A rat model to study the structural properties of the vagina and its supportive tissues

Histologic Analysis of 'Distraction Vaginogenesis' in a Rat Model

Vaginal agenesis (VA) is frequently associated with mullerian agenesis. VA treatments include mechanical dilation and surgical vaginoplasty. We created a vaginal expansion sleeve (VES) as a novel device to progressively lengthen the vaginal canal. This study evaluated the histologic effects of the VES on rat vaginal tissue. The VES is a spring-like device made of proprietary woven cylindrical material and flat resin caps. The VESs were constructed as 25-30 mm, pre-contracted springs, which were secured into the vaginas of six Sprague Dawley rats and allowed to re-expand post-surgically. After one week, the VESs were removed, and the vaginas were harvested and measured in length. Test (n = 6) and control (n = 4) formalin-fixed paraffin-embedded tissues were stained with hematoxylin and eosin (H&E), Masson's trichrome, and anti-Desmin antibodies. The VESs achieved significant vaginal lengthening. The mean vaginal canal length increased from 20.0 ± 2.4 mm to 23.8 ± 1.2 mm after removal of the VESs (n = 6, p < 0.001), a 19% increase. There was a positive correlation between the expander/tension generated in the vagina and the amount of acute and chronic inflammation. H&E staining revealed increased submucosal eosinophilia in five of the six test tissues. One VES sample that was lengthened to 30 mm long showed evidence of lymphocytic and neutrophilic inflammation. Desmin immunostaining and Masson's trichrome stain revealed a thinner muscularis with more infiltrative fibrous tissue between muscle fibers in the test tissue compared to the control tissue. Although effective, the VES may provoke at least a transient increase in eosinophils consistent with a localized immune reaction during muscularis remodeling.

Collagen organization and structure in FBLN5-/- mice using label-free microscopy: implications for pelvic organ prolapse

Pelvic organ prolapse (POP) is a gynecological disorder described by the descent of superior pelvic organs into or out of the vagina as a consequence of disrupted muscles and tissue. A thorough understanding of the etiology of POP is limited by the availability of clinically relevant samples, restricting longitudinal POP studies on soft-tissue biomechanics and structure to POP-induced models such as fibulin-5 knockout (FBLN5-/- ) mice. Despite being a principal constituent in the extracellular matrix, little is known about structural perturbations to collagen networks in the FBLN5-/- mouse cervix. We identify significantly different collagen network populations in normal and prolapsed cervical cross-sections using two label-free, nonlinear microscopy techniques. Collagen in the prolapsed mouse cervix tends to be more isotropic, and displays reduced alignment persistence via 2-D Fourier transform analysis of images acquired using second harmonic generation microscopy. Furthermore, coherent Raman hyperspectral imaging revealed elevated disorder in the secondary structure of collagen in prolapsed tissues. Our results underscore the need for in situ multimodal monitoring of collagen organization to improve POP predictive capabilities.

Establishing a Rat Model of Pelvic Organ Prolapse with All Compartment Defects by Persistent Cervical Tension

INTRODUCTION AND HYPOTHESIS

We hypothesized that applying cervical suction and persistent tension can develop a novel and efficient rat model of pelvic organ prolapse.

METHODS

Fifteen rats underwent pilot testing to optimize the protocol. Sixteen rats were subjected to pelvic organ prolapse induction by cervical suction and constant traction, while five rats served as controls. The pelvic organ prolapse rats were assessed by a Rat Pelvic Organ Prolapse Quantification system at different time points, and their diet, urine, and stool were monitored for 21 days. The pelvic organ prolapse rats were also evaluated for urinary incontinence, urinary retention, leak point pressure, and vaginal histopathology at 21 days after operation.

RESULTS

This rat model demonstrated pelvic floor prolapse in anatomic level, as well as physiological variations (urine incontinence, urinary retention) and pathological changes (collagen fracture, decreased collagen density).

CONCLUSIONS

This is the first establishment of the pelvic organ prolapse rat model with all compartment defects, which provides a valuable tool for elucidating pelvic organ prolapse mechanisms and evaluating potential interventions.

The mechanism of adipose mesenchymal stem cells to stabilize the immune microenvironment of pelvic floor injury by regulating pyroptosis and promoting tissue repair

Pelvic organ prolapse (POP) has a high incidence rate among Chinese women. Repeated mechanical stimulation is an important factor causing POP, but the injury mechanism has not yet been elucidated. The purpose of this study is to explore the related mechanisms of pelvic floor supporting tissue damage caused by mechanical force and the application of stem cell therapy. First, we obtained vaginal wall and sacral ligament tissue samples from clinical patients for examination. Pelvic floor support tissues of POP patients displayed high expression of inflammation and immune disorders. Then, we constructed a rat model of childbirth injury. In vivo and in vitro experiments investigated the key mechanism of pelvic floor support tissue injury caused by mechanical force. We discovered that after mechanical force, a large number of reactive oxygen species (ROS) and macrophages rapidly accumulated in pelvic floor tissues. ROS stimulated macrophages to produce NLRP3 inflammatory complex, induced the release of interleukin (IL-1β) and pyroptosis and exacerbated the inflammatory state of damaged tissues, persisting chronic inflammation of fibroblasts in supporting tissues, thus causing the pelvic floor's extracellular matrix (ECM) collagen metabolic disorder. Resultingly impeding the repair process, thereby causing the onset and progression of the disease. Through their paracrine ability, we discovered that adipose mesenchymal stem cells (ADSCs) could inhibit this series of pathological processes and promote tissue repair, asserting a good therapeutic effect. Simultaneously, to overcome the low cell survival rate and poor therapeutic effect of directly injecting cells, we developed a ROS-responsive PVA@COLI hydrogel with ADSCs. The ROS-scavenging properties of the gel could reshape the site of inflammation injury, enhance cell survival, and play a role in subsequent treatment. The findings of this study could serve as a basis for early, targeted intervention therapy for POP and representing a promising approach.

Collagen organization and structure in FLBN5-/- mice using label-free microscopy: implications for pelvic organ prolapse

Pelvic organ prolapse (POP) is a gynecological disorder described by the descent of superior pelvic organs into or out of the vagina as a consequence of disrupted muscles and tissue. A thorough understanding of the etiology of POP is limited by the availability of clinically relevant samples, restricting longitudinal POP studies on soft-tissue biomechanics and structure to POP-induced models such as fibulin-5 knockout (FBLN5-/-) mice. Despite being a principal constituent in the extracellular matrix, little is known about structural perturbations to collagen networks in the FBLN5-/- mouse cervix. We identify significantly different collagen network populations in normal and prolapsed cervical cross-sections using two label-free, nonlinear microscopy techniques. Collagen in the prolapsed mouse cervix tends to be more isotropic, and displays reduced alignment persistence via 2-D Fourier Transform analysis of images acquired using second harmonic generation microscopy. Furthermore, coherent Raman hyperspectral imaging revealed elevated disorder in the secondary structure of collagen in prolapsed tissues. Our results underscore the need for in situ multimodal monitoring of collagen organization to improve POP predictive capabilities.

A comprehensive evaluation of spontaneous pelvic organ prolapse in rhesus macaques as an ideal model for the study of human pelvic organ prolapse

Pelvic organ prolapse (POP) seriously affects a woman's quality of life, and the treatment complications are severe. Although new surgical treatments are being developed, the host tissue responses and safety need to be evaluated in preclinical trials. However, there is a lack of suitable animal models, as most quadrupeds exhibit different structural and pathological changes. In this study, 72 elderly rhesus macaques (Macaca mulatta) were physically examined, and the incidence of spontaneous POP was similar to that in humans. The vaginal wall from five control monkeys and four monkeys with POP were selected for further analysis. Verhoeff-van Gieson staining showed that elastin content decreased significantly in monkeys with POP compared with control samples. Immunohistological staining revealed that the smooth muscle bundles in monkey POP appeared disorganized, and the number of large muscle bundles decreased significantly. The collagen I/III ratio in monkey POP also significantly decreased, as revealed by Sirius Red staining. These histological and biochemical changes in monkeys with POP were similar to those in humans with POP. Moreover, we generated a single-cell transcriptomic atlas of the prolapsed monkey vagina. Cross-species analysis between humans and monkeys revealed a comparable cellular composition. Notably, a differential gene expression analysis determined that dysregulation of the extracellular matrix and an immune disorder were the conserved molecular mechanisms. The interplay between fibroblasts and macrophages contributed to human and monkey POP. Overall, this study represents a comprehensive evaluation of spontaneous POP in rhesus macaques and demonstrates that monkeys are a suitable animal model for POP research.

