Date of Award

12-2017

Degree Type

Thesis

Degree Name

Master of Science in Nuclear Engineering

Department

Nuclear Engineering

Committee Chair

Allen L. Garner

Committee Member 1

Gennady Miloshevsky

Committee Member 2

Raji Sundararajan

Abstract

Electric pulses (EPs) have been used for many biological applications from electrochemotherapy to wound healing. While conventional techniques use microsecond to millisecond pulses, more recent techniques use nanosecond EPs (NSEPs) with a much higher amplitude. Generally, the longer duration pulses fully charge the plasma membrane to permeabilize it in a process called electroporation. NSEPs fully charge the smaller intracellular organelles to enable the manipulation of intracellular function; however, they still partially charge the membrane to permeabilize it to facilitate the transport of smaller ions. Experiments have demonstrated this motion using dyes and long-term (on the order of minutes) electrical measurements. This thesis studies the net motion of ions during one or more NSEPs to establish the direction the ions flow, into or out of the cell, to better understand the mechanisms involved with electroporation. This was done by examining the change in electrical conductivity of a Jurkat cell suspension by measuring the voltage and current for three different energy densities determined at two pulse durations (60 ns and 300 ns), three buffer solutions (growth media, Hank’s balanced salt solution (HBSS), and a low conductivity buffer (LCB)), and pulse trains of one, five, and fifteen pulses. A simulation coupling the asymptotic Smoluchowski equation for EP induced membrane pore formation and the Nernst-Planck equation for ion motion due to diffusion and electrophoresis elucidated the contribution of various electrically driven mechanisms for ion motion. The electrical conductivity increased for each pulse duration for cell suspensions in growth media or HBSS, indicating net ion motion from the intracellular to extracellular fluid. Applying 300 ns pulses also increased suspension conductivity for the LCB; however, suspension conductivity decreased during the 60 ns pulse, indicating net ion motion into the cell. The simulations indicated that EP induced electrophoresis would reduce suspension conductivity, as observed for the 60 ns EPs in LCB. Thus, a nonelectrical mechanism, such as EP induced shock waves or cell membrane temperature gradients, which are both mitigated by shorter durations and lower buffer conductivity, or colloidosmotic swelling, must drive the increased suspension conductivity for other conditions. Similar results arose during the final pulse during cell treatment using one, five, and fifteen EPs. These results elucidate ion motion during the NSEP and provide a means for future studies on the efficacy of bipolar pulses to better optimize electroporation pulse parameters for various medical treatments.

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