Injectable wireless microstimulators for motor neuroprosthetics
Prof. Antoni Ivorra
Department of Information and Communication Technologies
Universitat Pompeu Fabra, Barcelona, Spain
Implantation of most electrical stimulation systems requires complex surgeries that hamper their use for the development of neuroprostheses. In particular, stimulation systems based on central units are not adequate for applications in which many sites must be individually stimulated over large and mobile body parts, thus hindering practical neuroprosthetic solutions for patients suffering paralysis due to spinal cord injury or other neurological disorders. It has been suggested that a solution to these challenges could consist in developing addressable single-channel wireless microstimulators which could be implanted via minimally invasive procedures such as injection. However, past attempts in this direction were not successful because the developed implants were stiff and too large. Further miniaturization was obstructed because of the use of inductive coupling and batteries as energy sources.
In this talk, I will present technological developments and assays in animals and in humans performed within the European projects eAXON and EXTEND. These projects were mainly aimed at exploring an innovative method for performing electrical stimulation in which the implanted microstimulators operate as rectifiers of bursts of innocuous high frequency (HF) current supplied through epidermal textile electrodes that can be shaped as garments. This approach allowed the development of injectable stimulators with a diameter of less than 1 mm. Most of the implants’ volume consists of materials whose density and flexibility match those of neighboring living tissues for minimizing invasiveness. In fact, the implants look like short pieces of flexible thread.
We first proposed the development of injectable microstimulators based on the rectification of HF current bursts in 2011. However, in these early prototypes and in others tested in a chronic study in 2015, where four-weeks implantation was in vivo demonstrated, the rectifiers included within the implants consisted only of conventional diodes, and addressability was not possible. Within the eAXON project, we have developed and in vivo demonstrated thread-like prototypes which are digitally addressable and which are intended for long-term implantation as their electronics is hermetically packaged. In this talk, I will present both published and unpublished in vivo assays with these implants. For instance, I will show assays in which the microstimulators are used to independently trigger different muscles to perform complex movements or to independently activate different portions of the same muscle group to minimize muscle fatigue.
Within the EXTEND project, we have performed acute assays in humans (unpublished results also to be presented in the talk) and we have demonstrated that the applied HF currents are innocuous and imperceptible.
- García-Moreno A, Comerma A, Tudela-Pi M, Minguillon J, Becerra-Fajardo L, Ivorra A, “Wireless networks of injectable microelectronic stimulators based on rectification of volume conducted high frequency currents”, Journal of Neural Engineering, 2022 ;19:056015. DOI 10.1088/1741-2552/ac8dc4
- Minguillon J, Tudela-Pi M, Becerra-Fajardo L, Perera-Bel E, del Ama AJ, Gil-Agudo Á, Megía-García Á, García-Moreno A, Ivorra A, “Powering Electronic Implants by High Frequency Volume Conduction: In Human Validation”, IEEE Transactions on Biomedical Engineering, 2023 ;70(2):659-670. DOI: 10.1109/TBME.2022.3200409
- Becerra-Fajardo L, Krob MO, Minguillon J, Rogrigues C, Welsch C, Tudela-Pi M, Comerma A, Barroso FO, Schneider A, Ivorra A, “Floating EMG Sensors and Stimulators Wirelessly Powered and Operated by Volume Conduction for Networked Neuroprosthetics”, Journal of NeuroEngineering and Rehabilitation, 2022 ;19:57. DOI: 10.1186/s12984-022-01033-3
Antoni Ivorra obtained PhD in electronic engineering from the Polytechnic University of Catalonia, Spain. Currently, he is a Full Professor at Universitat Pompeu Fabra in Barcelona, Spain, where he leads the Biomedical Electronics Research Group and coordinates the Bachelors’s degree in Biomedical Engineering. Prior to joining Universitat Pompeu Fabra in 2010, from 2005 to 2009, he enjoyed a four-year postdoctoral stay at the University of California at Berkeley followed by an eight-month postdoctoral position at the CNRS- Institut Gustave Roussy, Villejuif, France. His research is focused on bioelectrical phenomena and, in particular, on exploring the use of these phenomena for implementing new methods and devices for biomedical applications. Specifically, his main research topics are electroporation, particularly for tissue ablation, electrical bioimpedance for diagnostic purposes, and injectable electronics for neuroprosthetics. He is author or coauthor of 70 publications in peer-reviewed journals and he has been inventor or co-inventor of 12 families of patent applications. In 2016 he was awarded an ERC Consolidator Grant for his research on microstimulators for neuroprosthetics.