A Method for Determing Poisson’s Ratio of Cells Based on Micropipette Aspiration Technique / 医用生物力学

Objective To propose a method for determing cell Poisson’s ratio based on micropipette aspiration technique. Methods Based on the assumption of deformation symmetry, the analytical expression between Poisson’s ratio and the amount of deformation was derived by extracting the extrusion deformation characteristics of the cells under micropipette aspiration according to the generalized Hooke’s law. The accurate determination of Poisson’s ratio of cells was realized according to position changes of markers on the surface of cell membrane. ResultsThe Poisson’s ratio of LNCaP cells in prostate cancer cells was measured. The result showed that the Poisson’s ratio of LNCaP cells was between 0.44 and 0.46, with an average value of 0.45. The influence of the location of the same cell feature points on calculation results of Poisson’s ratio was within the error range of 1.6%. Conclusions This method is simple and feasible, can improve the measurement accuracy of Poisson’s ratio of cells, and is helpful for cell detection and screening by using cell mechanical properties in clinic.

Comparative Experiment on Physical Properties of Red Blood Cells in Newborn Infants and Elderly People / 医用生物力学

Objective By comparing the physical properties (cell area, volume and elastic modulus) of red blood cells (RBCs) between newborn infants and the elderly over 80 years old, and correlation with the physiological and biochemical parameters such as total cholesterol and glycosylated hemoglobin, the effects of different ages and biochemical parameters on RBC physical properties were analyzed. Methods The mcropipette aspiration was used to measure the surface area, volume and elastic modulus of erythrocytes in newborn infants and the elderly over 80 years old, and the data were analyzed by statistical distribution analysis, correlation analysis and regression analysis. Results The mean values of RBC volume, surface area and elastic modulus in the elderly over 80 years old were smaller than those in newborn infants, and the mean values of RBC mechanical parameters in the same age group were not significantly different. The erythrocytes geometric parameter distribution of newborn infants was more concentrated than that of the elderly, while the elastic modulus distribution of newborn infants was more dispersed than that of the elderly. The mechanical properties of RBCs in newborn infants were highly correlated with the total cholesterol and gestational week; the mechanical properties of RBCs in the elderly were highly correlated with diastolic blood pressure and glycated hemoglobin. Conclusions There are significant differences in physical properties of RBCs between newborn infants and the elderly over 80 years old, and the biochemical parameters that affect physical properties of RBCs at different ages are also different.

Microfluidic Chip Separation and Physical Property Measurement of Circulating Tumor Cells / 医用生物力学

Objective To establish a new method to measure the elastic modulus of living circulating tumor cells (CTCs) by micropipette aspiration. Methods Living CTCs were enriched by commercial microfluidic chips and identified individually using EpCAM antibody under fluorescence microscope. The elastic modulus of CTCs was measured using micropipette aspiration and compared with cancer cell lines. Results For the elastic modulus of different cancer cell lines, heterogeneity was found not only between the different types of cancer cell lines but also inside the same cell line. The CTCs in breast cancer had a smaller elasticity modulus compared with MCF-7 cancer cell line. Conclusions This method can measure the elastic modulus of living CTCs, which provides cell mechanics data for studying the relationship between physical properties of CTCs and diagnosis of cancers, as well as developing the physical biomarkers of tumor cells.

Viscoelastic properties of embryonic neuroepithelial cells in neural tube defects mice / 国际生物医学工程杂志

Objective To explore the role of mechanical properties of embryonic neuroepithelial cells in the process of neural tube closure.Methods Neural tube defects (NTDs) mouse model was established by intragastric administration with all-trans retinoic acid at embryo 7.25 day.All the pregnant mice were sacrificed at embryo 9.5 day and 11.5 day,respectively,and the primary neuroepithelial cells were isolated from neural tube tissue of normal and NTDs mice,respectively.The mechanical characteristics of neuroepithelial cells were analyzed using micropipette aspiration technique combined with a standard solid viscoelastic mechanical model.Results The mechanical characteristics of mouse embryonic neuroepithelial cells showed typical viscoelastic solid characteristics.Compared with the control group,the three viscoelastic parameters,i.e.equilibrium modulus,transient modulus and apparent viscosity coefficient,of the neuroepithelial cells in the NTDs group were significantly increased,and the differences were statistically significant (all P＜0.05).However,there was no significant difference in the viscoelastic parameters of the same group between embryo 9.5 d and 11.5 d (all P＞0.05).Conclusion The decrease in the deformability of embryonic neuroepithelial cells may be one of the factors responsible for neural tube closure disorders.