Molecular association of Candida albicans and vulvovaginal candidiasis: focusing on a solution

Candida albicans-mediated vulvovaginal candidiasis (VVC) is a significant challenge in clinical settings, owing to the inefficacy of current antifungals in modulating virulence, development of resistance, and poor penetration into the biofilm matrix. Various predisposition factors are molecular drivers that lead to the dysbiosis of normal microflora of the vagina, upregulation of central metabolic pathways, morphogenesis, hyphal extension, adhesion, invasion, and biofilm formation leading to chronic infection and recurrence. Hence, it is crucial to understand the molecular mechanism behind the virulence pathways driven by those drivers to decode the drug targets. Finding innovative solutions targeting fungal virulence/biofilm may potentiate the antifungals at low concentrations without affecting the recurrence of resistance. With this background, the present review details the critical molecular drivers and associated network of virulence pathways, possible drug targets, target-specific inhibitors, and probable mode of drug delivery to cross the preclinical phase by appropriate in vivo models.

Supramolecular Fibrous Hydrogel Augmentation of Uterosacral Ligament Suspension for Treatment of Pelvic Organ Prolapse

Uterosacral ligament suspension (USLS) is a common surgical treatment for pelvic organ prolapse (POP). However, the relatively high failure rate of up to 40% underscores a strong clinical need for complementary treatment strategies, such as biomaterial augmentation. Herein, the first hydrogel biomaterial augmentation of USLS in a recently established rat model is described using an injectable fibrous hydrogel composite. Supramolecularly-assembled hyaluronic acid (HA) hydrogel nanofibers encapsulated in a matrix metalloproteinase (MMP)-degradable HA hydrogel create an injectable scaffold showing excellent biocompatibility and hemocompatibility. The hydrogel can be successfully delivered and localized to the suture sites of the USLS procedure, where it gradually degrades over six weeks. In situ mechanical testing 24 weeks post-operative in the multiparous USLS rat model shows the ultimate load (load at failure) to be 1.70 ± 0.36 N for the intact uterosacral ligament (USL), 0.89 ± 0.28 N for the USLS repair, and 1.37 ± 0.31 N for the USLS + hydrogel (USLS+H) repair (n = 8). These results indicate that the hydrogel composite significantly improves load required for tissue failure compared to the standard USLS, even after the hydrogel degrades, and that this hydrogel-based approach can potentially reduce the high failure rate associated with USLS procedures.

Ex Vivo Uniaxial Tensile Properties of Rat Uterosacral Ligaments

This manuscript presents new experimental methods for testing the ex vivo tensile properties of the uterosacral ligaments (USLs) in rats. The USL specimens ([Formula: see text]) were carefully dissected to preserve their anatomical attachments, and they were loaded along their main in vivo loading direction (MD) using a custom-built uniaxial tensile testing device. During loading, strain maps in both the MD and the perpendicular direction (PD) were collected using the digital image correlation technique. The mean (± S.E.M.) maximum load and displacement at the maximum load were [Formula: see text] N and [Formula: see text] mm, respectively. The USLs were found to be highly heterogeneous structures, with some specimens experiencing strains in the MD that were lower than [Formula: see text] and others reaching strains that were up to [Formula: see text] in the intermediate region. At 0.5 kPa stress, a value reached by all the specimens, the mean strain in the MD was [Formula: see text] while at 5 kPa stress, a value achieved only by 9 out of the 21 specimens, the mean strain increased to [Formula: see text]. Under uniaxial loading, the specimens also elongated in the PD, with strains that were one order of magnitude lower than the strains in the MD; at the 0.5 kPa stress, the mean strain in the PD was recorded to be [Formula: see text] and, at the 5 kPa stress, the strain in the PD was [Formula: see text]. The directions of maximum principal strains remained almost unchanged with the increase in stress, indicating that little microstructural re-organization occurred due to uniaxial loading. This study serves as a springboard for future investigations on the supportive function of the USLs in the rat model by offering guidelines on testing methods that capture their complex mechanical behavior.

‘Distraction Vaginogenesis’: Preliminary Results Using a Novel Method for Vaginal Canal Expansion in Rats

Vaginal atresia is seen in genetic disorders such as Mayer–Rokitansky–Küster–Hauser (MRKH) syndrome, which can cause significant sexual dysfunction. Current treatments include surgical reconstruction or mechanical dilation of the vaginal canal. Mechanical dilation requires patients to be highly motivated and compliant while surgical reconstruction has high rates of complications. This study evaluated a novel vaginal expansion sleeve (VES) method as an alternative treatment for vaginal atresia. The proprietary cylindrical VES is a spring-like device consisting of polyethylene terephthalate helicoid trusses capped at each end with a fixed diameter resin cap for fixation within tissues. Following the development of the VES and mechanical characterization of the force–length relationships within the device, we deployed the VES in Sprague Dawley rat vaginas anchored with nonabsorbable sutures. We measured the VES length–tension relationships and post-implant vaginal canal expansion ex vivo. Vaginal histology was examined before and after implantation of the VES devices. Testing of 30 mm sleeves without caps resulted in an expansion force of 11.7 ± 3.4 N and 2.0 ± 0.1 N at 50% and 40%, respectively. The implanted 20 mm VES resulted in 5.36 mm ± 1.18 expansion of the vaginal canal, a 32.5 ± 23.6% increase (p = 0.004, Student t test). Histological evaluation of the VES implanted tissue showed a significant thinning of the vaginal wall when the VES was implanted. The novel VES device resulted in a significant expansion of the vaginal canal ex vivo. The VES device represents a unique alternative to traditional mechanical dilation therapy in the treatment of vaginal atresia and represents a useful platform for the mechanical distension of hollow compartments, which avoids reconstructive surgeries and progressive dilator approaches.

Comparison of in vivo visco-hyperelastic properties of uterine suspensory tissue in women with and without pelvic organ prolapse

The uterine suspensory tissue (UST) complex includes the cardinal (CL) and uterosacral "ligaments" (USL), which are mesentery-like structures that play a role in resisting pelvic organ prolapse (POP). Since there is no information on the time-dependent material properties of the whole structure in situ and in vivo, we developed and tested an intraoperative technique to quantify in vivo whether there is a significant difference in visco-hyperelastic behavior of the CL and USL between women with and without POP. Thirteen women with POP (cases) and four controls scheduled for surgery were selected from an ongoing POP study. Immediately prior to surgery, a computer-controlled linear servo-actuator with a series force transducer applied a continuous, caudally directed traction force while simultaneously recording the resulting cervical displacement in the same direction. After applying an initial 1.1 N preload, a ramp rate of 4 mm/s was used to apply a maximum force of 17.8 N in three "ramp-and-hold" test trials. A simplified bilateral four-cable biomechanical model was used to identify the material behavior of each ligament. For this, the initial cross-section areas of the CL and USL were measured on 3-T magnetic resonance image-based 3D models from each subject. The time-dependent strain energy function of CL/USL was defined with a three-parameter hyperelastic Mooney-Rivlin material model and a two-term Prony series in relaxation form. When cases were compared with controls, the estimated time-dependent material constants of CL and USL did not differ significantly. These are the first measurements that compare the in vivo and in situ visco-hyperelastic response of the tissues comprising the CL and USL to loading in women with and without prolapse. Larger sample sizes would help improve the precision of intergroup differences.

