Engineers at RMIT University have developed a 3D-printed titanium lattice material that floats in water while offering greater strength than stainless steel or high-density polyethylene, according to research published in Advanced Materials. The breakthrough addresses a long-standing limitation in materials science by combining extreme lightness with structural buoyancy, opening up new possibilities for marine infrastructure such as buoys, jetties, and floating sensors.
Overcoming the Metallic Sinking Problem
Although metallic lattices can achieve densities less than one-tenth that of water, their open and interconnected spaces traditionally allow fluid to enter and cause them to sink. According to Dr Jordan Noronha, lead researcher from RMIT’s Centre for Additive Manufacturing, the team solved this by filling only the hollow titanium struts with polyurethane foam. This design allows water to flow freely through the structure’s external openings while keeping the material buoyant, even after sustaining significant cracking, connection failures, or the fracture of an entire lattice layer.
Skeletal Density and Material Strength
To predict whether open structures will float, the RMIT research team developed a new measure called skeletal density. Traditional density calculations factor in all open space within a lattice, even though water occupies those voids and cancels out buoyancy. Skeletal density isolates only the parts of the structure that exclude water—specifically the titanium walls and sealed, foam-filled channels. According to Noronha, this gives engineers a clear design rule: if skeletal density is lower than the surrounding liquid, the structure floats.
Mechanical testing demonstrated that the 3D-printed titanium hybrid lattice is 70% stronger than the stainless steel and high-density polyethylene commonly used in marine applications at the same overall density. Furthermore, short-term corrosion testing in natural seawater from Melbourne’s Port Phillip Bay revealed that after two weeks of immersion, the lattice lost just 0.15% of its mass, with its strength declining by less than 1%.
Potential Applications and Future Testing
According to project leader Distinguished Professor Ma Qian, the research team successfully demonstrated the technology using a 3D-printed marine buoy. The unit remained stable in a turbulent seawater tank tilted up to 45 degrees without requiring a sealed casing, protective coating, or extra flotation devices. Next steps for the research group include scaling up the demonstration parts and evaluating long-term performance under realistic marine and deep-sea conditions.
Beyond marine infrastructure, the material’s tailorable architecture allows for alternative internal fillings. Researchers are currently exploring how modifying the framework could enable applications in energy absorption, thermal management, and vibration control across the aerospace, automotive, and coastal engineering sectors.
Did You Know? Tiny, sealed cells inside the polyurethane foam trap gas to prevent water from flooding the hollow struts, acting as a distributed barrier that maintains flotation after structural damage occurs.
Frequently Asked Questions
How does the 3D-printed titanium lattice stay afloat?
The hollow titanium struts are filled with polyurethane foam containing tiny, sealed cells that trap gas. This prevents water from flooding the struts, allowing the structure to remain buoyant even when water flows through its open external spaces.
How strong is the material compared to traditional marine options?
According to RMIT University testing, the titanium hybrid lattice is 70% stronger than the stainless steel and high-density polyethylene typically used for jetties and buoys, when compared at the same overall density.
What caused the lattice to finally sink during testing?
The structure only sank after being severely crushed and compacted, maintaining its flotation despite cracking, connection point failures, and the fracture of an entire lattice layer.
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