Assessing Novel Bioelectric Effects of Nanosecond Pulsed Electric Fields on Cell Stimulation, Proliferation and Microorganism Inactivation
Bioelectrics is the application of electric fields to cells in a conducting media, treating the cell as a circuit comprising resistors and capacitors (membranes and intracellular fluids respectively). Recent advancements in construction of nanosecond pulse generators allow for construction of low cost devices capable of generating nanosecond pulsed electric fields (nsPEFs). These fields are capable of forming pores on the extra and intra cellular membranes, while also affecting intracellular organelles, DNA and the nucleus. With the first generation of nano-signalling devices set to enter the medical field for treatments ranging from carcinomas to regenerative therapy, the intent of this study was to examine their effect on the growth dynamics of cancer cells under treatment and the potential to stimulate stem cells for use in regenerative healing therapies. A novel application to combat antibiotic resistance in microorganisms was explored. While pulsed electric fields (PEFs) can control cell population in vitro, the ability to specifically predict the types of cells (dividing or resting) targeted and optimize the PEF parameters remain critical challenges for potential cancer treatment applications. Mathematical models of cancer cell population dynamics based on coupled differential equations can predict the transition of cells between the proliferating, quiescent, and dead states to predict the progression of cell population over time. Chapter 2 of this dissertation will experimentally assess the impact of pulse duration, field intensity, and number of pulses on cell population dynamics and fit the mathematical model to assess the transition between proliferating, quiescent, and dead states. These results demonstrate the tenability of nsPEFs for controlling cell number, suggesting the potential impact of sublethal PEFs on cell populations, which may impact cancer therapy. Low intensity electric fields can induce changes in cardiomyocyte (heart muscle) differentiation, increasing the number of beating foci. These fields can also induce cytoskeletal stresses that facilitate manipulation of osteoblasts and mesenchymal stem cells. While effective, low intensity DC or AC electric fields require long (tens of minutes) application times, which are on the order of physiological mechanisms that can complicate the consistency of the treatments. We hypothesized that intense nanosecond pulsed electric fields (nsPEFs) can overcome these side effects by inducing similar stresses on a timescale shorter than physiological processes while additionally inducing plasma membrane nanoporation, ion transport, and intracellular structure manipulation. Chapter 3 of this dissertation examines the impact of pulse duration, field intensity and number of pulses on muscle stem cell population dynamics, demonstrating increased proliferation on a photospectrometer and observed increased differentiation under fluorescent microscopy. The increasing prevelance of antibiotic resistance mechanisms that render current antibiotics ineffective while requiring greater cytotoxicity and concentrations of newer and more powerful drugs to treat infections necessitates the design of new treatments by combining nsPEFs with antibiotics and combinations of antibiotics. This dissertation demonstrates the synergistic inactivation of clinically relevant gram negative Escherichia coli and gram positive Stapphylococcus aureus. Low electric fields which have no effect on gram positive microorganism populations by themselves, produced a 2.5 log reduction of bacterial colony forming units when combined with 1/20th of the clinical dose of certain antibiotics. This synergistic effect was magnified with an increase in drug concentration and an increase in field strength, individually. In combination, this leads to complete sterilization (a 9-log reduction) in colony forming units.
Garner, Purdue University.
Bioengineering|Biomedical engineering|Electrical engineering
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