2.1. Sample collection and initial preparation

Fetal membranes were obtained from patients undergoing caesarean sections at around 38 gestational weeks at the Obstetrics Department of the University Hospital Zurich, Switzerland. Informed written consent using a protocol approved by the Ethics Committee of the District of Zürich (KEK-StV-Nr. 07/07) was obtained from each patient before surgery. Fetal membranes were considered for this project if they derived from patients with no diabetes mellitus, no preterm rupture of the membrane, no labour contractions prior to delivery, and negative for HIV, chlamydia and hepatitis B. After delivery, fetal membranes were cut from the placental disc at a distance of around 2 cm. Samples were kept at room temperature and continuously hydrated before and during transport to the testing laboratory, as well as during the experiments using physiological saline solution (PS, 0.9% NaCl). All experiments were performed within 8 h after delivery. AM and CH were gently separated by hand and samples were cut to a desired geometry with a scalpel or stamps when laying on a plastic foil. Note that samples were cut along random directions, as a random orientation of collagen fibres is expected in the undeformed configuration [3–5,9].