Abstract
Since the invention of the optical stretcher in 2001, no direct method has been found for measuring the optical stress that produces the observed trapping and stretching of biological cells and other dielectrics. Hence, mathematical and computational models have been developed to calculate the optical stress and net stretching force. The ray optics (RO) model assumes that the light field can be divided up into very narrow discrete beams called rays, which interact with different media by reflection and refraction, such that the optical system can be analyzed by the process of ray tracing. This RO model has been successfully used to predict the trapping force. The measurement of the elastic modulus of hypo-osmotically swollen red blood cells (RBCs) and other cells has also been performed by assuming an approximate stress distribution function that permits analytical solution of the equations of deformation.|From the principles of continuum mechanics we have derived and solved the equations of deformation for arbitrary stress profiles and developed codes that analyze different stress distributions. We call this the Poikilostrephic (Changing Stress) Approach. We have extended the treatment by Guck, et al. (2001), to include stress distributions that we have calculated for spherical cells in the optical stretcher. Our new approach provides empirical equations for extracting the elastic modulus from experimental measurements of deformation using the 1064 nm optical stretcher. From results obtained so far, osteogenic (2T3 murine pre-osteoblast) cells are 18.4 +/-8.5 times stiffer than RBCs