Shear stress related hemolysis and its modelling by mechanical degradation of polymer solutions

Human or animal blood is normally used as a test fluid for in vitro evaluation of hemolysis by artificial organs. However, blood has some disadvantages (no transparence for visualization of the flow field, large biological variability and problems with cleaning the devices). For that reason, it would be of advantage to have a reproducibile transparent technical fluid with blood like flow characteristics and that exhibits similar shear depending destruction. We have shown that solutions of long-chaining polymer molecules are destroyed by heart valve prostheses in a similar manner as blood corpuscules. In the presented study, a direct comparison between erythrocyte destruction of bovine blood and degradation of Polyacrylamid molecules in a 300 ppm solution is given. A uniform shear field was applied to the fluid using a plate-plate geometry shear device. This device allows a variation of shear stress and shear time in the range of 15-500 N/m2 and 64-516 ms, respectively A correlation between the index of hemolysis (ratio of free plasma hemoglobin to total hemoglobin) and the percentage viscosity decrease (derived from low shear viscosity at a shear rate of 0.01/s) was found. Thus, PAA solutions are suitable model fluids for in vitro estimation of the damaging effects of artificial devices.