The central problem the team set out to solve is deceptively simple. Metallic lattice structures, in which thin struts form an open, interconnected framework, can be extraordinarily light. Some have densities less than one-tenth that of water, which in theory should make them ideal candidates for flotation. In practice, however, those open spaces are their undoing. Water pours freely through the interconnected pores of an open-cell lattice, filling every void until the structure loses whatever buoyancy its low density promised. According to lead researcher Dr Jordan Noronha of RMIT’s Centre for Additive Manufacturing, this fundamental flaw has made strong, lightweight metallic lattices unsuitable for marine applications, until now.

The RMIT team’s solution lies in a selective filling strategy. Rather than sealing the entire lattice or coating it in a waterproof shell, the engineers filled only the hollow titanium struts themselves with polyurethane foam, leaving the external openings of the structure unobstructed. The result is a hybrid material that allows seawater to flow through its open architecture while the sealed, foam-filled channels inside the struts retain their buoyancy. Crucially, the researchers validated this sustained flotation with samples that floated in freshwater for more than two months, demonstrating that the effect is not a fleeting laboratory curiosity but a durable property of the material itself.

Underpinning the achievement is a conceptual innovation in how engineers calculate whether an open structure will float. Conventional density measurements include all the open space within a lattice, even though water can occupy that space and it therefore contributes nothing to buoyancy. The RMIT team developed a new measure, which they call skeletal density, that considers only the parts of the structure that actually exclude water: the solid titanium walls and the sealed, foam-filled channels within the struts. This reframing yields an elegantly simple design rule. As Noronha explained, if the skeletal density of a structure is lower than that of the surrounding liquid, the structure will float, even when water flows freely through all of its external openings.

The mechanical performance of the new material is equally striking. When compared at the same overall density, the titanium hybrid lattice proved 70 percent stronger than the stainless steel or high-density polyethylene that is widely used in marine construction today. That comparison matters, because the plastics and steels currently deployed in jetties, buoys and floating sensor platforms represent the benchmark that any new material must beat, not merely match. A lattice that combines the corrosion resistance of titanium with strength well beyond these incumbent materials, while also floating, occupies a genuinely new position in the design space of marine engineering.

Corrosion, the perennial enemy of anything placed in the ocean, was addressed in short-term testing using natural seawater drawn from Melbourne’s Port Phillip Bay. After two weeks of immersion, the lattice lost only 0.15 percent of its mass, and its strength declined by less than 1 percent. While the researchers themselves describe this as short-term testing and point to long-term performance under realistic marine and deep-sea conditions as a next step, the early results suggest that the titanium framework can withstand the chemically aggressive environment that degrades so many conventional marine materials.

Perhaps the most remarkable property of the hybrid lattice is its resilience under damage. The structure remained buoyant even after significant cracking, failure at key connection points and the fracture of an entire lattice layer. It sank only after being severely crushed and compacted. The secret lies in the microstructure of the polyurethane foam: tiny, sealed cells within the foam trap gas and prevent water from flooding the hollow struts. In this way the foam acts as a distributed barrier against flooding, unlike conventional hollow marine structures, which can rapidly fill with water and lose flotation the moment their walls are breached. For safety-critical applications such as floating platforms and navigation buoys, this damage tolerance could prove decisive.

The team moved beyond laboratory coupons to demonstrate the technology at a functional scale with a 3D-printed marine buoy. Placed in a turbulent seawater tank that was rotated up to 45 degrees, the buoy remained stable without needing a sealed casing, a protective coating or any additional flotation aid. That the device survived these conditions with no supplementary buoyancy measures underscores the practicality of the skeletal-density approach: the flotation is intrinsic to the material’s architecture rather than bolted on as an afterthought.

Project leader Distinguished Professor Ma Qian said the next steps include scaling up the demonstration parts and testing long-term performance under realistic marine and deep-sea conditions. He also emphasised that the structure is highly tailorable, and the group is open to exploring applications well beyond marine infrastructure. By changing the material inside the titanium framework, he noted, a similar structure could be tailored for energy absorption, thermal management, vibration control and other uses. This versatility reflects a broader trend in metamaterials research, where the geometry of a structure, rather than its composition alone, dictates properties that no conventional solid material can offer.

