A Comparison of Single-Cell Elasticity of Osteogenic Cells Measured with the Optical Stretcher and Holographic Microscope

Abstract

While it has been known for some time that bone mass is remodeled in response to mechanical stress, the identity of the primary mechanosensor has yet to be clearly established. To determine if cellular elasticity may play a role in the cell's ability to detect a pressure variation, we have used the optical stretcher to measure the elasticity of individual osteogenic cells. To determine cell elasticity from measurements of cellular deformation, the optical pressure on the cell surface is computed using a ray optics model which assumes a value for the index of refraction of the cell. Previously we have estimated this value from measurements of other eukaryotic cells, but the optical pressure varies significantly with small changes in refractive index. Therefore, digital holographic microscopy is used to improve estimates of this critical parameter. We consider the overall impact that a spatial variation in the index of refraction can have on the determination of the optical stress, and compare single-cell elasticity measurements of red blood cells, 2T3 osteoblast and MLO-Y4 osteocyte cells. ∗ This work was supported by P20 RR016475 from the INBRE Program of the National Center for Research Resources.