The mechanical properties of cells play a very important role in various biological processes. Most living cells are small, fragile and highly heterogeneous. It is frequently observed that there is a large inherent variation in mechanical properties from cell to cell. Therefore, high throughput microrheology methods are particularly suitable for cell mechanics studies. A novel setup, which can be operated either in Magnetic Tweezers (MT) or in Magnetic Twisting Cytometry (MTC) function, was developed to efficiently measure the mechanical properties of cells.

Magnetic Particle Actuation for Microrheometry — (a) Blue spots: cell nuclei, small black dots: magnetic beads; (b) Displacement response of magnetic beads to applied force; (c) Viscosity distribution. (d) Shear elastic modulus distribution.

With our newly implemented microrheology tool, the mechanical properties of rat cardiomyocytes and brain cells were investigated. Both the creep and the frequency response of cardiomyocyte HL-1 cells were characterized with the instrument in MT and MTC mode. In both modes, the stiffness of HL-1 cells exhibits approximately log-normal distributions. High heterogeneity of single cell stiffness was also noticed. When HL-1 cells were cultured on a stiff substrate, there was an obvious stiffening effect at low frequency, which depends on the prestress generated by myosin activity.

In addition to a stiff cells like cardiomyocytes, the mechanical properties of fragile and soft brain cells were studied with MT. It was found that with increasing maturity, the stiffness of both neuron and glia increases. The power-law exponent of neuronal cells decreases with increasing cell maturity, but that of glia cells does not change. Both the elastic modulus of neurons and glia were also sensitive to the rigidity of the substrate.