Page 241 - Control Theory in Biomedical Engineering

222 Control theory in biomedical engineering

Peripheral nerve stimulation is the most common direct-neural stimula-
tion. This stimulation relies on the principle that, following upper limb
amputation, the original afferent neural pathways are proximally preserved
and can be exploited for interfacing with prostheses (Micera et al., 2010;
Dhillon and Horch, 2005; Ortiz-Catalan et al., 2014; Raspopovic and
Petrini, 2018). Direct-neural methods deliver feedback so that an amputee
senses the stimulus as though it were applied to the same corresponding loca-
tion of their missing limb (Schofield et al., 2014). This kind of modality-
matched feedback is the most natural and currently is gaining more attention
in the scientific community that is developing novel techniques to modulate
intraneural signals such as biomimetic techniques of frequency modulation
(Valle et al., 2018).
Another approach is by cortical control (Velliste et al., 2008), where cor-
tical electrical signal activity is acquired and processed in order to distinguish
desired human movements. These desires are then converted into control
signals for prosthetic movements as presented in Johannes et al. (2020).

4.6 Summary of wearable devices
There are some reviews of mechatronic WDs (Maciejasz et al., 2014; Jarrass
e
et al., 2014; Islam et al., 2017; and Gopura et al., 2016), but an update is
presented in Table 1, which shows an overview of WDs to describe their
classification in the sense of human-machine bidirectional communication
and somatosensory feedback.

5 Challenges

Regarding the aforementioned technologies, we address some important
challenges to achieve more naturally integrated mechatronic WDs for
amputees.
• Materials science: The need for including novel materials and intelligent
mechanical structures for sockets, liners, and prostheses is under consid-
eration because patient adherence with WDs depends on a natural inte-
gration of the machine and the human skin. This includes an anatomical
fit over the residual limb and the physiological behavior of materials in
contact with the skin (in a noninvasive approach). In addition, for an
invasive approach, the materials must be compatible with the internal tis-
sues, avoiding any rejection (biomaterials).