Aging of Pelvic Floor in Animal Models: A Sistematic Review of Literature on the Role of the Extracellular Matrix in the Development of Pelvic Floor Prolapse

Pelvic organ prolapse (POP) affects many women and contributes significantly to a decrease in their quality of life causing urinary and/or fecal incontinence, sexual dysfunction and dyspareunia. To better understand POP pathophysiology, prevention and treatment, many researchers resorted to evaluating animal models. Regarding this example and because POP affects principally older women, our aim was to provide an overview of literature on the possible biomechanical changes that occur in the vaginas of animal models and their supportive structures as a consequence of aging. Papers published online from 2000 until May 2021 were considered and particular attention was given to articles reporting the effects of aging on the microscopic structure of the vagina and pelvic ligaments in animal models. Most research has been conducted on rodents because their vagina structure is well characterized and similar to those of humans; furthermore, they are cost effective. The main findings concern protein structures of the connective tissue, known as elastin and collagen. We have noticed a significant discordance regarding the quantitative changes in elastin and collagen related to aging, especially because it is difficult to detect them in animal specimens. However, it seems to be clear that aging affects the qualitative properties of elastin and collagen leading to aberrant forms which may affect the elasticity and the resilience of tissues leading to pelvic floor disease. The analysis of histological changes of pelvic floor tissues related to aging underlines how these topics appear to be not fully understood so far and that more research is necessary.

International Urogynecological Consultation (IUC): pathophysiology of pelvic organ prolapse (POP)

INTRODUCTION AND HYPOTHESIS

This manuscript is the International Urogynecology Consultation (IUC) on pelvic organ prolapse (POP) chapter one, committee three, on the Pathophysiology of Pelvic Organ Prolapse assessing genetics, pregnancy, labor and delivery, age and menopause and animal models.

MATERIALS AND METHODS

An international group of urogynecologists and basic scientists performed comprehensive literature searches using pre-specified terms in selected biomedical databases to summarize the current knowledge on the pathophysiology of the development of POP, exploring specifically factors including (1) genetics, (2) pregnancy, labor and delivery, (3) age and menopause and (4) non-genetic animal models. This manuscript represents the summary of three systematic reviews with meta-analyses and one narrative review, to which a basic scientific comment on the current understanding of pathophysiologic mechanisms was added.

RESULTS

The original searches revealed over 15,000 manuscripts and abstracts which were screened, resulting in 202 manuscripts that were ultimately used. In the area of genetics the DNA polymorphisms rs2228480 at the ESR1 gene, rs12589592 at the FBLN5 gene, rs1036819 at the PGR gene and rs1800215 at the COL1A1 gene are significantly associated to POP. In the area of pregnancy, labor and delivery, the analysis confirmed a strong etiologic link between vaginal birth and symptoms of POP, with the first vaginal delivery (OR: 2.65; 95% CI: 1.81-3.88) and forceps delivery (OR: 2.51; 95% CI: 1.24-3.83) being the main determinants. Regarding age and menopause, only age was identified as a risk factor (OR : 1.102; 95% CI: 1.02-1.19) but current data do not identify postmenopausal status as being statistically associated with POP. In several animal models, there are measurable effects of pregnancy, delivery and iatrogenic menopause on the structure/function of vaginal support components, though not on the development of POP.

CONCLUSIONS

Genetics, vaginal birth and age all have a strong etiologic link to the development of POP, to which other factors may add or protect against the risk.

Mechanics of Uterosacral Ligaments: Current Knowledge, Existing Gaps, and Future Directions

The uterosacral ligaments (USLs) are important anatomical structures that support the uterus and apical vagina within the pelvis. As these structures are over-stretched, become weak, and exhibit laxity, pelvic floor disorders such as pelvic organ prolapse occur. Although several surgical procedures to treat pelvic floor disorders are directed toward the USLs, there is still a lot that is unknown about their function. This manuscript presents a review of the current knowledge on the mechanical properties of the USLs. The anatomy, microstructure, and clinical significance of the USLs are first reviewed. Then, the results of published experimental studies on the in vivo and ex vivo, uniaxial and biaxial tensile tests are compiled. Based on the existing findings, research gaps are identified and future research directions are discussed. The purpose of this exhaustive review is to help new researchers navigate scientific literature on the mechanical properties of the USLs. The use of these structures remains very popular in reconstructive surgeries that restore and augment the support of pelvic organs, especially as synthetic surgical mesh implants continue to be highly controversial.

Strains induced in the vagina by smooth muscle contractions

The ability of the vagina to contract gives rise to a set of active mechanical properties that contribute to the complex function of this organ in-vivo. Regional differences in the morphology of the vagina have been long recognized, but the large heterogeneous deformations that the vagina experiences during contractions have never been quantified. Furthermore, there is no consensus regarding differences in contractility along the two primary anatomical directions of the vagina: the longitudinal direction (LD) and the circumferential direction (CD). In this study, square vaginal specimens from healthy virgin rats (n=15) were subjected to isometric planar biaxial tests at four equi-biaxial stretches of 1.0, 1.1, 1.2, and 1.3. Contractions were induced at each stretch by a high concentration potassium solution. The digital image correlation method was used to perform full-field strain measurements during contractions. The vagina was found to undergo significantly higher compressive strains, tensile strains, and contractile forces along the LD than along the CD during contractions. Specifically, when computed over all the applied equi-biaxial stretches, mean (± std. dev.) absolute maximum compressive strains were -(13.43 ± 1.56)% along the LD and -(3.19 ± 0.25)% along the CD, mean absolute maximum tensile strains were (10.92 ± 1.73)% along the LD and (3.62 ± 0.57)% along the CD, and mean maximum contractile forces were 6.24 ± 0.55 mN along the LD and 3.35 ± 0.56 mN along the CD. Moreover, the vaginal tissue appeared to undergo compression in the proximal region and tension in the distal region while kept at constant equi-biaxial stretches. The active mechanical properties of the healthy vagina need to be fully investigated so that detrimental alterations in vaginal contractility, such as those caused by pelvic floor disorders and current treatment strategies, can be prevented. STATEMENT OF SIGNIFICANCE: Contractile forces of the vagina have been measured by several investigators using uniaxial tensile testing methods. Unlike previous studies, in this study planar-biaxial tests of vaginal specimens were performed while the full-field strains of the vagina, as induced by smooth muscle contraction, were measured. The vagina was found to generate significantly larger contractile strains and forces in the longitudinal direction than in the circumferential direction. Knowledge of the contractile mechanics of the healthy vagina is essential to understand the detrimental effects that pelvic organ prolapse and the use of surgical meshes have on the functionality of smooth muscle in the vagina.

Human umbilical cord mesenchymal stem cells reconstruct the vaginal wall of ovariectomized Sprague-Dawley rats: implications for pelvic floor reconstruction

Vaginal structural defects are involved in pelvic organ prolapse (POP). We tested whether mesenchymal stem cell (MSC) therapy can repair the weakened vaginal wall of POP patients as a novel POP treatment. Ninety-six ovariectomized rats were divided into 4 groups (n = 24/group): saline (sal), collagen (col), sal + MSC, and col + MSC groups. Two weeks after ovariectomy, rats received subepithelial injection of 0.3 ml saline, 0.3 ml collagen I gel, and 0.3 ml saline: 3 × 10⁶ human umbilical cord mesenchymal stem cells (HUMSCs), or 0.3 ml collagen I gel: 3 × 10⁶ HUMSCs into the anterior vaginal wall. Eight additional rats underwent in vivo bioluminescence imaging (BLI) to evaluate in vivo cell viability. The BLI signal disappeared within 1 week after MSC injection, and no in vivo MSC differentiation was found. Collagen I content was significantly lower at 4 and 12 weeks in the two MSC groups than in the sal and col groups, while collagen III was significantly higher (P < 0.001). The fraction of smooth muscle in the nonvascular muscularis increased significantly in the two MSC groups at 12 weeks (P < 0.001). ACTA2 mRNA in the col + MSC group was significantly higher than that in the sal group at 2 and 4 weeks (P = 0.042 and P = 0.040). mRNA levels of angiogenic factors (bFGF or VEGF) in the two MSC groups were significantly higher than those in the sal and col groups at different time points. HUMSCs normalized the fibromuscular structures of the vaginal wall of ovariectomized rats potentially through a paracrine effect.

Animal models for pelvic organ prolapse: systematic review

INTRODUCTION AND HYPOTHESIS

We aimed to summarize the knowledge on the pathogenesis of pelvic organ prolapse (POP) generated in animal models.

