Bionic knee v2.0

I am writing this blog entry on my sofa as I recover from my second knee surgery in three years. So… How did I end up here? If you read one of my previous entries on anaesthetics, you may recall that I had knee surgery in 2015 for torn cartilage. In the original surgery the cartilage was stitched back together with kevlar thread, so why did I have to go under the knife yet again? Although kevlar is widely slated as one of the toughest materials on the planet, it was no match for my body!

What is kevlar?

Kevlar was developed in the labs at DuPont – an American company responsible for developing many synthetic polymers including nylon, teflon, and (you guessed it!) kevlar. A polymer is a material made with one or more repeating units. In the case of kevlar, the repeating units are two molecules called 1,4-dianiline and terephthaloyl chloride, which for simplicity I will call A and B, respectively (shown below).

ABstructures

When the A and B units react together they make a long chain linked by amide bonds (highlighted in red below) in an ABAB pattern.

kevlar These long chains can be weaved together into a fibre which can be used as thread, and this thread was used to stitch together my torn cartilage last time. Amide bonds are normally very stable, but the body has special biological machines called enzymes which are specifically designed to break and made many types of bonds, including amides!

It took two years for my body to break down all the amide bonds in the kevlar stitches from last time, and unfortunately my cartilage didn’t manage to heal itself within that time. Let’s hope that after giving it another go my knee can return to full health…!

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About ChemistDan

A second year PhD student based in Sheffield researching the reasons behind the molecular blinking phenomenon that allowed for the development of super-resolution optical microscopy.
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