Visco-hyperelastic characterization of the mechanical properties of human fallopian tube tissue using atomic force microscopy

Abstract

Human ovum cells sense the physical stimuli of their environment and regulate their behavior based on these stimuli. The fallopian tube tissue, as the substrate on which the ovum is fertilized, has major physical interactions with the ovum which makes its mechanical properties of great significance. In in-vitro fertilization (IVF), however, the ovum cells are fertilized on non-biomechanical substrates that are more than five orders of magnitude harder than the fallopian tube. This huge difference in the mechanical properties of the natural and IVF substrates can have negative result on the development of the embryo, the success of the IVF process and long-term health effects on children born using IVF.As a first step toward replicating biologically relevant substrates for IVF process, this study characterizes the visco-hyperelastic properties of the fallopian tube. Nano-indentation experiments with rates ranging from 0.5 to 10 μm/s were conducted on the ampullary-isthmic junction of the human fallopian tube tissue using Atomic-Force Microscopy. Apparent Young's modulus found using Hertzian contact model showed a strong correlation with the indentation rate as it increased from 26.86 to 110.69 kPa when indentation rates increased from 0.5 to 10 μm/s. This rate dependency as well as the high nonlinearity observed in the data, were investigated by visco-hyperelastic model, using Ogden strain energy function. By developing an optimization based reverse finite element method the parameters of the visco-hyperelastic model were captured. The final results show the tangent shear modulus of 11.5 kPa and the relaxation time of 34.5 ms for this tissue.