METHODS

We searched MEDLINE, Embase, Cochrane and the Web of Science to establish what animal models are used in the study of suggested risk factors for the development of POP, including pregnancy, labor, delivery, parity, aging and menopause. Lack of methodologic uniformity precluded meta-analysis; hence, results are presented as a narrative review.

RESULTS

A total of 7426 studies were identified, of which 51 were included in the analysis. Pregnancy has a measurable and consistent effect across species. In rats, simulated vaginal delivery induces structural changes in the pelvic floor, without complete recovery of the vaginal muscular layer and its microvasculature, though it does not induce POP. In sheep, first vaginal delivery has a measurable effect on vaginal compliance; measured effects of additional deliveries are inconsistent. Squirrel monkeys can develop POP. Denervation of their levator ani muscle facilitates this process in animals that delivered vaginally. The models used do not develop spontaneous menopause, so it is induced by ovariectomy. Effects of menopause depend on the age at ovariectomy and the interval to measurement. In several species menopause is associated with an increase in collagen content in the longer term. In rodents there were no measurable effects of age apart of elastin changes. We found no usable data for other species.

CONCLUSION

In several species there are measurable effects of pregnancy, delivery and iatrogenic menopause. Squirrel monkeys can develop spontaneous prolapse.

Animal Models and Alternatives in Vaginal Research: a Comparative Review

While developments in gynecologic health research continue advancing, relatively few groups specifically focus on vaginal tissue research for areas like wound healing, device development, and/or drug toxicity. Currently, there is no standardized animal or tissue model that mimics the full complexity of the human vagina. Certain practical factors such as appropriate size and anatomy, costs, and tissue environment vary across species and moreover fail to emulate all aspects of the human vagina. Thus, investigators are tasked with compromising specific properties of the vaginal environment as it relates to human physiology to suit their particular scientific question. Our review aims to facilitate the appropriate selection of a model aptly addressing a particular study by discussing pertinent vaginal characteristics of conventional animal and tissue models. In this review, we first cover common laboratory animals studied in vaginal research-mouse, rat, rabbit, minipig, and sheep-as well as human, with respect to the estrus cycle and related hormones, basic reproductive anatomy, the composition of vaginal layers, developmental epithelial origin, and microflora. In light of these relevant comparative metrics, we discuss potential selection criteria for choosing an appropriate animal vaginal model. Finally, we allude to the exciting prospects of increasing biomimicry for in vitro applications to provide a framework for investigators to model, interpret, and predict human vaginal health.

Pelvic Organ Prolapse: A Review of In Vitro Testing of Pelvic Support Mechanisms

Background: Pelvic organ prolapse (POP) affects a significant portion of the female population, impacting quality of life and often requiring intervention. The exact cause of prolapse is unknown.

Methods: We review some of the current research that focuses on defining the elements involved in POP, with a focus on in vitro testing.

Results: Treatment for POP, ranging from physical therapy or pessary use to more invasive surgery, has varying success rates. This variation is, in part, because the pathophysiology of pelvic floor support—and thus dysfunction—is incompletely understood, particularly regarding the structural components and biomechanical properties of tissue. However, researchers are working to identify and quantify the structural and functional dysfunction that may lead to the development of this condition.

Conclusion: Given the limited understanding of prolapse development, more research is needed to quantify the microstructure of the pelvic organs and pelvic support structures, with and without prolapse. Identifying biomechanical properties in multiaxial configurations will improve our understanding of pelvic tissue support, as well as our ability to establish predictive models and improve clinical treatment strategies.

Is there any objective and independent characterization and modeling of soft biological tissues?

The characterization of soft tissue raises several difficulties. Indeed, soft biological tissues usually shrink when dissected from their in vivo location. This shrinkage is characteristic of the release of residual stresses, since soft tissues are indeed often pre-stressed in their physiological configuration. During experimental loading, large extension at very low level of force are expected and assumed to be related to the progressive recruitment and stretching of fibers. However, the first phase of the mechanical test is also aiming at recovering the pre-stressed in vivo behavior. As a consequence, the initial phase, corresponding to the recovering of prestress and/or recruitment of fiberes, is questionable and frequently removed. One of the preferred methods to erase it consists in applying a preforce or prestress to the sample: this allows to easily get rid of the sample retensioning range. However this operation can impact the interpretation of the identified mechanical parameters. This study presents an evaluation of the impact of the data processing on the mechanical properties of a numerically defined material. For this purpose, a finite element simulation was performed to replicate a uniaxial tensile test on a biological soft tissue sample. The influence of different pre-stretches on the mechanical parameters of a second order Yeoh model was investigated. The Yeoh mechanical parameters, or any other strain energy density, depend strongly on any pre- and post-processing choices: they adapt to compensate the error made when choosing an arbitrary level of prestretch or prestress. This observation spreads to any modeling approach used in soft tissues. Mechanical parameters are indeed naturally bound to the choice of the pre-stretch (or pre-stress) through the elongation and the constitutive law. Regardless of the model, it would therefore be pointless to compare mechanical parameters if the conditions for the processing of experimental raw data are not fully documented.

Effects of non-ablative Er:YAG laser on the skin and the vaginal wall: systematic review of the clinical and experimental literature

INTRODUCTION AND HYPOTHESIS

Er:YAG laser is frequently used in dermatology and gynecology. Clinical studies document high satisfaction rates; however, hard data on the effects at the structural and molecular levels are limited. The aim of this systematic review was to summarize current knowledge about the objective effects of non-ablative Er:YAG laser on the skin and vaginal wall.

METHODS

We searched MEDLINE, Embase, Cochrane, and the Web of Science. Studies investigating objectively measured effects of non-ablative Er:YAG laser on the skin or vaginal wall were included. Studies of any design were included. Owing to the lack of methodological uniformity, no meta-analysis could be performed and therefore results are presented as a narrative review.

RESULTS

We identified in vitro or ex vivo studies on human cells or tissues, studies in rats, and clinical studies. Most studies were on the skin (n = 11); the rest were on the vagina (n = 4). The quality of studies is limited and the settings of the laser were very diverse. Although the methods used were not comparable, there were demonstrable effects in all studies. Immediately after application the increase in superficial temperature, partial preservation of epithelium and subepithelial extracellular matrix coagulation were documented. Later, an increase in epithelial thickness, inflammatory response, fibroblast proliferation, an increase in the amount of collagen, and vascularization were described.

CONCLUSIONS

Er:YAG laser energy may induce changes in the deeper skin or vaginal wall, without causing unwanted epithelial ablation. Laser energy initiates a process of cell activation, production of extracellular matrix, and tissue remodeling.

Tissue engineering in female pelvic floor reconstruction

Pelvic organ prolapse is a common and frequently occurring disease in middle-aged and elderly women. Mesh implantation is an ideal surgical treatment. The polypropylene mesh commonly used in clinical practice has good mechanical properties, but there are long-term complications. The application of tissue engineering technology in the treatment of pelvic organ prolapse disease can not only meet the mechanical requirements of pelvic floor support, but also be more biocompatible than traditional polypropylene mesh, and can promote tissue repair to a certain extent. In this paper, the progress of tissue engineering was summarized to understand the application of tissue engineering in the treatment of pelvic organ prolapse disease and will help in research.

Simulated vaginal delivery causes transients vaginal smooth muscle hypersensitivity and urethral sphincter dysfunction

BACKGROUND

Although pelvic floor dysfunction (PFD) has a multifactorial etiology, pregnancy and childbirth are considered crucial events predisposing to urinary incontinence as well as pelvic organ prolapse, which are highly prevalent. Rats are the most frequently used animal model and pudendal nerve crush (PNC) and vaginal distension (VD) are often used to mimic vaginal delivery.

OBJECTIVE

To document the time course of events after simulated vaginal delivery (SVD) on the urethral sphincter and the vaginal smooth muscle layer.

MATERIALS AND METHODS

Virgin female Sprague-Dawley rats were subjected to SVD (PNC + VD) or sham surgery and evaluated at 7, 14, 21, and 42 days after the injury. Urethral function was determined in vivo by microultrasound during cystometry and vaginal smooth muscle layer was harvested for in vitro pharmacologic investigation by isometric tension recording. Furthermore, vaginal and urethral samples were investigated by immunohistochemistry and real-time quantitative polymerase chain reaction.

