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Mechanics, Failure and Repair of Human Fetal Membranes

Wilfried Bürzle

office: CLA G 21.1
phone: +41 44 632 77 91
email: buerzle@imes.mavt.ethz.ch


The fetal membranes, amnion and chorion, form a ~0.5 mm thin bilayer that serves as barrier and container throughout gestation. Rupture of membranes is part of the natural sequence of events for term delivery, but has serious complications when it occurs prior to term; spontaneous preterm premature rupture (sPPROM) before 37 weeks of gestation in the absence of labor affects 1-4% of pregnancies and accounts for 30-40% of preterm deliveries [18p]. In addition, introduction of needles or fetoscopes into the intrauterine cavity for diagnostic or operative purposes pose a significant risk for persisting membrane leakage and subsequent membrane failure (iatrogenic PPROM).
Understanding the deformation and rupture behavior of fetal membranes and the structural response of the membrane bilayer is a necessary foundation for attempts to prevent or to repair PPROM. We perform uniaxial and biaxial experiments on fetal membranes in order to determine constitutive model parameters, and to examine their relation to molecular correlates for mechanical function.

 


 

Experimental Mechanics

Different mechanical tests are applied to evaluate the deformation behavior of human fetal membranes under different loading conditions. The test results are analyzed within the realm of nonlinear continuum mechanics and representative scalar parameters are extracted. The experimental observations serve as basis for the development of suitable constitutive model formulation.

 

Histology

Biochemical assays are used for the determination of the amount of microstructural constituents, i.e. collagen, elastin and collagen cross-links. Comparison of these data with the corresponding parameters from mechanical tests enables the evaluation of the correlation between mechanical behavior and microstructure.

Our data show an inverse proportionality between uniaxial small strain stiffness and the elastin content within a uniaxial stress state [18p]. For a biaxial state of stress we found that the collagen content and its cross-links correlate with high strain stiffness as well as membrane strength [35p].
 

Continuum Mechanics

Mechanical response in different kinematic configurations is considered for selection of corresponding constitutive model formulations. Information on the architecture of the material, stiff collagen fibers embedded in a soft extracellular matrix, can be included in the model formulation [Holzapfel et al, J Elasticity 2000].
Phenomenological models are used for numerical simulations , for example to study and analyze different experimental setups or to investigate and optimize the puncture procedure of amniocentesis (to minimize the risk of PPROM).

 

Partners
Prof. Zimmermann, USZ, Obstetrics and Gynecology Dr. Martin Ehrbar, USZ, Obstetrics and Gynecology
MD Nicole Ochsenbein, USZ, Obstetrics and Gynecology

 

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09/05/18 | Francesco Filotto | ZfM | ETH