Development of a Microfluidics System for the examination of the effects of Cardiovascular Stenting on Blood Fluid Mechanics and Physiology: system validation study

Abstract

Blood is a composite non-Newtonian two-phase fluid that circulates though the vascular system and is mainly consisted out of red blood cells (RBC); white blood cells (WBC) and platelets suspended in plasma. Erythrocyte is the most common type of cell occurring in human blood and accounts for about 40-45% of blood’s volume, WBCs around 1% and plasma 55%. Mechanical heart valves, ventricular assist devices, devices used in cardiopulmonary bypass, extracorporeal membrane oxygenation and continuous renal replacement therapy are associated to increased hemolysis risk and physiological characteristics alternations. Intra-arterial stent implantation is widely used as treatment in restoring arterial stenosis. The presence of a foreign body like a cardiovascular stent alters local physiology, topology and flow conditions causing restenosis and various phenomena to appear. Numerous designs are commercially available; however, the examination on the influence and the effects on the hemodynamics is rare in the literature. In this study a microfluidics system that mimics a stented vessel of the human body was developed for the analysis of the effects of stenting on the rheological properties of blood. The main target is the detection and study of pressure drop across a tube, both restricted and unrestricted, under various volumetric flow rates. The main purpose of the project was the validation of the system and the preliminary testing on blood flow. The techniques utilized included pressure driven microfluidics and hemorheological methods. Validations were performed in static conditions; then the flow was produced by a pumping mechanism. Samples (distilled water, xanthan gum solution, glycerin solutions and blood) were tested at flow rates of 20, 40 and 60 ml/min in both constricted and non-constricted vessel. The results showed that the system has a satisfactory behavior, as regards the overall accuracy and repeatability with a maximum uncertainty 4%. The transient behavior of the pressure response to the applied flow rate was also quantified by modelling the process with a double exponential equation. It was found that increased flow rates and constricted flow configuration had an effect on pressure and on blood’s rheological properties. The viscosity of blood found to be increased when the fluid passed from the constricted tubes and the flow rate increases, while RBC, AI and EI appeared decreased.