The Myokinetic Interface: magnetic tracking and actuation for the restoration of dexterous control and proprioceptive feedback in transradial amputees

Developing dexterous hand prostheses which are controlled and perceived naturally by an amputee is one of the major challenges in biomedical engineering. With this goal in mind, many research efforts have been made, from proposing novel surgical techniques, to advancing technologies for biological signals acquisitions and neuromuscular stimulation. Most of the state-of-the-art approaches probe muscle electrical activity for control, and deliver electrical pulses to nerves for sensory feedback. An alternative approach based on the implantation of permanent magnets, dubbed the myokinetic interface, aims to monitor muscles contractions by localizing the magnetic markers implanted in them, and thus controlling the corresponding movements in the artificial hand. In this way, such an interface holds the potential for a biomimetic, direct, independent, and parallel control of multiple degrees of freedom of an artificial hand. Moreover, selectively vibrating the magnets also offers a unique opportunity to study kinesthetic percepts in humans, thus possibly becoming a bidirectional interface. The myokinetic interface could be combined with existing advanced human-machine interfaces for prosthetics, such as targeted muscle reinnervation or osseointegrated implants, to further improve its efficacy and comfort, and also opens new possibilities to interface humans with robotic technologies in an intuitive way. After presenting the latest advances in human-machine interfaces for prosthetics and the key enabling technologies to develop a myokinetic interface (Chapter 1), this thesis reports about part of the development stages of the latter, along three distinct topics: (i) modelling of the implanted magnets (Part I, Chapter 2), (ii) magnetic tracking (Part II, Chapter 3) and (iii) magnetic actuation (Part III, Chapter 4 and Chapter 5). Chapter 2 provides exact and robust expressions for field and field gradient for permanent magnets cylinders with generic uniform magnetization. In addition, expressions regulating the magnetic interaction between coaxial cylinders are presented. Chapter 3 treats an in-silico study aimed at quantifying the impact of sensors properties in the accuracy, precision and number of iterations of a magnetic tracker. Different number of magnets and their distances from the sensors plane are considered in order to evaluate the performance of the tracking algorithm for various sensors resolution and localization rates (frequencies of localization). Chapter 4 addresses in-vitro and in-vivo investigations of the magnetic actuation approach to deliver kinesthetic percepts. A coil-array system consisting of 8 stationary electromagnets is used to test directionality, frequency selectivity and the tuning of the vibration shape in a single remote magnet. Simplified systems with only one degree of freedom (using a single magnetic actuating source) are used to vibrate a magnet implanted in the forearm of an animal model. Chapter 5 presents the integration of magnetic tracking and actuation in a single device consisting of 12 coils capable to selectively vibrate moving magnets. Such a system exhibits individual actuation of a single magnet out of 4 that are still, or out of 2 that are moving, while simultaneously tracking all of them. Finally, Chapter 6 discusses the thesis work including limitations, outlooks and concluding remarks.