Biomechanical properties of fibroblasts after posterior scleral reinforcement treatment for rabbit experimental myopia / 医用生物力学

Objective To evaluate the biomechanical properties of fibroblasts for rabbit experimental myopia after Posterior Scleral Reinforcement (PSR) treatment, and discuss the mechanism of PSR in myopia treatment as viewed from biomechanics. Method 45 rabbits of three week old were randomly monocular treated by eyelid suture to prepare experimental myopia eye. After 60 days, the experimental myopia eyes were divided into two groups randomly. Group A was treated by PSR. Group B was treated by similar operation without placing reinforce strap. After three months and six month, the fibroblasts from each group were isolated and cultured in vitro respectively. The cultured cells were then determined to be fibroblasts by using immunocyte chemistry method. Micropipette aspiration technique was used to investigate the viscoelastic properties of the fibroblasts from each group with mechanical model of semi infinite somatic cells. ResultsThree months after operation, the viscoelastic properties of the scleral fibroblasts in Group A and Group B exhibit no significant difference (P>0.05) three months and six months as well (P>0.05) after operation with the equilibrium modulus, E∞, and apparent viscosity, μ of the scleral fibroblasts in Group A (E = (361.2± 121.1)Pa、μ=(2928.2±669.4)Pa·s) compared with that in Group B (E =(347.6± 82.1)Pa、μ=(2820.6± 593.5)Pa·s). Neither in Group A nor Group B, the E∞ and μ at different stages after operation have significant difference (P>0.05). The E∞ and μ in transition zone tissues at different stages after operation have no significant difference(P>0.05) either. Conclusions The enhancement of PSR is caused by transition zone tissues and the strip itself.

Effect of inhibiting cytoskeleton on the mechanical properties of normal rat kidney cells / 医用生物力学

Objective To determine whether the alteration of cytoskeleton interfere with the mechanical properties of normal rat kidney cells (NRKCs).Method NRKCs were treated with cytochalasin D, colchicine and blebbistatin using micropipette aspiration technique, and the changes in Young’s modulus and viscoelasticity of NRKCs were assessed. Results The Young's modulus of is significantly decreased after treated with all cytoskeleton inhibitors. Compared to the control, the viscoelasticity is significantly decreased in NRKCs treated with cytochalasin D and blebbistatin, but in not in colchicines treated cells. Conclusions The effect of blebbistatin on NRKCs mechanical properties is independent of cytoskeleton. Inhibition of assembling of actin meshwork or the activity of myosin II ATPase will reduce cell's Young's modulus and viscoelasticity. In addition, microtubule assembling is correlated with Young's modulus rather than viscoelasticity.

The effect of BCG - PSN on the mechanical properties of adhesion between PG cells or PAa cells and HUVEC / 重庆医科大学学报

Objectives :To investigate the effect of BCG - PSN on the mechanical properties of adhesion between lung cancer cells and human umbilical vein endothelial cells. Methods: Micropipette aspiration technique was used to investigate quantitatively the adhesion force (Fa) and the relative adhesion stress (S1) between high metastatic human lung giant cell carcinoma (PG) cells or low metastatic lung adenocarcinoma (PAa) cells and human umbilical vein endothelial cells (HUVEC). Further,we Invistgated the effect of bacillus of Calmette and Guerin - polysaccharide nucleic acid (BCG - PSN) on Fa and S1. Results: The adhesion force (Fa) of PG cells to HUVEC were higher than that of PAa cells under the experimental condition. With treatment using BCG - PSN, the values of the adhesion force of PAa cells to HUVEC decreased in a concentration - dependent and time - dependent manner. For PG cells, treatment with a concentration of 50?g/ml or higher resulted in a continuous decrease of the cell adhesion force. And the adhesion force to HUVEC decreased continuously with the duration of treament from 30 minutes to 48 hours, but they increased significantly again in 72 hours after treatment. The relative adhesion stress between lung cancer cells and HUVEC,S1,changed almost in the same tendency as the adhesion force,Fa. Conclusion :The adhesion forces of PG cells to HUVEC were higher than that of PAa cells under the experimental condition. The adhesion forces of both of the lung cancer cells to HUVEC can be inhibited by BCG - PSN. These results might be relative to the high metastatic potential of PG cells through blood circulation, and to the antitumor action of HCG-PSN.