Date of Award

Fall 2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical & Computer Engineering

Program/Concentration

Biomedical Engineering

Committee Director

Andrei G. Pakhomov

Committee Director

Shu Xiao

Committee Member

Olga Pakhomova

Committee Member

Esin Sozer

Committee Member

Venkat Maruthamuthu

Abstract

Ablation therapies aim to destroy tumors while maintaining minimal damage to surrounding healthy tissue. Pulsed electric field (PEF) ablation targets the cell membrane during the destruction of tissues, which consequently spares extracellular structures such as ducts and blood vessels, leaving the framework for tissue regeneration. However, the utility of PEF is limited by neuromuscular excitation, causing pain and involuntary muscle contraction. To identify PEF protocols that efficiently ablate tissue while minimizing neuromuscular stimulation, various PEF protocols differing in pulse duration, shape, and repetition rate were tested. The ratio of cell death and nerve excitation thresholds, which determines the range of stimulation, was reduced to 4-fold with bipolar nanosecond PEF compared to the 500-fold ratio observed with conventional 100-μs unipolar pulses.

Testing an in vitro model for PEF ablation of pre-malignant Barrett’s Esophagus showed normal epithelial cells were less sensitive to unipolar PEF than pre-malignant epithelial cells (15–20% higher LD50, p < 0.05). Spindle-shaped esophageal smooth muscle cells (SMC) oriented randomly in the electric field were more sensitive, with 30–40% lower LD50 (p < 0.01). SMC sensitivity showed remarkable dependence on cell orientation in the electric field. Aligning SMC with the electric field reduced electroporation uptake of YO-PRO-1 with 300-ns pulses 4-fold compared to cells oriented perpendicular to the field.

Further investigation into the effect of cell orientation on cell sensitivity to PEF was conducted using strobe photography, a novel method enabling direct recording of changes in transmembrane potential (TMP) on a nanosecond-scale. When subjected to 300-ns pulses, cells positioned perpendicular to the electric field exhibited a 2-fold greater change in TMP compared to cells aligned with the field. However, when exposed to longer 3-μs pulses, changes in TMP recorded with cells aligned to the electric field surpassed that of cells orthogonal to the field. Membrane charging data revealed the mechanistic basis for the observed differences in fusiform cell sensitivity based on cell orientation. Positioning cells perpendicular to the electric field resulted in a faster initial rate of membrane charging, resulting in greater TMP changes with nanosecond-duration pulses than when cells were aligned with the field. Along with gaining new fundamental understanding of cell charging kinetics of fusiform cells, this mechanism of membrane charging presents a versatile tool of attenuating the response of elongated cells to PEF simply by adjusting the electric field direction.

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DOI

10.25777/g39j-3w54

ISBN

9798381449174

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Available for download on Wednesday, February 05, 2025

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