Experimental Research On The Rheology Of Red Blood Cells Under High Shear Stress

With the development and application of the permanent implantable medical devices,the mechanical blood damage inherent in all implantable devices becomes a urgent problem,of which hemolysis and thrombosis are the two main issues.It is believed that the high shear stress in medical devices which is far beyond physiological range is responsible for the blood cell injury.Shear stress can cause damage to erythrocyte membrane and release the intracellular fluid,resulting in physiological disorders,which is the mechanical hemolysis.As for thrombosis,studies show that both shear stress and hemolysis have an effect on platelet activation.Thus,researching on the rheological response of red blood cells under high shear stress and analyzing the shear damage mechanism is of great significance to the design and optimization of implantable medical devices.Based on the current research progress of shear-induced hemolysis,this dissertation puts forward the goal of studying erythrocyte shear rheology from the cellular level.In this dissertation,a visualized experimental system of erythrocyte shear rheology is set up,which uses a parallel plate flow channel as the shear device and allows a stress loading ranging from 0 to 1300 Pa.Based on the erythrocyte rheological behavior,an analysis is given to the shear damage mechanism and the rheological process is quantified by digital image processing technology.What's more,the 3D shape reconstruction of cells is carried out using defocusing microscopy to achieve the complete quantification of cell morphology.Then,a strain-based theoretical model of eryth:rocyte rheology is adopted to analyze the shear rheological response,and the model is improved to fit well with the experimental data.Finally,some meaningful parameters such as the threshold of membrane area stain,the threshold of hemolysis and the characteristic time of respond,are estimated and compared with other studies.The main research contents of this dissertation are as follows:(1)The construction of erythrocyte shear rheological system.According to the goal of studying the shear-induced injury of erythrocyte,a visualized shear rheological experimental system is built.To meet the requirements of high shear stress,the experimental parameters are determined and the performance of the experimental system is evaluated by the theoretical calculation of flow field.The experimental system allows a large range of stress loading and all experimental variables are under controlled,providing the accurate shear rheological response of cells.(2)Shear rheological experiments.A method for preparing erythrocyte buffers with high viscosity and iso-osmotic is provided,and the shear rheological experiments of erythrocyte are conducted.According to the experimental results,an analysis on the shear damage mechanism is given,including the effect of both dynamic and static shear stress on the process of erythrocyte hemolysis(3)Quantification of erythrocyte rheological parameters.The digital image processing technology is used to deal with cell images,realizing image enhancement,denoising,cell recognition,tracking and rheological feature measurement.In order to achieve the complete quantification of cell shape,3D morphology reconstruction is carried out by defocusing microscopy,which is based on the principle of phase imaging.According to the quantitative results,the relationship between erythrocyte deformation parameters and flow field stress is obtained.(4)Theoretical analysis of erythrocyte shear rheological response.The shear rheological response of erythrocyte is quantitatively analyzed by using strain-based rheological model,and this theoretical model is calibrated and improved by the experimental data.The membrane strain and tension are calculated and used to estimate feature parameters including the threshold of membrane area stain,the threshold of hemolysis and the characteristic time of respond.All these parameters are analyzed by comparing with other studies.Finally,an improved model of erythrocyte shear rheology with variable parameters was proposed,and the law of erythrocyte shear rheology at short time scale and under strong shear stress was obtained.