Biomechanical analysis of human chorioamniotic membranes

Pregnancy state before the onset of labor: a holistic mechanical perspective

Successful pregnancy highly depends on the complex interaction between the uterine body, cervix, and fetal membrane. This interaction is synchronized, usually following a specific sequence in normal vaginal deliveries: (1) cervical ripening, (2) uterine contractions, and (3) rupture of fetal membrane. The complex interaction between the cervix, fetal membrane, and uterine contractions before the onset of labor is investigated using a complete third-trimester gravid model of the uterus, cervix, fetal membrane, and abdomen. Through a series of numerical simulations, we investigate the mechanical impact of (i) initial cervical shape, (ii) cervical stiffness, (iii) cervical contractions, and (iv) intrauterine pressure. The findings of this work reveal several key observations: (i) maximum principal stress values in the cervix decrease in more dilated, shorter, and softer cervices; (ii) reduced cervical stiffness produces increased cervical dilation, larger cervical opening, and decreased cervical length; (iii) the initial cervical shape impacts final cervical dimensions; (iv) cervical contractions increase the maximum principal stress values and change the stress distributions; (v) cervical contractions potentiate cervical shortening and dilation; (vi) larger intrauterine pressure (IUP) causes considerably larger stress values and cervical opening, larger dilation, and smaller cervical length; and (vii) the biaxial strength of the fetal membrane is only surpassed in the cases of the (1) shortest and most dilated initial cervical geometry and (2) larger IUP.

Unveiling the human fetal-maternal interface during the first trimester: biophysical knowledge and gaps

The intricate interplay between the developing placenta and fetal-maternal interactions is critical for pregnancy outcomes. Despite advancements, gaps persist in understanding biomechanics, transport processes, and blood circulation parameters, all of which are crucial for safe pregnancies. Moreover, the complexity of fetal-maternal interactions led to conflicting data and methodological variations. This review presents a comprehensive overview of current knowledge on fetal-maternal interface structures, with a particular focus on the first trimester. More in detail, the embryological development, structural characteristics, and physiological functions of placental chorionic plate and villi, fetal membranes and umbilical cord are discussed. Furthermore, a description of the main structures and features of maternal and fetal fluid dynamic exchanges is provided. However, ethical constraints and technological limitations pose still challenges to studying early placental development directly, which calls for sophisticated in vitro, microfluidic organotypic models for advancing our understanding. For this, knowledge about key in vivo parameters are necessary for their design. In this scenario, the integration of data from later gestational stages and mathematical/computational simulations have proven to be useful tools. Notwithstanding, further research into cellular and molecular mechanisms at the fetal-maternal interface is essential for enhancing prenatal care and improving maternal and fetal health outcomes.

Development of a multilayer fetal membrane material model calibrated using bulge inflation mechanical tests

The fetal membranes are an essential mechanical structure for pregnancy, protecting the developing fetus in an amniotic fluid environment and rupturing before birth. In cooperation with the cervix and the uterus, the fetal membranes support the mechanical loads of pregnancy. Structurally, the fetal membranes comprise two main layers: the amnion and the chorion. The mechanical characterization of each layer is crucial to understanding how each layer contributes to the structural performance of the whole membrane. The in-vivo mechanical loading of the fetal membranes and the amount of tissue stress generated in each layer throughout gestation remains poorly understood, as it is difficult to perform direct measurements on pregnant patients. Finite element analysis of pregnancy offers a computational method to explore how anatomical and tissue remodeling factors influence the load-sharing of the uterus, cervix, and fetal membranes. To aid in the formulation of such computational models of pregnancy, this work develops a fiber-based multilayer fetal membrane model that captures its response to previously published bulge inflation loading data. First, material models for the amnion, chorion, and maternal decidua are formulated, informed, and validated by published data. Then, the behavior of the fetal membrane as a layered structure was analyzed, focusing on the respective stress distribution and thickness variation in each layer. The layered computational model captures the overall behavior of the fetal membranes, with the amnion being the mechanically dominant layer. The inclusion of fibers in the amnion material model is an important factor in obtaining reliable fetal membrane behavior according to the experimental dataset. These results highlight the potential of this layered model to be integrated into larger biomechanical models of the gravid uterus and cervix to study the mechanical mechanisms of preterm birth.

Mechanical reinforcement of amniotic membranes for vesicovaginal fistula repair

INTRODUCTION

Amniotic membranes (AM) have shown its great potential in reconstructive surgery due to their regenerative capacity. However, AM is regarded to be relatively weak when applied for load-bearing purposes. This study aims to produce an AM-based scaffold that can withstand the mechanical loads applied in vesicovaginal fistula repair. Different strategies are investigated to improve the mechanical characteristics of AM.

METHODS

Single and multilayered AM, and composite constructs of AM with electrospun poly-4-hydroxybutyrate (P4HB) or bovine pericardial tissue combined with the use of fibrin glue, were mechanically tested in this study. Suture retention strength and mechanical characteristics (tensile stress, elongation, tangent modulus and maximum load) were assessed by uniaxial testing. The effect of degradation of the composite constructs on the mechanical characteristics was determined by uniaxial testing after 4 and 8 weeks.

RESULTS

Single and multilayered AM could not provide the mechanical requirements needed for surgical implantation (>2N load). AM was combined successfully with electrospun P4HB and bovine pericardium with the use of fibrin glue and were able to exceed the 2N load.

CONCLUSION

The composite constructs with AM showed sufficient mechanical characteristics for surgical implantation. Electrospun P4HB combined with AM seemed the most promising candidate since the mechanical characteristics of P4HB can be further modified to meet the requirements of the application site and the degradation of the P4HB allows a gradual transfer of load. Eventhough the scaffold is intended for fistula repair, it can potentially be applied in surgical reconstruction of other hollow organs by modifying the mechanical characteristics.

Development of a vascular substitute produced by weaving yarn made from human amniotic membrane

Because synthetic vascular prostheses perform poorly in small-diameter revascularization, biological vascular substitutes are being developed as an alternative. Although their in vivo results are promising, their production involves long, complex, and expensive tissue engineering methods. To overcome these limitations, we propose an innovative approach that combines the human amniotic membrane (HAM), which is a widely available and cost-effective biological raw material, with a rapid and robust textile-inspired assembly strategy. Fetal membranes were collected after cesarean deliveries at term. Once isolated by dissection, HAM sheets were cut into ribbons that could be further processed by twisting into threads. Characterization of the HAM yarns (both ribbons and threads) showed that their physical and mechanical properties could be easily tuned. Since our clinical strategy will be to provide an off-the-shelf allogeneic implant, we studied the effects of decellularization and/or gamma sterilization on the histological, mechanical, and biological properties of HAM ribbons. Gamma irradiation of hydrated HAMs, with or without decellularization, did not interfere with the ability of the matrix to support endothelium formation in vitro. Finally, our HAM-based, woven tissue-engineered vascular grafts (TEVGs) exhibited clinically relevant mechanical properties. Thus, this study demonstrates that human, completely biological, allogeneic, small-diameter TEVGs can be produced from HAM, thereby avoiding costly cell culture and bioreactors.

