RMIT University researchers have developed a new way to coat fragile surfaces, including living plant leaves, using high‑frequency sound waves to create a fine mist that can act like a plant sunscreen.
The approach tackles a long‑standing challenge in materials science: many promising coatings require high temperatures or harsh processing, making them unsuitable for delicate surfaces such as living tissue, soft plastics or emerging electronic materials.
Demonstrating the potential on living plants
To test how gentle the approach was, the researchers applied the coating to living plant leaves, treating only part of each leaf to allow direct comparison.
Lead author and PhD researcher Javad Khosravi Farsani said the coating acted as a UV shield while still allowing normal plant function.
"The coating absorbs harmful UV light while allowing visible light through," he said.
"That means the plant can continue photosynthesis while being protected from damage."
After the coating was removed, the leaves and plants continued growing normally for months, showing the process did not harm plant health.
The plant experiments were intended as a proof of concept, demonstrating the broader capability of the coating platform.
RMIT filed a provisional patent on this work earlier in the year.
In the study, the sound‑formed mist was made from a covalent organic framework, or COF, liquid that rapidly assembles into a solid, UV‑blocking layer as it is sprayed.
COFs belong to the same broader family of porous materials whose development and impact have been recognised by the Nobel Prize in Chemistry, highlighting their importance to modern materials science.
The work is among the first to show that highly ordered COF coatings can be both formed and applied in a single step, at room temperature, on almost any surface, including living tissue. Until now, achieving this level of material quality has typically required multiple processing steps or elevated temperatures, which has limited where and how such coatings could be used.
Why these materials have been hard to use
COFs belong to a broader family of porous materials that also include metal‑organic frameworks, or MOFs, which are valued for their ability to be precisely designed to absorb light, separate molecules or protect surfaces.
Distinguished Professor Leslie Yeo, from RMIT's School of Engineering and a senior author on the study, said this challenge had held back their practical use – until now.
"These materials have extraordinary properties, but you've typically had to choose between preserving their structure and protecting the surface you're applying them to," Yeo said.
"What this work shows is a way to avoid that trade‑off by forming and coating the material under very gentle conditions."
Coating without heat or damage
Conventional coating techniques often rely on ovens, aggressive solvents or specialised equipment, which can damage sensitive materials or restrict what can be coated.
Associate Professor Amgad Rezk from RMIT's School of Engineering said the new RMIT‑led approach removed those constraints by using sound waves to drive the coating process itself.
"By using sound waves, we're able to form and deposit the coating within minutes without heating or damaging the surface," he said.
"That's a major shift from conventional coating methods and it allows us to work with fragile materials, including living plant tissue."
How sound helps form a coating
Rather than manufacturing a coating first and then attaching it, the technique uses sound waves to do both at the same time.
High‑frequency vibrations break the liquid formulation into microscopic droplets. As the droplets travel through the air, the COF material rapidly assembles into an organised solid layer that settles evenly onto the surface below.
Associate Professor Joseph Richardson, a co‑corresponding author on the study, said the process works in open air at room temperature.
"Our method effectively combines manufacturing and coating into a single step," Richardson said.
"That simplicity is what makes it adaptable across different surfaces and applications."
Many emerging electronic components, sensors and membranes are highly sensitive to heat or chemicals but still require protective or functional surface layers to operate outside the lab.
"That opens up opportunities for industries working with sensitive materials that simply couldn't be processed this way before," Rezk said.
The research was conducted in collaboration with partners in Australia and Europe, including the Catalan Institute of Nanoscience and Nanotechnology (ICN2) in Spain.
The research paper, 'Ambient one‑step synthesis and direct coating of highly crystalline covalent organic frameworks on arbitrary surfaces', is published in Science Advances (DOI: 10.1126/sciadv.aee1769).
RMIT 'Plant sunscreen' media campaign images and b-roll footage (including slo-mo footage of the RMIT sound-wave nebuliser applying a fine mist coating to a plant leaf) available at: https://spaces.hightail.com/space/fqSVMxOL8a
