Development of Newly Designed Atomic Force Microscope System for Measuring of Mechanical Properties of Cells

We have developed a low-cost atomic force microscope (AFM) system for the measurement of surface topography and local mechanical properties of cells. An AFM unit was combined with an inverted confocal laser scanning microscope (CLSM) to observe the AFM image and the CLSM image simultaneously. The unit consists of an optical lever unit for the measurement of cantilever deflection, a feedback control system for the cantilever height, a cantilever drive unit with a piezo actuator, and a XY stage with large scanning area (150μm×150μm), which was attained by magnifying the deformation of piezo actuators by applying the principle of leverage. By assembling necessary parts by ourselves, the total cost of the system was reduced to about a million yen. Surface topography of the cells was obtained as the conventional AFMs in a contact mode. Mechanical properties of the cells were measured from the relationship between the indentation force F, and the indentation depth d during an indentation test. The F-d curve was fitted with a quadratic equation, F=k (d+ (p/2) d2), where k and p are the indices of initial stiffness and non-linearity of the cell stiffness, respectively. We measured the mechanical properties of the bovine aortic endothelial cells with this system to find that the two indices increased similarly in the cells exposed to shear stress of 2 Pa for 24 h. The present system is useful for the studies of cellular mechanics.