New limbs could be built from scratch as scientists create 3D printed cartilage

Brand new limbs and organs could be built from scratch after scientists created cartilage… on a 3D printer.

The material mimics biological tissue – mirroring the humanised machines in sci-fi film I, Robot.

Creating synthetic replacements that match its properties and behaviours was once thought impossible.

But the precision of today’s 3D printers has made it attainable – and now a US team has finally achieved the dream.

They are the first to 3D print a complex, porous lattice structure using liquid crystal elastomers (LCEs) – creating devices similar to real cartilage and other tissues.

The soft, multi-functional materials are known for their elasticity and extraordinary ability to dissipate high energy.

Professor Chris Yakacki, a mechanical engineer at Colorado University in Denver, said: ‘Everyone’s heard of liquid crystals because you stare at them in your phone display.

‘And you’ve likely heard of liquid crystal polymers because that’s exactly what Kevlar is.

‘Our challenge was to get them into soft polymers, like elastomers, to use them as shock absorbers. That’s when you go down the layers of complexity.’

LCEs are tricky to manipulate. Until now, most researchers could create either large objects with minimal detail or high detail in practically microscopic structures.

But as with phone screens, big devices with high resolutions are where the future lies. The chemicals and printing process took the difficulty down to nearly zero.

Prof Yakacki and colleagues used a 3D printing process called DLP (digital light processing).

They developed a honey-like liquid crystal resin that, when hit with ultraviolet light, forms new bonds in a succession of thin photo-polymer layers.

The final cured resin forms a soft, strong and compliant elastomer. When printed in lattice structures – levels of patterning akin to a honeycomb – it began to mimic cartilage.

The group printed several structures including a tiny lotus flower and a prototype of a spinal fusion cage – creating the largest LCE device with the most detail.

The combination of the resin and printing process also led to up to 27 times greater strain-energy dissipation compared to those printed from a commercially available photo-curable elastomer resin.

Going forward, the structures have several applications, like shock-absorbing football helmet foam or even small biomedical implants for toes.

Prof Yakacki whose findings are reported in Advanced Materials is most excited about its possibilities in the spine.

He said: ‘The spine is full of challenges and it’s a hard problem to solve. People have tried making synthetic spinal tissue discs and they haven’t done a good job of it.

‘With 3D printing – and the high resolution we’ve gotten from it – you can match a person’s anatomy exactly.

‘One day we may be able to grow cells to fix the spine. But for now we can take a step forward with the next generation of materials. That’s where we’d like to go.’

Biological tissues have evolved over thousands of years to be perfectly optimised for their specific functions.

Cartilage, for instance, is compliant and elastic – making it key to running, jumping and resisting daily wear and tear.

It’s soft enough to cushion joints but strong enough to withstand compression and the substantial load bearing of our bodies.

Prof Yakacki began working with LCEs in 2012. Two years ago he received a grant to revolutionise their production as a shock absorber for football helmets.

He said even then, he knew its applications could go further. The manufacture of human organs is the Holy Grail of research. It could end donor shortages.

Replacement organs and tissue are expected to become a reality in the next two decades.

Bioprinting is an emerging science, involving building biological material in laboratories into functional tissue for implantation – just like the 3D printing of objects in plastic.

Last year Israeli scientists unveiled the first 3D-printed heart, made from human tissue. About the size of a cherry, it had blood vessels, ventricles and chambers.

At the University of Edinburgh, researchers have been working on a bioprinted liver since 2014.

Prof Yakacki was part funded by the U.S. Army Research Laboratory and U. S. Army Research Office.

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