## 3 Microfluidics Methods and Devices for Evaluation of RBC Deformability
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline
**Device/Method** & **Key Features** & **Performance Metrics** & **Disease/Application Focus** \\ \hline Microfluidics & Micromachined flow channels, [PERSON] et al., 1997 [31; 32] & & Velocity/volume index across real-time imaging & Erythrocyte flow under physiological conditions \\ \hline Rheo-Dyn Laser Diffraction & Conventional method using laser diffraction & Elongation index (EI) & RBC response to chemicals and temperature \\ \hline Pressure-Driven Microfluidic & & & \\ Device + Imaging & Time-lapse imaging, [PERSON] et al., 2010; [PERSON] et al., 2020; [PERSON] et al., 2020 [3; 5; 17] & & \\ \hline Microfluidic Mimic of Microcirculation & Capillary-like channels, deformation/relaxation observation & Shape restoration under flow & RBCs stored in blood bank \\ \hline MC-FAN (Micro Channel & & & \\ Array Flow Analyzer) & Measures BPT under & & \\ [PERSON] et al., 2006 [34]; [PERSON] et al., 2020 [35] & & & \\ \hline Electrical Sensing & A 2-stage channel design, Microfluidic System & Current signal vs. RBC stiffness & RBC stiffness (e.g., glutaraldehyde-treated, heated) \\ \hline Integrated Shear Flow & Custom camera + microscope & Elongation index (I.E.), Microchamber [PERSON] et al., 2020 [3; 17] & & \\ \hline Adhesion + Deformability & Measures both adhesion energy and deformability & Max I.E. \(\sim\)0.3, Adhesion Energy: 1.1 \(\times\) 10\({}^{-6}\) Pa-m & Cell membrane receptor mobility; albumin concentration influence \\ \hline Microfluidic Physiometer ([PERSON] et al., 2020 [37]) & On-chip hydrodynamic + electronic units; electrical impedance & Viscosity, hematocrit, capacitance, plasma resistance & Whole-blood rheology and electrical property analysis \\ \hline Impedance-based Stiffness Detector ([PERSON] et al., 2013 [36]) & Measures current changes as cells pass through channels (\(\sim\)10 cells/\({}^{2}\)) & Electrical signal variations vs. stiffness & High-throughput RBC deformability differentiation \\ \hline Microfluidics for Blood Mechanics & High-throughput, low-cost alternative to older methods & Comparative deformability data vs. micropipette methods & Erythrocytes and leukocytes \\ \hline \end{tabular}
\end{table} 
Table 1: Microfluidic devices used for RBC deformability assessment. show that, despite changes in morphology during blood bank storage, RBCs maintain their deformability and relaxation ability in microcapillary conditions. This suggests that altered cell shape alone does not impair microvascular flow. However, increased membrane stiffness and internal viscosity may still reduce the ability of RBCs to pass through the spleen. [PERSON] et al. [14; 15] investigated how the microrheological properties of red blood cells (RBCs) contribute to the non-Newtonian behavior of whole blood. Using a microfluidic device, they measured RBC deformability and aggregation (Figure 1). This method was used to assess the effects of various drugs and pathological conditions on these RBC properties [6; 7]. The elongation index (I.E.) is calculated using Formula (2):  
\[\text{I.E.}=(\text{L}-\text{W})/(\text{L}+\text{W}), \tag{2}\]  
where:  
L = Length of the deformed RBC along the direction of flow. W = Width of the deformed RBC perpendicular to the flow. This index is determined for each shear rate, providing a quantitative measure of RBC deformability under varying flow conditions. A higher I.E. indicates greater cell elongation and better deformability, which is crucial for efficient microcirculatory blood flow. A regression analysis of erythrocyte elongation indices in a flow microchamber at a shear stress of 0.54 N/m\({}^{2}\), using [PERSON]'s method [11], revealed a very strong correlation (r = 0.997) between two groups of deformability indicators (I.E.1 and I.E.2). This high correlation confirms the consistency and reliability of the elongation index as a measure of RBC deformability.