Mechanical characterization of fixed undifferentiated and differentiating mESC

Conventionally, biologists detect cell status visually based on protein markers. These assays are often qualitative and do not quantitatively define the outcome of a cell progression during differentiation. Consequently, we propose to develop an atomic force microscopy (AFM) based system that can be used to mechanically manipulate and characterize an individual cell. We have also connected a haptic feedback interface comprising of a PHANToM haptic feedback device to obtain a qualitative force feedback response when the AFM probe contacts the cell membrane. The system has the capability of measuring forces in nN range and provides a haptic display of the cell indentation forces in real time. We conducted experiments on mouse embryonic stem cells (mESC) roughly 10 mum in diameter and 7-10 mum in height at the interphase stage of the cell division process. Specifically, we performed single indentation studies of 2-2.5 mum on multiple fixed mESC, - early differentiating (6 days under differentiation conditions) and undifferentiated to determine the local elastic modulus of the cell membrane. Our experimental results indicate that the mechanical property of undifferentiated mESC differs from differentiating mESC in fixed cells.