Printed Multi-EMG Electrodes on the 3D Surface of an Orthosis for Rehabilitation: A Feasibility Study

The article proposes the development of an innovative prototype of smart orthosis with a fully integrated multi-electrodes matrix for electromyography (EMG), to improve non-invasive personalized recording during rehabilitation. Both electrodes and conductive tracks were effectively printed onto the three-dimensional (3D) surface of the orthosis through Aerosol Jet Printing. Results from morphological and electrical characterization of printed elements showed an average thickness of 22.2 μm (relative standard deviation of 11%) with average resistivity of about 51 · 10
^{-8 Ω·}
m (relative standard deviation of 10%) and an electrode-to-skin impedance comparable to the one of commercial dry electrodes. Portability and comfort were enabled by customized light-weight conditioning electronics attached to the orthosis allowing wireless data transmission. Muscular activity from three subjects was then evaluated while performing the same tasks involving multiple muscles. Results confirmed the ability of the device to monitor the activity of gastrocnemius muscle during both a sit-to-stand task and isometric contractions, both for intra- and inter-subjects' analyses. A comparison with commercial surface EMG electrodes and with literature confirmed similar features both in time and frequency. Overall, the results presented suggest the possibility to exploit the potential to print customized electrodes onto 3D surfaces to fabricate smart personalized wearable orthoses useful to capture valuable feedback to improve effectiveness, consciousness, and interactivity during daily activities and specific exercises, for both patient and medical personnel.