With growing interest in alternative fuels, algae lipid harvesting is seen as a possible source of biofuel. Algae species under consideration include Chlorella vulgaris, Chlamydomonas reinhardtii and Dunaliella salina due to lipid contents as high as 30% to 56% of their dry weight (depending on growth conditions) and availability [5], [6]. In order to harvest lipids from algae, the cells must first be lysed. Lysing is achieved by breaking the algal cell wall or membrane to separate oil from the rest of the algae biomass. Current lysing procedures use enzymes, pressure homogenization, and/or sonication to lyse cells; however, these methods are costly and complicate oil extraction [9], [10]. This project examines a novel method of cell lysis through pulsed electric field (PEF) application that enables cost-effective extraction methods relative to current enzyme and sonication techniques. A theoretical model for cell membrane potential in the presence of electric field was developed, and PEF chambers were manufactured on microscope slides to enable microscope viewing and cell lysis recording during PEF application. Additionally, larger static chambers were created for testing higher volumes of algal solution. Electric field characteristics, such as pulse width, pulse number and magnitude, sufficient for lysis of Dunaliella salina and Chlorella vulgaris were found.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2004. / Includes bibliographical references (leaves 79-83). Also available in electronic version. Access restricted to campus users.

No description available.

No description available.

In this thesis, underlying concepts of transport phenomena through generated nanopores on a cell membrane during electroporation were studied. A comprehensive literature review was performed to find the pros and cons of the previous works and consequently extensive studies were accomplished to explain shortcomings of the former studies on this topic. The membrane permeabilization of the single cell located in the microchannel was studied, and the effects of microchannel’s wall and electrode size were investigated on cell electroporation. It was studied how the electrical (e.g., strength of the electric pulse) and geometrical parameters (e.g., microchannel height and electrode size) affect size, location, and number of created hydrophilic pores on the cell membrane. Because of a transmembrane potential, the electrokinetic effects have decisive influence on the transport process through the created nanopores. A comprehensive study was performed to explain the electrokinetic transport through the nanochannels. Effects of surface electric charge and radius of the nanochannel on the electric potential, liquid flow, and ionic transport were investigated. Unlike microchannels, the electric potential field, ionic concentration field, and velocity field are strongly size-dependent in the nanochannels. They are also affected by the surface electric charge of the nanochannel. More counter ions than co-ions are transported through the nanochannel. The ionic concentration enrichment at the entrance and the exit of the nanochannel is completely evident from the simulation results. The study also shows that the fluid velocity in the nanochannel is higher when the surface electric charge is stronger, or the radius of the nanochannel is larger. The obtained model of the electrokinetic effects in the nanochannels was utilized to examine the ionic mass transfer and the fluid flow through the generated hydrophilic nanopores of the cell membrane during electroporation. The results showed how the electric potential, velocity field, and ionic concentration vary with the size and angular position of the generated nanopores of the cell membrane. It was also shown that, in the presence of the electric pulse, the electrokinetic effects (the electroosmosis and the electrophoresis) had significant influences on the ionic mass transfer through the nanopores, while the effect of diffusion on the ionic mass flux was negligible in comparison with the electrokinetics. Increasing the radius of the nanopores intensified the effect of convection (electroosmosis) in comparison with the electrophoresis on the ionic flux. Furthermore, the electrokinetic motion of the nanoparticle through the nanochannel was investigated to mimic inserting the nanoscale biological samples, such as QDots and DNAs, through the created nanopores on the cell membrane. It was proved that, because of the large applied electric field over the nanochannel, the impact of the Brownian force was negligible in comparison with the electrophoretic and the hydrodynamic forces. It was demonstrated that increasing the bulk ionic concentration or the surface charge of the nanochannel will increase the electroosmotic flow, and hence affect the particle’s motion. It was also shown that, unlike the microchannels with thin EDL, the change in the nanochannel size will change the EDL field and the ionic concentration field in the nanochannel, affecting the particle’s motion. If the nanochannel size is fixed, a larger particle will move faster than a smaller particle under the same conditions. Finally, it was examined how the nanoscale biological samples (nanoparticles) reach openings of the generated nanopores on the cell membrane during electroporation. It was examined what forces (electrophoresis, diffusion, and convection) brings the nanoparticles into the nanopores and how the size and the surface electric charge of the nanoparticle affect its transport to the opening of the nanopores.

