Combining Atomic Force Microscopy And Finite Element Simulation To Analyze The Mechanical Properties Of Vascular Tissues And Cells

Cardiovascular disease(CVD)is a serious threat to human health,which has a very high morbidity and mortality.Vascular replacement is currently an effective method for treating cardiovascular diseases.However,due to age,disease and other complications,the source of autologous vessels is limited,and artificial vascular grafts made from composite materials commonly used in clinic.At present,larger-sized vascular grafts have been widely used,but smaller-sized grafts(vascular diameter less than 6mm)still have problems such as acute thrombosis,intimal hyperplasia,etc.These problems are related to the mechanical properties of vascular grafts and the cellular mechanical environment.This study analyzes the material properties of three kinds of blood vessels(native,decellularized and frozen blood vessels)and endothelial cells in terms of mechanics.Aims are to inspire mechanical ideas for solving the problem of small-diameter vascular grafts(SDVGs),and provide some data foundation for the research of vascular grafts and the construction of multilayer vascular models.Main research contents and results of this paper:(1)Preparation,cell staining and matrix components analysis of three kinds of blood vessels.The blood vessel samples in this study were isolated from the abdomen of the experimental Sprague-Dawley(SD)rats.The removed abdominal aortas were cleaned to obtain native blood vessels,and then they were treated by decellularization and freezing treatment.The results showed that there was no significant difference for native blood vessels;after decellularization,the cells in each layer of the blood vessel were completely removed;after freezing treatment,the cells in the lumen of the blood vessel were removed.(2)The Young's modulus of each layer of the three types of blood vessels was measured on different scales(micrometer and nanometer).At the microscale,the tunica media and tunica adventitia of the three types of blood vessels were measured with a1?m radius spherical probe;at the nanoscale,a 60 nm radius pyramidal probe was used to measure the tunica media,tunica adventitia and the lumen of the three types of blood vessels.The results illustrate that the mechanical properties of the arterial vessel wall are scale-dependent.At different scales,the mechanical properties of each layer of the blood vessel are significantly different,and the measurements of the nanometer scale are significantly higher than those of the micrometer scale.Decellularization increases the Young's modulus of tunica media and tunica adventitia of the blood vessel and reduces the stiffness of the lumen;freezing treatment does not change the relative mechanical relationship between the tunica media and tunica adventitia of blood vessel,which means the ratio of the Young's modulus of the tunica media and tunica adventitia of the frozen blood vessel is similar to the ratio of the Young's modulus of the tunica media and tunica adventitia of the native blood vessel.In addition,freezing treatment did not change the Young's modulus of the vascular lumen.(3)We used finite element simulation to verify the theoretical measurement of vascular tissues with different-scaled probes,and measured the viscoelasticity of the cells combined with AFM.In Abaqus software,a linear elastic vascular model and a viscoelastic cell model were constructed.We theoretically analyzed the effect of different-scaled probes on vascular tissue in the vascular model.In addition,we can obtain parameters from fitting the stress relaxation curve of AFM with the generalized Maxwell model,and then we constructed the cell model based on these parameters.Finally,the experimental curves are matched to obtain the relaxation times to characterize the cellular viscoelasticity.(4)The cellular elasticity and viscoelasticity were measured at different loading rates.In this study,fixed endothelial cells(ECs)and normal endothelial cells were used as samples.In terms of elasticity,the Young's modulus of normal ECs gradually increased with increasing loading rate,while the mechanical properties of fixed cells were relatively stable and did not change with varied speeds.For viscoelasticity,differences between fixed ECs and normal ECs are also significant.The long-term relaxation time of fixed ECs decreases with growing loading rate,while the long-term relaxation time of normal ECs gradually increases and then decreases.