RESULTS

Microultrasound showed no bursting of the urethral sphincter in the SVD group at 7 days with a functional recovery starting at 14 days, and normal bursting at 21 and 42 days. Vaginal smooth muscle showed higher sensitivity to carbachol at 14 and 21 days after injury; however, at 42 days, its sensitivity decreased when compared with sham.

CONCLUSION

SVD induces urethral dysfunction and a shift in vaginal smooth muscle contractile responses to carbachol.

Landmarks in vaginal mesh development: polypropylene mesh for treatment of SUI and POP

Vaginal meshes used in the treatment of stress urinary incontinence (SUI) and pelvic organ prolapse (POP) have produced highly variable outcomes, causing life-changing complications in some patients while providing others with effective, minimally invasive treatments. The risk:benefit ratio when using vaginal meshes is a complex issue in which a combination of several factors, including the inherent incompatibility of the mesh material with some applications in pelvic reconstructive surgeries and the lack of appropriate regulatory approval processes at the time of the premarket clearance of these products, have contributed to the occurrence of complications caused by vaginal mesh. Surgical mesh used in hernia repair has evolved over many years, from metal implants to knitted polymer meshes that were adopted for use in the pelvic floor for treatment of POP and SUI. The evolution of the material and textile properties of the surgical mesh was guided by clinical feedback from hernia repair procedures, which were also being modified to obtain the best outcomes with use of the mesh. Current evidence shows how surgical mesh fails biomechanically when used in the pelvic floor and materials with improved performance can be developed using modern material processing and tissue engineering techniques.

Smooth muscle regional contribution to vaginal wall function

Pelvic organ prolapse is characterized as the descent of the pelvic organs into the vaginal canal. In the USA, there is a 12% lifetime risk for requiring surgical intervention. Although vaginal childbirth is a well-established risk factor for prolapse, the underlying mechanisms are not fully understood. Decreased smooth muscle organization, composition and maximum muscle tone are characteristics of prolapsed vaginal tissue. Maximum muscle tone of the vaginal wall was previously investigated in the circumferential or axial direction under uniaxial loading; however, the vaginal wall is subjected to multiaxial loads. Further, the contribution of vaginal smooth muscle basal (resting) tone to mechanical function remains undetermined. The objectives of this study were to determine the contribution of smooth muscle basal and maximum tone to the regional biaxial mechanical behaviour of the murine vagina. Vaginal tissue from C57BL/6 mice was subjected to extension-inflation protocols (n = 10) with and without basal smooth muscle tone. Maximum tone was induced with KCl under various circumferential (n = 5) and axial (n = 5) loading conditions. The microstructure was visualized with multiphoton microscopy (n = 1), multiaxial histology (n = 4) and multiaxial immunohistochemistry (n = 4). Smooth muscle basal tone decreased material stiffness and increased anisotropy. In addition, maximum vaginal tone was decreased with increasing intraluminal pressures. This study demonstrated that vaginal muscle tone contributed to the biaxial mechanical response of murine vaginal tissue. This may be important in further elucidating the underlying mechanisms of prolapse, in order to improve current preventative and treatment strategies.

Tissue Composition and Biomechanical Property Changes in the Vaginal Wall of Ovariectomized Young Rats

Ideal animal models are needed to reflect the changes in the biochemical and biomechanical properties of the vagina that occur in pelvic organ prolapse (POP). In this study, we aimed to demonstrate the short and long-term effect of menopause on the biochemical and biomechanical properties of rat anterior vaginas. Here, Sprague-Dawley rats were bilaterally ovariectomized to induce menopause. Rats without ovariectomy served as the normal control group (n=12). The histology changes and the expression of collagen I, III, and a-SMA were assessed to indicate the biochemical changes in the vagina 2 weeks, 4 weeks, and 16 weeks after ovariectomy (n=6 for 2 and 4 weeks, n=12 for 16 weeks). Uniaxial biomechanical testing was conducted in the control group and ovariectomized rats 16 weeks after ovariectomy. Compared with the control group, the ovariectomy group showed a significant increase in the expression of collagen I 2 weeks after ovariectomy, while collagen III showed a declining trend. Two weeks after ovariectomy, the smooth muscle bundles began to become disorganized, and the fraction of smooth muscle in the nonvascular muscularis of the proximal vagina was significantly decreased (P<0.001). However, there was no difference in the expression of a-SMA in the distal vagina. Compared with the control group, the ovariectomy group had stiffer vaginas with a declining trend in the ultimate load 16 weeks after ovariectomy. In conclusion, surgically induced menopause had a significant short- and long-term impact on tissue composition and biomechanical properties of the rat vagina, which may lead to increased susceptibility to POP development.

Biaxial biomechanical properties of the nonpregnant murine cervix and uterus

From a biomechanical perspective, female reproductive health is an understudied area of research. There is an incomplete understanding of the complex function and interaction between the cervix and uterus. This, in part, is due to the limited research into multiaxial biomechanical functions and geometry of these organs. Knowledge of the biomechanical function and interaction between these organs may elucidate etiologies of conditions such as preterm birth. Therefore, the objective of this study was to quantify the multiaxial biomechanical properties of the murine cervix and uterus using a biaxial testing set-up. To accomplish this, an inflation-extension testing protocol (n = 15) was leveraged to quantify biaxial biomechanical properties while preserving native matrix interactions and geometry. Ultrasound imaging and histology (n = 10) were performed to evaluate regional geometry and microstructure, respectively. Histological analysis identified a statistically significant greater collagen content and significantly smaller smooth muscle content in the cervix as compared to the uterus. No statistically significant differences in elastic fibers were identified. Analysis of bilinear fits revealed a significantly stiffer response from the circumferentially orientated ECM fibers compared to axially orientated fibers in both organs. Bilinear fits and a two-fiber family constitutive model showed that the cervix was significantly less distensible than the uterus. We submit that the regional biaxial information reported in this study aids in establishing an appropriate reference configuration for mathematical models of the uterine-cervical complex. Thus, may aid future work to elucidate the biomechanical mechanisms leading to cervical or uterine conditions.

Inflation and rupture of vaginal tissue

Around 80% of women experience vaginal tears during labour when the diameter of the vagina must increase to allow the passage of a full-term baby. Current techniques for evaluating vaginal tears are qualitative and often lead to an incorrect diagnosis and inadequate treatment, severely compromising the quality of life of women. In order to characterize the failure properties of the vaginal tissue, whole vaginal tracts from rats (n = 18) were subjected to free-extension inflation tests until rupture using a custom-built experimental set-up. The resulting deformations were measured using the digital image correlation technique. Overall, the strain and changes in curvature in the hoop direction were significantly larger relative to the axial direction. At a failure pressure of 110 ± 23 kPa (mean ± s.d.), the hoop and axial stresses were computed to be 970 ± 340 kPa and 490 ± 170 kPa, respectively. Moreover, at such pressure, the hoop and axial strains were found to be 12.8 ± 4.4 % and 6.4 ± 3.7 % , respectively. Rupture of the vaginal specimens always occurred in the hoop direction by tearing along the axial direction. This knowledge about the rupture properties of the vaginal tissue will be crucial for the development of clinical approaches for preventing and mitigating vaginal tearing and the associated short- and long-term traumatic conditions.

Evaluating residual strain throughout the murine female reproductive system

Mounting evidence suggests that cells within soft tissues seek to maintain a preferred biomechanical state. Residual stress is defined as the stress that remains in a tissue when all external loads are removed and contributes to tissue mechanohomeostasis by decreasing the transmural gradient of wall stress. Current computational models of pelvic floor mechanics, however, often do not consider residual stress. Residual strain, a result of residual stress can be quantitatively measured through opening angle experiments. Therefore, the objective of this study is to quantify the regional variations in opening angles along the murine female reproductive system at estrus and diestrus, to quantify residual strain in the maintenance state of sexually mature females. Further, evidence suggests that hydrophilic glycosaminoglycan/proteoglycans are integral to cervical remodeling. Thus, variations in opening angles following hypo-osmotic loading are evaluated. Opening angle experiments were performed along the murine reproductive system in estrus (n = 8) and diestrus (n = 8) and placed in hypo-osmotic solution. Measurements of thickness and volume were also obtained for each group. Differences (p < 0.05) in opening angle were observed with respect to region and loading, however, differences with respect to estrous stage were not significant. Thickness values were significant (p < 0.05) with respect to region only. The effects of both estrous cycle and region resulted in significant differences (p < 0.05) in observed volume. The observed regional differences indicate variation in the stress-free state among the reproductive system which may have implications for future computational models to advance women's reproductive health.

