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A Bidirectional MyoKinetic Implanted Interface for Natural Control of Artificial Limbs

Periodic Reporting for period 4 - MYKI (A Bidirectional MyoKinetic Implanted Interface for Natural Control of Artificial Limbs)

Reporting period: 2021-03-01 to 2023-02-28

MYKI aims at developing and clinically evaluating a dexterous hand prosthesis which is naturally controlled and perceived by the amputee. This will be possible by overcoming the conventional approaches based on recording electrical signals from the peripheral nervous system (nerves or skeletal muscles) through the development of a radically new Human-Machine Interface (HMI) based on magnetic field principles, both able to decode voluntary motor commands and to convey sensory feedback to the individual. Core of this system is a multitude of magnets implanted in independent muscles and external magnetic readers/drivers (MRDs) able to (i) continuously localize the movements of the magnets and, at specific times, (ii) induce subtle movements in specific magnets. In fact, as a magnet is implanted it will travel with the muscle it is located in, and its localization will provide a direct measure of the contraction/elongation of that muscle, which is voluntarily controlled by the central nervous system. In this way it will be possible to decode the efferent signals sent by the brain by observing a by-product of the muscle fibres recruitment. On the other hand, a movement induced in the implanted magnet by the external MRD, could provide a perceivable stimulus, conveyed to the brain by means of the peripheral sensory receptors present in the muscle (e.g. muscle spindles or Golgi tendon organ) or in the neighbouring skin (tactile mechanoreceptors). In this way we aim to provide tactile and/or proprioceptive sensory information to the brain, thus restoring the physiological sensorimotor control loop. Remarkably, with passive magnetic tags (that do not require to be powered-on) and wearable readers/drivers, it will be possible to implement a wireless, bidirectional HMI with dramatically enhanced capabilities with respect to the state of the art interfaces.
The need/desire for functional replacement of a missing upper limb is an ancient one: historically humans have replaced a missing limb with a prosthesis for cosmetic, vocational, or personal autonomy reasons. In fact the loss of a hand causes severe physical and also mental illness. The inability to grasp and manipulate objects runs parallel with the inability to sense and explore the surrounding world as well as with the inability to use gestures to support speech and express emotions. Still today the restoration, following amputation, of dexterous control equivalent to that of the human hand is one of the major goals in applied neuroscience and bioengineering. To accomplish this requires achieving two important subgoals: the development of a multi-degree of freedom (DoF) artificial hand, and the implementation of an intuitive and effortless human–machine interface (HMI) that maps the sources of volition to the DoFs of the artificial hand, bi-directionally. Although MYKI targets this goal as a whole, is the HMI the primary focus of the project.
The overall objective of the MYKI project is to investigate, design, develop and clinically assess on one selected transradial amputee what we defined MyoKinetic interface, i.e. a magnetic field-based HMI with features beyond the state of the art, for the natural control and perception of a transradial hand prosthesis. This goal will be achieved by addressing the following technological objectives (TOs) and specific scientific objectives (SSOs):

TO1: Localizer of implantable magnets
SSO1: Efferent processing algorithms for MyoKinetic Interface
TO2: Remote actuation of implantable magnets
SSO2: Is it possible to convey physiologically appropriate touch information related to tactile events in the hand prosthesis through implanted magnets?
SSO3: Is it possible to convey physiologically appropriate proprioceptive information of a missing finger or DoF through implanted magnets?
TO3: Smart hand-wrist prosthesis with tactile sensors and shared control
TO4: Biocompatible packaging for implanted magnets
At conclusion of the project, all the foreseen Technological Objectives (TOs) were successfully accomplished. The first volunteer underwent surgery to receive the myokinetic implant on April 1st 2023. Six magnets were implanted in three forearm muscles through a minimally-invasive surgical procedure. Outcomes from the first implant will be available after the explant, set for May 13th 2023.
All the necessary steps to get to the final demonstrator have been done, including the technology development (self-contained multi-magnet tracking system, multi-magnet stimulator, prosthetic arm), and the acquisition of extensive theoretical and applied knowledge, as demonstrated by 30+ scientific publications in reputable journals. The main results achieved within MYKI can be summarized as follows:
- the investigation, through simulations and a physical forearm mockup, of multi-magnet tracking systems capable to localize many more magnets than those described earlier.
- the development of dedicated hardware solutions for multi-magnet tracking suitable for integration on wearable devices.
- the development of different prototypes for the delivery of selective remote vibrations, at arbitrary frequencies and with different shapes, to multiple targets, an unprecedented tool to study proprioception in humans.
- The integration of the magnetic tracking and actuation technologies in a unique system so that controlled vibrations can be delivered in moving magnets.
- The identification of Parylene C as a safe coating for short-term implants in humans.
- The self-contained arm prosthesis with myokinetic control used for pilot clinical assessment with one patient.
- The first implantation of six magnets in humans for the myokinetic control of a arm prosthesis.
MYKI, by abandoning the paradigm of transducing electrical signals, aims to develop a solution with all the basic ingredients necessary for achieving natural control and sensory feedback of a transradial hand prosthesis, exploiting the magnetic field. Our MyoKinetic interface will combine in a unique system the bi-directionality offered by peripheral neural implants with the mechanical stability and direct and simultaneous control (muscle selectivity) allowed by Implantable myoelectric sensors. MYKI is based on implantable technologies but remarkably, the implanted devices will not require to be powered.
The development of the above mentioned key enabling technologies (TOs and SSOs) permitted MYKI to perform the first in-human implant of the MyoKinetic interface, that in turn will allow to assess the proposed control and sensory feedback strategies. Due to its nature the implant was minimally invasive. Interestingly, although it is being first clinically assessed with a transradial amputee (the most prevalent case), it is worth mentioning that the MyoKinetic interface concept adapts nicely to all cases of upper limb amputation (from partial hand amputations, to shoulder disarticulation) and could also find use in lower limb prostheses. Hence, the project could also have a major socioeconomic impact for disabled people in general by providing new interfacing solutions resulting in better quality of life.
Concept of MyoKinetic Interface proposed in MYKI