Experimental Study Of Red Blood Cell Transporting In Microchannel

In order to carry out the experimental study on the red blood cells(RBCs)transporting process in the microchannel,a set of visual experimental device for rheological properties of erythrocyte were designed and constructed in this paper,including precision syringe pump,LED cold light source,optical microscope,CMOS high speed camera,image acquisition computers and PDMS microchannels as well.After the physical size of the single pixel of the camera was obtained by using micrometer calibration plate,the experimental investigations on the cell motion statistics including trajectories,velocities,accelerations and forces as well as the diffusion process for a typical group of RBC in a microchannel were carried out.The main investigations are as follows:Firstly,the complex structured microchannels processed by PDMS chip were designed and fabricated to simulate the capillary network.The main experimental study was carried out on the erythrocyte suspension flow in one of microchannels with width of 70?m and depth of 5?m.In the experiments,the high-speed CMOS camera was employed to capture the transient motion images of the RBCs,and the filter technique was used to smooth the image of the static RBCs,and the equalization of the map was applied to enhance the local contrast,edge detection based on Canny operator for preliminary.Furthermore,the mathematical morphology of corrosion and expansion algorithm were employed to optimize the binary image,and finally the binary images being able to reflect the outline of real RBC were obtained.The image process above lay the foundations for the RBC image accurate recognition.On the basis of image processing,the centroid coordinates of 10 red blood cells which had the same initial streamwise positions were calculated,and the movement trajectories of RBCs were obtained according to the time series of the centroid coordinates.The forward difference method was used to obtain the time evolutions of the cell velocities and accelerations,and accordingly their probability distribution function(PDF)curves were obtained.The deformation were characterized by the defining two deformation rate parameters of D and K,respectively.The angle statistical probability distribution of cell rotating around its own long axis were calculated.The experimental results show that the cell motions and forces in the pressure driven flow is a kind of typical stochastic process,and shows that in the spanwise random drift superposition on the cell motions along the main flow movement.The orders of velocity magnitude along two different directions are both ?m/s under the condition of the flow rate being 5?l/min.The nondimensional force coefficient of two components were calculated,and both fall into the circles with radius R about 400.From the force coefficients distribution in the four quadrants,we can see that the power and resistance have the uniform distributions.The cell deformation rate parameters of D and K are between 0.056~0.08 and 0.944~1.033,respectively,which indicates that the total deformation was not significant.The probability distribution of the rotation angle covers 0o to 180o,and the dominant probability being greater than 10% is between 0o and 90o,and the probability peak appears at 55o,whose value is about 18%.The rotational angular probability distribution may be related to the combined effects including the cell location,the number density of cells and fluid shear force and so on.Since the RBC transportations are typical random processes,it is important to investigate their diffusion properties.In this paper,Langevin equations of the active diffusion process of RBCs was established,and the semi-analytical solutions of the diffusion process of RBCs motions in the microchannel were carried out in combination with the experimental statistics.By solving the different equations,the semi-analytic relationships(theoretical solutions)between the mean square displacement(MSD)and time were given,and the theoretical results were compared with the experimental solutions.The results indicate that both the theoretical and the experimental MSD show the weak nonlinear and the strong nonlinear,respectively.The theoretical curves of 10 typical RBCs were basically coincident under some simplifications including flow velocity,viscosity coefficient and the same random force term.Due to the differences in the number density of surrounding cells,the experimental curves of different cells were significantly different,but the experimental points basically fell into the quadratic fitting curve.By averaging the theoretical and experimental solutions of all RBCs,respectively,the average results are consistent with the general trend though there are deviations between both average solutions.Hence,the experimental and theoretical solutions are verified by each other.Analogy to Einstein equation of two-dimensional Brownian motion,we calculated the nominal diffusion coefficients of the RBCs' active diffusion processes,and established the relationship between a nominal diffusion coefficient and the time.The results show that active diffusion processes of RBCs have the super-diffusion characteristics.Finally,we carried out some preliminarily experimental investigations on the rheological properties of erythrocytes in the chip capillary network.The trajectories of single RBC in curve microchannel and deformations of RBCs in complex capillary network were observed and analyzed,the results are consistent with existing studies.