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Stability of PEDOT materials intended for implants
KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701). (Neuronik)
KTH, School of Technology and Health (STH). (Neuronik)
KTH, School of Technology and Health (STH), Neuronic Engineering (Closed 20130701). (Neuronik)
(Biomolecular and Organic Electronics)
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(English)Manuscript (Other (popular science, discussion, etc.))
Abstract [en]

This study presents a set of experiments designed to study the stability over time of the conducting polymer poly(3,4-ethylene dioxythiophene) (PEDOT), under simulated physiological conditions. Especially, the influence of switching the counter ion used in electropolymerisation, from surfactant polystyrene sulphonate (PSS) to heparin, was investigated. Electropolymerised PEDOT was exposed to different solutions at 37 °C over a 5-6 weeks study period. Two methods were used to study changes over time, spectroscopy and cyclic voltammetry. Phosphate buffer solution (PBS) and diluted hydrogen peroxide (H2O2) (0.01 M) were used to simulate in vivo environment. Some PEDOT electrodes in PBS were also subject to voltage pulsing to further stress the material.


The vast part of the samples of both types lost both electroactivity and optical absorbance within the study period, when exposed to H2O2. An overall slightly higher stability of PEDOT:PSS compared to PEDOT:heparin could be seen. The time dependence of the decline also differed, with a linear decrease of electroactivity for PEDOT:heparin while for PEDOT:PSS a comparably stable appearance initially, followed by a marked decrease after 8-15 days.


Polymers were relatively stable in PBS throughout the study period, with around 80% of electroactivity remaining after five weeks. Disregarding a slight drop in electroactivity during the first day, voltage pulsing in PBS did not increase degradation (tested over 11 days). Delamination of PEDOT exposed to PBS was however a significant problem, especially for polymer on ITO substrates.


PEDOT is sensitive to oxidising agents, also in the dilute concentrations used here, and counter ion influences the time course of degradation. Even without oxidising agents, some decline in electroactivity can be expected and it is unclear whether this decrease will continue over time, or if the polymer will stabilise. Such stabilisation was however not seen within the five weeks studied here. Delamination of polymer is likely to be a problem on implantation, especially with unwisely chosen substrates, and might be an even more serious threat to long term applications than degradation in biological fluids.

National Category
Other Engineering and Technologies not elsewhere specified
URN: urn:nbn:se:kth:diva-9846OAI: diva2:133567

QC 20100623

Available from: 2009-01-12 Created: 2009-01-12 Last updated: 2014-09-24Bibliographically approved
In thesis
1. Conjugated Polymers for Neural Interfaces: Prospects, possibilities and future challenges
Open this publication in new window or tab >>Conjugated Polymers for Neural Interfaces: Prospects, possibilities and future challenges
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Within the field of neuroprosthetics the possibility to use implanted electrodes for communication with the nervous system is explored. Much effort is put into the material aspects of the electrode implant to increase charge injection capacity, suppress foreign body response and build micro sized electrode arrays allowing close contact with neurons. Conducting polymers, in particular poly(3,4-ethylene dioxythiophene) (PEDOT), have been suggested as materials highly interesting for such neural communication electrodes. The possibility to tailor the material both mechanically and biochemically to suit specific applications, is a substantial benefit with polymers when compared to metals. PEDOT also have hybrid charge transfer properties, including both electronic and ionic conduction, which allow for highly efficient charge injection.


Part of this thesis describes a method of tailoring PEDOT through exchanging the counter ion used in electropolymerisation process. Commonly used surfactants can thereby be excluded and instead, different biomolecules can be incorporated into the polymer. The electrochemical characteristics of the polymer film depend on the ion. PEDOT electropolymerised with heparin was here determined to have the most advantageous properties. In vitro methods were applied to confirm non-cytotoxicity of the formed PEDOT:biomolecular composites. In addition, biocompatibility was affirmed for PEDOT:heparin by evaluation of inflammatory response and neuron density when implanted in rodent cortex.


One advantage with PEDOT often stated, is its high stability compared to other conducting polymers. A battery of tests simulating the biological environment was therefore applied to investigate this stability, and especially the influence of the incorporated heparin. These tests showed that there was a decline in the electroactivity of PEDOT over time. This also applied in phosphate buffered saline at body temperature and in the absence of other stressors. The time course of degradation also differed depending on whether the counter ion was the surfactant polystyrene sulphonate or heparin, with a slightly better stability for the former.


One possibility with PEDOT, often overlooked for biological applications, is the use of its semi conducting properties in order to include logic functions in the implant. This thesis presents the concept of using PEDOT electrochemical transistors to construct textile electrode arrays with in-built multiplexing. Using the electrolyte mediated interaction between adjacent PEDOT coated fibres to switch the polymer coat between conducting and non conducting states, then transistor function can be included in the conducting textile. Analogue circuit simulations based on experimentally found transistor characteristics proved the feasibility of these textile arrays. Developments of better polymer coatings, electrolytes and encapsulation techniques for this technology, were also identified to be essential steps in order to make these devices truly useful.


In summary, this work shows the potential of PEDOT to improve neural interfaces in several ways. Some weaknesses of the polymer and the polymer electronics are presented and this, together with the epidemiological data, should point in the direction for future studies within this field.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. vi, 77 p.
Trita-STH : report, ISSN 1653-3836 ; 2009:1
neuroprosthetics, conjugated polymers, conducting polymers, PEDOT, functional electrical stimulation, neural electrodes
National Category
Medical Laboratory and Measurements Technologies Neurosciences Other Materials Engineering
urn:nbn:se:kth:diva-9817 (URN)978-91-7415-213-5 (ISBN)
Public defence
2009-01-30, Sal 3-221, Alfred Nobels Allé 10, Huddinge, 13:00 (English)
QC 20100623Available from: 2009-01-13 Created: 2009-01-09 Last updated: 2010-06-23Bibliographically approved

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Thaning, ElinAsplund, MariaNyberg, Tobiasvon Holst, Hans
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