On the Mechanical Experiments and Modeling of Human Cervix

The mechanical function of the uterine cervix is critical for a healthy pregnancy. During pregnancy, the cervix undergoes a significant remodeling from a mechanical barrier into a compliant structure to allow for a successful delivery. A too early or too late cervical softening will lead to spontaneous preterm births (sPTB) or dystocia. PTB is a leading cause of neonatal death, affecting 15 million newly born babies each year around the world. According to CDC, the rate of PTB increases in recent years. Dystocia increases the risk to both mother and newborn babies, leading to neonatal asphyxia, neonatal infection, uterine rupture, or other dangerous sequelae. Therefore, it is significant to have a better correlation of the mechanical properties change and the biological remodeling process of the cervix during pregnancy. This thesis will focus on (1) mechanical experiments of the human cervix, and (2) the development of a material constitutive model for cervix to characterize the complex microstructure-related mechanical property of the cervix. In this thesis, a spherical indentation test was designed and conducted on human cervical samples sliced perpendicular to the axial direction, to characterize the compressive mechanical behavior of the human cervix. A uniaxial tensile was designed and conducted on the strip samples cut along and perpendicular to the preferential fiber direction from the indentation samples, to characterize the tensile mechanical behavior of the cervix. Based on the detailed experimental investigation, a nonlinear time-dependent anisotropic microstructure-inspired constitutive model has been developed. The basic idea of the model is that the mechanical behavior of the human cervix can be decomposed into an equilibrium and a time-dependent part, and the tension and compression mechanical behaviors are caused by disparate mechanisms. Specifically, the collagen fibrous network plays a major role in the tensile mechanical response, while proteoglycans (PGs), glycosaminoglycans (PGs),, and liquid cause the compressive mechanical response. The tensile time-dependent mechanical behavior of the human cervix is mostly attributed to the interactions between the collagen fiber and other components, while the compressive time-dependent mechanical behavior is mainly attributed to the porous effect. The equilibrium and time-dependent mechanical responses have been well captured using the model, and the results reveal the connection between the ECM microstructure remodeling and mechanical properties change during pregnancy