ИСТИНА

Optical trapping and manipulation of blood cells without mechanical contact have become feasible with implication of optical tweezers (OT). They open up new horizons for the hemorheologic research as they offer new possibilities for studying the interactions of blood cells on individual cell level under the influence of different endogenous and exogenous factors, in particular, measuring the pN-scale forces underlying these interactions. Here we discuss the basic features of these techniques and provide some examples of the challenging hemorheologic studies. The principle of operation of OT is based on the property of strongly focused laser beam to act on the dielectric microparticles 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 trapped 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 red blood cells (RBC), e.g., by shear stresses, and of their interaction with each other, e.g., during aggregation, and with vessel walls. Using our home made double channel OT we have conducted extensive experiments including the in vitro measurement of the forces arising during two RBCs interaction with formation of a minimal aggregate – a doublet (aggregating forces), and the forces needed to disaggregate the doublet (disaggregating forces). The measurements were performed in various environments in norm and at different pathologic conditions. Our main findings are that the disaggregating force is always higher than the aggregating force and that there exists a synergetic effect in the action of the proaggregant proteins of blood plasma on the interacting RBCs. We conclude that providing means to measure the aggregation and disaggregation forces without mechanical contact using the OT allows studying on single cell level the fundamental mechanisms of interactions of RBCs and other blood cells that was impossible earlier. This work was supported by RFBR grant №16-52-51050.