JEC COMPOSITES MAGAZINE - Issue #120 - April 2018 - 52

SOLUTlONS medical

Kevlar-based artificial cartilage
Last November, researchers at the University of Michigan and Jiangnan
University announced that they had developed an artificial cartilage made with
a Kevlar-based hydrogel. Nicholas Kotov, the Joseph B. and Florence V. Cejka
Professor of Engineering at University of Michigan, led the study.

T

he unparalleled liquid
strength of cartilage,
which is about 80% water,
withstands some of the toughest
forces on our bodies. Synthetic
materials could not match it -
until "Kevlartilage" was developed
by researchers at the University of
Michigan and Jiangnan University.
We know that our bodies consist
mostly of water - all life does - and
yet they have a lot of structural
stability. Understanding cartilage
is understanding how life forms
can combine properties that are
sometimes unthinkable together.
850,000 patients in the USA
Many people with joint injuries
would benefit from a good
replacement for cartilage, such as
the 850,000 patients in the USA
who undergo surgeries removing
or replacing cartilage in the knee.
While other varieties of synthetic
cartilage are already undergoing
clinical trials, these materials fall
into two camps that choose between cartilage attributes, unable
to achieve that unlikely combination of strength and water content.
The other synthetic materials that
mimic the physical properties of

52

cartilage do not contain enough
water to transport the nutrients
that cells need to thrive.
Meanwhile, hydrogels - which
incorporate water into a network
of long, flexible molecules - can
be designed with enough water to
support the growth of the chondrocyte cells that build up natural
cartilage. Yet those hydrogels are
not especially strong. They tear
under strains a fraction of what
cartilage can handle.
Kevlar-based hydrogel
The new Kevlar-based hydrogel
recreates the magic of cartilage
by combining a network of tough
nanofibres from Kevlar - the
"aramid" fibres best known for
making bulletproof vests - with
a material commonly used in
hydrogel cartilage replacements,
called polyvinyl alcohol, or PVA.
In natural cartilage, the network of
proteins and other biomolecules
gets its strength by resisting the
flow of water among its chambers.
The pressure from the water reconfigures the network, enabling
it to deform without breaking.
Water is released in the process,
and the network recovers by
absorbing water later.
This mechanism enables high-impact joints, such as knees, to stand
up to punishing forces. Running

jec composites magazine / N°120 April 2018

repeatedly pounds the cartilage
between the bones, forcing water
out and making the cartilage more
pliable as a result. Then, when the
runner rests, the cartilage absorbs
water so that it provides strong
resistance to compression again.
Aramid nanofibres
The synthetic cartilage boasts the
same mechanism, releasing water
under stress and later recovering
by absorbing water like a sponge.
The aramid nanofibres build the
framework of the material, while
the PVA traps water inside the net-

work when the material is exposed
to stretching or compression. Even
versions of the material that were
92% water were comparable in
strength to cartilage, with the 70%
version achieving the resilience of
rubber.
As the aramid nanofibres and PVA
do not harm adjacent cells, Kotov
anticipates that this synthetic
cartilage may be a suitable implant
for some situations, such as the
deeper parts of the knee. He also
wonders whether chondrocytes
might be able to take up residence
inside the synthetic network to

Kevlar based artificial cartilage mimics the magic of the real thing twist
Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #120 - April 2018
