JEC COMPOSITES MAGAZINE - Issue #119 - March 2018 - 71

medical SOLUTlONS

lmproving lives with carbon composites

Nathalie schMitz,
HexTow® Carbon Fiber,
Business Development
Manager for Europe
Hexcel

H

eavy, uncomfortable and
poorly engineered artificial
limbs, or prosthetics,
have long since been improved
upon with the introduction of
composite materials in three
principal areas. Composites, that
are mainly carbon fibre in the
most sophisticated designs, are
seen throughout the construction
of prosthetic devices in the socket,
pylon (the limb's load-bearing
frame) and even in the foot,
hand or fingers that complete the
artificial limb.
Enhanced mobility
in prosthetics
Weight reduction, reducing
the load on the user, improving
endurance and helping to
reduce discomfort caused by the
unbalanced loading of a heavier
replacement limb on the patient
are the key drivers for using
carbon fibre reinforcements with
parts offering up to 80% weight
savings over steel and 50%
savings over aluminium.
Other key factors are that
composites provide a very high

Having seen the images from the Paralympics at Rio 2016, we are all familiar with the use of carbon fibre in sporting prosthetics and wheelchairs, but
these are just two of the most visible areas where lightweight composites
have a hugely beneficial impact. Hexcel looks first at some of the more
established medical applications that use carbon fibre and discusses its
newer technologies.

specific stiffness. Typically, a
carbon fibre part would have
around twice the specific stiffness
(approximately 56 x 106 m2s-2 for
a carbon fibre part with fibres
running in two directions) of a
steel or aluminium part and, by
using more unidirectional fibres
or higher modulus fibres, this
difference can be increased up to
ten times.
Carbon fibre composites also
allow designers and engineers
almost complete freedom to
adjust shape, strength and
stiffness throughout the part by
adding fibres in certain sections
or varying the fibre orientations,
something that is not possible
with the isotropic structure of a
metal.
Carbon fibre springs are also
incorporated into leg prosthetics
as an efficient way to build in
effective energy return and a
more natural walking or running
action. The most common are
the curved blade shape springs
often used by sprinters and other
athletes, though leaf spring-type
carbon fibre feet are also being
used in devices for everyday use.
In most cases for prosthetics,

the carbon fibre is in the form of
stitched or woven fabrics used to
mould structural parts, often with
epoxy resins, or as pre-impregnated materials (in woven, unidirectional or multiaxial format) where
the fibres or fabrics are combined
by machine with the resin matrix
before being frozen to stop the
curing reaction. These "prepregs"
are then brought back to room
temperature by the customer
before being cut into shaped
plies, which are generally hand
positioned into moulds, before
curing under vacuum in ovens
or high-pressure autoclaves.
Filament winding, where the
carbon fibres are drawn through a
resin bath, wound around a rotating former and then cured with a
heat shrink tape consolidating the
laminate, is also used to produce
more cost-effective tubes for limb
components.
Radiolucent composites
Digging a little deeper uncovers
a hugely diverse range of less
obvious carbon fibre applications
in equipment for treatment
and diagnosis, sometimes even
beneath the skin of the patients
themselves.
N°119 March 2018

Commercially available carbon-fiber-reinforced polyetheretherketone
intramedullary plates. (Carbofix,
Herzeliya, Israel)

Our typical image of a surgical
instrument is the glint of polished
stainless steel, but the matt black
finish of carbon fibre is becoming
more common in some branches
of surgery. In orthopaedic
surgery, the radiolucent properties of carbon fibre composites
give these new instruments
almost complete transparency
under a fluoroscope (the real-

/ jec composites magazine

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Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #119 - March 2018
