Magnetically-Coupled Circuits Systems for Wireless Excitation of Passive Stimulators for Stimulation Therapies and Application as a Treatment for Glaucoma

The practice of delivering an electrical current waveform to an excitable tissue such as a structure in the brain, nerve fiber, or muscle to relieve the symptoms of disease constitutes an electrical stimulation therapy. Electrical stimulation therapies supported by implantable devices provide effective treatment options for people suffering from treatment-resistant chronic diseases that often fail to respond to medication and other traditional therapies [1, 2]. However, implantable electrical stimulators traditionally approved by the Food and Drug Administration (FDA) use implanted batteries that require surgical replacement over years of operation and limit therapies to applications with minimal constraints on implant mass, volume, and rigidity [3, 4]. Previous works have proposed to eliminate batteries in implantable stimulators by using magnetically-coupled coils to deliver energy through radio-frequency (RF) fields, exciting alternating currents on implantable devices to be converted into stimulus pulses by rectifiers [5, 6]. Implantable stimulators without batteries may be excited by an alternative theory of operation without the use of RF fields that eliminates the need for a rectifier and permits stimulators with minimal complexity.
This work proposes an original use of magnetically-coupled circuits theory for the wireless excitation of electrical stimulation current waveforms on passive stimulators that eliminates the need for an implanted battery. The principle of the technique is to drive stimulation current waveforms on passive stimulators with electromotive forces excited by applied time-varying magnetic fields via the phenomena described by Faraday’s law of induction [7-9]. The proposed systems require a wearable driving component and a passive driven component that may either be worn or implanted. The wearable driving component must include a battery, pulse-generating circuitry, and a primary coil, whereas the driven component is a passive device requiring only a secondary coil with electrodes to contact tissue. The pulse-generating circuitry of the driving component may be implemented readily such that the design of the coils defines the challenge in the implementation of the proposed systems. The design of the coils for the proposed systems presents the potential for a nontrivial optimization problem with conflicting objectives; possible objectives for the design of the coils include maximizing the attainable peak amplitudes of the stimulation currents, obtaining various characteristics of a desired stimulation current waveform, and minimizing the variation of the stimulation currents with varying displacements between the coils. The problem posed by the design of the coils for the proposed systems is addressed by direction obtained from theoretical analyses and experiments performed in this work that supplement direction from the literature [5, 10-12]. The potential utility of the proposed theory of operation is demonstrated by enabling the first chronic electrical stimulation therapy for glaucoma, the leading cause of irreversible blindness worldwide. The system designed for the glaucoma stimulation therapy and the methods used to quantify its electrical performance are presented along with data from experimental therapeutic trials with human participants.