Abstract
Depending on their use, electrodes must have a certain size and design so as not to compromise their electrical characteristics. It is fundamental to be aware of all dependences on external factors that vary the electrochemical characteristics of the electrodes. When using implantable electrodes, the maximum charge injection capacity (CIC) is the total amount of charge that can be injected into the tissue in a reversible way. It is fundamental to know the relations between the characteristics of the microelectrode itself and its maximum CIC in order to develop microelectrodes that will be used in biomedical applications. CIC is a very complex measure that depends on many factors: material, size (geometric and effectiveness area), and shape of the implantable microelectrode and long-term behavior, composition, and temperature of the electrolyte. In this paper, our previously proposed measurement setup and automated calculation method are used to characterize a graphene microelectrode and to measure the behavior of a set of microelectrodes that have been developed in the Fraunhofer Institute for Biomedical Engineering (IBMT) labs. We provide an electrochemical evaluation of CIC for these microelectrodes by examining the role of the following variables: pulse width of the stimulation signal, electrode geometry and size, roughness factor, solution, and long-term behavior. We hope the results presented in this paper will be useful for future studies and for the manufacture of advanced implantable microelectrodes.
Highlights
The most common method of charge injection in the context of functional electrostimulation (FES) is known as the galvanostatic or current-controlled method [1], which is based on the use of two-phase balanced charge electric pulses that inject the same magnitude of anodic and cathodic charge, resulting in zero charge transfer in a stimulation pulse [2]
Automated calculations were done by using the program that we developed on the ORIGIN platform
This program allows for the performance of a comparative study of different electrodes immersed in an isotonic solution as the electrolyte at constant room temperature based on the pulse width of a 50 Hz symmetric biphasic excitation signal
Summary
The most common method of charge injection in the context of functional electrostimulation (FES) is known as the galvanostatic or current-controlled method [1], which is based on the use of two-phase balanced charge electric pulses that inject the same magnitude of anodic and cathodic charge, resulting in zero charge transfer in a stimulation pulse [2]. The electrodes can be excited with different current waveforms; the only requirement is to avoid exceeding the limit charge values by which the electrode or the tissue can be damaged. The most common RE is Ag/AgCl (Silver/Silver Chloride). When both electrode and electrolyte phases are put in contact with each other, a redistribution of charge appears until the electrochemical equilibrium is achieved
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