Researchers develop underwater superhydrophobic surface with stable plastron

The Argyroneta aquatica, an underwater-dwelling spider with lungs adapted for atmospheric oxygen, survives by utilizing millions of water-repellent hairs to create a protective layer of air called a plastron. This ingenious adaptation has piqued the interest of material scientists for years, as it could potentially revolutionize underwater surface technology.

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences, the Wyss Institute for Biologically Inspired Engineering at Harvard, the Friedrich-Alexander-Universität Erlangen-Nürnberg in Germany, and Aalto University in Finland have made significant strides in this field. They’ve developed a superhydrophobic surface with a stable plastron that remains effective underwater for extended periods, even months.

This breakthrough has promising implications across various industries, from biomedicine to industrial applications. The surface’s ability to repel liquids, including blood, and deter the adhesion of marine organisms like barnacles and mussels, could have far-reaching benefits.

Joanna Aizenberg, a renowned figure in materials science and chemistry, emphasized the exciting potential of bioinspired materials. This research showcases how nature’s solutions can inspire the creation of novel materials with unprecedented properties.

A aerophilic surface made from a commonly used and inexpensive titanium alloy with a long-lasting plastron keeps dry during hundreds of dunks in a petri dish of blood. Credit: Alexander B. Tesler/Friedrich-Alexander-Universität Erlangen-Nürnberg

Researchers have been aware of the theoretical possibility of a stable underwater plastron for two decades but struggled to demonstrate it experimentally. The challenge with plastrons lies in their requirement for rough surfaces, akin to the hairs of the Argyroneta aquatica. However, this roughness also renders the surface mechanically unstable, sensitive to temperature, pressure changes, and minor defects.

Current methods for assessing artificial superhydrophobic surfaces only consider two parameters, which lack the depth needed to gauge plastron stability underwater. A team led by Joanna Aizenberg, Jaakko V. I. Timonen, Robin H. A. Ras from Aalto University, and Alexander B. Tesler, and Wolfgang H. Goldmann from FAU introduced a broader set of parameters, including surface roughness, the hydrophobicity of surface molecules, plastron coverage, contact angles, and more, combined with thermodynamic theory. This approach allowed them to predict the stability of the air plastron.

Utilizing this new method and a straightforward manufacturing process, they crafted an “aerophilic” surface from an affordable titanium alloy. This surface maintained a long-lasting plastron, keeping it dry for thousands of hours longer than previous attempts and surpassing even the plastrons found in living species.

To confirm plastron stability, the team subjected the surface to rigorous testing, including bending, twisting, exposure to hot and cold water, and abrasion with sand and steel. It endured 208 days submerged in water and resisted the growth of E. coli and barnacles while preventing mussels from adhering.

Stefan Kolle, a graduate student involved in the research, highlighted the value of this system’s stability, simplicity, and scalability, particularly in real-world applications. Biomedical applications could benefit, potentially reducing post-surgery infections or serving as biodegradable implants such as stents. Furthermore, underwater applications could use this technology to combat corrosion in pipelines and sensors. Future possibilities include combining this innovation with SLIPS (Slippery Liquid-Infused Porous Surfaces) for enhanced surface protection against contamination.

Source: Harvard John A. Paulson School of Engineering and Applied Sciences

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