Fluid physicists studying coronavirus primarily focus on transmission, namely how it travels and thrives in various circumstances. However, its peplomers – commonly known as spikes – also play a role in how the coronavirus attacks and infects our cells. To help understand the impacts of its shape, Kanso et al. modeled the bulbous spikes of the coronavirus particle as three-bead triangles to calculate its diffusivity.

In previous work, the group used single, spherical beads to model 74 peplomers. When these single-bead spikes were replaced with three-bead triangles – which is much truer to their shape – the group found the rotational diffusivity of a coronavirus particle suspended in fluid decreased by 39%. Additionally, this diffusivity continued to decrease with increasing numbers of peplomers.

These results point to the important function of the virus particle’s intricate geometry.

“Coronavirus particles cannot move themselves. Instead, they rely on collisions by their surroundings to jiggle and jitter into place so that they can dock, like a spaceship to its space station, with their targets,” said author Mona Kanso.

The spikes, she said, slow this jitter down just enough to allow the virus to align with and attach to its target.

Combining electrostatics, polymer dynamics and fluid mechanics, the researchers constructed models of the coronavirus as rigid spheres with its peplomers at fixed positions relative to one another, and each bead in the triad as a point charge. In reality, however, the picture is much more complicated: The peplomers are flexible and may twist and rearrange, and the particle can be an ellipsoid rather than perfectly spherical. These complexities in coronavirus geometry are just some of the researchers’ considerations in their ongoing work.

Source: “Peplomer bulb shape and coronavirus rotational diffusivity,” by M. A. Kanso, V. Chaurasia, E. Fried, and A. J. Giacomin, Physics of Fluids (2021). The article can be accessed at https://doi.org/10.1063/5.0048626.

This paper is part of the Flow and the Virus Collection, learn more here.