Structure and Strength of Bovine and Equine Amniotic Membrane

Simple Summary

Thin, strong scaffold materials are needed for surgical applications. There is a limited selection of available materials and new materials are required. Amnionic membrane from cattle and horses were investigated for this purpose. The structure of these materials was characterized with synchrotron techniques and the strength was measured. A possible relationship between the structure and strength was identified. These amnion materials from animal sources are strong, thin, and elastic materials, although weaker than some other collagen tissues. They may be suitable for use in surgery as an alternative to material from human donors.

Abstract

Thin, strong scaffold materials are needed for surgical applications. New materials are required, particularly those readily available, such as from non-human sources. Bovine amniotic membrane (antepartum) and equine amniotic membrane (postpartum) were characterized with tear and tensile tests. The structural arrangement of the collagen fibrils was determined by small-angle X-ray scattering, scanning electron microscopy, and ultrasonic imaging. Bovine amnion had a thickness-normalized tear strength of 12.6 (3.8) N/mm, while equine amnion was 14.8 (5.3) N/mm. SAXS analysis of the collagen fibril arrangement yielded an orientation index of 0.587 (0.06) and 0.681 (0.05) for bovine and equine, respectively. This may indicate a relationship between more highly aligned collagen fibrils and greater strength, as seen in other materials. Amnion from bovine or equine sources are strong, thin, elastic materials, although weaker than other collagen tissue materials commonly used, that may find application in surgery as an alternative to material from human donors.

New approaches suggest term and preterm human fetal membranes may have distinct biomechanical properties

Preterm prelabour rupture of membranes is the leading cause of preterm birth and its associated infant mortality and morbidity. However, its underlying mechanism remains unknown. We utilized two novel biomechanical assessment techniques, ball indentation and Optical Coherence Elastography (OCE), to compare the mechanical properties and behaviours of term (≥ 37 weeks) and preterm (33-36 weeks) human fetal membranes from ruptured and non-ruptured regions. We defined the expression levels of collagen, sulfated glycosaminoglycans (sGAG), matrix metalloproteinase (MMP-9, MMP-13), fibronectin, and interleukin-1β (IL-1β) within membranes by biochemical analysis, immunohistochemical staining and Western blotting, both with and without simulated fetal movement forces on membrane rupture with a new loading system. Preterm membranes showed greater heterogeneity in mechanical properties/behaviours between ruptured and non-ruptured regions compared with their term counterparts (displacement rate: 36% vs. 15%; modulus: 125% vs. 34%; thickness: 93% vs. 30%; collagen content: 98% vs. 29%; sGAG: 85% vs 25%). Furthermore, simulated fetal movement forces triggered higher MMP-9, MMP-13 and IL-1β expression in preterm than term membranes, while nifedipine attenuated the observed increases in expression. In conclusion, the distinct biomechanical profiles of term and preterm membranes and the abnormal biochemical expression and activation by external forces in preterm membranes may provide insights into mechanisms of preterm rupture of membranes.

Streptococcus agalactiae do not penetrate human chorioamniotic membranes in vitro but alter their biomechanical properties

INTRODUCTION

Vaginal colonization with Streptococcus agalactiae (group B streptococci) is hypothesized to constitute a risk factor for preterm prelabor rupture of membranes. In vitro studies have shown that S. agalactiae strains isolated from infants with neonatal sepsis adhere to chorion cells of the human chorioamniotic membrane. However, it is still unknown whether S. agalactiae strains penetrate the chorioamniotic membranes and whether S. agalactiae colonization affects the biomechanical properties of the membranes and thus contributes to increased risk of preterm prelabor rupture. The aim of this in vitro study was to explore if different strains of S. agalactiae penetrate and affect the biomechanical properties of human chorioamniotic membranes.

MATERIAL AND METHODS

Three different strains of S. agalactiae were obtained, one from an early-onset neonatal infection, one from a case of preterm prelabor rupture of membranes and one from a healthy pregnant carrier. Chorioamniotic membranes from elective cesarean deliveries were either incubated with S. agalactiae or mounted in a two-chamber incubation cell generating a "maternal" and a "fetal" chamber and incubated with S. agalactiae in the maternal chamber. Subsequently the membranes were examined to evaluate S. agalactiae attachment, penetration and the effect on the biomechanical properties.

RESULTS

At 5 h after incubation, S. agalactiae adhered to the chorioamniotic membranes with increased number at 20 h. Streptococcus agalactiae did not penetrate the membranes even after 20 h of incubation. Streptococcus agalactiae increased the ultimate tensile stress needed to rupture the membranes and increased the work needed to rupture the membranes as well as the elastic modulus.

CONCLUSIONS

Human chorioamniotic membranes constitute a physical barrier against S. agalactiae infections. Moreover, S. agalactiae infection leads to increased strength of the membranes.

Antimicrobial Activity of Human Fetal Membranes: From Biological Function to Clinical Use

The fetal membranes provide a supportive environment for the growing embryo and later fetus. Due to their versatile properties, the use of fetal membranes in tissue engineering and regenerative medicine is increasing in recent years. Moreover, as microbial infections present a crucial complication in various treatments, their antimicrobial properties are gaining more attention. The antimicrobial peptides (AMPs) are secreted by cells from various perinatal derivatives, including human amnio-chorionic membrane (hACM), human amniotic membrane (hAM), and human chorionic membrane (hCM). By exhibiting antibacterial, antifungal, antiviral, and antiprotozoal activities and immunomodulatory activities, they contribute to ensuring a healthy pregnancy and preventing complications. Several research groups investigated the antimicrobial properties of hACM, hAM, and hCM and their derivatives. These studies advanced basic knowledge of antimicrobial properties of perinatal derivatives and also provided an important insight into the potential of utilizing their antimicrobial properties in a clinical setting. After surveying the studies presenting assays on antimicrobial activity of hACM, hAM, and hCM, we identified several considerations to be taken into account when planning future studies and eventual translation of fetal membranes and their derivatives as antimicrobial agents from bench to bedside. Namely, (1) the standardization of hACM, hAM, and hCM preparation to guarantee rigorous antimicrobial activity, (2) standardization of the antimicrobial susceptibility testing methods to enable comparison of results between various studies, (3) investigation of the antimicrobial properties of fetal membranes and their derivatives in the in vivo setting, and (4) designation of donor criteria that enable the optimal donor selection. By taking these considerations into account, future studies will provide crucial information that will enable reaching the optimal treatment outcomes using the fetal membranes and their derivatives as antimicrobial agents.

Does preconditioning lower the rupture resistance of chorioamniotic membrane?

