ИСТИНА

Laser tweezers (LT) is a promising tool for trapping and manipulating single microsized dielectric particles without direct mechanical contact. Operation of LT is based on using highly focused laser beam. One of the perspective features of LT is the possibility to measure forces in a range of pN values, which can be used for characterizing the interaction between the biological cells such as erythrocytes [1]. The red blood cells (RBCs) are involved in the two independent processes both in vivo and in vitro: spontaneous aggregation in stasis and at low shear stresses and disaggregation forced by higher shear stresses occurring in the blood flow. Spontaneous aggregation of RBCs significantly influences the blood viscosity at low shear stress conditions and thus affects the blood circulation.The RBC aggregation can be characterized by the aggregation force (FA) – the interaction force between a pair of RBCs forming an aggregate. Disaggregation of RBCs leads to the disintegration of the aggregates. This process can be characterized by the disaggregation force (FD) – the force that is required to disassemble an aggregate. The higher is FD, the higher is the hydrodynamic strength (HS) of the aggregate. Elevated HS is characteristic of many pathologies. Both FA and FD can be measured in vitro using LT [2]. The ratio R=F_D⁄F_A is proposed as the diagnostic parameter of the aggregation/disaggregation process. The relevance of this parameter to characterize the pathologies is still to be verified. In this work, we assessed the FA and FD forces using a home-made two-channel LT comprising two Nd:YAG lasers (1064 nm, 200 mW) and a high numerical aperture objective (N.A. = 1.00, x100). The position of the beam waist of one laser beam could be manipulated using a motorized mirror. The measurements were performed in highly diluted suspension of RBCs (~ 0.05%) in autologous plasma. Blood was sampled by venipuncture from patients suffering from Diabetes Mellitus Types I and II (DMI and DMII respectively) and from healthy donors. Each set of FA and FD measurements was performed on 15 pairs of RBC for each blood sample and within 3 hours after drawing the blood. Each group of donors included 5-7 persons. The results showed that FD significantly (p < 0.05) exceeds FA in all groups. The results also showed that FA had the smallest magnitude in the case of DMII (FA = 2.3 ± 0.5 pN) while it was nearly the same in the control group (FA = 2.9 ± 1.2 pN) and in the DMI group (FA = 3.0 ± 0.9 pN). FD measured in the control group was found to be the highest (FD = 5.2 ± 0.9 pN) in comparison with the diabetic groups (FD = 4.0 ± 0.7 pN in DMI and FD = 3.5 ± 0.5 pN in DMII). The value of the RBCs parameter R was the highest in the control group (R = 2.0 ± 0.6), which differs from the values obtained in the diabetic groups (R = 1.5 ± 0.5 in DMII; R = 1.3 ± 0.4 in DMI). Basing the obtained results we can conclude that the largest difference between FA and FD was found for healthy donors. This difference decreased with the FD magnitude in case of DMII and finally almost vanished in case of DMI. Different magnitudes of R were obtained in the control and in the diabetic groups.This finding allows us to speculate that R might be considered as a diagnostic parameter of the aggregational state of blood of diabetics. Further measurements and better statistics are needed to definitely state this suggestion.