Microsensor for Cell Force Measurement

Cell elasticity, motility and migration are very important for understanding various biological processes. Currently, monitoring cellular traction forces is desired as new marker to monitor cell functionality. We developed a sensor system for cell force measurement based upon a polymer microchip covered with a micropillar matrix. The spring constant is chosen to enable pillar bending by cellular forces. The microchip is read out optically. Besides a transmission image to analyze pillar bending, two different fluorescence images of dye markers can be taken sequentially. Matrix with the cells is illuminated by spatially homogenized LED radiation. The focal position during long term experiments can be maintained by means of a piezo stage in order to obtain highly resolved images from the CCD imager. Sophisticated software controls the optical system and performs image registration. First, one transmission (red) as well as two fluorescence images (blue & green) are taken using appropriate CCD gain and integration times. Fluorescence information yields those pillar positions that are at least covered by a cell. The transmission image is used to calculate the magnitude and direction of pillars deflection. Therefore, detection of single pillar position and its deviation from a hexagonal grid is analyzed automatically, enabling a mapping of traction forces. The system containing transducer polymer chip, optics, and dedicated software analysis is a complete imaging system for image registration, single cell visualization and cellular force measurement. First results of cellular force measurements obtained are presented.