; IMPEDANCE SPECTROSCOPY; TANTALUM ELECTRODES; NIOBIUM ELECTRODES; PASSIVATED NIOBIUM; INITIAL-STAGES; FILMS; IMPLANTS
National Category
Materials Chemistry Natural Sciences
Identifiers
urn:nbn:se:kth:diva-60484 (URN)10.1149/1.2196788 (DOI)000237945300027 ()2-s2.0-33744786291 (Scopus ID)
Note
© The Electrochemical Society, Inc. 2006. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS). The archival version of this work was published in: J. Electrochem. Soc. / Volume 153 / Issue 7. Qc 20120118Available from: 2012-01-18 Created: 2012-01-13 Last updated: 2017-12-08Bibliographically approved
7. Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications
Open this publication in new window or tab >>Electrochemical Behavior of Stimulation/Sensing Materials for Pacemaker Electrode Applications
2005 (English)In: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 152, no 9, 110-119 p.Article in journal (Refereed) Published
Abstract [en]

The electrochemical behavior of nanoporous and smooth carbon electrodes was investigated in a phosphate-buffered saline solution. The interfacial properties were characterized by electrochemical impedance spectroscopy. The influence of charging/discharging rate on the capacitive behavior was investigated by cyclic voltammetry between –3 and 1  V at fast sweep rates. The transient processes taking place at the electrode upon stimulation pulse were also studied by using a pulse generator. For the nanoporous electrode at sufficiently high sweep rates, the charge-transfer characteristics change from capacitive to resistive, due to voltage drop down the pores. Only a small part of total available capacitance of the porous electrode can be utilized at high charging/discharging rates. This is probably the reason for the observed relationship between pacing impedance and geometric electrode surface area. When subjected to stimulation pulses, compared to the smooth electrode, the nanoporous electrode delivers more charge due to lower pacing impedance. At high pulse potentials, some faradaic reaction seems to occur, which is more pronounced on the smooth electrode.

Keyword
carbon, electrochemical electrodes, nanoporous materials, pacemakers, electrochemical impedance spectroscopy, voltammetry (chemical analysis), capacitance, charge exchange, electrical resistivity
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-5066 (URN)10.1149/1.1972981 (DOI)
Note

Uppdaterad från submitted till published: 20101014. QC 20101014

Available from: 2005-04-25 Created: 2005-04-25 Last updated: 2017-06-09Bibliographically approved

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