Comment on "Acoustic deformation for the extraction of mechanical properties of lipid vesicle populations".

In a recent paper, Silva et al. [Phys. Rev. E 99, 063002 (2019)10.1103/PhysRevE.99.063002] consider the deformation of vesicles in response to the acoustic radiation stresses of ultrasonic standing waves. An important part of the analysis concerns the quadrupole projection of the radial component of radiation stress on a spherical vesicle having a radius much smaller than the acoustic wavelength evaluated with a software-aided expansion approach. Here we note that their projection agrees with results previously found for compressible spheres in the corresponding limit [J. Acoust. Soc. Am. 69, 1499 (1981)10.1121/1.385785] provided an error in Eq. (B5) of Silva et al. is corrected.