Premature rupture of fetal membrane occurs in about 3% of all pregnancies. The physical integrity of chorioamnion (CA) membrane should be retained until delivery for a healthy pregnancy. To explore the effect of pre-conditioning and probe size on the mechanical properties of human chorioamniotic sac, the mechanical properties of 17 human chorioamniotic membranes, collected from cesarean delivery, were examined using biaxial puncture tests with and without preconditioning by different probe sizes. For preconditioned samples, the mean ± std. of ultimate rupture stress was calculated to be 1.73 ± 0.13, 1.61 ± 0.29 and 1.78 ± 0.26 MPa for the probe sizes of 3, 5 and 7 mm, respectively. For samples with no preconditioning, these values were calculated to be 2.38 ± 0.29, 2.36 ± 0.37, and 2.59 ± 0.43 MPa for the above-mentioned probe sizes. The force to probe diameter for samples with no preconditioning was in the range of 1087-1301 N/m for the three probe diameters, well in the range of 850-1580 N/m reported by previous studies. Our results show that the preconditioned samples had significantly lower ultimate puncture force and ultimate stress compared to non-preconditioned samples. In addition, a correlation between the probe size and the magnitude of puncture force was observed, while the stress values were not significantly affected by changing probe size.

Dynamic measurement of amnion thickness during loading by speckle pattern interferometry

INTRODUCTION

In previous studies on the mechanical parameters of amnions (AM), there is a limitation due to the lack of an accurate thickness measurement, which is an important parameter for determining AM-specific mechanical properties. As a bottleneck, the characterization of the basic mechanical properties of AM are greatly restricted, even with the proposal of fracture criteria.

METHOD

First, the initial thickness of the AM is estimated by the interpolated-volume-area method. Second, through combinations of our self-developed mini-biaxial tensile device with speckle pattern interferometry, this is the first time that researchers can accurately obtain the AM thickness at each transient moment in the process of loading.

RESULTS

Based on the experimental results, an accurate stress-strain curve could be obtained. Two important mechanical parameters-the fracture energy density and amnion rupture modulus-could be extracted as 0.184±0.036MPa and 108.57±17.32MPa, respectively. The fracture energy density and amnion rupture modulus provide objective criteria and a scientific basis for the evaluation of AM rupture.

DISCUSSION

The tensile stress-strain curve of a normal human amnion shows a distinct J-shape. This proves that the experimental results are basically reliable. Both important parameters --the fracture energy density and amnion rupture modulus, can be calculated from the stress-strain curve. Extracting these two parameters is critical for the evaluation and prediction of ROM, PROM and PPROM.

In vivo Assessment of Supra-Cervical Fetal Membrane by MRI 3D CISS: A Preliminary Study

In approximately 8% of term births and 33% of pre-term births, the fetal membrane (FM) ruptures before delivery. In vitro studies of FMs after delivery have suggested the series of events leading to rupture, but no in vivo studies have confirmed this model. In this study, we used a three-dimensional constructive interference in steady state (3D-CISS) sequence to examine the FM at the cervical internal os zone during pregnancy; 18 pregnant women with one to three longitudinal MRI scans were included in this study. In 14 women, the FM appeared normal and completely intact. In four women, we noted several FM abnormalities including cervical funneling, chorioamniotic separation, and chorion rupture. Our data support the in vitro model that the FM ruptures according to a sequence starting with the stretch of chorion and amnion, then the separation of amnion from chorion, next the rupture of chorion, and finally the rupture of amnion ruptures. These findings hold great promise to help to develop an in vivo magnetic resonance imaging marker that improves examination of the FMs.

On the defect tolerance of fetal membranes

A series of mechanical experiments were performed to quantify the strength and fracture toughness of human amnion and chorion. The experiments were complemented with computational investigations using a 'hybrid' model that includes an explicit representation of the collagen fibre network of amnion. Despite its much smaller thickness, amnion is shown to be stiffer, stronger and tougher than chorion, and thus to determine the mechanical response of fetal membranes, with respect to both, deformation and fracture behaviour. Data from uniaxial tension and fracture tests were used to inform and validate the computational model, which was then applied to rationalize measurements of the tear resistance of tissue samples containing crack-like defects. Experiments and computations show that the strength of amnion is not significantly reduced by defects smaller than 1 mm, but the crack size induced by perforations for amniocentesis and fetal membrane suturing during fetal surgery might be larger than this value. In line with previous experimental observations, the computational model predicts a very narrow near field at the crack tip of amnion, due to localized fibre alignment and collagen compaction. This mechanism shields the tissue from the defect and strongly reduces the interaction of multiple adjacent cracks. These findings were confirmed through corresponding experiments, showing that no interaction is expected for multiple sutures for an inter-suture distance larger than 1 mm and 3 mm for amnion and chorion, respectively. The experimental procedures and numerical models applied in the present study might be used to optimize needle and/or staple dimensions and inter-suture distance, and thus to reduce the risk of iatrogenic preterm premature rupture of the membranes from amniocentesis, fetoscopic and open prenatal surgery.

Cartography of the mechanical properties of the human amniotic membrane

Because of its low immunogenicity, biological properties, and high availability, the Human Amniotic Membrane (HAM) is widely used in the clinic and in tissue engineering research. However, while its biological characteristics are well described, its mechanical properties remain understudied especially in terms of inter- and intra-HAM variability. To guide bioengineers in the use of this natural biomaterial, a detailed cartography of the HAM's mechanical properties was performed. Maximal force (Fmax) and strain at break (Smax) were identified as the relevant mechanical criteria for this study after a combined analysis of histological sections, thickness measurements after dehydration, and uniaxial tensile tests. Eight HAMs were studied by mechanical cartography using a standardized cutting protocol and sampling pattern. On average, 103 ± 10 samples were retrieved and tested per HAM. Intra-tissue variability highlighted the fact that there were two mechanically distinct areas (placental and peripheral) in each HAM. For all HAMs, placental HAM was significantly stronger by 82 ± 45% and more stretchable by 19 ± 6% than their peripheral counterparts. Our results also demonstrated that placental, but not peripheral, HAM presented isotropic mechanical properties. Thus, placental HAM can be a raw material of choice that could be favored especially in the development of tissue engineering products where mechanical properties play a key role.

Stresses and strains on the human fetal skeleton during development

Mechanical forces generated by fetal kicks and movements result in stimulation of the fetal skeleton in the form of stress and strain. This stimulation is known to be critical for prenatal musculoskeletal development; indeed, abnormal or absent movements have been implicated in multiple congenital disorders. However, the mechanical stress and strain experienced by the developing human skeleton in utero have never before been characterized. Here, we quantify the biomechanics of fetal movements during the second half of gestation by modelling fetal movements captured using novel cine-magnetic resonance imaging technology. By tracking these movements, quantifying fetal kick and muscle forces, and applying them to three-dimensional geometries of the fetal skeleton, we test the hypothesis that stress and strain change over ontogeny. We find that fetal kick force increases significantly from 20 to 30 weeks' gestation, before decreasing towards term. However, stress and strain in the fetal skeleton rises significantly over the latter half of gestation. This increasing trend with gestational age is important because changes in fetal movement patterns in late pregnancy have been linked to poor fetal outcomes and musculoskeletal malformations. This research represents the first quantification of kick force and mechanical stress and strain due to fetal movements in the human skeleton in utero, thus advancing our understanding of the biomechanical environment of the uterus. Further, by revealing a potential link between fetal biomechanics and skeletal malformations, our work will stimulate future research in tissue engineering and mechanobiology.

