Publication
Neural implants have demonstrated efficacy in implementing therapies for neurological disorders but their rigid design often leads to complications due to the mechanical mismatch with soft neural tissue. Current research focuses on developing flexible electrode interfaces to improve biocompatibility. However, the challenge of miniaturizing components such as wires and power sources remains. Wireless implants offer a solution by eliminating these bulky components thus reducing the overall size and invasiveness of the implant. This thesis explores the development and characterization of an organic near-infrared photovoltaic implant for wireless neural stimulation. First, the work focuses on the fabrication and characterization of green-sensitive organic photovoltaic pixels. The chosen material, P3HT:PCBM, was selected for its established use in organic photovoltaics and its absorption spectrum in the visible range. A series of characterization techniques were employed to assess the performance of these pixels. These methods provided insights into the electrical properties, light-harvesting capabilities, and dynamic response of the photovoltaic pixels under various conditions. Next, the work investigated the performance targets required to elicit cortical stimulation in the in vivo setting. Bipolar electrical stimulation of the mouse motor cortex served as a benchmark to establish the threshold charge and current values necessary for eliciting a motor response. This involved systematically varying the implant design to investigate electrode layout and stimulation parameters while monitoring muscle activity. The results from these in vivo experiments demonstrated that direction and distance were key in minimizing the current threshold amplitude to elicit a motor response. These findings served as a reference point for subsequent photovoltaic stimulation studies. Finally, these guidelines were used to fabricate a near-infrared sensitive organic photovoltaic pixel capable of stimulating neural tissue. The material PDPP3T was chosen for its absorption range and combined with the acceptor molecule Y6. Extensive characterization of the pixels was performed to assess their electrical properties, light-harvesting capabilities, and stability. While promising results were obtained in terms of charge generation, a critical challenge arose regarding the stability of the pixels in aqueous environments. Various encapsulation techniques were explored to mitigate this issue with varying degrees of success. Preliminary in vivo experiments were conducted to evaluate the efficacy of the near-infrared photovoltaic pixel for neural stimulation. However, no significant neural responses were observed in vivo. This outcome underscores the complexities associated with translation to in vivo devices and highlights the need for further refinement and optimization of the photovoltaic implant design. Overall, by defining clear metrics and fabrication processes, this thesis make