There's Now
an Artificial Cartilage Gel Strong Enough to Work in Knees
By David Nield, Science Alert
July 5, 2020 -- It's no surprise that
scientists have struggled to find an artificial substitute for natural knee
cartilage: it's an amazing biological substance that combines the properties of
a soft cushion and a tough barrier to keep our busy leg joints from harm.
But it looks like we've arrived at a
long-awaited breakthrough - researchers think they may have finally developed a
material that is a match to the cartilage found in our bodies, and could be
used as a replacement after injuries or in old age.
"We set out to make the first
hydrogel that has the mechanical properties of cartilage," says
chemist Ben Wiley from Duke University.
A significant number of people could
benefit from something like this, as more than 790,000 knee replacements happen
in the US every year. Currently those replacements -- which involve pretty
invasive surgery -- may only last for a couple of decades before they need to
be replaced again.
Imagine if you could replace just the
worn-out or damaged cartilage, instead of having to rip out the entire knee
joint.
As with other hydrogels, the main
ingredients in this new material are water-absorbing polymers: in this
case one polymer made of spaghetti-like strands, intertwined with another
polymer that's less flexible and more basket-like. A third polymer, made of
cellulose fibres, acts as a mesh holding everything together.
When the material is stretched, it's the
third polymer that keeps the gel intact. When it's squeezed, polymers one and
two – with negative charges running along their length – repel each other and
stick to water, so the original shape can be restored.
The hydrogel passed with top marks in
both these crucial categories – stretching and squishing – and showed better
performance than other existing hydrogels. In one test of 100,000 repeated
pulls, the artificial cartilage held up as well as the porous titanium material
used in bone implants.
"Only this combination of all three
components is both flexible and stiff and therefore strong," says
materials scientist Feichen Yang, also from Duke University.
In tests where the hydrogel was rubbed
against natural cartilage – a million times, no less – it was shown to be just
as resistant to wear and tear as the real thing, and more durable than the
artificial cartilage that's used today in big toe operations (notable because
that gel has regulatory approval in the US).
However, getting this new hydrogel
approved for use in humans could take up to three years, the researchers say –
so there's some way to go yet before patients will be able to take advantage of
the innovation.
So far the non-toxicity of the hydrogel
has only been tested against lab-grown cells. The next step is to see if it can
be safely transplanted into sheep, and only after that can trials on actual
people get underway.
Eventually though, the new material
shows plenty of promise as an option for those experiencing knee pain: they
might one day be able to restore a joint to full working order, without long
recovery times or a short lifespan for the replacement cartilage. It should
help until we learn how to regrow our own cartilage, at least.
The research has been published in Advanced
Functional Materials
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