Biochemical characterization of pure dehydrated binate amniotic membrane: role of cytokines in the spotlight

AIM

Placental allografts used for tissue regeneration differ in membrane compositions and processing techniques. A uniquely folded dehydrated binate amniotic membrane (DBAM) was biochemically characterized to evaluate its potential role in wound healing.

METHODS

Histology, Luminex-based immunoassay and standard in vitro cell biology techniques were employed.

RESULTS

Histological staining confirmed that the DBAM was chorion free with epithelial cell layer of the respective amnion membranes facing outward. DBAM had quantifiable levels of relevant cytokines that induced proliferation and migration while bolstering secretory activity of the cells. DBAM retained biological efficacy at a broad range of temperatures.

CONCLUSION

Cytokines in DBAM stimulate bone marrow stromal and stem cells that may lead to tissue regeneration and wound healing in a clinical setup.

Understanding the Impact of Preservation Methods on the Integrity and Functionality of Placental Allografts

INTRODUCTION

Human placental membranes (hPMs) have a long history in treating burns and wounds. The composition of hPMs includes structural matrix, growth factors, and neonatal cells, all of which contribute to their regenerative potential. However, most hPM products are devitalized after dehydration and irradiation. We compared the functionality of single-layer viable cryopreserved human amniotic membrane (vCHAM) with multilayer devitalized dehydrated human amnion/chorion membrane (dHACM) in wound-relevant models to determine the effect of different processing methods on hPMs.

METHODS

Viable cryopreserved human amniotic membrane and dHACM were compared with fresh hPM for structural integrity and viability. Viable cell persistence in vCHAM over time was evaluated in vitro and in vivo in a diabetic chronic wound mouse model. Proliferation of cells within fresh hPM and vCHAM was evaluated with bromodeoxyuridine and Ki-67 staining, and proliferation of isolated cells in culture was evaluated. Growth factor release over time and in vitro response to chronic wound stimuli (tumor necrosis factor α, lipopolysaccharide, and hypoxia) were used to compare the functionality of vCHAM and dHACM.

RESULTS

The structure and thickness of fresh hPM were retained in vCHAM but were compromised in dHACM. Similar to fresh hPM, vCHAM contained viable cells, whereas dHACM did not. Cells in vCHAM remained viable after 4 and 7 days in culture and in an in vitro chronic wound environment and after 4 and 8 days in vivo after application to a mouse chronic wound. Staining for bromodeoxyuridine and Ki-67 did not reveal proliferative cells within fresh hPM and vCHAM. However, isolated cells proliferated in culture. Viable cryopreserved human amniotic membrane increased platelet-derived growth factor BB, hepatocyte growth factor, and epidermal growth factor levels over time and responded to chronic wound stimuli in vitro by significantly increasing levels of vascular endothelial growth factor and prostaglandin E2. Dehydrated human amnion/chorion membrane showed no significant accumulation of growth factors and did not respond to chronic wound stimuli.

CONCLUSIONS

These results indicate that vCHAM retains intact, native matrix, and viable, active cells and responds to chronic wound stimuli in vitro. The inclusion of multiple layers of hPM does not compensate for structural degradation and loss of viability caused by dehydration as evidenced by a lack of functional response by dHACM. The clinical significance of these results remains to be answered.

Villous Tree Model with Active Contractions for Estimating Blood Flow Conditions in the Human Placenta

Background:

In the human placenta, maternal and fetal bloods exchange substances through the surface of the villous trees: the fetal blood circulates in the villous trees, around which the maternal blood circulates. The blood flows directly influence fetal growth. Stem villi, the main supports of the villous tree, have contractile cells along the axes, whose contractions are expected to influence the blood circulations in the placenta. The displacement is neither measurable nor predictable while non-invasive measurements such as umbilical Doppler waveforms are helpful to predict the histological changes of the villous trees and vascularization in the placenta.

Objective:

The displacement caused by the contraction of the villous tree is necessary to predict the blood flows in the placenta. Hence, a computational villous tree model, which actively contracts, was developed in this study.

Method:

The villous tree model was based on the previous reports: shear moduli of the human placenta; branching patterns in the stem villi. The displacement pattern in the placenta was estimated by the computational model when the shear elastic moduli were changed.

Results:

The results show that the displacement caused by the contraction was influenced by the shear elastic moduli, but kept useful for the blood flows in the placenta. The characteristics agreed with the robustness of the blood flows in the placenta.

Conclusion:

The villous tree model, which actively contracts, was developed in this study. The combination of this computational model and non-invasive measurements will be useful to evaluate the condition of the placenta.

Function and failure of the fetal membrane: Modelling the mechanics of the chorion and amnion

The fetal membrane surrounds the fetus during pregnancy and is a thin tissue composed of two layers, the chorion and the amnion. While rupture of this membrane normally occurs at term, preterm rupture can result in increased risk of fetal mortality and morbidity, as well as danger of infection in the mother. Although structural changes have been observed in the membrane in such cases, the mechanical behaviour of the human fetal membrane in vivo remains poorly understood and is challenging to investigate experimentally. Therefore, the objective of this study was to develop simplified finite element models to investigate the mechanical behaviour and rupture of the fetal membrane, particularly its constituent layers, under various physiological conditions. It was found that modelling the chorion and amnion as a single layer predicts remarkably different behaviour compared with a more anatomically-accurate bilayer, significantly underestimating stress in the amnion and under-predicting the risk of membrane rupture. Additionally, reductions in chorion-amnion interface lubrication and chorion thickness (reported in cases of preterm rupture) both resulted in increased membrane stress. Interestingly, the inclusion of a weak zone in the fetal membrane that has been observed to develop overlying the cervix would likely cause it to fail at term, during labour. Finally, these findings support the theory that the amnion is the dominant structural component of the fetal membrane and is required to maintain its integrity. The results provide a novel insight into the mechanical effect of structural changes in the chorion and amnion, in cases of both normal and preterm rupture.

