Theses Doctoral

Compressive Mechanical Properties and Collagen Fiber Orientation and Dispersion in the Cervix of Non-Pregnant and Pregnant Women

Yao, Wang

The cervix serves as the passage for the fetus during birth. The mechanical function of the cervix is crucial for a healthy term pregnancy: 1) prior to term it must remain closed and resist the increasing mechanical load from the growing pregnancy and 2) at time of parturition it must soften, deform and dilate to allow for delivery of the fetus. After delivery, the cervix must repair and close. The timing and characteristics of this remodeling behavior is currently an active research focus because it is hypothesized that premature remodeling in pregnancy can lead to preterm birth, a leading cause of neonatal death or significant neonatal morbidity. The research goal was to measure and characterize anisotropic material properties because they contribute to keeping cervix shut.
In this thesis, the collagen fiber network orientation and dispersion of non-pregnant and pregnant human cervical tissue samples were analyzed using optical coherence tomography, and the samples were tested using mechanical indentation and digital image correlation techniques. Human cervices were acquired from non-pregnant and pregnant consented patients that went through hysterectomy. Axial cervical slices were imaged using optical coherence tomography and fiber orientation and dispersion data was analyzed using a new pixel-wise fiber orientation algorithm and was compared among four anatomical quadrants and among patients with different obstetric backgrounds. Two radial zones with different fiber orientations were found. The posterior and anterior quadrants of the outer zone were found to have distinct fiber dispersion features and their fiber dispersion shifted most dramatically from non-pregnant to pregnant. In an effort to characterize the compressive mechanical behavior of human cervical tissue, we present a novel indentation test with digital correlation imaging to visualize the real-time deformation of cervical slice during indentation and measure the compressive mechanical properties through coupled finite element analysis with collagen fiber orientation and dispersion information informed by OCT of non-pregnant and term pregnant cervical tissue. Heterogeneity within the same cervix and difference between non-pregnant and pregnant cervices were found. The upper cervix was found to have a stronger ground substance. The anterior and posterior quadrants were less compressible than the left and right quadrants for non-pregnant specimens. The upper cervix of non-pregnant patients had a stronger ground substance than that of pregnant patients.
A workflow of optical, mechanical, and chemical experiments on the same piece of specimen with most fibers intact was also proposed in this thesis and these experiments would validate and inform each other.


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More About This Work

Academic Units
Mechanical Engineering
Thesis Advisors
Myers, Kristin M.
Ph.D., Columbia University
Published Here
July 23, 2017