A microfluidic-based blood viscometer

Blood viscosity is a sensitive diagnostic marker for detecting subtle physiological and pathological changes. The previous method required a considerable amount of blood to remove entrapped air bubbles and occupy all fluidic passages. Red cell sedimentation directly affects blood viscosity during prolonged blood delivery (∼10 min). In this study, a novel method was suggested to probe blood viscosity in a microfluidic-based platform to overcome these challenges. For effective blood delivery to the microfluidic chip, a handheld pump was fabricated by assembling a disposable syringe (∼1 ml) to secure the air cavity, a specific fixture for setting the air compression volume, and a 3-way stopcock for infusing air pressure. A small blood volume (∼microliter scale) was loaded into large-bore tubing between a microfluidic chip and a portable pump. The blood velocity in the microfluidic chip was obtained using micro-particle image velocimetry, and its inaccuracy improved by adopting a correction factor. The flow rate and air pressure drop were estimated over time using the analytical and fluidic circuit models. The blood viscosity was finally obtained by substituting both quantities into the Hagen–Poiseuille law. The experimental results confirm that the proposed method can accurately measure blood viscosity within a short period of blood delivery. Furthermore, when the blood loading volume is set to exceed 20 μl, blood viscosity is obtained consistently. In conclusion, the suggested method can accurately measure blood viscosity with 20 μl blood volume without being influenced by sedimentation.