Multiaxial mechanical behavior of human fetal membranes and its relationship to microstructure

Abstract

This study was directed to the measurement of the mechanical response of fetal membranes to physiologically relevant loading conditions. Characteristic mechanical parameters were determined and their relation to the microstructural constituents collagen and elastin as well as to the pyridinium cross-link concentrations analyzed. 51 samples from twelve fetal membranes were tested on a custom-built inflation device, which allows mechanical characterization within a multiaxial state of stress. Methods of nonlinear continuum mechanics were used to extract representative mechanical parameters. Established biochemical assays were applied for the determination of the collagen and elastin content. Collagen cross-link concentrations were determined by high-performance liquid chromatography measurements. The results indicate a distinct correlation between the mechanical parameters of high stretch stiffness and membrane tension at rupture and the biochemical data of collagen content and pyridinoline as well as deoxypyridinoline concentrations. No correlation was observed between the mechanical parameters and the elastin content. Moreover, the low stretch stiffness is, with a value of 105 ± 31 × 10(-3) N/ mm much higher for a biaxial state of stress compared to a uniaxial stress configuration. Determination of constitutive model equations leads to better predictive capabilities for a reduced polynomial hyperelastic model with only terms related to the second invariant, I 2, of the right Cauchy-Green deformation tensor. Relevant insights were obtained on the mechanical behavior of fetal membranes. Collagen and its cross-linking were shown to determine membrane's stiffness and strength for multiaxial stress states. Their nonlinear deformation behavior characterizes the fetal membranes as I 2 material.

About Puncture Testing Applied for Mechanical Characterization of Fetal Membranes

“…The work by Arikat et al [8] provided evidence of the rupture sequence of FM by video docu mentation of puncture tests, showing that chorion ruptures first. This is in contrast to observations from recent inflation and uniaxial tension experiments on intact FM as well as on separate amnion and chorion layers [16][17][18],…”

Time-dependent mechanical behavior of human amnion: Macroscopic and microscopic characterization

“…Finally, λ was calculated as current divided by initial width. For inflation experiments, membrane tension was evaluated as described in [31] from pressure values and current curvature of the specimen. The apex displacement d was quantified with a custom-made algorithm in Matlab (The MathWorks Inc., Massachusetts, USA).…”

“…A posteriori analysis showed that by this means a nominal strain rate of approximately 0.04 s -1 was achieved over the major part of the loading phase. Additionally, creep inflation tests (I) were performed with our custom-built inflation device [31] modified in order to perform creep experiments with a fast initial loading: a large reservoir filled with physiological saline solution and placed on a platform with an adjustable vertical position, was connected to the inflation chamber through a tube equipped with a valve. The reservoir was placed at a specific height to generate a target pressure in the chamber within a very short time of the opening of the valve.…”

“…Tests were performed in saline solution to ensure hydration of the tissue during the experiment. Specimens with 50 mm diameter were clamped on the inflating cylinder with the help of sand paper rings [31]. The pressure values and images were recorded at 4 Hz.…”

“…In addition to its essential physiological function, it was also proposed as a promising candidate to be used as scaffold material for tissue engineering applications [10,11]. The mechanical response of the intact FM and of the separated amnion was investigated in uniaxial tensile tests [7,12,13,14,15,16,17,18], biaxial tensile tests [16,19], puncture tests [9,17,20,21,22,23,24] and inflation tests [3,25,26,27,28,29,30,31]. These studies focused primarily on the quasi-static monotonic deformation and rupture behavior, with only a few works investigating the time-dependent response of the intact membrane [26,28,29] or of the amnion alone [15,16,32].…”