Biaxial Mechanical Assessment of the Murine Vaginal Wall Using Extension-Inflation Testing

Progress toward understanding the underlying mechanisms of pelvic organ prolapse (POP) is limited, in part, due to a lack of information on the biomechanical properties and microstructural composition of the vaginal wall. Compromised vaginal wall integrity is thought to contribute to pelvic floor disorders; however, normal structure-function relationships within the vaginal wall are not fully understood. In addition to the information produced from uniaxial testing, biaxial extension-inflation tests performed over a range of physiological values could provide additional insights into vaginal wall mechanical behavior (i.e., axial coupling and anisotropy), while preserving in vivo tissue geometry. Thus, we present experimental methods of assessing murine vaginal wall biaxial mechanical properties using extension-inflation protocols. Geometrically intact vaginal samples taken from 16 female C57BL/6 mice underwent pressure-diameter and force-length preconditioning and testing within a pressure-myograph device. A bilinear curve fit was applied to the local stress-stretch data to quantify the transition stress and stretch as well as the toe- and linear-region moduli. The murine vaginal wall demonstrated a nonlinear response resembling that of other soft tissues, and evaluation of bilinear curve fits suggests that the vagina exhibits pseudoelasticity, axial coupling, and anisotropy. The protocols developed herein permit quantification of biaxial tissue properties. These methods can be utilized in future studies in order to assess evolving structure-function relationships with respect to aging, the onset of prolapse, and response to potential clinical interventions.

Transcriptional Regulation of Connective Tissue Metabolism Genes in Women With Pelvic Organ Prolapse

OBJECTIVE

The aim of this study was to compare differences in expressions and relationships between key genes involved in extracellular matrix metabolism and tissue cellularity in women with and without pelvic organ prolapse (POP).

METHODS

A total of 80 biopsies (anterior cuff, posterior cuff, and/or leading edge) were obtained from 30 women: n = 10 premenopausal without POP (controls), n = 10 premenopausal with POP, and n = 10 postmenopausal with POP. Quantitative reverse-transcriptase polymerase chain reaction was used to assess gene expression of bone morphogenetic protein 1 (BMP1), collagen types I (COL1) and III (COL3), relaxin family peptide receptor 1 (RXFP1), matrix metallopeptidase 2, and TIMP metallopeptidase inhibitors 2 and 3. Hematoxylin and eosin staining was used to assess cellularity of the connective tissue layer. Kruskal-Wallis test, Mann-Whitney U test, Pearson correlation, or linear regression analyses were used, as appropriate.

RESULTS

Bone morphogenetic protein 1 expression was significantly up-regulated in patients with POP compared with controls. Bone morphogenetic protein 1 expression was correlated with COL1 expression in all groups but only correlated with TIMP metallopeptidase inhibitor 3 expression in controls. Similarly, COL3 expression was correlated with RXFP1 expression in women with POP but not in controls. The degree of dependence (slope of the regression line) between COL1 and COL3 expressions was significantly elevated in premenopausal women with POP compared with the other 2 groups. The slopes between COL1-COL3, COL3-matrix metallopeptidase 2, COL1-RXFP1, and COL3-RXFP1 expressions were significantly lower in postmenopausal women compared with premenopausal women with POP. No differences were found in overall tissue cellularity.

CONCLUSIONS

Bone morphogenetic protein 1 expression may play a significant role in the pathophysiology of POP. The finding that BMP1 expression was correlated with COL1 expression in all groups suggests a conserved association between BMP1 and collagen synthesis in the vaginal wall. The elevated slope between COL1 and COL3 expressions may be associated with early (premenopausal) development of POP. The expression of RXFP1 in postmenopausal women and its altered intergene regulation suggests a role for RXFP1 in connective tissue metabolism outside pregnancy.

Effects of repeated biaxial loads on the creep properties of cardinal ligaments

The cardinal ligament (CL) is one of the major pelvic ligaments providing structural support to the vagina/cervix/uterus complex. This ligament has been studied mainly with regards to its important function in the treatment of different diseases such as surgical repair for pelvic organ prolapse and radical hysterectomy for cervical cancer. However, the mechanical properties of the CL have not been fully determined, despite the important in vivo supportive role of this ligament within the pelvic floor. To advance our limited knowledge about the elastic and viscoelastic properties of the CL, we conducted three consecutive planar equi-biaxial tests on CL specimens isolated from swine. Specifically, the CL specimens were divided into three groups: specimens in group 1 (n = 7) were loaded equi-biaxially to 1 N, specimens in group 2 (n = 8) were loaded equi-biaxially to 2N, and specimens in group 3 (n = 7) were loaded equi-biaxially to 3N. In each group, the equi-biaxial loads of 1N, 2N, or 3N were applied and kept constant for 1200s three times. The two axial loading directions were selected to be the main in-vivo loading direction of the CL and the direction that is perpendicular to it. Using the digital image correlation (DIC) method, the in-plane Lagrangian strains in these two loading directions were measured throughout the tests. The results showed that CL was elastically anisotropic, as statistical differences were found between the mean strains along the two axial loading directions for specimens in group 1, 2, or 3 when the equi-biaxial load reached 1N, 2N, or 3N, respectively. For specimens in group 1 and 2, no statistical differences were detected in the mean normalized strains (or, equivalently, the increase in strain over time) between the two axial loading directions for each creep test. For specimens in group 3, some differences were noted but, by the end of the 3rd creep test, there were no statistical differences in the mean normalized strains between the two axial loading directions. These findings indicated that the increase in strain over time by the end of the 3rd creep test were comparable along these directions. The greatest mean normalized strain (or, equivalently, the largest increase in strain over time) was measured at the end of the 1st creep test (t=1200s), regardless of the equi-biaxial load magnitude or loading direction. Mean normalized strains during the 2nd and 3rd creep tests (t = 100, 600, and 1200s), along each loading direction, were not statistically different. Isochronal data collected at 1N, 2N, or 3N equi-biaxial loads indicated that the CL may be a nonlinear viscoelastic material. Overall, this experimental study offers new knowledge of the mechanical properties of the CL that can guide the development of better treatment methods such as surgical reconstruction for pelvic organ prolapse and radical hysterectomy for cervical cancer.

Cell-based secondary prevention of childbirth-induced pelvic floor trauma

With advancing population age, pelvic-floor dysfunction (PFD) will affect an increasing number of women. Many of these women wish to maintain active lifestyles, indicating an urgent need for effective strategies to treat or, preferably, prevent the occurrence of PFD. Childbirth and pregnancy have both long been recognized as crucial contributing factors in the pathophysiology of PFD. Vaginal delivery of a child is a serious traumatic event, causing anatomical and functional changes in the pelvic floor. Similar changes to those experienced during childbirth can be found in symptomatic women, often many years after delivery. Thus, women with such PFD symptoms might have incompletely recovered from the trauma caused by vaginal delivery. This hypothesis creates the possibility that preventive measures can be initiated around the time of delivery. Secondary prevention has been shown to be beneficial in patients with many other chronic conditions. The current general consensus is that clinicians should aim to minimize the extent of damage during delivery, and aim to optimize healing processes after delivery, therefore preventing later dysfunction. A substantial amount of research investigating the potential of stem-cell injections as a therapeutic strategy for achieving this purpose is currently ongoing. Data from small animal models have demonstrated positive effects of mesenchymal stem-cell injections on the healing process following simulated vaginal birth injury.

