UC San Diego

The increasing expected lifespan is causing a higher prevalence of neurological diseases. These diseases carry an emotional and economical cost that can not be neglected by society. Key to understanding and treating these diseases are the recording and stimulating technologies available to researchers and clinicians. While metal electrodes are the oldest recording technology utilized, recent developments in optics have allowed biologists to understand nervous system function on a new level. In the past decade, engineers have begun to combine both electrical and optical modalities into a single device to increase the amount of information gained from recording and stimulation. A limiting factor for all of these implantable devices is the body's immune system response, which results in dead tissue surrounding the implant in less than 6 months. Designing a multimodal device which reduces immune response is a solution sought after in the neuroscience field. While some purely electrical devices have begun to show reduced immune response by reducing device size, there has not been a multimodal device on these size scales. This dissertation combines microfabrication techniques with small optical cores to create a minimally invasive implantable device which can perform optical and electrical interrogation of the nervous system. Chapter 2 addresses the electrical and optical challenges associated with scaling these technologies to small dimensions. Strategies to overcome these issues are described along with trade-offs of different materials used in fabrication. Chapter 3 takes these fabricated devices and looks at limitation for inserting them into tissue. Due to limitations in size, device mechanical failure is modeled as a function of each fabrication layer added to the device. These characterized devices were then tested on brain and spinal cord tissue samples to determine the maximum device length before device failure. Chapter 4 takes all of the lessons learned in fabrication and characterization to create devices which are then tested \textit{in vivo}. We are able to demonstrate that a single device can concomitantly optically stimulate neurons in the cortex and electrically record action potentials. Through immunohistology we demonstrate a negligible immune response for devices after implantation of 6 days: a critical time point in the immune system response. These results show promise for scaling this technology into arrays that can interface with larger regions of the brain.