The physiology of fetal membrane weakening and rupture: Insights gained from the determination of physical properties revisited

Rupture of the fetal membranes (FM) is precipitated by stretch forces acting upon biochemically mediated, pre-weakened tissue. Term FM develop a para-cervical weak zone, characterized by collagen remodeling and apoptosis, within which FM rupture is thought to initiate. Preterm FM also have a weak region but are stronger overall than term FM. Inflammation/infection and decidual bleeding/abruption are strongly associated with preterm premature FM rupture (pPROM), but the specific mechanisms causing FM weakening-rupture in pPROM are unknown. There are no animal models for study of FM weakening and rupture. Over a decade ago we developed equipment and methodology to test human FM strength and incorporated it into a FM explant system to create an in-vitro human FM weakening model system. Within this model TNF (modeling inflammation) and Thrombin (modeling bleeding) both weaken human FM with concomitant up regulation of MMP9 and cellular apoptosis, mimicking the characteristics of the spontaneous FM rupture site. The model has been enhanced so that test agents can be applied directionally to the choriodecidual side of the FM explant consistent with the in-vivo situation. With this enhanced system we have demonstrated that the pathways involving inflammation/TNF and bleeding/Thrombin induced FM weakening overlap. Furthermore GM-CSF production was demonstrated to be a critical common intermediate step in both the TNF and the Thrombin induced FM weakening pathways. This model system has also been used to test potential inhibitors of FM weakening and therefore pPROM. The dietary supplement α-lipoic acid and progestogens (P4, MPA and 17α-hydroxyprogesterone) have been shown to inhibit both TNF and Thrombin induced FM weakening. The progestogens act at multiple points by inhibiting both GM-CSF production and GM-CSF action. The use of a combined biomechanical/biochemical in-vitro human FM weakening model system has allowed the pathways of fetal membrane weakening to be delineated, and agents that may be of clinical use in inhibiting these pathways to be tested.

Development of an implantable synthetic membrane for the treatment of preterm premature rupture of fetal membranes

Preterm premature rupture of fetal membranes is a very common condition leading to premature labour of a non viable fetus. Significant morbidities may occur when preterm premature rupture of fetal membranes management is attempted to prolong the pregnancy for fetal maturation. Reducing the rate of loss of amniotic fluid and providing a barrier to bacterial entry may allow the pregnancy to continue to term, avoiding complications. Our aim is to develop a synthetic biocompatible membrane to form a distensible barrier for cervical closure which acts to reduce fluid loss and provide a surface for epithelial ingrowth to help repair the damaged membranes. Therefore, a bilayer membrane was developed using an electrospinning technique of combining two FDA-approved polymers, poly-L-lactic acid (PLA) and polyurethane (Z3) polymer. This was compared to a plain electrospun Z3 membrane. The physical and mechanical properties were assessed using scanning electron microscope images and a BOSE tensiometer, respectively, and compared to native fetal membranes. The performance of the membranes in preventing fluid loss was assessed by measuring their ability to support a column of water. Finally the ability of the membranes to support cell ingrowth was assessed by culturing adipose-derived stem cells on the membranes for two weeks and assessing metabolic activity after 7 and 14 days. The physical properties of the bilayer were similar to that of the native fetal membranes and it was resistant to fluid penetration. This bilayer membrane presented mechanical properties close to those for fetal membranes and showed elastic distention, which may be crucial for progress of the pregnancy. The membrane was also able to retain surgical sutures. In addition, it also supported the attachment and growth of adipose-derived stem cells for two weeks. In conclusion, this membrane may prove a useful approach in the treatment of preterm premature rupture of fetal membranes and now merits further investigation.

Mechanical and microstructural investigation of the cyclic behavior of human amnion

The structural and mechanical integrity of amnion is essential to prevent preterm premature rupture (PPROM) of the fetal membrane. In this study, the mechanical response of human amnion to repeated loading and the microstructural mechanisms determining its behavior were investigated. Inflation and uniaxial cyclic tests were combined with corresponding in situ experiments in a multiphoton microscope (MPM). Fresh unfixed amnion was imaged during loading and changes in thickness and collagen orientation were quantified. Mechanical and in situ experiments revealed differences between the investigated configurations in the deformation and microstructural mechanisms. Repeated inflation induces a significant but reversible volume change and is characterized by high energy dissipation. Under uniaxial tension, volume reduction is associated with low energy, unrecoverable in-plane fiber reorientation.

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

Characterizing the mechanical response of the human amnion is essential to understand and to eventually prevent premature rupture of fetal membranes. In this study, a large set of macroscopic and microscopic mechanical tests have been carried out on fresh unfixed amnion to gain insight into the time-dependent material response and the underlying mechanisms. Creep and relaxation responses of amnion were characterized in macroscopic uniaxial tension, biaxial tension and inflation configurations. For the first time, these experiments were complemented by microstructural information from nonlinear laser scanning microscopy performed during in situ uniaxial relaxation tests. The amnion showed large tension reduction during relaxation and small inelastic strain accumulation in creep. The short-term relaxation response was related to a concomitant in-plane and out-of-plane contraction, and was dependent on the testing configuration. The microscopic investigation revealed a large volume reduction at the beginning, but no change of volume was measured long-term during relaxation. Tension-strain curves normalized with respect to the maximum strain were highly repeatable in all configurations and allowed the quantification of corresponding characteristic parameters. The present data indicate that dissipative behavior of human amnion is related to two mechanisms: (i) volume reduction due to water outflow (up to ∼20 s) and (ii) long-term dissipative behavior without macroscopic deformation and no systematic global reorientation of collagen fibers.

Tensile strain increased COX-2 expression and PGE2 release leading to weakening of the human amniotic membrane

INTRODUCTION

There is evidence that premature rupture of the fetal membrane at term/preterm is a result of stretch and tissue weakening due to enhanced prostaglandin E2 (PGE2) production. However, the effect of tensile strain on inflammatory mediators and the stretch sensitive protein connexin-43 (Cx43) has not been examined. We determined whether the inflammatory environment influenced tissue composition and response of the tissue to tensile strain.

METHODS

Human amniotic membranes isolated from the cervix (CAM) or placenta regions (PAM) were examined by second harmonic generation to identify collagen orientation and subjected to tensile testing to failure. In separate experiments, specimens were subjected to cyclic tensile strain (2%, 1 Hz) for 24 h. Specimens were examined for Cx43 by immunofluorescence confocal microscopy and expression of COX-2 and Cx43 by RT-qPCR. PGE2, collagen, elastin and glycosaminoglycan (GAG) levels were analysed by biochemical assay.

RESULTS

Values for tensile strength were significantly higher in PAM than CAM with mechanical parameters dependent on collagen orientation. Gene expression for Cx43 and COX-2 was enhanced by tensile strain leading to increased PGE2 release and GAG levels in PAM and CAM when compared to unstrained controls. In contrast, collagen and elastin content was reduced by tensile strain in PAM and CAM.

DISCUSSION

Fibre orientation has a significant effect on amniotic strength. Tensile strain increased Cx43/COX-2 expression and PGE2 release resulting in tissue softening mediated by enhanced GAG levels and a reduction in collagen/elastin content.

CONCLUSION

A combination of inflammatory and mechanical factors may disrupt amniotic membrane biomechanics and matrix composition.

Do mechanical properties of human fetal membrane depend on strain rate?

AIM

The objective of this study was to examine the effect of strain rate on the mechanical properties of human fetal membranes.

METHODS

Different strain rates were employed to quantify the stress-strain relation of the chorioamnion membrane. The mechanical properties of nine human amnion membranes, four collected from cesarean delivery and five collected from normal vaginal delivery, were examined in uniaxial tension tests under strain rates of 0.1, 1 and 10%/min.