The research presented in this dissertation is the result of our laboratory's effort to develop a microfluidic platform to interrogate, manipulate, isolate, and enrich rare mammalian cells dispersed within heterogeneous populations. Relevant examples of these target cells are stem cells within a differentiated population, circulating tumor cells (CTCs) in the blood stream, and tumor initiating cells (TICs) in a population of benign cancer cells. The ability to isolate any of these rare cells types with high efficiency will directly lead to advances in tissue engineering, cancer detection, and individualized medicine. This work lead directly to the development of a new cell manipulation technique, termed contactless dielectrophoresis (cDEP). In this technique, cells are isolated from direct contact with metal electrodes by employing fluid electrode channels filled with a highly conductive media. Thin insulating barriers, approximately 20 μ­m, serve to isolate the fluid electrode channels from the low conductivity sample buffer. The insulating barriers in a fluid-electrical system create a number of unique and interesting challenges from an electrical engineering standpoint. Primarily, they block the flow of DC currents and create a non-constant frequency response which can confound experimental results attempting to characterize the electrical characteristics of cells. Due to these, and other, considerations, the use of high-voltage high-frequency signals are necessary to successfully manipulate cells. The effect of these high frequency fields on cells are studied and applied to microfluidic and tissue level applications. In later chapters, theoretical and experimental results show how high frequency and pulsed electric fields can ablate cells and tissue. Understanding the parameters necessary to electroporate cells aids in the development of cDEP devices where this phenomenon is undesirable and gives insight towards the development of new cancer ablation therapies where targeted cell death is sought after. This work shows that there exists a finite frequency spectrum over which cDEP devices can operate in which cells are minimally affected by the induced electric fields. Finally, lessons learned in the course of the development of cDEP were adapted and applied towards cancer ablation therapies where electroporation are favorable. It was found that bursts of high frequency pulsed electric fields can successfully kill cells and ablate tissue volumes through a process termed High Frequency Irreversible Electroporation (H-FIRE). This technique is advantageous as these waveforms mitigate or eliminate muscle contractions associated with traditional IRE technologies. Similarly, the use of fluid electrodes in cDEP inspired the use of an organs vascular system as the conductive pathway to deliver pulses. This novel approach allows for the ablation of large volumes of tissue without the use of puncturing electrodes. These techniques are currently undergoing evaluation in tissue engineering applications and pre-clinical evaluation in veterinary patients. / Ph. D.

Thesis (M.Sc.)--Memorial University of Newfoundland, 1999. / Restricted until November 2000. Bibliography: leaves 114-123.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2003. / Bibliography: leaves 107-127.

Irreversible electroporation (IRE) is an energy directed focal ablation technique. This procedure typically involves the placement of two or more electrodes into, or around, a region of interest within the tissue and administering a sequence of short, intense, pulsed electric fields (PEFs). The application of these PEFs results in an increase in the transmembrane potential of all cells within the electric field above a critical value, destabilizing the lipid bilayer of the cellular membrane and increasing the cell-tissue permeability. For years, many have used this phenomenon to assist the transport of macromolecules typically unable to penetrate the cell membrane with the intent of avoiding cell necrosis or irreversible electroporation. More recently, however, irreversible electroporation has proven to be a successful alternative for the treatment of cancer. Proper tuning of the pulse parameters has allowed for a targeted treatment of localized tumors, and has shown immense value in the treatment of surgically inoperable tumors located near major blood vessels and nerves. While it is critical to ensure sufficient treatment of the target tissue, it can be equally vital to the treatment and patients overall outcome that the pulsing conditions are set to moderate the associated thermal effects with the electroporation of biological tissue. The development of thermal mitigation strategies for IRE treatment is the focus of this dissertation. Herein, the underlying theory and thermal considerations of tissue electroporation in various scenarios are described. Additionally, new thermal mitigation approaches with the intention of maintaining tissue temperature below a thermally damaging threshold, while also preserving or improving IRE lesion volume are detailed. Further, numerical models were developed and ex vivo tissue experiments performed using a perfused organ model to examine three thermal mitigation strategies in their ability to moderate temperature. Tests conducted using thermally mitigating treatment delivery on live tissue confirm the capacity to deliver more energy to the tissue at a thermally acceptable temperature, and provide the potential for a replete IRE lesion. / Doctor of Philosophy / Irreversible electroporation (IRE) is a minimally invasive therapy utilized to treat a variety of cancers. This procedure involves the delivery energy in the form of pulsed electric fields (PEFs) through two or more needle electrodes. These PEFs destabilize the cell membrane, increase the cell-tissue permeability, and ultimately induce cell death for any given cell within the targeted treatment region. Over the years, this treatment modality has shown a great deal of promise in the treatment of unresectable tumors in which the tumor is positioned near or around sensitive regions making the surgical removal of the tumor impossible and thermal ablation techniques limited in their ability to treat without irrevocably damaging the underlying tissue architecture and other critical surrounding structures. Thus, it can be vital to the treatment and patients overall outcome that the IRE therapy is set to moderate any associated thermal effects with the electroporation of biological tissue. However, the design of an electric field that simultaneously maps the entire region of interest for a single treatment and avoids undesirable thermal effects can be challenging when treating larger or irregularly shaped volumes of tissue. Thus, in this dissertation, we demonstrate various treatment delivery methods/ enhancements to reduce temperature rise during IRE therapy. The underlying theory of tissue electroporation and associated thermal considerations are described to provide a foundation and general context. Additionally, novel approaches to tissue electroporation therapy with the intention of maintaining tissue temperature below a thermally damaging threshold throughout treatment are detailed.

Includes bibliographical references (p. 71-77).