Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (pages 73-75).To facilitate the usage of neural prosthesis, a sustainable recording method of cleaner neural signals is desired. While invasive neural electrodes can record neural activities with less noise than non-invasive methods and provide the ideal spatial-temporal resolution of the recorded signal, one major challenge of this invasive method is the potential tissue responses. The scar tissue that forms around the penetrating tip of the electrode may significantly degrade the signal quality in time, which causes the reading to be unreliable in the long-term. Solving this problem is key to enabling chronic usage of neural prosthetic systems. To tackle this challenge, previously Aalap Dighe has designed a reconfigurable neural probe using flexible polyimide material. The design used a spring-like structure to allow the electrode probe tip to move further inside the brain weeks after the initial implantation surgery. The latest generation of the devices, Gen 3, was tested both in vitro and in vivo using rodent models. In this thesis, the author continued the characterization of Gen 3 devices based on problems and observations occurred during the in vivo tests by Dighe, and proposed and tested an improved version of the device design, Gen 4. In particular, this thesis focused on solving the mechanical failure of some devices post-implantation and on reducing the instability of electrical properties of the electrodes. An improved structural mechanics simulation model of the design was used to characterize the mechanical properties of the devices. The simulation results were partially validated using benchtop load force tests, and were used to revise device design parameters for Gen 4. Experiments with Gen 4 devices showed that the new design met the design target well. Long-term in vitro impedance analysis of the electrodes was also performed using Gen 3 devices, which confirmed the observation of decreasing impedance over time in the previous in vivo tests. The results suggested delamination occurring between the polyimide layers, and the fabrication process was modified based on this hypothesis. Benchtop impedance tests of the new generation of devices confirmed that the delamination issue has been significantly improved.by Boying Meng.S.M.