Developed by engineers at RMIT University in Melbourne, Australia, the ‘double lattice’ design was inspired by the intricate skeleton of a deep-sea sponge known as Venus' flower basket, which lives in the Pacific Ocean.
Dr Jiaming Ma, lead author of a new RMIT study into the structure, said extensive testing and optimisation revealed the pattern's impressive combination of stiffness and strength, mixed with an ability to contract when compressed. This last aspect – known as auxetic behaviour – opens up a wide range of possibilities in structural engineering and other applications, the researchers said.
“While most materials get thinner when stretched or fatter when squashed… auxetics do the opposite,” Ma said. “Auxetics can absorb and distribute impact energy effectively, making them extremely useful.”
Natural auxetic materials include tendons and cat skin, while synthetic ones are used to make heart and vascular stents that expand and contract as required.
But while auxetic materials have useful properties, their low stiffness and limited energy absorption capacity limits their applications. The team’s nature-inspired double lattice design is significant, they said, because it overcomes these main drawbacks.
“Each lattice on its own has traditional deformation behaviour, but if you combine them – as nature does in the deep-sea sponge – then it regulates itself and holds its form, and outperforms similar materials by quite a significant margin,” Ma said.
The research found that the lattice is 13 times stiffer than existing auxetic materials based on ‘re-entrant honeycomb’ designs, using the same amount of materials. It can also absorb 10% more energy while maintaining its auxetic behaviour, with a 60% greater strain range compared with existing designs.
Dr Ngoc San Ha, who also worked on the project, said that the combination of properties opened up several exciting avenues for the new structure. “This bio-inspired auxetic lattice provides the most solid foundation yet for us to develop next-generation sustainable building,” he said.
“Our auxetic metamaterial with high stiffness and energy absorption could offer significant benefits across multiple sectors, from construction materials to protective equipment and sports gear or medical applications.”
The bio-inspired lattice structure could be built out of steel to act as a building frame, for example, using less steel and concrete to achieve similar results to conventional frames. It could also form the basis of lightweight sports protective equipment, bulletproof vests or medical implants, the team said.
RMIT honorary professor Mike Xie said the project highlighted the value in taking inspiration from nature. “Not only does biomimicry create beautiful and elegant designs like this one, but it also creates smart designs that have been optimised through millions of years of evolution that we can learn from,” he said.
The team at RMIT’s Centre for Innovative Structures and Materials tested the design using computer simulations and lab testing on a 3D-printed sample made from thermoplastic polyurethane.
They now plan to produce steel versions of the design to use with concrete and rammed earth structures, a construction technique using compacted natural raw materials.
“While this design could have promising applications in sports equipment, PPE and medical applications, our main focus is on the building and construction aspect,” Ma said.
“We’re developing a more sustainable building material by using our design’s unique combination of outstanding auxeticity, stiffness and energy absorption to reduce steel and cement usage in construction.
“Its auxetic and energy-absorbing features could also help dampen vibrations during earthquakes.”
The team plans to integrate the design with machine-learning algorithms for further optimisation and to create programmable materials.
The work was published in Composite Structures.
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