Development of an advanced force measurement bench for in vivo studies with injectable intramuscular microstimulators

Abstract

The Biomedical Electronics Research Group (BERG) is exploring an innovative method for performing intramuscular electrical stimulation aimed at restoring functional movements in paralysis patients. In this method, injectable flexible devices with a diameter below 1 mm named eAXONs (for electronic axon), perform neuromuscular stimulation by rectifying volume conducted high frequency (HF) current bursts supplied by external textile electrodes. The activation of the muscles generated by these microstimulators can be used to produce specific force patterns associated to functional movements. Currently, the technology is assayed in rabbits for performing plantarflexion and dorsiflexion movements and isometric forces. However, the force measurement system now in use by BERG exhibits some limitations in terms of robustness. The presented project has consisted in the development and engineering of an advanced version of the force measurement bench by means of using mechanical components and designing specific 3D printed pieces according to the rabbit’s biomechanical features while including the electronic circuitry comprising the sensor, the DAQ and computer connection. Additionally, the quality of the measured data was improved by means of signal filtering and conditioning using a digital filter properly tuned according to the force measurement ranges (0-10 N). As a result, a robust yet easily adjustable system of 770 mm x 560 mm x 170 mm and 7 kg was built up to measure the isometric unidimensional forces generated by a rabbit’s hindlimb dorsiflexion or plantarflexion in a fast, efficient, robust, and non-invasive manner by means of fixating the limb in an adjustable manner towards the sensor while preventing the structure from interfering with the force measurement. The developed bench was brought to experimental sessions outperforming previous setups but left room for future scaling of the system to bigger animals (sheep).