As the RBCs’ shape changes with varying osmolality, their deformability is also altered. The biconcave disk shape of RBCs is transformed into a sphere in a hypotonic medium (for echinocytes, this occurs in a hypertonic medium). The shape and deformability of RBCs can be greatly altered by deviation from normal physiological conditions (i.e., 295 mOsm/kg). Therefore, in this paper, we present an updated review of the tools used for measuring RBC deformability, as well as the determinants of RBC deformability. Additionally, there have been significant advances in the experimental methods and techniques used to measure RBC deformability, and these have helped to accelerate fundamental researches and clinical studies. A number of studies have investigated RBC deformability, and these include comprehensive review papers. However, many researchers believe that RBC deformability holds the key to understanding molecular alteration to vascular diseases. The subcellular (or molecular) mechanism associated with alterations in RBC deformability remains unclear. Indeed, various pathophysiological environments such as hyperglycemia can alter the deformability of RBCs, and reduced RBC deformability may in turn affect pathophysiology. Thus, reduced RBC deformability is frequently reported in microvascular diseases such as diabetic complications. If deformable RBCs are replaced by solid 6- μm-sized particles, then the viscosity value at 50% volume concentration may increase 10-fold and thereby prevent flow in the vascular network. A slight decrease in RBC deformability causes a significant increase in microvascular flow resistance and blood viscosity, as shown in Fig. 1. The deformability of RBCs plays an important role in their main function, the transport of gases (O 2 and CO 2) via blood circulation. In mammals, RBCs are non-nucleated and consist of a concentrated hemoglobin solution enveloped by a highly flexible membrane. RBCs are biconcave discs, typically 6–8 μm in diameter and 2 μm thick, and their deformation can involve a change in cell curvature, a uniaxial deformation, or an area expansion.

In fact, RBCs are more deformable than any other biomaterial.

Human RBCs have the ability to undergo large deformations when subjected to external stresses, which allows them to pass through capillaries that are narrower than the diameter of a resting RBC. Deformability, defined as the ability of a subject to change its shape in response to an external force, is a unique characteristic of soft matter including red blood cells (RBCs).

Test viscosity of hemoglobin in rbc