Microfluidic-based speckle analysis for sensitive measurement of erythrocyte aggregation: A comparison of four methods for detection of elevated erythrocyte aggregation in diabetic rat blood.

Biochemical alterations in the plasma and red blood cell (RBC) membrane of diabetic blood lead to excessive erythrocyte aggregation (EA). EA would significantly impede the blood flow and increase the vascular flow resistance contributing to peripheral vascular diseases. In this study, a simple microfluidic-based method is proposed to achieve sensitive detection of hyperaggregation. When a blood sample is delivered into the device, images of blood flows are obtained with a short exposure time for a relatively long measuring time. A micro-particle image velocimetry technique was employed to monitor variation of the flow rate of blood as a function of time. Given that EA formation in the channel creates clear speckle patterns, the EA extent can be estimated by calculating a speckle area (ASpeckle) through a normalized autocovariance function. The hematocrit effect is assessed by comparing optical images transmitted through blood samples. EA variations caused by dextran treatment are quantitatively evaluated using characteristic time (λSpeckle) obtained by fitting the variations of ASpeckle. Other indices including number of RBCs in an aggregate (NRBC), characteristic time of erythrocyte sedimentation rate (λESR), and aggregation index estimated from ultrasound signals (AIEcho) are determined under different EA conditions using conventional techniques. The four different methods are applied to diabetic blood samples to compare their indices under hyperaggregation conditions. It is found that the proposed method can detect variation of EA reasonably, compared with conventional measurement techniques. These experimental demonstrations support the notion that the proposed method is capable of effectively monitoring the biophysical properties of diabetic blood.