Faculty of
Engineering, Architecture and Information Technology

19 February 2019

Turning weaknesses into strengths

Sean Johnston is paving the way for new medical possibilities, through metal biocorrosion – a move that could revolutionise the way our bones heal.

Sean is a PhD student at UQ’s School of Mechanical and Mining Engineering and he’s been working to understand how magnesium alloys break down in the human body, and if this could be used to a medical advantage.

Well known for their high-strength to weight ratio, pound for pound magnesium alloys is significantly stronger than steel. However, they are also quite reactive, meaning it can corrode easily in many environments. But what if this weakness was really a strength in disguise? Sean says that is exactly what it is.

“I’ve always loved the idea of finding strength or opportunity in a perceived weakness. My little sister isn’t short, she’s fun-sized. My uncles not bald, he’s aerodynamic,” Sean said.

Sean says biodegradable metals such as magnesium could be the perfect candidate for temporary medical devices. He says magnesium alloys could potentially be used as medical implants replacing screws and plates.

“When something in the body breaks, it is common to use implants to help support that part of the body as it heals,” he said.

“What if we could make these implants out of safe, absorbable materials, which can slowly corrode into the body: getting weaker, as the body gets stronger?”

If implants were able to be safely absorbed by the body, it would eliminate the need for a second surgery. For this to work the corrosion would need to be slow, controlled, and predictable. Otherwise the implant could fail before the body has fully healed.

During his research journey, Sean has managed to better understand the influence of various organic materials and chemical ions on magnesium biocorrosion. He has also developed surface treatments, which can slow the corrosion rate by almost 50 per cent aiming to match body tissue healing rates. He identified ways to safely sterilise magnesium alloys, without harming their corrosion rates. This proved vital during a live animal trial where, in a global first, he compared the corrosion rates of samples implanted in male and female Sprague-Dawley rats.

During this trial, with the grateful help from UQ vets and imaging specialists, he has discovered that the samples implanted in females corrode more quickly than those implanted in the males, possibly due to the consumption of bodily magnesium stores during the females’ menstrual cycle.

“I plan to use this research to develop the next generation of absorbable medical implants made with magnesium components. Turning this material’s greatest weakness into its greatest strength,” he said.