Characterization of irreversible physio-mechanical processes in stretched fetal membranes

Area of Science:

• Biomaterials Science
• Mechanobiology
• Reproductive Biology

Background:

• The mechanical properties of the fetal membrane (FM) are crucial for understanding labor.
• Previous studies have not fully characterized the mechanical behavior of FM under pre-contraction conditions.

Purpose of the Study:

• To investigate the mechanical response of live fetal membrane (FM) tissues under simulated pre-contraction conditions.
• To develop a new constitutive model for collagenous tissues that accounts for observed irreversible deformation.
• To explore the molecular mechanisms underlying the observed mechanical behavior and its potential link to labor initiation.

Main Methods:

• Bulge tests were performed on live fetal membrane (FM) tissues.
• Experimental data were used to develop and validate a new mechanical model for collagenous tissues.
• Analysis of stress-strain relationships and residual strain was conducted.
• Physio-mechanical processes were discussed to explain the observed irreversible behavior.

Main Results:

• Live FM tissues exhibit significant irreversible mechanical behavior during loading, distinct from unloading or subsequent cycles.
• An irreversible strain was observed that did not recover upon unloading.
• The irreversible behavior demonstrated a linear stress-strain relationship.
• A new model accurately predicted the experimental stress-strain curves, identifying a threshold strain for irreversible transformation.

Conclusions:

• Pre-contraction mechanical stretch of FM induces irreversible deformation, likely due to a collagen molecule phase transformation (α-helix to β-sheet).
• This molecular change alters tissue structure and may trigger biological changes leading to labor initiation.
• The study introduces a novel model for collagenous tissue mechanics and highlights a key property related to irreversible transformation.