The research was led by RMIT’s Centre for Additive Manufacturing in collaboration with the Conservatoire National des Arts et Métiers in France, with support from the Australian Research Council and RMIT’s School of Engineering. The study, titled Breaking the surface: buoyant metal–polymer open–cell hybrid lattice metamaterials, was published in Advanced Materials on 28 August 2026. For a field in which the ocean has always demanded a trade-off between strength and weight, the arrival of a titanium structure that floats, survives damage and shrugs off seawater marks a genuinely new chapter, one that engineers of jetties, buoys and deep-sea systems will be watching closely.

Subject of Research: Buoyant metal–polymer hybrid lattice metamaterials for marine infrastructure

Article Title: Engineers create world-first floating titanium

Article References: Engineers create world-first floating titanium. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: titanium lattice, metamaterial, 3D printing, buoyancy, marine infrastructure, polyurethane foam, skeletal density, corrosion resistance, RMIT University, Advanced Materials, additive manufacturing, floating structures

The secret of superhydrophobicity lies in a partnership between chemistry and geometry. A surface made of low-surface-energy material, such as a silicone or fluorinated compound, naturally resists wetting. But chemistry alone cannot push a flat surface past the superhydrophobic threshold. Roughness is the second ingredient, and it must exist on multiple length scales, with microstructures decorated by even smaller nanostructures. When water meets such a hierarchically rough, low-energy surface, it cannot penetrate the valleys between the peaks. Instead it rests on the tips, with air trapped underneath, a configuration known as the Cassie-Baxter state. The alternative, in which water fully saturates the roughness, is the Wenzel state, and the difference between the two is everything. A droplet in the Cassie-Baxter state rolls off easily; a droplet in the Wenzel state can become pinned so firmly that it behaves more like glue than liquid.

What makes foams special, the authors argue, is that the roughness is not confined to a skin. An open-cell foam is a continuous skeleton of polymer struts surrounding a labyrinth of connected pores, giving the material an enormous internal surface area relative to its weight. That architecture delivers properties a flat film never could: mechanical toughness, compressibility, rapid uptake of liquids into the pore network, and the ability to be squeezed dry and reused again and again. The physics of that uptake is governed by capillary action, described classically by the Lucas-Washburn equation, which relates how fast a wetting liquid penetrates a pore to the pore radius and the liquid’s surface tension. The review emphasizes that connected pores, capillary-driven infiltration and even deliberate wettability gradients inside the foam determine how efficiently oil can be absorbed, a point of direct consequence for the field’s flagship application.

That application is oil spill cleanup. When a foam is both superhydrophobic and superoleophilic, it drinks oil and refuses water, making it a selective sponge for petroleum slicks. Polyurethane foam, cheap, elastic and commercially ubiquitous, has been the workhorse substrate. Researchers have modified it with silica nanoparticles, polysiloxane-modified clay nanotubes, zinc oxide microrods wrapped in carbon cloth, silanized nanoclay and magnetite particles that let a magnetic field steer the saturated sponge. More recent work has added photothermal coatings, layers that convert sunlight into heat, so that viscous crude oil, which barely flows at ambient temperature, warms up and wicks into the foam faster. One 2025 study described a fire-extinguishing polyurethane foam for solar-assisted recovery of viscous crude oil, combining absorption with an intrinsic safety feature.

Polyurethane is only the beginning of the materials list the review assembles. Polystyrene foams, including those made by high internal phase emulsion templating, a technique that produces well-defined, highly connected pore structures, have been engineered with carbon black or graphene for photothermal oil capture and continuous separation of even emulsified oil-water mixtures. Polypropylene and polyethylene foams, often fabricated by supercritical carbon dioxide foaming, a solventless process in which pressurized gas expands the polymer into a microcellular structure, have shown robust superhydrophobicity, self-cleaning behavior, anti-icing performance and selective oil absorption. Ethylene propylene diene monomer rubber, polyethylene terephthalate and even biodegradable polylactic acid have all been converted into water-repellent sponges, the latter sometimes by a simple skin-peeling method that exposes a naturally rough interior.

