The study shows how high-frequency sound waves could revolutionize ultrasound-driven chemistry

Reviewed by Emily Henderson, B.Sc.November 25, 2020

Researchers have revealed how high-frequency sound waves can be used to build new materials, make smart nanoparticles, and even deliver medications to the lungs for painless, needle-free vaccinations.

While sound waves have been a part of science and medicine for decades – ultrasound was first used for clinical imaging in 1942 and to drive chemical reactions in the 1980s – technologies have always relied on low frequencies. .

Now researchers at RMIT University in Melbourne, Australia, have shown how high-frequency sound waves could revolutionize the field of ultrasound-guided chemistry.

A new review published in Advanced science reveals the bizarre effects of these sound waves on materials and cells, such as molecules that seem to spontaneously order themselves after being hit by the sonic equivalent of a semi-trailer.

The researchers also describe various interesting applications of their pioneering work, including:

• Lung Drug Delivery: Patented nebulization technology that could deliver life-saving drugs and vaccines by inhalation, rather than by injection
• Drug-protecting nanoparticles: Encapsulate drugs in special nano-coatings to protect them from deterioration, control release over time, and ensure they target precisely the right places on the body such as tumors or infections
• Innovative Smart Materials: Sustainable production of super porous nanomaterials that can be used to store, separate, release and protect almost anything
• 2D nanoproduction materials: precise, economical and rapid exfoliation of thin quantum dots and atomically thin nanosheets

Lead researcher Distinguished Professor Leslie Yeo and his team have spent over a decade researching the interaction of sound waves at frequencies above 10 MHz with different materials.

But Yeo says they are only now beginning to understand the range of strange phenomena they often observe in the laboratory.

When we couple high-frequency sound waves into fluids, materials and cells, the effects are extraordinary. “

Leslie Yeo, study lead researcher, distinguished professor, RMIT University

“We harnessed the power of these sound waves to develop innovative biomedical technologies and synthesize advanced materials.

“But our findings also changed our fundamental understanding of ultrasound-guided chemistry and revealed how little we really know.

“Trying to explain the science of what we see and then apply it to solve practical problems is a great and exciting challenge.”

Sonic waves: how to enhance chemistry with sound

The RMIT research team, which includes Dr Amgad Rezk, Dr Heba Ahmed and Dr Shwathy Ramesan, generates high frequency sound waves on a microchip to precisely manipulate fluids or materials.

Ultrasound has long been used at low frequencies – from about 10 kHz to 3 MHz – to drive chemical reactions, a field known as “sonochemistry”.

At these low frequencies, sonochemical reactions are driven by the violent implosion of air bubbles.

This process, known as cavitation, results in enormous pressures and extremely high temperatures, like a tiny and extremely localized pressure cooker.

But it turns out that if you increase the frequency, these reactions change completely.

When high-frequency sound waves were transmitted into various materials and cells, the researchers saw behavior that had never been observed with low-frequency ultrasound.

“We have seen self-ordering molecules that appear to orient themselves in the crystal along the direction of the sound waves,” says Yeo.

“The wavelengths of sound involved can be over 100,000 times larger than a single molecule, so it’s incredibly baffling how something so small can be manipulated with precision into something so large.

“It’s like driving a truck through a random scatter of Lego bricks, then finding those pieces stacked on top of each other – it shouldn’t be!”

Biomedical Advances

While low-frequency cavitation can often destroy molecules and cells, they remain mostly intact under high-frequency sound waves.

This makes them delicate enough to be used in biomedical devices to manipulate biomolecules and cells without compromising their integrity, the basis for the various drug delivery technologies patented by the RMIT research team.

One such patented device is an inexpensive, lightweight, portable advanced nebulizer that can accurately deliver large molecules such as DNA and antibodies, unlike existing nebulizers.

This opens up the potential for painless, needle-free vaccinations and treatments.

The nebulizer uses high-frequency sound waves to excite the surface of the fluid or drug, generating a fine mist that can deliver larger biological molecules directly to the lungs.

Nebulizer technology can also be used to encapsulate a drug in protective polymer nanoparticles, in a one-step process that combines nano production and drug delivery.

Furthermore, the researchers showed that irradiating cells with high-frequency sound waves allows therapeutic molecules to be inserted into cells without damage, a technique that can be used in emerging cell therapies.

Smart materials

The team used sound waves to drive crystallization for the sustainable production of metal-organic structures or MOFs.

Intended to be the defining material of the 21st century, MOFs are ideal for detecting and trapping substances in minimal concentrations, for purifying water or air, and can also hold large amounts of energy, for making batteries and storage devices of better energy.

While the conventional process for creating an MOF can take hours or days and requires the use of aggressive solvents or energy intensive processes, the RMIT team has developed a clean, sound wave-driven technique that can produce a custom MOF in minutes. and can be easily expanded for efficient mass production.

Sound waves can also be used for nano-manufacturing 2D materials, which are used in a myriad of applications, from flexible electrical circuits to solar cells.

Climb and overcome borders

The next steps for the RMIT team focus on expanding the technology.

At a low cost of just $ 0.70 per device, the sound wave-generating microchips can be produced using standard processes for mass-manufacturing silicon computer chips.

“This opens up the possibility of producing industrial quantities of materials with these sound waves through massive parallelization, using thousands of our chips simultaneously,” said Yeo.

The team from the Micro / Nanophysics Research Laboratory, at RMIT’s School of Engineering, is one of the few research groups in the world that brings together high-frequency sound waves, microfluidics and materials.

Yeo says the research challenges long-standing theories of physics, opening a new field of “high-frequency excitation” in parallel with sonochemistry.

“The classical theories established since the mid-1800s don’t always explain the strange and sometimes contradictory behavior we see – we’re pushing the boundaries of our understanding.”