Characterization at the individual cell level and in whole blood samples of shear stress preventing red blood cells aggregation  K. Lee, M. Kinnunen, A.V. Danilina, V.D. Ustinov, S. Shin, I. Meglinski, A.V. Priezzhev  Journal of Biomechanics  Volume 49, Issue 7, Pages 1021-1026 (May 2016) DOI: 10.1016/j.jbiomech.2016.02.011 Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 1 (a) Schematic layout of the shear-stress scanning microfluidic aggregometer that is based on the backscattered light (BSL) detection system. (b) Variation of the BSL intensity over time during I – disaggregation and II – aggregation, and (c) the shear-stress variation for the blood sample, τc – critical shear stress value (Shin et al., 2007). Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 2 Schematic layout of the optical tweezers setup. Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 3 The sequence of RBC lifting and trapping. (a) Single cell is at rest on the glass surface, (b–c) optical trap slowly lifts the cell and the cell turns to a side, (d) the cell is lifted and trapped. Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 4 Schematic illustration of force measurement. RBCs are trapped by two independent optical traps shown as springs. The points of force application are shown only to give an idea of force direction; the actual force is applied through a certain volume. The trapping force applied by the unmovable trap (Ftrap1) was always slightly stronger than that of the movable trap (Ftrap2). (a) The cells are trapped and held from spontaneously overlapping each other with the trapping force greater than FA. (b) The cell escapes from the trap, as trapping force becomes slightly weaker or equal to FA. At this moment FA is considered to match Ftrap2. Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 5 (a) Set of frames demonstrating the aggregating force measurement process. The red cross marks show the positions of the optical traps, the blue arrows show the direction of trapping and the aggregating force applied. (b) Aggregating force dependence on the interaction area (N=112 cell pairs from 8 healthy donors). Deviation in force measurement results was 15% (not shown here). It was introduced by the calibration error. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 6 Single cell aggregating shear stress (SASS) dependence on the interaction area (N=112 cell pairs from 8 healthy donors). Deviation in shear stress measurement results did not exceed 15% (not shown here). Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 7 Set of frames demonstrating the measurement process. The cross marks show the positions of the optical traps and the arrow shows the directions of pulling by the trap. Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 8 Comparison of SASS (single cell aggregating shear stress), SDSS (single cell disaggregating shear stress), CSS (critical shear stress) values for the erythrocytes from 8 healthy donors (14 cells pairs per donor). Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions

Fig. 9 Comparison of SASS (single cell aggregating shear stress) and CSS (critical shear stress) – averaged over all 8 healthy donors. Journal of Biomechanics 2016 49, 1021-1026DOI: (10.1016/j.jbiomech.2016.02.011) Copyright © 2016 Elsevier Ltd Terms and Conditions