Type of Document	Dissertation
Author	Korivi, Naga Srinivas
Author's Email Address	nkoriv1@tigers.lsu.edu
URN	etd-04272011-144941
Title	Bio-Implantable Microdevices and Structures for Functional Electrical Stimulation Applications
Degree	Doctor of Philosophy (Ph.D.)
Department	Electrical & Computer Engineering
Advisory Committee	Advisor Name Title Ajmera, Pratul Committee Chair Greenway, Frank Committee Member Daniels-Race, Theda Committee Member Feldman, Martin Committee Member Lee, Hwang Dean's Representative
Keywords	neural signal recording neural stimulation functional electrical stimulation (FES) cuff electrodes
Date of Defense	2011-04-14
Availability	unrestricted
Abstract This dissertation describes the development of microstructures and devices for applications in functional electrical stimulation. A nerve cuff electrode design has been developed for applications in neural electrical stimulation and recording, which addresses limitations with existing cuff electrodes. The developed clip-on micro-cuff electrode design consists of a naturally closed cuff with inner diameter in the micro-scale or above. A novel pinch-hinge feature allows a user to easily open the cuff and place it on target nerve tissue for stimulation or recording purposes. Upon release of the pinch-hinge, the cuff assumes its normally closed nature. The device conducts and reads electrical signals in the amplitude and frequency range of typical neural signals. A typical clip-on cuff device with 800 µm inner diameter is opened to its maximum extent by a relatively low force of less than 0.8 N, offering an alternative to other designs requiring application of a force for cuff closure. For applications involving gastric muscle stimulation, a novel gastric pacing electrode is fabricated in biocompatible silicone elastomer. In response to physiological temperature of about 37 ˚C, polyethylene glycol embedded inside the device body melts due to which the structure changes from a more rigid state initially to a more flexible state. This is expected to reduce tissue penetration during and after electrode implantation. A comprehensive piece-wise discrete element equivalent circuit model has been developed to represent an electrode-neural tissue interface. This model addresses internal aspects of both the tissue and the electrode surface and is an improvement over previous models. The equivalent circuit is employed in conjunction with electronic circuit simulation software to study the electrical response of an axon to external stimulus. Simulation results broadly correlate with practical observations reported by others. Lastly, a new percutaneous access device functioning as an interface between implants and the external world is reported here. The device made of silicone elastomer incorporates stress concentration features and shows promise for improved robustness and reliability. The device also incorporates micro-scale porous structures to allow for tissue in-growth to facilitate anchoring of the device.
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