A quieter revolution in the field concerns where the chemistry comes from. Fluoroalkyl silanes and other fluorinated modifiers are superb at lowering surface energy, but their toxicity and environmental persistence are increasingly unacceptable. The review highlights a shift toward fluorine-free systems: silicone-based chemistries, hydrophobic silica, stearic acid, and, strikingly, lignin, the aromatic polymer that woody plants use to waterproof their own cell walls. Lignin-based polyurethane foams, lignin nanosphere coatings and biomass-derived porous carbon combined with carbon nanotubes in melamine foam all demonstrate that nature’s own hydrophobic building blocks can do the job. Bioinspired design runs through the whole field, from lotus-leaf mimicry to a 2025 foam modeled on dragonfly wings, and even to self-healing surfaces that repair mechanical damage the way living tissue does.

The applications extend well beyond mopping up oil. Because water cannot adhere to these surfaces, they resist icing, and superhydrophobic polyethylene and polyurethane foams have been demonstrated for anti-icing and photothermal deicing, melting frost off their own surfaces using embedded light-absorbing fillers such as graphene or carbon nanotubes. The trapped air and low density of polymer foams make them excellent thermal insulators, and some formulations add flame retardants, producing foams that repel water and resist fire simultaneously, in one case with a built-in fire alarm response. Conductive fillers such as carbon nanotubes, MXene nanosheets and graphene turn the foams into pressure sensors and electromagnetic interference shields, so the same sponge that cleans an oil slick might also monitor compression or block radio-frequency noise in damp environments.

Yet the review is candid about why these materials are not already everywhere. Coatings of nanoparticles bonded weakly to a foam surface wear away under abrasion, and once the delicate micro-nano texture is destroyed, the Cassie-Baxter state collapses and the foam wets permanently. Fluorinated chemistry raises regulatory and toxicological concerns. Most laboratory syntheses involve dip-coating, chemical vapor deposition, sol-gel processing, electrospinning or freeze-drying, none of which scale gracefully or cheaply to industrial volumes, and the authors point to persistent discrepancies between laboratory results and real-world performance. Durability, scalability and cost form a triangle of constraints that the field has not yet fully escaped, a theme echoed in broader assessments of superhydrophobic surface commercialization.

The path forward, the authors suggest, lies in fluorine-free chemistries, self-repairing structures borrowed from biology, and fabrication processes that are scalable at reasonable cost. Some of those pieces already exist in prototype form: mechanochemically durable self-healing coatings, water-based nonfluorinated dispersions for large-area application, extrusion plus supercritical foaming routes that use commodity processing equipment, and even three-dimensional printable self-foaming silicone inks that produce bulk superhydrophobic objects rather than fragile surfaces. If durability and manufacturing can be solved together, superhydrophobic foams could move from demonstration papers to deployed products, cleaning spills, shedding ice, insulating buildings and sensing pressure, all while refusing, like the lotus leaf, to let water stick.

Subject of Research: Superhydrophobic polymeric foams: wetting theory, fabrication methods and applications in oil-water separation and multifunctional materials

Article Title: Superhydrophobic polymeric foam: A review

Article References: Patel, P., Pichare, P., & More, A. P. (2026). Superhydrophobic polymeric foam: A review. Polymer Bulletin, 83(12), Article 663. https://doi.org/10.1007/s00289-026-06713-x

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06713-x

Keywords: superhydrophobic foams, Cassie-Baxter state, Wenzel state, oil spill cleanup, polyurethane foam, supercritical CO2 foaming, lignin, fluorine-free coatings, photothermal conversion, anti-icing, electromagnetic shielding, self-healing surfaces