Antoni Ivorra

Injectable wireless microstimulators for motor neuroprosthetics 

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 established 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.