Researchers at RMIT University have developed a 3D-printed titanium material that can float in water while remaining strong even after substantial structural damage. The metal-polymer lattice could provide a new material option for marine infrastructure such as buoys, jetties, and floating sensors.
Metallic lattices can have extremely low densities, but their interconnected openings allow water to enter, making them unsuitable for flotation. The RMIT team addressed this problem by creating hollow titanium struts and filling only their internal channels with polyurethane foam. Water can flow freely through the lattice’s external openings, while sealed cells in the foam trap gas and prevent the hollow struts from flooding. Samples remained afloat in freshwater for more than two months.
The researchers also introduced a measure called skeletal density to predict whether an open structure will float. Unlike conventional density calculations, skeletal density considers only the material that excludes water, including the titanium walls and sealed foam-filled channels. If this density remains below that of the surrounding liquid, the structure can stay buoyant even when water passes through its open spaces.
Mechanical testing showed that the titanium lattice was 70% stronger than stainless steel or high-density polyethylene at the same overall density. After two weeks in natural seawater from Melbourne’s Port Phillip Bay, it lost just 0.15% of its mass, while its strength decreased by less than 1%. The structure also continued floating after cracking, connection failures, and the fracture of an entire lattice layer.
A prototype 3D-printed buoy remained stable in turbulent seawater testing without a sealed casing, protective coating, or additional flotation. Researchers now plan to scale up the technology and evaluate its long-term performance in realistic marine and deep-sea environments. By changing materials within the titanium framework, the same approach could also support energy absorption, thermal management, and vibration control applications.
