Orientational dynamics of human red blood cells in an optical trap

Abstract

We report here on studies of reorientation of human red blood cells (RBCs) in an optical trap. We have measured the time required, tre, for the plane of the RBC entering the optical trap to undergo a 90-deg rotation to acquire an edge on orientation with respect to the beam direction. This has been studied as a function of laser power, P, at the trap center. The variation of tre with increasing P shows an initial sharp decrease followed by a much smaller rate of further decrease. We find that this experimentally measured variation is not in complete agreement with the variation predicted by a theoretical model where the RBC is treated as a perfectly rigid circular disk-like body. We argue that this deviation arises due to deformation of the RBC. We further reason that this feature is dominated by the elastic behavior of the RBC membrane. We compare the studies carried out on normal RBCs with RBCs where varying conditions of membrane stiffness are expected. We propose that the value of energy used for maximum deformation possible during a reorientation process is an indicator of the membrane elasticity of the system under study.

Estimation of membrane bending modulus of stiffness tuned human red blood cells from micropore filtration studies

“…Note that for a comparative study to be valid, it is important that the same solution of PBS is used to carry out all experiments. This is because minor variations in the osmolarity of the PBS could have an effect on the measurements [14]. The suspensions with BSA were prepared not more than an hour prior to the commencement of the experiment.…”

“…Studies on viscoelastic properties of RBCs involve either observing the response of an RBC subjected to a well calibrated deforming stress or an analysis of the detailed observation of a process where RBC deformations occur. These have been widely reported in literature and involve a wide variety of techniques based on micro pipette aspiration [11–13], optical tweezers (reorientation [14], stretching [15–17]), observation of membrane fluctuations [18, 19], optical stretcher [20, 21] and micro fluidic channel flows [3, 22, 23]. Though all these techniques, in principle, provide a measure of the RBC CMS, the stress regimes in which the experiments are done are extremely different and can lead to a varied conclusion on the viscoelastic response of the RBC.…”

Effect of Bovine Serum Albumin on Red Blood Cell Optical Anisotropy Probed Through the Optomechanical Response in an Optical Trap

“…We draw the attention of our readers to Ref. for a detailed description of the determination of α. ϕ is the degree of ellipticity which is zero for linearly polarized light, P is the laser power, ω the angular frequency of the laser and λ its wavelength. R is the birefringence induced retardation in the laser light propagating through the RBC.…”

“…Details of the experimental setup appear elsewhere . About 30 µl of blood drawn from a healthy donor using a finger‐prick method was suspended in 0.5 ml of Phosphate Buffer Saline (PBS).…”

“…When an asymmetrical microstructure is trapped in a linearly polarized OT, it reorients such that it maximizes its volume along the region of highest electric field . Therefore by measuring the reorientation time for a viscoelastic material such as a human RBC in a linearly polarized OT, it is possible to gauge its elastic modulus . The reorientation dynamics of trapped objects become more interesting when trapped entities possess optical anisotropy along with anisotropy of the shape.…”