Scientists Are Defying Physics to Mimic It For Longer-Lasting Hip Replacements

New materials designed by artificial intelligence promise to provide stronger hip replacements and improve how fractures heal.

A few years ago, Amir Zadpoor was searching for a peculiar new material. He needed one that would get thicker when stretched, yet also be stiff like bone.

It was quite an ask. Think about what happens when you pull an elastic band from both ends – as it elongates, the elastic gets ever thinner. Zadpoor, a professor of orthopaedics at the Leiden University Medical Center in the Netherlands, and his team needed something that would do the exact opposite. It would almost need to defy the laws of physics.

The problem they were facing were hips. Hip replacements are one of the most common orthopaedic procedures conducted around the world. The problem is that people with artificial hips take around two million steps per year, which subjects an implant to forces that gradually wear it down. After a decade or more of use, implants often need to be replaced.

Zadpoor and his colleagues hoped to solve this problem by putting two different materials that behave in opposite ways when stretched on either side of an implant's base – one that becomes thicker when compressed and the other that would thicken when stretched. This would help to cushion the femur when the joint was under pressure and ensure implant stay fixed snugly against the bone.

"That would reinforce the connection between the bone and the implant," says Zadpoor. All their research had suggested it would work. Only there was another catch – the few known materials that become thicker when stretched, called auxetic materials, tend to be soft and compliant. They are used in crash helmets and knee pads, for example.

"We were trying to find this holy grail of auxeticity and also a high stiffness to be able to carry the loads," says Zadpoor. "That becomes a formidable hunt."

"Machine learning may even make it possible to tailor individual bone implants to a patient's anatomy"

The team turned to artificial intelligence for help. Using an AI system trained to predict how different materials might behave, they were able to plug in the specific properties they desired. The machine came back with a design for something known as a "metamaterial" – materials that can be engineered to have bizarre properties by altering their microscopic structure.

Their work is just one example of how scientists are increasingly turning to AI to help them dream up materials that would have once been inconceivable. And it is proving to be particularly powerful for those trying to mimic the properties of biological tissues.

"With machine learning, you can make (the process) orders of magnitude faster and that allows you to explore thousands to millions of more structures to find what you need," says Zadpoor.

- Author; Sandrine Ceurstemont, BBC

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