Sea sponge inspires RMIT engineers to develop new construction material with high compressive strength

The humble deep-sea sponge has inspired RMIT University engineers to develop a new material with remarkable compressive strength and stiffness that could potentially be used in the building and construction industry to improve architectural and product designs.

The double lattice design of the new material takes inspiration from the intricate skeleton of a deep-sea sponge known as Venus' flower basket, which lives in the Pacific Ocean.

Lead author of the study, Dr Jiaming Ma 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 characteristic – known as auxetic behaviour – opens up a whole range of possibilities to apply the design across structural engineering and other applications.

“While most materials get thinner when stretched or fatter when squashed, like rubber, auxetics do the opposite,” Ma says. “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. However, despite their useful properties, the low stiffness and limited energy absorption capacity of auxetic materials limit their applications. The RMIT team’s nature-inspired double lattice design is significant because it overcomes these shortcomings.

“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 says.

Results published in Composite Structures show with the same amount of material usage, the lattice is 13 times stiffer than existing auxetic materials, which are based on re-entrant honeycomb designs. It can also absorb 10% more energy while maintaining its auxetic behaviour with a 60% greater strain range compared to existing designs.

“This bioinspired auxetic lattice provides the most solid foundation yet for us to develop next generation sustainable building,” Dr Ngoc San Ha says. “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.”

As a steel building frame, for example, the bioinspired lattice structure would require less steel and concrete to be used to achieve similar results as a traditional frame. Lightweight sports protective equipment, bullet proof vests or medical implants are some of the other potential applications for the material.

Honorary Professor Mike Xie says 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,” Xie says.

Having tested the design using computer simulations and lab testing on a 3D printed sample made from thermoplastic polyurethane, the team at RMIT’s Centre for Innovative Structures and Materials now plan to produce steel versions of the design to use along with concrete and rammed earth structures.

“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 says. “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.

The material’s auxetic and energy-absorbing features could also help dampen vibrations during earthquakes, he says.

The team is also planning to integrate this design with machine learning algorithms for further optimisation and to create programmable materials.

‘Auxetic behaviour and energy absorption characteristics of a lattice structure inspired by deep-sea sponge’ is published in Composite Structures (DOI: 10.1016/j.compstruct.2024.118835)

Image: The team's double lattice structure (left) outperforms the standard re-entrant honeycomb design (right). Credit: RMIT University