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Electrical Characterization of 3D Au Microelectrodes for Use in Retinal Prostheses.

Lee S, Ahn JH, Seo JM, Chung H, Cho DI - Sensors (Basel) (2015)

Bottom Line: As the number of microelectrodes is increased, the dimensions of each microelectrode must be decreased, which in turn results in an increased microelectrode interface impedance and decreased injection current dynamic range.In order to examine the effects of the structural difference, 2D and 3D Au microelectrodes with different base areas but similar effective surface areas were fabricated and evaluated.These results indicate that more electrodes can be implemented in the same area if 3D designs are used.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, ISRC/ASRI, Seoul National University, Seoul 151-742, Korea. sangmlee@snu.ac.kr.

ABSTRACT
In order to provide high-quality visual information to patients who have implanted retinal prosthetic devices, the number of microelectrodes should be large. As the number of microelectrodes is increased, the dimensions of each microelectrode must be decreased, which in turn results in an increased microelectrode interface impedance and decreased injection current dynamic range. In order to improve the trade-off envelope between the number of microelectrodes and the current injection characteristics, a 3D microelectrode structure can be used as an alternative. In this paper, the electrical characteristics of 2D and 3D Au microelectrodes were investigated. In order to examine the effects of the structural difference, 2D and 3D Au microelectrodes with different base areas but similar effective surface areas were fabricated and evaluated. Interface impedances were measured and similar dynamic ranges were obtained for both 2D and 3D Au microelectrodes. These results indicate that more electrodes can be implemented in the same area if 3D designs are used. Furthermore, the 3D Au microelectrodes showed substantially enhanced electrical durability characteristics against over-injected stimulation currents, withstanding electrical currents that are much larger than the limit measured for 2D microelectrodes of similar area. This enhanced electrical durability property of 3D Au microelectrodes is a new finding in microelectrode research, and makes 3D microelectrodes very desirable devices.

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Related in: MedlinePlus

Experimental setup. (a) Interface impedance measurement (schematic of impedance measurement (left), fabricated MEA on PCB (right)); (b) Charge injection limit measurement (schematic of current stimulator (left), experimental setup (right)).
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sensors-15-14345-f002: Experimental setup. (a) Interface impedance measurement (schematic of impedance measurement (left), fabricated MEA on PCB (right)); (b) Charge injection limit measurement (schematic of current stimulator (left), experimental setup (right)).

Mentions: Figure 2 shows the experimental setups for measuring the electrode-electrolyte interface impedance and charge injection limit. It is necessary to measure the electrode-electrolyte interface impedance to determine the stimulation current level for the charge injection experiment. SI 1287 and SI 1260 impedance analyzers (Solatron, Schaumburg, IL, USA) were used to measure the impedance. Fabricated Au MEAs are dipped in a phosphate buffered saline (PBS) solution. Then, impedances are measured at 1 kHz, since the conventional current stimulation method is performed using biphasic currents of a 1 ms pulse duration. In order to measure the charge injection limit of each microelectrode, a current stimulator developed in our previous research [16] is used. The external current stimulator is a voltage controlled current source (VCCS), and it is a biphasic current stimulator with 5 V/12 V dual operation voltages. As shown in Figure 2a, when the SNK signal is “on”, the square-wave current waveform moves from REF to CH, and the current is measured as a voltage signal by using the built-in 5 kΩ load. After the intermediate duration of 1 ms, the SRC signal is turned “on” and the current waveform from CH to REF is measured and vice versa. From the built-in 5 kΩ load, the current passing through the microelectrode can be directly measured.


Electrical Characterization of 3D Au Microelectrodes for Use in Retinal Prostheses.

Lee S, Ahn JH, Seo JM, Chung H, Cho DI - Sensors (Basel) (2015)

Experimental setup. (a) Interface impedance measurement (schematic of impedance measurement (left), fabricated MEA on PCB (right)); (b) Charge injection limit measurement (schematic of current stimulator (left), experimental setup (right)).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4507638&req=5

sensors-15-14345-f002: Experimental setup. (a) Interface impedance measurement (schematic of impedance measurement (left), fabricated MEA on PCB (right)); (b) Charge injection limit measurement (schematic of current stimulator (left), experimental setup (right)).
Mentions: Figure 2 shows the experimental setups for measuring the electrode-electrolyte interface impedance and charge injection limit. It is necessary to measure the electrode-electrolyte interface impedance to determine the stimulation current level for the charge injection experiment. SI 1287 and SI 1260 impedance analyzers (Solatron, Schaumburg, IL, USA) were used to measure the impedance. Fabricated Au MEAs are dipped in a phosphate buffered saline (PBS) solution. Then, impedances are measured at 1 kHz, since the conventional current stimulation method is performed using biphasic currents of a 1 ms pulse duration. In order to measure the charge injection limit of each microelectrode, a current stimulator developed in our previous research [16] is used. The external current stimulator is a voltage controlled current source (VCCS), and it is a biphasic current stimulator with 5 V/12 V dual operation voltages. As shown in Figure 2a, when the SNK signal is “on”, the square-wave current waveform moves from REF to CH, and the current is measured as a voltage signal by using the built-in 5 kΩ load. After the intermediate duration of 1 ms, the SRC signal is turned “on” and the current waveform from CH to REF is measured and vice versa. From the built-in 5 kΩ load, the current passing through the microelectrode can be directly measured.

Bottom Line: As the number of microelectrodes is increased, the dimensions of each microelectrode must be decreased, which in turn results in an increased microelectrode interface impedance and decreased injection current dynamic range.In order to examine the effects of the structural difference, 2D and 3D Au microelectrodes with different base areas but similar effective surface areas were fabricated and evaluated.These results indicate that more electrodes can be implemented in the same area if 3D designs are used.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical and Computer Engineering, ISRC/ASRI, Seoul National University, Seoul 151-742, Korea. sangmlee@snu.ac.kr.

ABSTRACT
In order to provide high-quality visual information to patients who have implanted retinal prosthetic devices, the number of microelectrodes should be large. As the number of microelectrodes is increased, the dimensions of each microelectrode must be decreased, which in turn results in an increased microelectrode interface impedance and decreased injection current dynamic range. In order to improve the trade-off envelope between the number of microelectrodes and the current injection characteristics, a 3D microelectrode structure can be used as an alternative. In this paper, the electrical characteristics of 2D and 3D Au microelectrodes were investigated. In order to examine the effects of the structural difference, 2D and 3D Au microelectrodes with different base areas but similar effective surface areas were fabricated and evaluated. Interface impedances were measured and similar dynamic ranges were obtained for both 2D and 3D Au microelectrodes. These results indicate that more electrodes can be implemented in the same area if 3D designs are used. Furthermore, the 3D Au microelectrodes showed substantially enhanced electrical durability characteristics against over-injected stimulation currents, withstanding electrical currents that are much larger than the limit measured for 2D microelectrodes of similar area. This enhanced electrical durability property of 3D Au microelectrodes is a new finding in microelectrode research, and makes 3D microelectrodes very desirable devices.

Show MeSH
Related in: MedlinePlus