Inspired by an aquatic spider, researchers have created a new surface material that remains dry for months underwater and is highly resistant to the adhesion of bacteria and marine life such as barnacles. They say the surface material is easy to produce, scalable and has broad practical applications.

What works in nature often works for humans as well. The problem is creating the required bioinspired materials using existing tools, which is sometimes easier said than done.

Now, researchers led by Harvard's John Paulson School of Engineering and Applied Sciences (SEAS) have done just that, developing a superhydrophobic metal surface inspired by an aquatic spider; that is, it repels water and can stay dry underwater for months.

Joanna Aizenberg, one of the study's co-authors, said: "Bio-inspired materials research is an extremely exciting field that continues to bring elegant solutions evolved in nature into the realm of man-made materials, allowing us to introduce new materials with unprecedented properties. This study exemplifies how uncovering these principles can lead to the development of surfaces that remain superhydrophobic underwater."

Argyroneta aquatica, also known as the diving bell spider, is the only spider known to live almost entirely underwater. Millions of rough, hydrophobic villi trap air around the body, creating a reservoir of oxygen and creating a barrier between the spider's lungs and the water. The thin layer of air trapped by the spider's hair is called the plastron.

Researchers have known for decades that it was theoretically possible to create a stable underwater chassis. In practice, however, creating a rough surface like a diving bell spider would make the surface less mechanically strong and susceptible to small changes in temperature and pressure. And in previous experiments, surfaces could only stay dry for a few hours.

Researchers know that wettability is very sensitive to surface properties at the molecular level and is strongly influenced by surface topography. So they created an aerophilic titanium surface—that is, a surface that attracts and expels air or gas bubbles—and used electrochemical oxidation to form an oxide layer while chemically dissolving the formed oxides to produce nanometer-scale roughness.

To test the surface's stability, the researchers subjected it to bending, twisting, hot and cold water sprays, and sand and steel abrasion, and found that it remained aerophilic. It was continuously soaked in water for more than 208 days (at the time of the study's publication, the surface was still soaked in water, showing no signs of degradation) and hundreds of times in a Petri dish filled with blood. The surface significantly reduces the growth of E. coli and barnacles and completely prevents mussels from attaching.

Alexander Tesler, first author of the study, said: "We used a characterization method proposed by theorists 20 years ago to show that our surface is stable, which means that not only did we create a new type of extremely repellent, extremely durable superhydrophobic surface, but we can do it again with different materials."

The researchers say the surface has multiple uses. It could be used in biomedical equipment to reduce postoperative infections or prevent corrosion of underwater pipes and sensors. It can also be used with another bioinspired material developed by the SEAS team more than 10 years ago, called synovial fluid-infused porous surface technology (SLIPS).

Stefan Kolle, co-author of the study, said: "The stability, simplicity and scalability of this system make it very valuable in real-world applications. With the characterization method presented here, we show a simple toolkit that allows you to optimize superhydrophobic surfaces for stability, which significantly changes your application space."

The research was published in the journal Nature Materials, and two videos produced by SEAS below show how the new surface repels water and blood.