Page 199 - Handbook of Biomechatronics

196 Georgios A. Bertos and Evangelos G. Papadopoulos

based on their function in a prosthetic device, as materials that come into
contact with the human body such as sockets, materials employed as a cover
of the prostheses (esthetics, feel), and materials employed in the internal con-
struction of the prostheses, such as structural elements. The former are made
of biocompatible materials such as fiberglass, thermoplastics, (acrylics, poly-
ester fiber, Perlon), carbon fiber, and Kevlar (Prosthetic, Orthotic
Components & Orthopaedic Solutions Catalogue, 2013). For esthetic rea-
sons, a number of foams, such as hard expanded polyurethane foam, are
used. However, due to the exceptional strength-to-weight characteristics
and quality of superior bio-compatibility, a majority of today’s upper-limb
prostheses are made from composites with an underlying polymer matrix
(Bhuiyan et al., 2015). Still, materials for structural and active components
are made of titanium, aluminum, cobalt alloys, or stainless steel (Pandey
et al., 2016; Niinomi, 2002). The recent advances in 3D printing added
another parameter in the choice of materials, that is, whether they can be
applied by a 3D printer. New generations of reasonable cost 3D printers
can use composite materials such as carbon fiber, Kevlar, or glass fiber,
and therefore can be used in producing functional custom sockets at small
cost (Krausz et al., 2016).
When it comes to the design and construction of an active prosthesis that
can interact with the environment, then titanium is the best material, as it has
high strength, durability, and low density (56% that of steel’s), can withstand
high and low temperatures and resists corrosion. Therefore, for the same
strength, titanium is lighter than steel; however, it is more expensive. On
the other hand, aluminum and especially some of its alloys, is also light-
weight, is less expensive than titanium, it is easy to form and work with,
and is lightweight. Therefore, it can be used in light load and low cost appli-
cations. Stainless steel is strong material, of reasonable cost, but heavy. It can
be treated to have specific qualities, such as have a hardened surface, and can
be machined relatively easy. However, its high density restricts its use to spe-
cialized components of active prostheses, such as transmission axles and gears
(Bhuiyan et al., 2015).

1.5.2 Control
Upper-limb prostheses replace a missing upper limb of the human body,
such as a hand, or an arm. A prosthesis is called active when it includes joints,
motors, sensors, a power supply, and the like. From the control point of
view, active control of a limb requires two levels of control: (a) the high
level, which issues commands to the limb, and receives feedback