Floating EMG Sensors and Stimulators Wirelessly Powered and Operated by Volume Conduction for Networked Neuroprosthetics

Abstract

Background: Implantable neuroprostheses consisting of a central electronic unit wired to electrodes benefit thousands of patients worldwide. However, they present limitations that restrict their use. Those limitations, which are more adverse in motor neuroprostheses, mostly arise from their bulkiness and the need to perform complex surgical implantation procedures. Alternatively, it has been proposed the development of distributed networks of intramuscular wireless microsensors and microstimulators that communicate with external systems for analyzing neuromuscular activity and performing stimulation or controlling external devices. This paradigm requires the development of miniaturized implants that can be wirelessly powered and operated by an external system. To accomplish this, we propose a wireless power transfer (WPT) and communications approach based on volume conduction of innocuous high frequency (HF) current bursts. The currents are applied through external textile electrodes and are collected by the wireless devices through two electrodes for powering and bidirectional digital communications. As these devices do not require bulky components for obtaining power, they may have a flexible threadlike conformation, facilitating deep implantation by injection. Methods: We report the design and evaluation of advanced prototypes based on the above approach. The system consists of an external unit, floating semi-implantable devices for sensing and stimulation, and a bidirectional communications protocol. The devices are intended for their future use in acute human trials to demonstrate the distributed paradigm. The technology is assayed in vitro using an agar phantom, and in vivo in hindlimbs of anesthetized rabbits. Results: The semi-implantable devices were able to power and bidirectionally communicate with the external unit. Using 13 commands modulated in innocuous 3 MHz HF current bursts, the external unit configured the sensing and stimulation parameters, and controlled their execution. Raw EMG was successfully acquired by the wireless devices at 1 ksps. Conclusions: The demonstrated approach overcomes key limitations of existing neuroprostheses, paving the way to the development of distributed flexible threadlike sensors and stimulators. To the best of our knowledge, these devices are the first based on WPT by volume conduction that can work as EMG sensors and as electrical stimulators in a network of wireless devices.

First-in-human demonstration of floating EMG sensors and stimulators wirelessly powered and operated by volume conduction

“…However, it must be noted that the designed communication protocol allows the control of up to 256 devices per low-level control unit, and the possibility to have several low-level units connected to a high-level controller. In fact, we have in vitro demonstrated that more than 10 floating devices can be wirelessly powered and digitally controlled from the external system (50).…”

Multi-resonator Wireless Inductive Power Link for Wearables on the 2D Surface and Implants in 3D Space of the Human Body

“…However, medical devices relying on built-in batteries present drawbacks, necessitating periodic surgeries for replacements, with associated risks and financial burdens [1]- [11]. To address these challenges, various wirelessly powered technologies, including inductively coupled WPT, capacitively coupled short-ranged WPT, and newer options like ultrasonic, mid-field, and far-field coupled WPT, are widely used for implants and wearables, although challenges persist [1]- [2], [13]- [15], [20]- [23], [35]. Inductive power links face issues like suboptimal performance during misalignments, requiring innovative design solutions [1]- [2], [35].…”

“…Inductive power links face issues like suboptimal performance during misalignments, requiring innovative design solutions [1]- [2], [35]. Near-field capacitive coupling encounters obstacles, including heightened sensitivity to Tx-Rx separation and increased power fluctuations [23], [35]. Ultrasonic energy transfer faces challenges due to varying organ densities, soft tissue attenuation, and sensitivity to distance, potentially impacting overall system performance [1], [21], [35].…”

“…The implantable and wearable medical devices encompass a wide range of applications, which can be categorized as follows: 1) brain-related diseases and neurodegenerative diseases (NDDs): brain-machine interfaces (BMIs), deep brain stimulation (DBS) electrodes and implants, neuro-stimulator, neuro-prosthetics, optogenetic implants, and brain-wearables for monitoring NDD-related motor impairments [1], [13], [14], cochlear implant, retinal implant [1], [3], 2) cardiovascular diseases: pacemakers, defibrillators, ventricular assist devices (VADs) [1], [15], stents, cardiac loop recorders [16], 3) tissue repair and regeneration: photo-bio-modulation (PBM) and lowlevel light/laser therapy (LLLT) [17]- [19], 4) gastrointestinal diseases and urology: wireless capsule endoscopy [5], [6], insulin pump, implanted bladder stimulator [20], 5) monitoring multiple physiological parameters in real-time: implantable and wearable biosensors [1], smart electronic contact lens [21], fitness tracker, smart textiles with integration of wearable medical devices (WMDs) [22], and 6) others: orthopedic implants, foot drop implants, bone growth stimulator [1], [20], floating implants capable of electromyography (EMG) sensing [23], portable pulse monitoring [24], doppler ultrasound blood flowmeter used for a smart graft [25] and more.…”