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

Abstract

Background: Very recently we reported the design and evaluation of floating semi-implantable devices that receive power from and bidirectionally communicate with an external system using coupling by volume conduction. The proposed approach, of which the semi-implantable devices are proof-of-concept prototypes, may overcome some of the limitations presented by existing neuroprostheses, especially those related to the size of the implantable devices and the need to perform complex surgical procedures. This is accomplished as the implants do not require rigid and bulky components within them and can be developed as flexible threadlike devices, a form factor that is beneficial for motor neuroprostheses. Here we report the first-in-human demonstration of these semi-implantable devices for both electromyography (EMG) sensing and electrical stimulation in an acute study. Methods: A single floating device, consisting of implantable thin-film electrodes and a non implantable miniature electronic circuit connected to them, was deployed in the upper or lower limb of six healthy participants. Two external textile electrodes were strapped around the limb and were connected to the external system, which delivered high frequency current bursts. Within these bursts, 13 different commands were modulated to communicate with the wireless implant. In one participant, isometric forces were measured while acquiring EMG activity of voluntary muscle contractions using the semi-implantable device. Results: The floating EMG sensors and stimulators were successfully deployed in the biceps brachii and the gastrocnemius medialis muscles, and the external system was able to power them and bidirectionally communicate with them. Both sensing and stimulation parameters were configured externally using the communication protocol developed for the system. In one participant, both electrical stimulation and EMG acquisition assays were successfully performed, demonstrating the feasibility of the approach to power and communicate with the floating devices. Conclusions: This is the first time that floating EMG sensors and electrical stimulators that are powered and communicate by volume conduction are demonstrated in humans. These devices, which can be highly miniaturized using current microelectronic technologies, open the possibility of using coupling by volume conduction in networked neuroprosthetics, obtaining fully implantable wireless devices with sensing and stimulation capabilities.