By Rowenna Hoskin | Science Editor
New research has revealed the way in which high-frequency sound waves can be used to create new materials, from smart nanoparticles and even to deliver drugs to the lungs for needle-free vaccinations. 
Sound waves themselves are not a new discovery; they have been part of science and medicine for decades – 1942 was the year that ultrasound was first used for clinical imaging.┬á
Researchers at RMIT University in Melbourne, Australia, have provided new evidence that high frequency sound waves could revolutionise the field of ultrasound-driven chemistry. 
Advanced Science published a new review which revealed the unusual effects of these sound waves on materials and cells, such as molecules that seem to spontaneously order themselves after being hit with the sonic equivalent of a truck. 
The scientists noted that this pioneering work could be used in many new areas of application. 
It can be used to deliver drugs to the lungs, for example in patented nebulisation technology which can deliver life-saving drugs and vaccines by inhalation, as opposed to injections. The nebuliser uses the high-frequency to excite the surface of the fluid or drug to create a fine mist which can deliver larger biological molecules to the lungs. 
Another area of application would be encapsulated drugs in special nano-coatings to protect them from deterioration. This would help to control their release over time and ensure they precisely target the right places in the body like tumours or infections. 
Scientists believe that this technology would also be a breakthrough in the sector of smart materials. The sustainable production of super-porous nanomaterials would be able to be stored, separated, released, and protected from almost anything. The conventional way to create metal-organic frameworks (MOFs) can take days and uses harsh solvents and intensive energy processes, the RMIT team has developed a clean technique using these soundwaves to create MOFs in minutes and can be easily scaled up for mass production. 
Lastly, researchers see these sound waves as being valuable in the nano-manufacturing of 2D materials as they would be cost-effective and produce a fast exfoliation of automatically-thin quantum dots and nanosheets. 
The 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. 
Yeo says that it is only now that they are beginning to understand the strange phenomenon that they often observe in the labs. He told:
ÔÇ£When we couple high-frequency sound waves into fluids, materials and cells, the effects are extraordinary,ÔÇØ
ÔÇ£WeÔÇÖve harnessed the power of these sound waves to develop innovative biomedical technologies and to synthesise advanced materials.
ÔÇ£But our discoveries have also changed our fundamental understanding of ultrasound-driven chemistry – and revealed how little we really know.
ÔÇ£Trying to explain the science of what we see and then applying that to solve practical problems is a big and exciting challenge.”
The research team generates high-frequency sound waves on a microchip to precisely manipulate fluids or materials. 
Ultrasound has been used at 10 kHz to 3 MHz – to drive chemical reactions for a long time. At such low frequencies, these chemical reactions are driven by the violent implosion of air bubbles.┬á
This process is known as cavitation, and results in high pressures and extremely high temperatures. 
If you turn these frequencies up, however; these reactions are entirely changed. 
When high frequency sound waves were transmitted into various materials and cells, the researchers saw behaviour that had never been observed with the lower-frequency ultrasound. 
ÔÇ£WeÔÇÖve seen self-ordering molecules that seem to orient themselves in the crystal along the direction of the sound waves,ÔÇØ Yeo says.┬á
ÔÇ£The sound wavelengths can be over 100,000 times larger than an individual molecule, so itÔÇÖs incredibly puzzling how something so tiny can be precisely manipulated with something so big.┬á
ÔÇ£ItÔÇÖs like driving a truck through a random scattering of Lego bricks, then finding those pieces stack nicely on top of each other – it shouldnÔÇÖt happen!ÔÇØ┬á
While low frequency cavitation often destroys molecules and cells, under high-frequency sound waves they remain mostly intact. 
This means that they are gentle enough to use in biomedical devices to manipulate biomolecules and cells without affecting their integrity. 
This new discovery will revolutionise many different areas of science and technology, be it vaccinations or smart materials. High-frequency sound waves have created a new horizon and many new outlets for research and innovation. 
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