Continuous and simultaneous measurement of the biophysical properties of blood in a microfluidic environment.

The biophysical properties of blood have been considered as promising indices for effectively screening the cardiovascular diseases. In this study, a method for the continuous and simultaneous measurement of the biophysical properties of blood, including viscosity, viscoelasticity, and RBC (red blood cell) aggregation is suggested, using a microfluidic device. The microfluidic device has two inlets (A, B), two outlets (A, B), two identical side channels, and one bridge channel. To sequentially induce steady and transient flows of blood samples, a blood sample is carefully delivered into the inlet (A) at a pulsatile flow rate (Q) (Qmax = 1 mL h-1, Qmin = 0 mL h-1, T = 240 s). By operating a pinch valve connected to the outlet (A), the blood flow is stopped or passed in the left-lower side channel. Three biophysical properties of the blood sample are quantified by analyzing the flow rate in the left-upper side channel (QμPIV), the image intensity in the left-lower side channel (〈I〉Blood), and the blood-filled width in the right-lower side channel (αBlood). First, based on the modified parallel flow method, the blood viscosity (μBlood) is measured by analyzing the variation in αBlood. Second, using a discrete fluidic circuit model, the time constant (λ) is evaluated by analyzing temporal variations in QμPIV and 1/(1 - αBlood). Then, the blood elasticity (GBlood) is calculated by assuming the linear Maxwell model (i.e., λ = μBlood/GBlood). Third, the RBC aggregation is quantified in terms of three parameters (〈I〉Slope, ARatio, and AUpp) obtained by analyzing temporal variations in the image intensity. From the experimental demonstrations using various blood samples, it is concluded that the proposed method has the ability to measure the biophysical properties of blood with consistency, as compared with the previous methods. In the near future, the proposed method will be employed for evaluating variations in the biophysical properties of blood, circulating in the extracorporeal rat bypass loop.