RESULTS

Statistical analysis revealed significant (P < 0.05) correlation between the change in strain rate and the elastic modulus as well as failure strain of amnion samples. The rupture stress, though, did not show dependency on strain rates.

CONCLUSION

Human chorioamnion is strongly viscoelastic. By increasing the rate of the test, the stiffness of amnion increases considerably.

Proteomic analysis of equine amniotic membrane: characterization of proteins

INTRODUCTION

Human amniotic membrane (AM) has been used as a biomaterial for surgical wound skin and ocular surface reconstruction for several years. Currently, equine AM has been used for corneal reconstruction in several animal species, and appears to have the same properties as human AM. Despite the observed positive healing abilities of this tissue in horses with ulcerative keratitis the proteins of equine AM have not been described.

OBJECTIVE

To identify proteins known to be associated with corneal healing from frozen equine AM.

PROCEDURES

Placentas were acquired from healthy live foal births from a local Thoroughbred breeding farm. The amnion was removed from the chorion by blunt dissection, washed with phosphate-buffered saline (PBS), and treated with 0.05% trypsin and 0.02% ethylene diaminetetraacetic acid in PBS. Amnion was attached to nitrocellulose paper (epithelial side up), and cut into 4 × 4 cm pieces. The sheets were frozen at -80 °C. The protein samples were solubilized, and analyzed by 2D gel electrophoresis and shotgun proteomics.

RESULTS

A reference identification map of the equine AM proteins was produced and 149 different proteins were identified. From gel-based proteomics, 49 spots were excised and 43 proteins identified by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). Shotgun proteomics identified 116 proteins with an overlap of 10 proteins in both analyses.

CONCLUSIONS

We have described a reference map for equine AM proteins that may provide a background to explain the positive results found in horses with ulcerative keratopathies using this biomaterial.

Synergy and interactions among biological pathways leading to preterm premature rupture of membranes

Preterm premature rupture of membranes (PPROM) occurs in 1% to 2% of births. Impact of PPROM is greatest in low- and middle-income countries where prematurity-related deaths are most common. Recent investigations identify cytokine and matrix metalloproteinase activation, oxidative stress, and apoptosis as primary pathways to PPROM. These biological processes are initiated by heterogeneous etiologies including infection/inflammation, placental bleeding, uterine overdistention, and genetic polymorphisms. We hypothesize that pathways to PPROM overlap and act synergistically to weaken membranes. We focus our discussion on membrane composition and strength, pathways linking risk factors to membrane weakening, and future research directions to reduce the global burden of PPROM.

Optical coherence tomography: A potential tool to predict premature rupture of fetal membranes

A fundamental question addressed in this study was the feasibility of preterm birth prediction based on a noncontact investigation of fetal membranes in situ. Although the phenomena of preterm birth and the premature rupture of the fetal membrane are well known, currently, there are no diagnostic tools for their prediction. The aim of this study was to assess whether optical coherence tomography could be used for clinical investigations of high-risk pregnancies. The thickness of fetal membranes was measured in parallel by optical coherence tomography and histological techniques for the following types of birth: normal births, preterm births without premature ruptures and births at full term with premature rupture of membrane. Our study revealed that the membrane thickness correlates with the birth type. Normal births membranes were statistically significantly thicker than those belonging to the other two groups. Thus, in spite of almost equal duration of gestation of the normal births and the births at full term with premature rupture, the corresponding membrane thicknesses differed. This difference is possibly related to previously reported water accumulation in the membranes. The optical coherence tomography results were encouraging, suggesting that this technology could be used in future to predict and distinguish between different kinds of births.

Fetal membranes structure and prelabour rupture

In most pregnancies labour begins at term in the presence of intact fetal membranes. Without intervention the membranes usually spontaneously rupture near the end of the first stage of labour. In 10% of pregnancies that deliver at term the fetal membranes fail to maintain their structural integrity and this results in their “prelabour rupture”, defined as spontaneous rupture of membranes at least one hour before the onset of labour. In 95–98% of these cases at term, labour is precipitated within 48 hours. Although preterm birth, defined as birth prior to 37 completed weeks of pregnancy, occurs in only 7–8% of all pregnancies, 40–60% of these deliveries are preceded by prelabour rupture of the fetal membranes.

Decreased adherence and spontaneous separation of fetal membrane layers--amnion and choriodecidua--a possible part of the normal weakening process

INTRODUCTION

The fetal membrane (FM) layers, amnion and choriodecidua, are frequently noted to have varying degrees of separation following delivery. FM layers normally separate prior to rupture during in vitro biomechanical testing. We hypothesized that the adherence between amnion and choriodecidua decreases prior to delivery resulting in separation of the FM layers and facilitating FM rupture.

METHODS

FM from 232 consecutively delivered patients were examined to determine the extent of spontaneous separation of the FM layers at delivery. Percent separation was determined by the weight of separated FM tissue divided by the total FM weight. Separately, the adherence between intact FM layers was determined. FM adherence was tested following term vaginal delivery (13), term unlabored cesarean section (10), and preterm delivery (6).

RESULTS

Subjects enrolled in the two studies had similar demographic and clinical characteristics. FM separation was present in 92.1% of membranes. Only 4.3% of FM delivered following spontaneous rupture of the fetal membranes (SROM) had no detectable separation. 64.7% of FM had greater than 10% separation. FM from term vaginal deliveries had significantly more separation and were less adherent than FM of term unlabored, elective cesarean section (39.0+/-34.4% vs 22.5+/-30.9%, p=.046 and 0.041+/-0.018N/cm vs 0.048+/-0.019N/cm, p<.005). Preterm FM had less separation and were more adherent than term FM (9.95+/-17.7% vs 37.5+/-34.4% and 0.070+/-0.040N/cm vs 0.044+/-0.020N/cm; both p<.001).

CONCLUSIONS

Separation of the amnion from choriodecidua at delivery is almost universal. Increased separation is associated with decreased adherence as measured in vitro. Increased separation and decreased adherence are seen both with increasing gestation and with labor suggesting both biochemical and mechanical etiologies. The data are consistent with the hypothesis that FM layer separation is part of the FM weakening process during normal parturition.

Biomechanics of the fetal membrane prior to mechanical failure: review and implications

Annually, premature birth is a major public health problem accounting for over 13,000 deaths and 30,000 surviving infants with life-long morbidity. Preterm premature rupture of the membranes is the initiating event leading to preterm birth of 40% of these premature infants. Fetal membrane (FM) rupture is a catastrophic tissue failure, a unique event in normal physiology; other tissue failures (bone breaks, aneurism ruptures) are pathological processes. The mechanisms which cause FM failure and thereby rupture are not understood. A full understanding of FM failure process requires a complete characterization of structural and biomechanical behavior at near/full term under sub-failure (forces well below that which induce rupture) and failure conditions as well as elucidating the biological factors which modulate its failure. The relatively, highly loaded state of the FM in vivo may also facilitate its susceptibility to enzymatic degradation, which was shown to be augmented with increased load in collagenous tissues. Indeed, this last observation may help to provide the link between biomechanical degradation and premature mechanical failure in the FM. This integrated approach will further the understanding of this unique physiological event and thereby provide insight into how to anticipate and when appropriate, intervene to prevent preterm FM rupture.

