You're right that shear-wave speed is mainly relevant in solids, where the material has shear rigidity. Most biological cells — like CTC (Circulating Tumor Cells) including MCF-7 and human blood cells — behave more like soft viscoelastic bodies (closer to fluids than rigid solids), so their shear-wave speed is extremely low, often near zero.

However, in some advanced elastography methods (like acoustic or optical tweezers, Brillouin microscopy), researchers still try to estimate an "effective" shear modulus for cells to approximate a shear-wave speed.

Typical Observations:

• Shear-wave speed in soft biological cells: ~1–10 mm/s (very low)
• MCF-7 cells: ~
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I don't even know how the shear-wave speed of human blood cells is actually measured in real-life clinical settings, or how accurate those measurements are. Would this value be consistent across different individuals? What confounding factors might cause variations in this value, such as high cholesterol, high blood pressure, diabetes, or other diseases? What is the true benefit of knowing these values? And if it were indeed measurable, how significant would the difference be between normal cells and cancer cells in these values? Would it be accurate enough to be used for diagnostic purposes, especially given that current diagnostic methods are significantly more reliable than these potential measurements?

The shear-wave speed in biological cells such as MCF-7 (a breast cancer cell line commonly used as a model for circulating tumor cells) and human blood cells largely depends on their viscoelastic nature. These cells are not solid in the classical sense like tissues; instead, they behave more like soft, deformable materials with both elastic and viscous components. As a result, they do not propagate shear waves in the traditional manner, but it is still possible to estimate their shear-wave speed based on their effective shear modulus.

In the case of MCF-7 cells, cellular stiffness can vary widely depending on the microenvironment and proliferative status, but generally leads to an estimated shear-wave speed in the range of 0.3 to 0.7 meters per second. This indicates that, although cancer cells are softer than solid tissues, they still possess enough mechanical stiffness to support localized shear-wave propagation at the cellular level.

Red blood cells, on the other hand, have a highly deformable biconcave structure and a much lower shear modulus. As a result, their estimated shear-wave speed typically falls within 0.05 to 0.2 meters per second, while white blood cells—which are larger and stiffer—can reach values up to 0.6 meters per second under certain conditions.

It’s important to note that these values are not obtained through classical shear-wave imaging used in tissues, but rather through microrheological techniques such as atomic force microscopy (AFM), Brillouin microscopy, and optical or magnetic tweezers. These tools allow us to explore the mechanical behavior of individual cells in great detail, including their deformability, response to mechanical stress, and internal stiffness.

Although the shear-wave speeds in these cells are significantly lower than those found in tissues (which typically range from 1 to 4 m/s), the values are still biologically meaningful. They provide critical insight into cellular mechanobiology, especially in applications like identifying circulating tumor cells or evaluating the mechanical properties of blood cells in health and disease.