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A Bidirectional MyoKinetic Implanted Interface for Natural Control of Artificial Limbs

Periodic Reporting for period 3 - MYKI (A Bidirectional MyoKinetic Implanted Interface for Natural Control of Artificial Limbs)

Reporting period: 2019-09-01 to 2021-02-28

MYKI aims at developing and clinically evaluating a dexterous hand prosthesis with tactile sensing 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
"A forearm mockup was developed and used to simulate the implantation of several magnetic markers in the forearm, providing a valuable tool for the validation of the magnets localizer and actuator. Several pilot sensory feedback studies were carried out, investigating (i) important parameters regulating the mechanisms underlying the vibration-induced illusion of movement (important to restore proprioception) and (ii) the best strategy to deliver sensory feedback in terms of object slip prevention so to be able to replicate such behaviour with the hand prosthesis. Regarding the identification of a clinical partner, the PI is in contact with several Italian hospitals and is evaluating the institution from which the project can benefit the most.

Both the magnets reader and driver (MRD) are at an advanced development stage, being these systems able to, respectively, track or drive up to 4 magnets independently. Online trackers/drivers were developed and tested on different platforms and will be integrated in a closed-loop system the near future.

The IH2 Azzurra robotic hand available at the Scuola Sant'Anna was prepared and made available for pilot sensory feedback studies. Additionally, the artificial hand for the MYKI project was developed exploiting synergies with the EU H2020 DeTOP project (GA #687905). The resulting prototype was also integrated with an advanced sensory system based on strain-gage technologies. In addition, the development of the active wrist is at advanced stage, with few prototypes being currently tested. The team also started studying how humans exchange objects in order to implement in the MYKI prosthesis mechanisms that allow individuals to perceive fluent handover.

In-vitro biocompatibility tests were performed and in-vivo tests are currently ongoing. Both tests aim to identify an appropriate material that can be used as a bio-compatible coating for the magnetic markers. In particular, parylene, titanium, diamond-like carbon and titanium nitride were selected for the tests based on their good bio-compatibility properties emerged from the literature.

Most of this research was submitted for publication on reputable journals and international conferences.
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 will be based on implantable technologies but remarkably, the implanted devices will not require to be powered. If successful, this approach will have an impact not only on transradial amputees but on all amputees because it can be extended to all kind of upper limb amputations (from partial hands to shoulder disarticulations) and lower limb amputations, and combined to Targeted Muscle Reinnervation for a more stable interface.

The exciting thing of the MyoKinetic implant is that it will allow natural (or close-to-natural) control – with control we refer to both the efferent and afferent pathways. Indeed, the same pair of magnets implanted in antagonist muscles (e.g. the flexor and extensor pollicis longus), not only will be used to control the physiologically appropriate DoF in the prosthesis (e.g. thumb flexion/extension), but also to evoke proprioceptive feedback through the physiologically appropriate receptors, and to provide physiologically appropriate tactile feedback exploiting biomimetic approaches.

The development of the above mentioned key enabling technologies (TOs and SSOs) will permit MYKI to perform the first in-human implant of the MyoKinetic interface and to assess the proposed control and sensory feedback strategies. Due to its nature the implant is expected to be minimally invasive. Interestingly, although it will be 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