Scientists have developed a way to use sound waves to create microscopic layers of protection, demonstrating the method’s delicate handling on the leaves of the common houseplant Epipremnum aureum by blocking damaging ultraviolet (UV) rays without impeding photosynthesis.
Researchers from Melbourne’s RMIT University tested their work on the plants, proving just how gentle yet functional this coating is. Yet the technology is aimed squarely at other materials – including textiles, plastics, glass, and silicon.
“The coating absorbs harmful UV light while allowing visible light through,” says Javad Khosravi Farsani, lead author and PhD researcher at RMIT University. “That means the plant can continue photosynthesis while being protected from damage.”
The process works by using high-frequency sound waves to destabilize liquid transferred to the leaves in the form of a fine mist, with the “micrometer-sized aerosol droplets” creating a covalent organic framework (COF) that acts as a consistent but ultra-fine layer of protection.
RMIT University
“As proof of concept, we demonstrate that COFs can constitute protective coatings on plant leaves for solar ultraviolet shielding, thus highlighting the potential of the platform to extend the deployment of COFs in real-world devices, biological systems, and environmental interfaces,” the scientists describe in the paper.
COFs are a class of highly porous crystalline materials often described as molecular scaffolding, a latticed structure with nanoscale holes that can be engineered to absorb light, trap chemicals, or protect surfaces.
But the building blocks that form COFs are notoriously “fussy” with their self-assembly, which has been hard to master in the laboratory and even more difficult to apply beyond it. As such, COFs have largely remained lab materials, requiring precursor materials, extreme heat, and lengthy processing that would do more harm than good to delicate surfaces in the real world.
“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,” says Distinguished Professor Leslie Yeo, from RMIT’s School of Engineering and a senior author on the study. “What this work shows is a way to avoid that trade‑off by forming and coating the material under very gentle conditions.”
The researchers used acoustomicrofluidics – ultra-high-frequency sound vibrations – to manipulate liquids, using a tiny chip that generates 10-MHz waves.
Essentially, when a precursor liquid flows onto the vibrating chip, sound waves stretch the liquid, blasting its structure into the fine mist. As the aerosol travels through the air, the droplets organize themselves into protective layers on the surfaces of materials, even those as delicate as tissue.
“Our method effectively combines manufacturing and coating into a single step,” says Associate Professor Joseph Richardson, a co‑corresponding author, who adds that the process is even simpler because it doesn’t need heat or lab controls; it works in open air at room temperature. “That simplicity is what makes it adaptable across different surfaces and applications.”
Associate Professor Amgad Rezk, from RMIT’s School of Engineering, adds that this method greatly increases the use of COFs in real-world scenarios – and, as such, the team filed for an Australian Provisional Patent Application at the end of February.
Will Wright/RMIT University
“By using sound waves, we’re able to form and deposit the coating within minutes without heating or damaging the surface,” Rezk says. “That’s a major shift from conventional coating methods, and it allows us to work with fragile materials, including living plant tissue.”
“That opens up opportunities for industries working with sensitive materials that simply couldn’t be processed this way before,” he adds.
While the team’s demonstration was on plant leaves – which retained no damage for a measured period (60 days), following application, UV exposure, and coating removal – there are plenty of questions about the technology’s staying power when exposed to the elements.
Still, finding a way to coat new electronics, sensors, and membranes, which are traditionally too heat-sensitive for current techniques but still need protection, could change how we see COFs. And the researchers have no concerns about scalability, which has been another limiting factor.
“Owing to its miniature, lightweight footprint, the chipscale acoustomicrofluidic platform can readily be mounted on a drone or autonomous vehicle to enable precision deposition on plant leaves, while the chip’s low costs, enabled by leveraging the economies of scale inherent in mass nanofabrication, offers a path toward massive parallelization for deployment in large-scale real-world biotechnology applications,” the scientists conclude in the paper.
The research was published in the journal Science Advances.
Source: RMIT
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