Relation between mechanical properties and microstructure of human fetal membranes: an attempt towards a quantitative analysis

OBJECTIVE

We sought to measure the mechanical baseline behavior of fetal membranes in order to determine constitutive mechanical model parameters for fetal membranes, and to examine their relation to molecular correlates for mechanical function, i.e. collagen and elastin.

STUDY DESIGN

The uniaxial stress-strain response of nine human term fetal membranes was measured. Methods of nonlinear continuum mechanics were applied for the analysis of the stress-strain curves. Thickness of amnion and chorion were determined from histologic sections for each fetal membrane sample. Complementary biochemical analysis was performed to quantify the soluble collagen and soluble elastin components for each sample.

RESULTS

We report a straightforward histologic modality for measurements of amnion and chorion thickness. Average thickness of the amnion and chorion layers were 111+/-78 microm, and 431+/-113 microm, respectively, which are about twice larger than previously reported. The average content of acid-soluble elastin was 2.1% of wet weight and the one of pepsin/acetic acid-soluble collagen was 10.5% of dry weight. Our data show an inverse proportionality between soluble elastin and soluble collagen content. The low strain elastic modulus ranged between 10 and 25 kPa. Correlations were found between biochemical data and mechanical parameters: there is clearly a direct proportionality between small strain elastic modulus and elastin content. Further, a (less pronounced) direct correlation was observed also between soluble collagen content and the parameter governing the increase in stiffness at larger strains in the nonlinear mechanical model. The mechanical tests revealed a relatively low variability for samples from the same membrane but a large variation between donors. The proposed nonlinear model provides a good fit of the experimental data, with a coefficient of determination, R(2), typically in the range of 0.94. Membranes failure originated at the clamping points thus impairing the quantification of ultimate stress and strain. Thus, no correlation was found between maximum stress and collagen or elastin content.

CONCLUSIONS

This study provides a starting point for comprehensive quantitative analysis of the relationship between fetal membranes microstructure and their nonlinear deformation behavior. These insights could become useful in identifying potential medical interventions to prevent membranes rupture.

Connective tissue and related disorders and preterm birth: clues to genes contributing to prematurity

To identify candidate genes contributing to preterm birth, we examined the existing literature on the association between known disorders of connective tissue synthesis and metabolism and related diseases and prematurity. Our hypothesis was that abnormal matrix metabolism contributes to prematurity by increasing risk of preterm premature rupture of membranes (PPROM) and cervical incompetence. Based on this review, we identified gene mutations inherited by the fetus that could predispose to preterm birth as a result of PPROM. The responsible genes include COL5A1, COL5A2, COL3A1, COL1A1, COL1A2, TNXB, PLOD1, ADAMTS2, CRTAP, LEPRE1 and ZMPSTE24. Marfan syndrome, caused by FBN1 mutations, and polymorphisms in the COL1A1 and TGFB1 genes have been associated with cervical incompetence. We speculate that an analysis of sequence variation at the loci noted above will reveal polymorphisms that may contribute to susceptibility to PPROM and cervical incompetence in the general population.

Chronic stretching of amniotic epithelial cells increases pre-B cell colony-enhancing factor (PBEF/visfatin) expression and protects them from apoptosis

In normal pregnancy, the fetal membranes become increasingly distended towards term and in multifetal gestations they become over-distended. Apoptosis of the amniotic epithelium increases with advancing gestation and may contribute to fetal membrane weakening and rupture. The effects of chronic static stretching for 36h have been investigated using primary amniotic epithelial cells. Pre-B cell colony-enhancing factor (PBEF) is a stretch-responsive cytokine and expression of its gene, intracellular and secreted protein were all significantly increased by 4h and its secretion sustained over 36h, contrasting with the rapid increase and decline in expression of IL-8. Increased expression of SIRT1 and decreased p53 paralleled the changes in PBEF, are known to be responsive to PBEF, and contribute to cell survival. Distension had no effects on proliferation or necrosis but protected the cells from apoptosis, knocking-down PBEF with antisense probes abrogated this protective effect. There was increased immunostaining of PBEF in the compact layer of the amnion in multifetal tissues and significantly fewer apoptotic amniotic epithelial cells. These results show that chronic stretching of the amniotic epithelial cells increases PBEF expression, which protects them from apoptosis.

Microstructure and mechanics of the chorioamnion membrane with an emphasis on fracture properties

The normal mechanical functioning of an intact chorioamnion (CA) membrane is essential to successful human reproduction. The amnion and the chorion, separately and together as the bilayer chorioamnion, serve barrier and container functions throughout gestation, and these two important roles are required from conception to birth. The event associated with the "breaking of waters" is a landmark event in labor and delivery. Mechanical rupture of the CA membrane is part of the natural sequence of term delivery, but has serious implications when rupture occurs prior to term; preterm premature rupture of the CA membrane (PPROM) is associated with one-third of premature births. The current manuscript reviews PPROM from a clinical, anatomical, and mechanical perspective with a special focus on the clinically relevant fracture properties of these membranes. Emphasis is given to the link between membrane structure and properties at macroscopic and microscopic length scales. Because it has been demonstrated that the mechanical properties of prematurely failed membranes are not different from membranes of the same gestational age that have remained intact, membrane failure is a local process that must be explored in terms of local changes in structure and properties of isolated portions of the membrane. Future diagnostic techniques aimed at detection of changes in membrane structure (including thickness) and altered mechanical stiffness or strength may allow for prefailure diagnosis of membrane weak spots, thus opening the door for potential intervention and treatment techniques for preterm membrane rupture.

The Young's modulus of fetal preterm and term amniotic membranes

OBJECTIVE

To examine the Young's modulus of the human amniotic membranes, as well as its relationship to gestational age. To determine whether cellular and material-related parameters affect this modulus.

STUDY DESIGN

In a prospective study at the Obstetric outpatient clinic of the University Hospital Zurich Young's modulus, thickness and mesenchymal:epithelial cell ratio of amniotic membranes of preterm (N=23) and term (N=40) placentae were examined. Significance (P<0.05) was calculated with the Mann-Whitney two-sample rank sum test and Wilcoxon signed rank test, while correlations were made using the Spearman's correlation.

RESULTS

The Young's modulus of preterm amniotic membranes was significantly higher than that of term membranes. It varied within the same amniotic membrane. The thickness of the amnion in both preterm and term membranes did not differ significantly. The thinner the preterm and term amniotic membranes, the higher the Young's modulus was. There was no relation to the mesenchymal:epithelial cell ratio in the amnion.

