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Electroporation is the critical step in an electric field mediated drug or gene delivery protocol. Electroporation based protocols have been successfully demonstrated in cancer clinical trials, however, its impact in other applications is still under investigation. A significant roadblock to long term functioning of implantable biosensors in vivo is the tissue reaction in the form of fibrous encapsulation that results in reduced transport to the sensing element of the biosensor. In vivo gene electroporation has a great potential as a means to modify the transport properties of tissues in the proximity of the sensing element of implantable biosensors. This dissertation examines two postulated electroporation based strategies to modify tissue for enhanced performance of an implantable biosensor. In the first, the implantation protocol is modified to accommodate in vivo electroporation. In the second strategy, the the modification is applied post implantation. This post-implantation in vivo electroporation application requires that electric energy be delivered at the site of electroporation close to the biosensor while minimizing effects far from such site. A novel method, focusing electric fields, developed for this purpose is presented. A theoretical framework as well as in vitro and in vivo experiments are provided as the introduction to the method and in support of its potential as the basis of a viable technology.

Energy harvesting is identified as a promising alternative solution for powering implantable biosensors. It can completely replace the batteries, which are introducing many limitations, and it enables the development of self-powered implantable biosensors. An interface circuit is necessary to correct for differences in the voltage and power levels provided by an energy harvesting device from one side, and required by biosensor circuits from another. This thesis investigates the available energy harvesting sources within the human body, selects the most suitable one and proposes the power management unit (PMU), which serves as an interface between a harvester and biosensor circuits. The PMU targets the efficient power transfer from the selected source to the implantable biosensor circuits. Based on the investigation of potential energy harvesting sources, a thermoelectric energy harvester is selected. It can provide relatively high power density of 100 μW/cm2 at very low temperature difference available in the human body. Additionally, a thermoelectric energy harvester is miniature, biocompatible, and it has an unlimited lifetime. A power management system architecture for thermoelectric energy harvesters is proposed. The input converter, which is the critical block of the PMU, is implemented as a boost converter with an external inductor. A detailed analysis of all potential losses within the boost converter is conducted to estimate their influence on the conversion efficiency. The analysis showed that the inevitable conduction and switching losses can be reduced by the proper sizing of the converter’s switches and that the synchronization losses can be almost completely eliminated by an efficient control circuit. Additionally, usually neglected dead time losses are proved to have a significant impact in implantable applications, in which they can reduce the efficiency with more than 2%. An ultra low power control circuit for the boost converter is proposed. The control is utilizing zero-current switching (ZCS) and zero-voltage switching (ZVS) techniques to eliminate the synchronization losses and enhance the efficiency of the boost converter. The control circuit consumes an average power of only 620 nW. The boost converter driven by the proposed control achieves the peak efficiency higher than 80% and can operate with harvested power below 5 μW. For high voltage conversion ratios, the proposed boost converter/control combination demonstrates significant efficiency improvement compared to state-of-the-art solutions. / <p>QC 20150413</p>