Implantable neural interfaces that can simultaneously record and perturb the neuronal circuitry with neuron scale precision have profound implications in neuroscience and medicine. They hold great potential for the diagnosis and treatment of several neurological disorders such as Parkinson's disease and epilepsy. In addition, they play a crucial role in the development of neuroprosthetics and brain-computer interface (BCI) technologies that can restore functionality in patients with nervous system impairments. Despite the promise of such neuron-scale interfaces, most of the neural electrode technologies developed to date are incapable of providing simultaneous multi-channel neural recording in conjunction with micro stimulation desired for the above stated applications [59]. For instance, metal electrodes suffer limited performance in providing stable neuronal scale recording and micro stimulation because of their poor electrochemical and mechanical properties.

Carbon nanotube (CNT) fiber is a novel material with a unique combination of extraordinary electrical, thermal, and mechanical properties like CNTs, their microscopic counterparts [6]. Recent studies show CNT fibers (CNTfs) as the ideal candidate material for the development of safe, effective, stable, and multifunctional neural microelectrodes without the need for any additional surface modification [78, 143, 144, 165]. This dissertation focused on developing a scaled-up high density, CNTf microelectrode array for simultaneous recording and micro-stimulation. The thesis has two portions. In the first, we present a parylene-C insulation scheme for CNTf electrodes, the first step in CNTf -based electrode development. The integrity of parylene-C coated CNTf electrodes was evaluated using modified leakage current, electron microscopy, bending stiffness, and in vitro electrochemical analysis under normal and H2O2 aging conditions at different temperatures. We demonstrated that the parylene-C alone scheme offers high conformal, flexible, minimal leakage current, and stable long-term insulation performance and is a better insulation strategy for CNTf electrodes.

In the second part of this thesis, we developed and optimized micro fabrication and assembly techniques to successfully fabricate multi-channel parylene-C coated CNTf microelectrode arrays (n=8/16/32). The novel arrays demonstrate one of the lowest electrode channel impedance, high charge storage injection capacity to the metal and state-of-the-art neural electrode materials in vitro. In the final portion, we validated the implantation strategy and recording function of the developed arrays to metal electrodes using acute in vivo studies in rat models. The combination of the low impedance, better charge transfer properties, and the initial in vivo performance of the developed CNTf electrode arrays suggest they are a promising technology for neural recording and stimulation applications.