Inspired by nature, research developed a new load-bearing material
From: University of Leeds
April 22, 2021 -- Engineers have
developed a material that mimics human cartilage – the body’s shock absorbing
and lubrication system, and it could herald the development of a new generation
of lightweight bearings.
Cartilage is a soft fibrous tissue found
around joints which provides protection from
the compressive loading generated by walking, running or lifting. It
also provides a protective, lubricating layer allowing
bones to pass over one another in a frictionless way.
For years, scientists have been trying
to create a synthetic material with the properties of cartilage. To date,
they have had mixed results.
But in a paper published in the
journal Applied
Polymer Materials, researchers at the University of Leeds and Imperial
College London have announced that they have created a material that
functions like cartilage.
The research team believes a
cartilage-like material would have a wide-range of uses across engineering.
Nature's cushion
Cartilage is
a bi-phasic porous material, meaning it exists
in solid and fluid phases. It switches to its fluid phase
by absorbing a viscous substance produced in the
joints called synovial fluid. This fluid not only lubricates the
joints but when held in the porous matrix of the cartilage,
it provides a hydroelastic cushion against compressive
forces.
Because the cartilage is porous, the
synovial fluid eventually drains away and as it does,
it helps dissipate the energy forces travelling
through the body, protecting joints from wear and tear and impact
injuries. At this point the cartilage returns to its sold phase,
ready for the cycle to be repeated.
Many potential applications'
Dr Siavash Soltanahmadi, Research
Fellow in the School of Mechanical Engineering at
Leeds, who led the research, said: “Scientists and engineers have been trying
for years to develop a material that has the amazing properties of
cartilage.
"We have now developed a
material for engineering applications that mimics some of the most important
properties found in cartilage, and it has only been possible because we have
found a way to mimic the way nature does it.
“There are many applications in
engineering for a synthetic material that is soft but can withstand heavy
loading with minimum wear and tear, such as in bearings. There
is potential across engineering for a material that behaves like
cartilage.”
Earlier attempts at developing a
synthetic cartilage system have focused on the use of hydrogels, materials
that absorb water. Hydrogels are good at reducing friction but perform poorly
when under compressive force.
One of the problems is that it takes
time for the hydrogel to return to its normal shape after it has been
compressed.
The researchers have overcome
this problem by creating a synthetic porous material made of a
hydrogel held in a matrix of polydimethylsiloxane or PDMS - a
silicone-based polymer. The matrix keeps the shape of the
hydrogel.
The hydrogel also provided a
lubricating layer.
In the paper, the scientists report
that the load-bearing behaviour of the hydrogel held in the
PDMS matrix was 14 to 19 times greater than the hydrogel on its
own. The equilibrium elastic modulus of the composite was 452 kPa at a
strain range of 10%-30%, close to the values reported for the modulus of
cartilage tested.
Water as an effective lubricant
The scientists believe future
applications of a new material based on the function of cartilage
could challenge many traditional oil-lubricated engineering systems.
Dr Michael Bryant, Associate Professor
in the School of Mechanical Engineering, who supervised the research,
said: “The ability to use water as an effective lubricant has many applications
from energy generation to medical devices. However this often
requires a different approach when compared to traditional
engineering systems which often use oil-based lubricants and hard-surface
coatings.
“This project has helped us to better
understand these requirements and develop new tools to address this
need.”
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