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Engineering aspects of polypyrrole actuators and their application in active catheters Shoa Hassani Lashidani, Tina

Abstract

Polypyrrole has shown potential as an electrochemically driven artificial muscle. It has also been studied as an electromechanical sensor. Despite its potential as an engineering material, its actuation and sensing behaviours have not been fully characterized and modelled. In this thesis, polypyrrole is characterized in terms of electrochemical stability, mechanical stiffness and sensing capability. A link between actuation and sensing is also presented, suggesting a new mechanism of electromechanical coupling. An analytical model is developed to predict the dynamic actuation response. Finally, polypyrrole is applied to actively deform a catheter. Characterization studies were performed on a PF₆- (hexafluorophosphate) doped polypyrrole inside an aqueous solution of sodium hexafluorophosphate (NaPF₆) - a combination that has shown large repeatable actuation. Polypyrrole is found to be electrochemically stable from -0.4 V to 0.8 V versus an Ag/AgCl reference electrode. Its stiffness is a function of actuation voltage as well as the amplitude and the frequency of the applied load. Its sensitivity as a load sensor is ~ 4 x 10ˉ¹¹ V/Pa and it responds up to at least 100 Hz. A 2D transmission line model representing polypyrrole electrochemical properties (e.g. ionic and electronic conductivities and charge storage) is used to determine charging and hence actuation as a function of time and position. This model is coupled with a mechanical model to predict deflection and is used to design a polypyrrole driven catheter. The capability of polypyrrole to (1) manoeuvre catheters inside arteries and (2) scan catheter tips for imaging were evaluated by fabricating in vitro devices and testing their degree of bending and actuation speed. The feasibility of using the polypyrrole sensor as a feedback loop element on the catheter was also studied and the sensitivity was found to be insufficient for practical use. Polypyrrole driven catheters are able to provide the degree of bending needed for manoeuvring; however actuation speed needs to be improved for the imaging application investigated, which requires operation at frequencies > 10 Hz. According to the model polypyrrole electrodes with thin conductive backings on a flexible catheter can provide the required scanning speed. Further work is required to create encapsulated designs which contain the electrolyte needed for actuation.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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