Micro-structural and Biaxial Creep Properties of the Swine Uterosacral-Cardinal Ligament Complex

The uterosacral ligament and cardinal ligament (USL/CL) complex is the major suspensory tissue of the uterus, cervix, and vagina. This tissue is subjected primarily to bi-axial forces in-vivo that significantly alter its structure and dimension over time, compromising its support function and leading to pelvic floor disorders. In this study, we present the first rigorous characterization of the collagen fiber microstructure and creep properties of the swine USL/CL complex by using scanning electron microscopy and planar biaxial testing in combination with three-dimensional digital image correlation. Collagen fiber bundles were found to be arranged into layers. Although the fiber bundles were oriented in multiple directions, 80.8% of them were aligned within ±45[Formula: see text] to the main in-vivo loading direction. The straightness parameter, defined as the ratio of the end-to-end distance of a fiber bundle to its length, varied from 0.28 to 1.00, with 95.2% fiber bundles having a straightness parameter between 0.60 and 1.00. Under constant equi-biaxial loads of 2 and 4 N, the USL/CL complex exhibited significant creep both along the main in-vivo loading direction (the parallel direction) and along the direction perpendicular to it (the perpendicular direction). Specifically, over a 120-min period, the mean strain increased by 20-34[Formula: see text] in the parallel direction and 33-41[Formula: see text] in the perpendicular direction. However, there was no statistically significant difference in creep strains observed after 120 min between the parallel and perpendicular directions for either the 2 or 4 N load case. Creep proceeded slightly faster in the perpendicular direction under the equi-biaxial load of 2 N than under the equi-biaxial load of 4 N ([Formula: see text]). It proceeded significantly faster in the parallel direction under the equi-biaxial loads of 2 N than under the equi-biaxial loads of 4 N ([Formula: see text]). Overall, our findings contribute to a greater understanding of the biomaterial properties of the USL/CL complex that is needed for the development of new surgical reconstruction methods and mesh materials for pelvic floor disorders.

BIOMECHANICAL PROPERTIES OF MESHES FOLLOWING IMPLANTATION IN THE RAT ABDOMINAL WALL MODEL

The objective of our study was to (1) evaluate mesh strength and collagen incorporation after 4 and 12 weeks of implantation in a rat abdominal wall model and (2) determine the relationship between collagen deposition and mechanical strength of a chitosan-coated polypropylene mesh. We implanted 0.5% chitosan-coated polypropylene mesh (PPM), collagen-coated PPM (PelvitexTM; C.R. Bard), and PPM (Avaulta Solo[Formula: see text]; C.R. Bard) using a rat abdominal defect model. Mechanical properties were determined from uniaxial tensile testing and collagen deposition of each mesh was evaluated 4 and 12 weeks post-implantation. We found that after implantation, the neo tissue of Ch-PPM is stiffer than the commercially available meshes. We also observed no significant difference in the ratio of collagen types I/III between mesh samples at 4 weeks or 12 weeks. We found no relationship between the ratio of collagen types I/III and the mechanical strength of mesh samples after implantation. The increased stiffness with chitosan coating could be due to increased muscle tissue ingrowth.

Comparative histology of mouse, rat, and human pelvic ligaments

INTRODUCTION AND HYPOTHESIS

The uterosacral (USL) and cardinal ligaments (CL) provide support to the uterus and pelvic organs, and the round ligaments (RL) maintain their position in the pelvis. In women with pelvic organ prolapse (POP), the connective tissue, smooth muscle, vasculature, and innervation of the pelvic support structures are altered. Rodents are commonly used animal models for POP research. However, the pelvic ligaments have not been defined in these animals. In this study, we hypothesized that the gross anatomy and histological composition of pelvic ligaments in rodents and humans are similar.

METHODS

We performed an extensive literature search for anatomical and histological descriptions of the pelvic support ligaments in rodents. We also performed anatomical dissections of the pelvis to define anatomical landmarks in relation to the ligaments. In addition, we identified the histological components of the pelvic ligaments and performed quantitative analysis of the smooth muscle bundles and connective tissue of the USL and RL.

RESULTS

The anatomy of the USL, CL, and RL and their anatomical landmarks are similar in mice, rats, and humans. All species contain the same cellular components and have similar histological architecture. However, the cervical portion of the mouse USL and RL contain more smooth muscle and less connective tissue compared with rat and human ligaments.

CONCLUSION

The pelvic support structures of rats and mice are anatomically and histologically similar to those of humans. We propose that both mice and rats are appropriate, cost-effective models for directed studies in POP research.

Histo-mechanical properties of the swine cardinal and uterosacral ligaments

The focus of this study was to determine the structural and mechanical properties of two major ligaments that support the uterus, cervix, and vagina: the cardinal ligament (CL) and the uterosacral ligament (USL). The adult swine was selected as animal model. Histological analysis was performed on longitudinal and cross sections of CL and USL specimens using Masson׳s trichrome and Verhoeff-van Giesson staining methods. Scanning electron microscopy was employed to visualize the through-thickness organization of the collagen fibers. Quasi-static uniaxial tests were conducted on specimens that were harvested from the CL/USL complex of a single swine. Dense connective tissue with a high content of elastin and collagen fibers was observed in the USL. Loose connective tissue with a considerable amount of smooth muscle cells and ground substance was detected in both the CL and USL. Collagen fibers, smooth muscle cells, blood vessels, and nerve fibers were arranged primarily in the plane of the ligaments. The USL was significantly stronger than the CL with higher ultimate stress and tangent modulus of the linear region of the stress-strain curve. Knowledge about the mechanical properties of the CL and USL will aid in the design of novel mesh materials, stretching routines, and surgical procedures for pelvic floor disorders.

Anatomical and histological examination of the porcine vagina and supportive structures: in search of an ideal model for pelvic floor disorder evaluation and management

OBJECTIVE

: The objective of the study was to examine the anatomy and histology of the swine vagina and adjacent supportive structures in comparison to human tissues to determine the potential utility of this model for pelvic floor disorder evaluation and management.

METHODS

: This is a descriptive study of the gross anatomy and histology of the swine vagina, uterosacral ligament, cardinal ligament, and rectovaginal space. Tissue was collected from 6 different sites in each of the 6 animals, processed, and stained with hematoxylin-eosin, Masson trichrome, and van Gieson and evaluated by both gynecologic and veterinary pathologists.

RESULTS

: Porcine tissues were similar to the human vagina and supporting structures. The origin, insertion, and course of the uterosacral and cardinal ligaments appeared similar to those in humans. Histologically, both the porcine and human vagina and rectum consist of a mucosal, muscular, and adventitial layers. The swine vaginal smooth muscle is arranged in an inner circular and outer longitudinal manner. Collagen, elastin, and smooth muscle were identified in 5 sites. Collagen was highest in the cardinal compared with the uterosacral ligament (P = 0.03), whereas elastin was highest in the uterosacral ligament. The vaginal epithelium measured approximately 40 μm at the vaginal cuff and 50 to 200 μm at anterior and posterior vagina. The swine vagina appeared thinner and contained less elastin. The rectovaginal region contained a smooth muscle layer leading to a thin adventitial layer.

CONCLUSIONS

: The swine vagina and adjacent supportive structures appear to be grossly and histologically similar to human vaginal anatomy, and these similarities could lead to further investigation of the porcine model in the study of pelvic support and support disorders.

Impact of birth in the presence and absence of simulated birth injury on vaginal glycosaminoglycan content

INTRODUCTION AND HYPOTHESIS

This study aims to evaluate the effects of simulated birth trauma and vaginal and Cesarean delivery on glycosaminoglycans (GAGs) in the vagina of female rats.

METHODS

One hundred ten rats were divided into six groups: A (control), B (vaginal trauma), C (Cesarean delivery), D (Cesarean delivery followed by vaginal trauma), E (vaginal delivery), and F (20th day of gestation). In each group, half of the animals were killed 4 days after the procedure (time 1) and 12 weeks later (time 2). GAGs were extracted, isolated, and identified by using agarose gel electrophoresis and quantified by densitometry. Statistical analysis was performed using Kruskal-Wallis and Mann-Whitney tests.

