Determination of human coronary artery endothelial cells membrane potentials for the re-endothelialisation of vascular stents

Abstract

Small vessel stents have become one of the most common treatments for Coronary Artery Disease. A metal tubular mesh that is called a stent, is placed inside the blocked or narrowed artery where there is an accumulation of plaques or other disruptions that reduce luminal patency; this results in a reduction of blood flow to the heart muscle with potentially catastrophic outcomes. Deployment of the stent inside the affected artery dilates the diseased lumen, allowing normal blood flow to resume. As the stent is a foreign object, consisting of synthetic material, it can elicit an immune system reaction, leading to blood clots, vascular spasm and/or proliferation of local cells that may result in the risk of re-occurrence of blockage of the vessel lumen; this is known as restenosis. The work undertaken in this thesis aims to reduce or eliminate the risk of restenosis by applying an oppositely polarised electrical potential onto the surface of the stent to attract vascular endothelial cells that normally inhabit arteries and veins. It has been extensively documented in the scientific literature that these specialised vascular cells play a leading role in maintaining vascular tone and stasis if continuous uninterrupted squamous endothelial cells layers populate the lumen of blood carrying vessels. Therefore, electrical attraction of vascular endothelial cells on the surface of stents generates a layer that inhibits thrombus formation and consequent instent restenosis. In addition, a unique approach is used to measure exactly the membrane potential of relevant human cells without interference from other electrical fields. Other techniques like di-electrophoresis and zeta potential measurements were performed to validate data of a novel direct voltage measurement technique. Cell membrane potentials were then used in a human cardiovascular bio mimicked experiment that was performed with the aim of re-endothelialisation of the stent using an external electrical field. An electrophoresis validation method was performed in a different manner, compared to gel and liquid electrophoresis methods, instead of molecular or protein species, human cell were used to determine the impact of electrical fields and polarisation status on migration and orientation of cells, specifically human coronary artery endothelial cells. To help in understanding how effective this technique would be, osteoblasts were used as a surrogate cell to support and characterise the process. Moreover, electrode passivation has been studied in this work to ensure that changes in resistance and impedance was evaluated as thin-films of oxides or other species play an important roles in electrical measurements when touching cells directly with a metal microelectrode. Experiments have been done to explore the influence of different ionic solutions on metal electrodes and how surface changes affect their electrical profile, after immersing in different liquids that approximate biological media. The experimental results collected in this thesis show the movements of adherent cells under the application of external electrical fields during the electrophoresis experiment. Similarly, results of a bio mimic artery experiments, describe the response of cells to externally applied electrical fields on stents, with the potential to reduce the failure rates (restenosis) after stent deployment.