Ultrasound has potential to damage coronaviruses, study finds

 The coronavirus’s structure is an all-too-familiar image, with its densely packed surface receptors resembling a thorny crown. These spike-like proteins latch onto healthy cells and trigger the invasion of viral RNA. While the virus’s geometry and infection strategy is usually understood, little is understood about its physical integrity.

A new study by researchers in MIT’s Department of engineering suggests that coronaviruses could also be susceptible to ultrasound vibrations, within the frequencies utilized in medical diagnostic imaging.

Through computer simulations, the team has modeled the virus’s mechanical response to vibrations across a variety of ultrasound frequencies. They found that vibrations between 25 and 100 megahertz triggered the virus’s shell and spikes to collapse and begin to rupture within a fraction of a millisecond. This effect was seen in simulations of the virus within the air and water.

The results are preliminary and supported limited data regarding the virus’s physical properties. Nevertheless, the researchers say their findings are the primary hint at a possible ultrasound-based treatment for coronaviruses, including the novel SARS-CoV-2 virus. How exactly ultrasound might be administered, and the way effective it might be in damaging the virus within the complexity of the physical body, are among the main questions scientists will need to tackle going forward.

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

The team’s results appear online within the Journal of the Mechanics and Physics of Solids. Wierzbicki’s co-authors are Wei Li, Yuming Liu, and Juner Zhu at MIT.

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A spiky shell

As the Covid-19 pandemic took hold around the world, Wierzbicki looked to contribute to the scientific understanding of the virus. His group’s focus is on solid and structural mechanics and therefore the study of how materials fracture under various stresses and strains. With this attitude, he wondered what might be learned about the virus’s fracture potential.

Wierzbicki’s team began to simulate the novel coronavirus and its mechanical response to vibrations. They used simple concepts of the mechanics and physics of solids to construct a geometrical and computational model of the virus’s structure, which they supported limited information within the scientific literature, like microscopic images of the virus’s shell and spikes.

From previous studies, scientists have planned out the overall structure of the coronavirus — a family of viruses that s HIV, influenza, and therefore the novel SARS-CoV-2 strain. This structure consists of a smooth shell of lipid proteins, and densely packed, spike-like receptors protruding from the shell.

With this geometry in mind, the team modeled the virus as a skinny elastic shell covered in about 100 elastic spikes. because the virus’s exact physical properties are uncertain, the researchers simulated the behavior of this easy structure across a variety of elasticities for both the shell and therefore the spikes.

“We don’t know the fabric properties of the spikes because they're so tiny — about 10 nanometers high,” Wierzbicki says. “Even more unknown is what’s inside the virus, which isn't empty but crammed with RNA, which itself is surrounded by a protein capsid shell. So this modeling requires tons of assumptions.”

“We feel confident that this elastic model may be a good start line,” Wierzbicki says. “The question is, what are the stresses and strains which will cause the virus to rupture?”

A corona’s collapse

To answer that question, the researchers introduced acoustic vibrations into the simulations and observed how the vibrations rippled through the virus’s structure across a variety of ultrasound frequencies.

The team started with vibrations of 100 megahertz, or 100 million cycles per second, which they estimated would be the shell’s natural vibrating frequency, supported what’s known of the virus’s physical properties.

When they exposed the virus to 100 MHz ultrasound excitations, the virus’s natural vibrations were initially undetectable. But within a fraction of a millisecond the external vibrations, resonating with the frequency of the virus’ natural oscillations, caused the shell and spikes to buckle inward, almost like a ball that dimples because it bounces off the bottom.

As the researchers increased the amplitude, or intensity, of the vibrations, the shell could fracture — a physical phenomenon referred to as a resonance that also explains how opera singers can crack a wineglass if they sing at just the proper pitch and volume. 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's similar in density to fluids within the body.

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

To refine and validate their simulations, the team is functioning with microbiologists in Spain, who are using atomic force microscopy to watch the consequences of ultrasound vibrations on a kind of coronavirus found exclusively in pigs. If ultrasound is often experimentally proven to wreck coronaviruses, including SARS-CoV-2, and if this damage is often shown to possess a therapeutic effect, the team envisions that ultrasound, which is already wont to hack kidney stones and to release drugs via liposomes, could be harnessed to treat and possibly prevent coronavirus infection. The researchers also envision that miniature ultrasound transducers, fitted into phones and other portable devices, could be capable of protecting people from the virus.

Wierzbicki stresses that there's far more research to be done to verify whether ultrasound is often an efficient treatment and prevention strategy against coronaviruses. As his team works to enhance the prevailing simulations with new experimental data, he plans to zero in on the precise mechanics of the novel, rapidly mutating the SARS-CoV-2 virus.

“We checked out the overall coronavirus family, and now are looking specifically at the morphology and geometry of Covid-19,” Wierzbicki says. “The potential is some things that would be great within the current critical situation.”

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