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Wearable mechatronic devices for upper-limb amputees 207

research groups and companies worldwide (Maciejasz et al., 2014; Jarrass
e
et al., 2014; Castellini, 2020). Despite these efforts, WDs are not yet widely
used, as there are still many challenges to overcome (Armstrong et al., 2019;
Kristjansdottir et al., 2019). WD users would like a cost-friendly device that
is similar in shape and function to their lost limb; low-cost WDs are still very
limited (Biddiss and Chau, 2007). Another big challenge is that amputees do
not feel as though the WD is a part of their body due to the lack of bilateral
communication and sensory feedback between the device and the amputee
(Kuiken, 2006; Marasco et al., 2018).
In this chapter, we review wearable mechatronic devices for upper limb
amputees. First, we examine the human sensory feedback and physiology of
the skin, a topic we consider very important to improve bilateral commu-
nication between amputees and their WD. Second, we provide some pre-
liminary concepts about WDs and classify them in order to better understand
the existing types (see Fig. 1). Then, we delve deeper into prosthetic WDs
by describing body-powered and externally powered prosthetic WDs, put-
ting emphasis on myoelectric WDs. Finally, we explain the modalities of
sensory feedback prostheses as a way of integrating the bilateral communi-
cation between user and WD in a manner that significantly improves user
adherence.

2 Human sensory feedback and physiology of the
human skin
Every WD is in physical contact with the human skin, and communicates
different sensations to the human user through sensory feedback. This
human sensory feedback generally includes hearing, sight, taste, smell,
and sense of touch. Sense of touch is described by the term “haptics,” which
is the science that studies the sense of touch on human skin. Sense of touch
allows us to manipulate objects and perceive sensations around us, such as
textures, temperature, pain, and so on. In recent years, haptics has been used
in several applications such as telerobotics, virtual reality, video games, and
others for simulating physical experiences perceived by the other human
senses. Unlike the other human sensations, sense of touch is distributed
throughout the human skin, muscles, and tendons (Culbertson et al.,
2018). Hence, the human sensory feedback of the sense of touch is consid-
ered haptic feedback and divided into two modalities: tactile and kinesthetic
feedback, depending on the sensation experienced by the individual.