Correlating the viscoelasticity of breast cancer cells with their malignancy

Initiation and development of cancer are usually accompanied by alterations in the cellular mechanical properties such as its stiffness and viscosity. Understanding the viscoelasticity of cancer cells can provide a better insight into the mechanics of the metastasis of cancer cells. Here, we use atomic force microscopy to compare the viscoelasticity of mammary epithelial cells with different metastatic potentials in their adherent and suspended states. We measure cell elasticity through the spatial mapping of Young's modulus using the force-indentation technique and cell viscosity using stress relaxation. The viscoelastic properties of cancer cells are associated with their malignancy and intrinsic cytoskeletal structures. Our results suggest that the Young's modulus of adherent cells inversely correlates to their malignancy and that the F-actin arrangement and intensity support the mechanical phenotype. For suspended cells, we observe that they exhibit lower elasticity than adhered cells due to the distribution of actin filaments at the cell cortex as well as reduced polymerization. Our viscosity results suggest that in both adhered and suspended cases, normal breast epithelial cells exhibit higher viscosity than that of cancer cells. Actin distribution and higher nucleus to cytoplasmic ratio in cancer cells are observed to be the two main factors in determining cell viscosity.