Abstract
Silicon intracortical microelectrodes arrays (MEA) provide some of the best performance for brain computer interfaces but suffer from lifetime limitations that prevent clinical adoption. A primary contributor of lifetime limitations is the chronic foreign body response (FBR) which remains active in response to the brain tissue strain caused by implanted probes during brain micromotion. Designing probes with softer materials can reduce the chronic FBR and improve device lifetime. A high-aspect ratio CNT MEA could provide several advantages as an intracortical MEA but has yet to be mechanically characterized. CNT MEAs are infiltrated with 3 degrees of carbon infiltration and mechanically tested to determine their Young’s modulus. A novel dual deflection (DD) test is designed to measure the cantilever bending of the CNT electrodes and determine their modulus. The CNT diameters of the microelectrodes are measured with SEM as a quantification method of carbon infiltration. A total of 64 CNT microelectrodes (MEs) are tested with the DD test and the modulus is calculated for a subset of 59 CNT MEs. The modulus results are grouped by infiltration level for statistical calculations. The DD test measured a mean modulus of 19.6 ± 14.5 MPa, 67.7 ± 22.7 MPa, and 168 ± 62.3 MPa for arrays fabricated with 0 second, 15 second, and 30 second infiltrations, respectively. A finite element analysis (FEA) model is developed to examine the brain tissue strain under a static, 10 µm, micromotion deflection of penetrating probes with the maximum (1.7 GPa), median (72 MPa), and minimum (3.9 MPa) CNT moduli we measured, as well as the modulus of silicon (165 GPa) for comparison. The max CNT and Si probes induced similar strain in the brain model at the probe tip, while the minimum and median CNT probes showed almost no strain at the tip. The model implies that for the CNT MEA probe geometry, significant reductions in the brain tissue strain can be achieved by CNT MEs with moduli in tens of MPa range, which can be fabricated with 15 seconds of carbon infiltration. Microelectrodes with 15 seconds of infiltration also demonstrated increased resilience compared to the other infiltration time groups, indicating that CNT MEAs with 15 seconds of infiltration might be a viable candidate material for a neural probe array.
Degree
MS
College and Department
Computational, Mathematical, and Physical Sciences; Physics and Astronomy
Rights
https://lib.byu.edu/about/copyright/
BYU ScholarsArchive Citation
Roberts, Spencer McLeod, "Mechanical Characterization of Vertically Aligned Carbon Nanotube Forest Microelectrodes for Neural Interfacing" (2023). Theses and Dissertations. 10639.
https://scholarsarchive.byu.edu/etd/10639
Date Submitted
2023-12-18
Document Type
Thesis
Handle
http://hdl.lib.byu.edu/1877/etd13476
Keywords
carbon nanotube, microelectrode array, intracortical neural probes, Utah electrode array, mechanical testing, cantilevers, Young's modulus, finite element analysis, dual deflection
Language
english