CONCLUSIONS

Preterm amniotic membranes are stiffer than term amniotic membranes. Tentatively, we hypothesise that there may be a correlation between the extracellular matrix components and the elastic properties of the membrane.

Premature rupture of the fetal membranes: is the amnion the major determinant?

OBJECTIVE

The objective of the study was to evaluate the relative contributions of amnion and chorion to the strength of fetal membranes and to correlate these findings with gestational age.

STUDY DESIGN

Fetal membranes from 78 pregnancies were tested for biaxial puncture force using a blunt, instrumented probe with a low-force load cell connected through a load cell conditioner to an oscilloscope. The average of 2 to 4 tests performed on independent regions of the membrane was recorded. Means and SDs were calculated through the gestational age ranges of less than 32, 32 to 36, or 37 weeks or longer. Linear regression analysis was performed across gestational age after grouping data by labor and mode of delivery.

RESULTS

There were trends toward decreasing puncture force with gestational age for both chorioamnion and amnion for both vaginal deliveries and cesarean sections. The trends were significant by linear regression for labored deliveries but not unlabored cesarean sections for both chorioamnion and amnion alone. There was no trend in chorion puncture force with either gestational age or delivery mode and the mean puncture force values were, on average, half those for the amnion.

CONCLUSION

The amnion is significantly stronger than the chorion when subjected to biaxial strength testing. The amnion but not the chorion is significantly affected by the chemical and mechanical changes during gestation and the labor process. These data will help direct future studies on the effects of clinical and molecular modulators of inflammation on membrane rupture thresholds with special emphasis on the biochemical and structural changes in the amnion.

Separation of amnion from choriodecidua is an integral event to the rupture of normal term fetal membranes and constitutes a significant component of the work required

OBJECTIVE

This study was undertaken to determine the sequence of events that occur during fetal membrane (FM) rupture and to compare the biophysical properties of intact FM with its separated individual components (amnion and choriodecidua).

STUDY DESIGN

FM physical properties were determined with computerized, specially adapted, industrial, strength testing equipment and the rupture sequence (in vitro) video documented. Separated individual FM component properties were compared with those of reapproximated components, and of intact FMs.

RESULTS

The sequence of FM rupture was (1) FM components stretch together under load; (2) amnion separates from choriodecidua; (3) choriodecidua ruptures; (4) amnion distends further, nonelastically; and (5) amnion ruptures. In all FMs tested, amnion was stronger, stiffer, and more ductile than choriodecidua. The sum of work required to rupture separated FM components (amnion + choriodecidua), or reapproximated components, was significantly less than that of intact FMs.

CONCLUSION

Separation of amnion from choriodecidua occurs as part of normal term FM rupture. FMs become significantly weaker as a result of this separation.

A histological study of fetoscopic membrane defects to document membrane healing

OBJECTIVE

To evaluate the rate of spontaneous healing in human fetal membranes after fetoscopy.

STUDY DESIGN

Membranes from patients that had undergone fetoscopic interventions and delivered in one of the two treatment centers were included in the study. The membranes were examined macroscopically for any remaining defects and if present, the size of the defect in chorion and amnion was measured. Subsequently, the defect was excised and stained with HE for histological evaluation. Additional immunohistochemical staining was performed with Ki-67, cytokeratin and vimentin. The proliferation index (percentage of proliferating cells) was calculated in amnion and chorion.

RESULTS

Nineteen membrane defects were included in the study. The median time interval between invasive procedures and delivery was 60 days (range 3-112). All fetoscopic defects (n=19) could be identified in the gestational sac and in none spontaneous closure had occurred. Proliferation indices as measured by inmunohistochemistry were very low (median 2.8%, range 0-7%) in the chorion and 0% in the amnion.

CONCLUSION

No evidence of spontaneous membrane healing was found after fetoscopic procedures, suggesting that the membrane defect normally persists until delivery. Absence of amniotic fluid leakage after invasive procedures may be based on mechanisms other than histologic membrane repair.

Term Human Fetal Membranes Have a Weak Zone Overlying the Lower Uterine Pole and Cervix Before Onset of Labor1

The etiology of fetal membrane (FM) rupture is unknown. A hypothesis that the FM weakens by a process of collagen remodeling and apoptosis to facilitate rupture has been proposed. Human FMs reportedly exhibit a zone of altered histology, postulated to be the FM rupture site, but concomitant FM weakness has not been demonstrated. We hypothesized that a discrete zone of FM with marked weakness, histological change, and evidence of remodeling and apoptosis, develops in late gestation in the FM overlying the cervix. FM tissue from women undergoing prelabor cesarean delivery were perioperatively marked to identify the FM overlying the cervix, cut with a procedure that facilitates remapping the rupture strength of FM pieces to their former location and orientation on a three-dimensional model, and tested for strength. A 10-cm FM zone centered at the cervical mark was compared with the remaining FM. Mean rupture strength within the cervical zone was 55% of the remaining FM. The cervical zone also exhibited increased MMP-9 protein, decreased tissue inhibitor of metalloproteinases-3 (TIMP-3) protein, and increased PARP cleavage coincident with the previously reported zone of altered histology. A discrete zone of weakness is present in term prelabor FMs overlying the cervix and has biochemical characteristics consistent with tissue remodeling and apoptosis.

The Influence of Amphotericin B and Neomycin on the Effect of Human Relaxin-2 on Foetal Membranes and Isolated Myometrium

In vitro studies have documented effects of relaxin on utero-placental tissues. Previously unpublished experiments indicate that neomycin and amphotericin B in vitro influences the effect of human relaxin-2 on the strength of human foetal membranes. The aim of the current study was to investigate the interaction between neomycin and amphotericin B and human relaxin-2 using human foetal membranes, human myometrium and rat myometrium. Chloramphenicol, erythromycin and penicillin were also examined. Human foetal membranes were stretched until rupture in a materials-testing machine while the contractility of rat and human myometrium were examined by myography. Human relaxin-2 (hrlx-2, 10(-9) M) induced a decreased strength in human foetal membranes, although this effect of hrlx-2 was inhibited after co-incubation with neomycin and amphotericin B. Hrlx-2 (10(-9) M) in combination with chloramphenicol induced a decreased strength of human foetal membranes. Hrlx-2 (10(-9) M) decreased myometrial contractility on amplitude and frequency in the rat myometrium, but had no effect on baseline tension. After exposure to amphotericin B, hrlx-2 induced a more pronounced decrease in amplitude, increased baseline tension and increased the frequency of contractions of the rat myometrium. Hrlx-2 (10(-9) M) had no effect on the human myometrium. However, after exposure to amphotericin B or neomycin+amphotericin B, hrlx-2 induced an increase in baseline tension and a decrease in amplitude. Amphotericin B and neomycin+amphotericin B increased the frequency of contractions and this effect was further enhanced by the addition of hrlx-2. We therefore conclude that amphotericin B and neomycin + amphotericin B may have an influence on relaxin's effect on isolated foetal membranes and myometrium.