Publicação
High-aspect-ratio tridimensional electrode arrays for neural applications
| Resumo: | Neural electrodes are a valuable tool that allows neuroscientists to monitor the neural activity of the brain with great spatial and temporal resolution. Micro and nanotechnology has allowed the development of high-density neural electrode arrays. In the present work, two different materials were used to perform neural arrays, namely silicon and aluminum. The main objective was the ability to reach areas of the brain between 2 mm and 4 mm deep due to its importance in small animal models such as the rat. In such animals, important brain structures such as the hippocampus are situated in this range of depth. Another key objective was the fabrication of probes with high-aspect-ratio in order to minimize tissue displacement and consequent adverse reactions caused by implantation. Four different prototypes each using a specific fabrication approach, were performed and described in detail. Two of these prototypes were performed with aluminum while the other two were performed with silicon. Standard microfabrication processes such as dicing, wet-etching, physical vapor deposition, and non-standard processes such as thermomigration, aluminum anodizing, polymer casting, and sanding were used. The combination of these standard and nonstandard processes allowed a simpler and cheaper fabrication approach when compared with commercially available arrays. The first aluminum prototype was composed by 100 micropillars with a gold electrode at each tip. The aluminum micropillars were encapsulated by aluminum oxide and were 3 mm long with an aspect-ratio of 12:1. The second version was composed by 25 micropillars encapsulated with medical grade epoxy each with a platinum electrode at the tip. Each micropillar was 3 mm long with an aspect-ratio of 19:1. The first silicon prototype was composed by 100 silicon micropillars, each 3 mm long with an aspect-ratio of 5:1. The second version was composed by 36 silicon micropillars encapsulated with medical grade epoxy, each with a platinum electrode at the tip. Each micropillar was 4 mm long with an aspect-ratio of 22:1. A slanted version of the second prototype was also fabricated, allowing progressively increasing penetration depths. Mechanical characterization was performed by implantation in agar gel and porcine cadaver brain while electrical characterization was performed by electrochemical impedance tests as well as cyclic voltammetry. Overall, aluminum showed to be a suitable alternative to silicon in terms of structural material. Also, a dicing based approach proved to be a cost-effective method able to perform high-aspect-ratio neural arrays. |
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| Autores principais: | Peixoto, Alexandre Coumiotis Moreira |
| Assunto: | Engenharia e Tecnologia::Outras Engenharias e Tecnologias |
| Ano: | 2015 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade do Minho |
| Idioma: | inglês |
| Origem: | RepositóriUM - Universidade do Minho |
| Resumo: | Neural electrodes are a valuable tool that allows neuroscientists to monitor the neural activity of the brain with great spatial and temporal resolution. Micro and nanotechnology has allowed the development of high-density neural electrode arrays. In the present work, two different materials were used to perform neural arrays, namely silicon and aluminum. The main objective was the ability to reach areas of the brain between 2 mm and 4 mm deep due to its importance in small animal models such as the rat. In such animals, important brain structures such as the hippocampus are situated in this range of depth. Another key objective was the fabrication of probes with high-aspect-ratio in order to minimize tissue displacement and consequent adverse reactions caused by implantation. Four different prototypes each using a specific fabrication approach, were performed and described in detail. Two of these prototypes were performed with aluminum while the other two were performed with silicon. Standard microfabrication processes such as dicing, wet-etching, physical vapor deposition, and non-standard processes such as thermomigration, aluminum anodizing, polymer casting, and sanding were used. The combination of these standard and nonstandard processes allowed a simpler and cheaper fabrication approach when compared with commercially available arrays. The first aluminum prototype was composed by 100 micropillars with a gold electrode at each tip. The aluminum micropillars were encapsulated by aluminum oxide and were 3 mm long with an aspect-ratio of 12:1. The second version was composed by 25 micropillars encapsulated with medical grade epoxy each with a platinum electrode at the tip. Each micropillar was 3 mm long with an aspect-ratio of 19:1. The first silicon prototype was composed by 100 silicon micropillars, each 3 mm long with an aspect-ratio of 5:1. The second version was composed by 36 silicon micropillars encapsulated with medical grade epoxy, each with a platinum electrode at the tip. Each micropillar was 4 mm long with an aspect-ratio of 22:1. A slanted version of the second prototype was also fabricated, allowing progressively increasing penetration depths. Mechanical characterization was performed by implantation in agar gel and porcine cadaver brain while electrical characterization was performed by electrochemical impedance tests as well as cyclic voltammetry. Overall, aluminum showed to be a suitable alternative to silicon in terms of structural material. Also, a dicing based approach proved to be a cost-effective method able to perform high-aspect-ratio neural arrays. |
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