Date of Award

Fall 2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Aerospace Engineering

Committee Director

Sebastian Bawab

Committee Member

Hargsoon Yoon

Committee Member

Stacie Ringleb

Call Number for Print

Special Collections; LD4331.E56 P65 2013

Abstract

Neural probes are utilized to obtain information regarding the activity of brain cells for neural stimulation. The functional longevity of a probe is dependent upon its ability to minimize injury risk during insertion and the recording period in vivo, which could be related to micromotion-related strain between the probe and surrounding tissue. A series of finite element analyses were conducted using the nonlinear transient dynamic code LSDYNA (LSTC, Livermore, CA) to study the strain induced within the brain in an area around a neural probe. A variety of displacement pulses were input into the brain, first where a high magnitude, low frequency pulse was input which signifies respiration, and second where a low magnitude, high frequency pulse was input into the brain signifying vascular pulsation. Four different materials were considered for this study: (a) silicon, (b) polyimide, (c) hypothetical material with 0.06 GPa stiffness, and (d) hypothetical material with 0.006 GPa stiffness. The study was then expanded to include frequencies from 1 Hz to 40 Hz and utilizing displacement magnitudes of 4 μm and 25 μm while examining the effects the probe material would have on deformations in the brain under micromotion. The four different materials considered for this study were: (a) silicon, (b) polyimide, ( c) arbitrary material with 0.006 GPa stiffness, and ( d) arbitrary material with 0.0002 GPa stiffness. ln this study, only longitudinal motion was considered since previous studies have shown the mode of deformation that would cause greater injury to brain cells, when the nodes on the top surface of the probe were fixed. This study showed that when the probe had the durometer of polyimide, little to no reduction is seen in either stresses or strains during longitudinal motion, relative to that of a probe with the stiffness of silicon. However, up to a 62% reduction in stress and strain with respect to a silicon probe resulted when a 0.006 GPa probe stiffness is utilized, and up to a 99.7% reduction in stress and strain resulted when a 0.0002 GPa probe stiffness is utilized. To achieve strain relief in the tip region of the brain for the full range of conditions tested, the stiffness ratio between the probe and the brain should be no greater than 103 , but achieving a stiffness ratio of 10 can provide strain relief to the brain. Ln addition, the analysis showed the importance of setting model parameters to account for the effect of micromotion.

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DOI

10.25777/kvc3-8n27

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