The structural and mechanical properties of the cervix change dramatically during pregnancy. Cervix tissue is firm early in gestation to maintain the fetus in the uterus, but undergoes extreme biochemical, structural, and mechanical changes as pregnancy progresses. In this remodeling process, collagen fibers become increasingly disorganized and the tissue softens as a result to allow for birth. The relationship between the changes in the tissue microstructure and mechanical properties remains poorly understood, but is important in the context of preterm birth. We investigated this relationship at the microscale for non-pregnant rat cervix (N=5) by co-registering micromechanical and 3D microstructural data. We also used a new representation tool, an optomechanogram, to visualize the results. An indenter measured the indentation modulus along a semi-continuous line and second-harmonic generation (SHG) microscopy provided information about the 3D microstructure. Fourier transform analysis, along with a modified definition of spherical variance tailored for fibrous materials, quantified the SHG images. To relate the two independently measured data sets, we employed a custom co-registration approach to co-locate the indentation and SHG data. We classified the measurements based on anatomical location and collagen fiber organization as ring, septum, and near septum. Quantitative image analysis revealed differences in the microstructure of the near septum, with more out-of-plane and disorganized fibers, compared with the ring and septum. The micromechanical measurements showed a similar trend; the indentation modulus was significantly higher in the near septum compared to the other two regions (p<0.05). The optomechanogram visually illustrated the correlation between microstructure and mechanical properties on the micro-scale. The results offer new information about the structure-mechanical properties relationship of the cervix and open up new avenues to better understand cervical remodeling and prediction of preterm birth. While we focused on cervix, the findings are more broadly applicable to any other collagenous tissue.

An optomechanogram: co-registered microstructural and micromechanical properties of the cervix

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