Tired and stressed: direct holographic quasi-static stretching of aging echinocytes and discocytes in plasma using optical tweezers [Invited]

Abstract

Red blood cells (RBCs) undergo a progressive morphological transformation from smooth biconcave discocytes into rounder echinocytes with spicules on their surface during cold storage. The echinocytic morphology impacts RBCs’ ability to flow through narrow sections of the circulation and therefore transfusion of RBC units with a high echinocytic content are thought to have a reduced efficiency. We use an optical tweezers-based technique where we directly trap and measure linear stiffness of RBCs under stress without the use of attached spherical probe particles or microfluidic flow to induce shear. We study RBC deformability with over 50 days of storage performing multiple stretches in blood plasma (serum with cold agglutinins removed to eliminate clotting). In particular, we find that discocytes and echinocytes do not show significant changes in linear stiffness in the small strain limit (∼20% change in length) up to day 30 of the storage period, but do find differences between repeated stretches. By day 50 the linear stiffness of discocytes had increased to approximately that measured for echinocytes throughout the entire period of measurements. These changes in stiffness corresponded to recorded morphological changes in the discocytes as they underwent storage lesion. We believe our holographic trapping and direct measurement technique has applications to directly control and quantify forces that stretch other types of cells without the use of attached probes.

Red blood cell flickering activity locally controlled by holographic optical tweezers

“… 23 , 24 The advancement in coherent optics led to the development of holographic optical tweezers (HOTs), which can exert multiple dynamical optical traps in three dimensions. 25 , 26 , 27 Additionally, HOTs can transfer orbital angular momentum of light to trapped objects making them rotate or spin by manipulating vortex and non-Gaussian beams. 28 , 29 To generate the requested hologram, diffractive optical elements such as spatial light modulators (SLMs) are commonly employed.…”