Could ultrasound frequencies kill coronavirus?

New simulations have shown that ultrasound waves at medical imaging frequencies have the potential to kill coronavirus by causing the virus’s shell and spikes to collapse and rupture.

A new study, carried out by researchers at MIT‘s Department of Mechanical Engineering, has suggested that coronaviruses may be vulnerable to ultrasound vibrations, within the frequencies used in medical diagnostic imaging. The team modelled the virus’s response to the mechanical vibration across a range of different ultrasound frequencies using computer simulations, finding that vibration between 25 and 100 megahertz causes the shell of the virus to collapse and rupture with in a fraction of a millisecond.

The researchers say this was observed in both air and water, and although the results are preliminary, the researchers say their findings are a first hint at a possible ultrasound-based treatment for coronaviruses, including the novel SARS-CoV-2 virus.

The study has been published in the Journal of the Mechanics and Physics of Solids.

Killing coronavirus with frequencies

Throughout the COVID-19 pandemic, Tomasz Wierzbicki, professor of applied mechanics at MIT and his team have been exploring solid and structural mechanics, and the study of how materials fracture under various stresses and strains, leading to the exploration of the fracture potential of the coronavirus that causes COVID-19.

To explore the matter, the team simulated the novel coronavirus and its mechanical response to vibrations using simple concepts of the mechanics and physics of solids to construct a geometrical and computational model of the virus’s structure.

With the geometry of the virus in mind, the team modelled the virus as a thin elastic shell covered in about 100 elastic spikes. As the virus’s exact physical properties are uncertain, the researchers simulated the behaviour of this simple structure across a range of elasticities for both the shell and the spikes.

“We don’t know the material properties of the spikes because they are so tiny – about 10 nanometres high,” Wierzbicki says. “Even more unknown is what is inside the virus, which is not empty but filled with RNA, which itself is surrounded by a protein capsid shell. So, this modelling requires a lot of assumptions. “We feel confident that this elastic model is a good starting point.”

To find out what might cause the virus to collapse, the researchers introduced acoustic vibrations into the simulations and observed how the vibrations rippled through the virus’s structure across a range of ultrasound frequencies. Starting with vibrations of 100 megahertz, or 100 million cycles per second, which the team estimated would be the shell’s natural vibrating frequency, the virus’s natural vibrations were initially undetectable. However, within a fraction of a millisecond the external vibrations, resonating with the frequency of the virus’s natural oscillations, caused the shell and spikes to buckle inward.

Low-frequency waves

As the amplitude was increased the shell would fracture –  an acoustic phenomenon known as resonance. At lower frequencies of 25 MHz and 50 MHz, the virus buckled and fractured even faster, both in simulated environments of air, and of water that is similar in density to fluids in the body.

“These frequencies and intensities are within the range that is safely used for medical imaging,” says Wierzbicki.

To validate their simulations, the team is working with microbiologists in Spain, using atomic force microscopy to observe the effects of ultrasound vibrations on a coronavirus found exclusively in pigs.

If ultrasound can be experimentally proven to damage coronaviruses, including SARS-CoV-2, and if this damage can be shown to have a therapeutic effect, the team envisions that ultrasound could be harnessed to treat and possibly prevent coronavirus infection.

How exactly ultrasound could be administered, and how effective it would be in damaging the virus within the complexity of the human body, are among the major questions scientists will have to tackle going forward.

“We’ve proven that under ultrasound excitation the coronavirus shell and spikes will vibrate, and the amplitude of that vibration will be very large, producing strains that could break certain parts of the virus, doing visible damage to the outer shell and possibly invisible damage to the RNA inside,” says Wierzbicki. “The hope is that our paper will initiate a discussion across various disciplines.”

The researchers also envision that miniature ultrasound transducers, fitted into phones and other portable devices, might be capable of shielding people from the virus.