Abstract
Despite several decades of research, electrically powered hand and arm prostheses are still controlled with very simple algorithms that process the surface electromyogram (EMG) of remnant muscles to achieve control of one prosthetic function at a time. More advanced machine learning methods have shown promising results under laboratory conditions. However, limited robustness has largely prevented the transfer of these laboratory advances to clinical applications. In this paper, we introduce a novel percutaneous EMG electrode to be implanted chronically with the aim of improving the reliability of EMG detection in myoelectric control. The proposed electrode requires a minimally invasive procedure for its implantation, similar to a cosmetic micro-dermal implant. Moreover, being percutaneous, it does not require power and data telemetry modules. Four of these electrodes were chronically implanted in the forearm of an able-bodied human volunteer for testing their characteristics. The implants showed significantly lower impedance and greater robustness against mechanical interference than traditional surface EMG electrodes used for myoelectric control. Moreover, the EMG signals detected by the proposed systems allowed more stable control performance across sessions in different days than that achieved with classic EMG electrodes. In conclusion, the proposed implants may be a promising interface for clinically available prostheses.
Highlights
Electromyography (EMG) has been used to control electrically powered hand and arm prostheses since decades (Parker et al, 2006; Farina et al, 2014)
In order to address some of the main reliability problems in machine learning based EMG control, in this work we present a novel type of electrode, fabricated with medical titanium and implanted percutaneously
At f = 100 Hz, which is approximately in the center of the EMG bandwidth, the dry electrodes had an impedance of approximately 100–200 k, the Ag/AgCl electrodes of approximately 10–20 k, and the implants of approximately 200–300
Summary
Electromyography (EMG) has been used to control electrically powered hand and arm prostheses since decades (Parker et al, 2006; Farina et al, 2014). The techniques most often used in commercial prostheses are very simple and allow the control of only one degree of freedom (DoF) at a time. The amplitudes of two bipolar surface EMG signals from antagonistic muscle-groups are subtracted to control one DoF in positive or negative direction. An extension of this approach, known as direct or differential control, is not possible with surface EMG, as usually not enough independent control sites are available. An exception consists of users with targeted muscle reinnervation (TMR), in which additional control sites are obtained by reinnervating the nerves that controlled the lost limb into other muscles (Kuiken, 2006).
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