A Study of Electrolytic Processes in Micro-Electroporation and Electroporation

A Study of Electrolytic Processes in Micro-Electroporation and Electroporation By Arie Meir A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor in Philosophy in Biophysics in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Boris Rubinsky, Chair Professor Luke Lee Professor Mohammad Mofrad Professor Ralph Greif Spring 2015 Abstract A Study of Electrolytic Processes in Micro-Electroporation and Electroporation by Arie Meir Doctor of Philosophy in Biophysics University of California, Berkeley Professor Boris Rubinsky, Chair Tissue ablation with minimally invasive surgery is important for treatment of many diseases and has an increasing role in treatment of solid neoplasms. A variety of biophysical and biochemical processes are used for this purpose. They include thermal ablation with heating, cooling or freezing, electroporation (pulsed electric fields), injection of chemical agents, photodynamic effects, sonoporation effects and many others. Electrolysis, the passage of a low magnitude direct ionic current through the tissue, between two electrodes, is a biochemical/biophysical process that has been considered for tissue ablation since the 19th century. Electrolysis affects the ionic species in tissue, which change into compounds that can ablate cells. The advantage of electrolysis in comparison to other ablation techniques can be attributed to its simplicity and low cost of instrumentation, which might make it a suitable treatment modality for resource constrained communities where more expensive medical treatment is often not available. Electrolytic effects have been conveniently ignored by earlier work focusing on pulsed electric fields. The induced fields were considered brief enough and the resulting currents small enough to ignore changes in pH occurring due to electrolytic processes arising in the tissue. Recent research findings however, indicate that under some practical conditions, the observed effects which were believed to be driven by reversible electroporation can be traced to electrolysis. This dissertation is primarily focused on electrolytic effects occurring during electric stimulation of living tissues and the development of innovative research tools that enable characterization and research of these effects. The dissertation covers three main parts: first the fundamental phenomena and the necessary conditions are characterized. The second part focuses on research tools design and development. These tools allow to study electrolytic effects during electro-stimulation via imaging (EIT,MRI) and mathematical models. Finally, the last part focuses on application development – two novel applications are proposed which take the electrolytic effects into account. The first application leverages the electrolytic effects in order to make electroporation more efficient, and the second application prevents electrolytic effects by using capacitative coupling of the electrodes to the electroporated medium. 1 Dedicated to my family whom I love dearly. i This work would not have been possible without the help of trusted mentors and friends who were generous in lending a helping hand along the way: First and foremost, my advisor, Professor Boris Rubinsky has been very supportive and understanding when the results of imaging experiments looked like shapeless blobs and the simulation results didn’t converge. Professor Rubinsky has become not only a mentor but also a friend and I am forever indebted to him for the intellectual toolkit he helped me acquire while working under his wing. My qualifying committee chair, the late Professor Harold Lecar who helped me understand the big picture view and make connections between different branches of science into one coherent narrative. My lab mates and friends Greg, Mary, Charlotte, Liel and Christian who were super helpful in helping brainstorm through experiments but also supportive in sharing the joy and challenges of graduate student life. My sister Vlada who helped me proof-read the dissertation and held me accountable to high standards of english grammar. Having said that, the responsibility for any mistake in this manuscript is purely my own. And last, but not least, the machine shop crew in Etcheverry Hall, Mic, Gordon, Dennis and Scott who taught me to build things with my own hands. ii Table of Contents Chapter 1: Overview and Introduction ....................................................................................................... 1 Overview and Thesis Structure ............................................................................................................... 1 Underlying Motivation ............................................................................................................................ 2 Chapter 2 : Background and Related Work ................................................................................................. 3 Tissue Ablation – review of different modalities..................................................................................... 3 Electrolysis .............................................................................................................................................. 4 Introduction and Historical context .................................................................................................... 4 Mechanism ......................................................................................................................................... 5 Electro-Chemical Model .................................................................................................................. 5 Damage Mechanisms ...................................................................................................................... 6 Electric Parameters ............................................................................................................................. 7 Existing Research Methods and Tools ................................................................................................. 7 Mathematical Models ..................................................................................................................... 8 pH Sensitive Dyes ............................................................................................................................ 8 Visual Observation .......................................................................................................................... 9 Electrolysis Applications ..................................................................................................................... 9 Electroporation ..................................................................................................................................... 10 Introduction and Historical Context .................................................................................................. 10 Mechanisms of Electroporation ........................................................................................................ 12 Electrical Parameters of Electroporation .......................................................................................... 14 AC Electroporation ............................................................................................................................ 15 Joule Heating and Other Related Effects .......................................................................................... 17 Nano-Second Pulses.......................................................................................................................... 18 Research Methods and Tools ............................................................................................................ 18 Mathematical Models ................................................................................................................... 18 Molecular Dynamics Simulations .................................................................................................. 20 Dyes - General Purpose and Voltage-Sensitive ............................................................................. 20 Single Cell Electroporation ............................................................................................................ 21 Imaging-Based Approaches ........................................................................................................... 22 Applications of Electroporation ........................................................................................................ 22 Chapter 3: Fundamental Models .............................................................................................................. 24 Mathematical Modeling of Electrolysis ................................................................................................. 24 Boundary Conditions and Implementation Approach ........................................................................... 25 Experimental Procedure and Results .................................................................................................... 28 The Rising Importance of Electrolysis ................................................................................................... 30 iii Practical demonstration of electrolysis ................................................................................................. 31 Chapter 4: Monitoring Electrolysis by Electrical Impedance Tomography ...............................................

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