Designing Accessible Hardware for Electrical Neuromodulation Applications

Abstract

From the development of the first cochlear implant in 1957 until this day, neural implants have been successfully treating neurological diseases and disorders by directly interfacing with the biological tissue. Electrical stimulation, the most common form of neuromodulation, can excite or inhibit the activity of neural cells, thus inducing targeted therapeutic effects and alleviating symptoms, or restoring lost or degenerating functions of the nervous system. The development of implantable devices has seen great progress over the past decades, improving their functionality, robustness and lifetime. Still, many key features of commercial devices remain unchanged, given their technological maturity and the demanding and complex procedures required for their medical use approval. However, the constant advancement of technology and neuroscientific knowledge calls for further improvement and development of the functionality and configuration of neural implants. To this end, this thesis explores means of enhancing the capabilities of implantable devices through a higher programmability of the stimulation parameters, the integration of wireless powering, and the introduction of methods to increase energy efficiency and stimulation efficacy. Two neural stimulators are designed and developed, one for the purpose of dorsal root ganglion (DRG) stimulation for motor recovery after a spinal cord injury, and one designed for, but not limited to, vagus nerve stimulation applications. They are developed as benchtop prototypes, using commercially available components to increase their accessibility and reproducibility by other research labs, and are intended for experimental preclinical and clinical studies. The safety of the devices is considered a high priority, by taking the necessary measures to provide a safe operation, such as developing and integrating mechanisms that monitor and compensate for unwanted reactions at the targeted tissue site. Both designs offer multichannel operation for increased stimulation specificity and spatial resolution by individually controlling the electrodes connected to the system’s output. Following the emerging trends in the design of neural implants, and working towards miniaturised and low-power systems, various methods for improving power efficiency are explored and implemented. An adaptive power supply architecture is proposed to increase energy efficiency in systems that perform non-rectangular waveform stimulation. Furthermore, the possibility of entirely eliminating the need for a constant power supply is investigated and implemented, increasing the system’s energy efficiency by wirelessly powering the device through ultrasound while using the same transferred and rectified signal for both powering and neural stimulation. The development of such hardware aims at enhancing neuroscientific knowledge by providing advanced, functional solutions that follow current needs and requirements, and can aid in further exploring the potential of neuromodulation applications in providing targeted, personalised therapies.