Measuring Viscoelastic Properties of Living Cells

Precise measurement of mechanical properties of living cells is important in understanding their mechanics-biology relations. In this study, we adopted the atomic force microscope to measure the creep deformation and stress relaxation of six different human cell lines. We examined whether the measured creep and relaxation trajectories satisfy a verification relation derived based on the linear viscoelastic theory. We compared the traditional spring-dashpot and the newly developed power-law-type constitutive relations in fitting the experimental measurements. We found that the human normal liver (L02), hepatic cancer (HepG2), hepatic stellate (LX2) and gastric cancer (NCI-N87) cell lines are linear viscoelastic materials, and human normal gastric (GES-1) and gastric cancer (SGC7901) cell lines are nonlinear due to failing in satisfying the verification relation for linear viscoelastic theory. The three-parameter power-law-type constitutive relation can fit the experimental measurements better than that of the five-parameter classical spring-dashpot.