Potentialities of laser trapping and manipulation of blood cells in hemorheologic research.

Laser trapping and manipulation of blood cells without mechanical contact have become feasible with implication of laser tweezers. They open up new horizons for the hemorheologic researches, offer new possibilities for studying live cells interactions on individual cell level under the influence of different endogenous and exogenous factors. The operation principle of laser tweezers is based on the property of strongly focused laser beam to act on a dielectric microparticle located in the vicinity of the beam waist with a force that drives the particle to the equilibrium location and holds it there. If the beam waist position is manipulated, so is the position of the particle. The displacement of the particle from the equilibrium position by external forces can be calibrated so that these forces can be precisely measured in the range ca. 0.1-100 pN. This is the range of forces of elastic deformation of blood cells and of their interaction with each other and with vessel walls. Being able to measure these forces without mechanical contact allows for studying on single cell level the mechanisms of interactions that was impossible earlier. Here we discuss the basic features of these techniques and give some examples of challenging hemorheologic studies.