چكيده به لاتين
In most contact theories, whose most popular one could be mentioned as three models of Hertz, DMT and JKR, biological cells have been considered as elastic material which is not an appropriate assumption. Elastic assumption in case of biological cells could lead to neglecting the loading history as a result of which the stresses and strains applied on the material would not be studied accurately. Developing the three mentioned elastic models into viscoelastic, simulating and comparing them with empirical data obtained through indentation test of MCF-7 cancer cell in this thesis have shown that viscoelastic state presents a better prediction of biological cells behavior compared to that of elastic state.
Selecting the suitable creep function for objects in contact is another issue having significant importance in viscoelastic case which has been investigated. Different mechanical models of a cell have been studied and simulated for all three named theories among which the creep function obtained from Kelvin model, parallel combination of spring-damper, simplified simulation and gave more precise results for modeling due to the fact that the obtained results from this model are closer to experimental ones and it is simpler than other models.
After choosing the suitable mechanical model for the cell, capability of the developed theories in predicting the results for biological liquid environments was scrutinized. Although the results of the Hertz and DMT viscoelastic models would be closer to experimental ones in comparison with viscoelastic JKR, neglecting adhesion makes their prediction in biological liquid environments weak and erroneous. Therefore, it can be concluded that the developed viscoelastic model of JKR is more accurate and has better performance in different environments than other mentioned models; so this model was used in order to model and simulate 3D manipulation moving phases and the results were compared with analogous elastic theory. For more accurate explanation of friction forces in manipulation, in this step, friction models were used.
In experimental part, MCF-7 cell properties were extracted. In this section, cell geometry and topography, elasticity modulus and its variations in different point of cell with different thicknesses, adhesion and its variations in different point of cell, viscoelastic properties (including damping coefficient and spring coefficient) in different penetration depth, were obtained using experiment.
