Microstimulation has been an invaluable tool for neuroscience researchers to infer functional connections between brain structures or causal links between structure and behavior. In recent years, therapeutic microstimulation is gaining interest for the restoration of visual, auditory and somatosensory functions as well as emerging applications in bioelectronic medicine. Current neural stimulation parameters and safety limits need to be revised for microelectrodes using more systematic and advanced methodologies. Stimulations via microelectrodes often require high charge injection for effective modulation of neural tissue without exceeding the threshold to harm the tissue or the electrodes. Therefore, advanced electrode materials with high charge injection capability and stability are highly desired. We have developed several types of stimulation materials based on conducting polymer PEDOT and nanomaterial composites. These materials present different charge transfer and electrochemical properties as well as biocompatibility, and the effects of these properties on microstimulation have yet to be comprehensively characterized. This proposal aims to establish new in vitro and in vivo models to examine the efficiency and safety of stimulation via multiple electrode materials, ranging from the clinically approved Pt and Iridium Oxide (IrOx) to the emerging PEDOT nanocomposites. Another challenge with micro-stimulation is its sensitivity to host tissue responses. Implantation of electrodes causes electrode fouling, progressive neuronal loss and inflammatory gliosis immediately surrounding the implants. Loss of nearby neurons and axons leads to decreased stimulation efficacy, while electrode fouling and gliosis increase impedance. Additionally, stimulation itself may further exacerbate host tissue responses if above the safety limit, which has yet to be defined for microelectrodes and emerging electrode materials. Using in vivo imaging in fluorescently labeled mice, we will examine the acute and chronic effects of microstimulation on neurons, microglia and vasculature, while monitoring the electrode material and electrochemical products. We will use an in vitro multielectrode arrays (MEA) system to study the effects of electrical stimulation on material and cells, in order to pinpoint the mechanisms of material and tissue damage. The first aime is to assess the efficiency and safety limit of neural stimulation via different electrode materials in vivo in acute experiments. For efficiency testing, we will implant the electrodes in the cortices of GCaMP mice and use 2-photon microscopy to image the calcium signal in order to determine stimulation threshold and optimum stimulation parameter for each electrode material. as a function of stimulation parameters. Stimulation threshold and efficiency for different pulse width, interphase period, bias potential and frequency from each electrode material type will be determined. For safety testing, we will use S...