RESULTS

We observed a significant decrease in total GAGs and dermatan sulfate (DS) at time 1. Evaluation at time 2 showed a significant increase in total GAGs, DS, and heparan sulfate.

CONCLUSIONS

Levels of sulfated GAGs in the rat vagina are affected by delivery and simulated birth trauma.

Vulnerability of continence structures to injury by simulated childbirth

The goal of this study was to examine acute morphological changes, edema, muscle damage, inflammation, and hypoxia in urethral and vaginal tissues with increasing duration of vaginal distension (VD) in a rat model. Twenty-nine virgin Sprague-Dawley rats underwent VD under anesthesia with the use of a modified Foley catheter inserted into the vagina and filled with saline for 0, 1, 4, or 6 h. Control animals were anesthetized for 4 h without catheter placement. Urogenital organs were harvested after intracardiac perfusion of fixative. Tissues were embedded, sectioned, and stained with Masson's trichrome or hematoxylin and eosin stains. Regions of hypoxia were measured by hypoxyprobe-1 immunohistochemistry. Within 1 h of VD, the urethra became vertically elongated and displaced anteriorly. Edema was most prominent in the external urethral sphincter (EUS) and urethral/vaginal septum within 4 h of VD, while muscle disruption and fragmentation of the EUS occurred after 6 h. Inflammatory damage was characterized by the presence of polymorphonuclear leukocytes in vessels and tissues after 4 h of VD, with the greatest degree of infiltration occurring in the EUS. Hypoxia localized mostly to the vaginal lamina propria, urethral smooth muscle, and EUS within 4 h of VD. Increasing duration of VD caused progressively greater tissue edema, muscle damage, and morphological changes in the urethra and vagina. The EUS underwent the greatest insult, demonstrating its vulnerability to childbirth injury.

Fibulin-5: two for the price of one maintaining pelvic support

Pelvic organ prolapse (POP) is a disabling disorder in women characterized by a loss of pelvic floor support leading to the herniation of the uterus into or through the vagina. POP is a complex problem that likely involves multiple mechanisms, and available therapies are limited. In this issue of the JCI, Budatha et al. explore the dual role carried out by fibulin-5 in facilitating the assembly of normal elastic fibers and inhibiting MMP-9 activity, revealing a new mechanism critical to the maintenance of pelvic organ support.

Impact of pregnancy and vaginal delivery on the passive and active mechanics of the rat vagina

Remodeling of vaginal extracellular matrix and smooth muscle likely plays a critical role in reducing the risk of maternal injury during vaginal delivery by altering the mechanical properties to increase distension and reduce stress. Long-Evans rats were divided into five groups to examine the passive mechanical and active contractile properties throughout pregnancy and postpartum: virgin (n=17), mid-pregnant (Day 14-16, n=12), late-pregnant (Day 20-22, n=14), immediate postpartum (0-2 h after delivery, n=14), and 4 week postpartum (n=15). Longitudinal sections of vaginal tissue were loaded to failure uniaxially for passive mechanical or active contractile properties were examined. For passive mechanics, the tangent modulus decreased 45% by mid-pregnancy and immediately postpartum (p<0.001). The ultimate strain continuously increased up to 43% higher than virgin animals (p=0.007) in the immediate postpartum group. For active mechanics, the maximal contractile force was 36-56% lower through immediate postpartum animals, and was significantly more sensitive to K+ throughout pregnancy and postpartum (p=0.003). The changes observed in the passive and active properties of the rat vagina are consistent with what would be expected from a tissue that is remodeling to maximize its ability to distend at the time of vaginal delivery to facilitate passage of the fetus with minimal injury.

Tissue mechanics, animal models, and pelvic organ prolapse: a review

Pelvic floor disorders such as pelvic organ prolapse, urinary incontinence, and fecal incontinence affect a large number of women each year. The pelvic floor can be thought of as a biomechanical structure due to the complex interaction between the vagina and its supportive structures that are designed to withstand the downward descent of the pelvic organs in response to increases in abdominal pressure. Although previous work has highlighted the biochemical changes that are associated with specific risk factors (i.e. parity, menopause, and genetics), little work has been done to understand the biomechanical changes that occur within the vagina and its supportive structures to prevent the onset of these pelvic floor disorders. Human studies are often limited due to the challenges of obtaining large tissue samples and ethical concerns. Therefore, it is necessary to investigate the use of animal models and their importance in understanding how different risk factors affect the biomechanical properties of the vagina and its supportive structures. In this review paper, we will discuss the different animal models that have been previously used to characterize the biomechanical properties of the vagina: including non-human primates, rodents, rabbits, and sheep. The anatomy and preliminary biomechanical findings are discussed along with the importance of considering experimental conditions, tissue anisotropy, and viscoelasticity when characterizing the biomechanical properties of vaginal tissue. Although there is not a lot of biomechanics research related to the vagina and pelvic floor, the future is exciting due to the significant potential for scientific findings that will improve our understanding of these conditions and hopefully lead to improvements in the prevention and treatment of pelvic disorders.

Hormones restore biomechanical properties of the vagina and supportive tissues after surgical menopause in young rats

OBJECTIVE

The objective of the study was to determine the impact of hormones on the biomechanical properties of the vagina and its supportive tissues following surgical menopause in young vs middle-aged rats.

STUDY DESIGN

Long-Evans rats (4-month virgin [n = 34], 4-month parous [n = 36], and 9-month parous [n = 34]), underwent ovariectomy (OVX) or sham surgery. OVX animals received hormones (estrogen [E2] or estrogen plus progesterone [E2 plus P4]), placebo, or a matrix metalloproteinase inhibitor (chemically modified tetracycline-8 [CMT-8]). Animals were euthanized after 8 weeks and the biomechanical properties of the vagina and supportive tissues determined. Data were analyzed using a 1-way analysis of variance and posthoc tests.

RESULTS

OVX induced a rapid decline in the biomechanical properties of pelvic tissues in young but not middle-aged rats. Supplementation with E2, E2 plus P4, or CMT-8 restored tissues of young rats to control levels with no effect on middle-aged tissues. Parity did not have an impact on tissue behavior.

CONCLUSION

OVX has a differential effect on the tissues of young vs middle-aged rats.

Combined estrogen and ghrelin administration decreases expression of p27(kip1) and proportion of isomyosin type I in the striated urethral and anal sphincters and levator ani of old ovariectomized rats

We compared estrogen and/or ghrelin effects on pelvic floor muscles in old versus young adult ovariectomized rats. Ovariectomized Fisher 344 rats (18 and 3 months old, n = 24 x 2) received 42 daily intraperitoneal 17-beta estradiol (10 microg kg(-1)), ghrelin (2 microg kg(-1)), both, or vehicle (n = 6 x 4/group). Cytoplasmic p27(kip1) expression and isomyosin I proportion in striated urethral and anal sphincters and levator ani were measured, respectively, by Western blot analysis and gel electrophoresis with immunohistochemistry of muscle ghrelin receptors and radioimmunoassay of circulating growth hormone. In young adult rats, estrogen significantly decreased cytoplasmic p27(kip1) and isomyosin I signal intensities. In old rats, ghrelin and estrogen/ghrelin significantly decreased both intensities with greater estrogen/ghrelin effect. Ghrelin receptors were not immunostained in any muscle. Estrogen and/or ghrelin significantly increased or decreased, respectively, circulating growth hormone in old and young adult rats. Estrogen/ghrelin administration reversed pelvic floor muscle ageing changes in old ovariectomized rats through growth hormone production.

HOXA11 is critical for development and maintenance of uterosacral ligaments and deficient in pelvic prolapse

Pelvic organ prolapse (POP) is a common, debilitating disorder affecting millions of women. Uterosacral ligaments (USLs) are the main supportive structures of the uterus and vagina and are often attenuated in women with POP. Although the mechanical strength of USLs is known to be dependent on collagen synthesis and catabolism and the degradation protein MMP2 has been implicated in POP, the molecular mechanisms involved in the development of POP are currently unknown. Homeobox (HOX) genes are transcriptional regulators that orchestrate embryonic development of the urogenital tract. We demonstrated here that HOXA11 was essential for organogenesis of the USL by showing that USLs were absent in Hoxa11-null mice. We compared expression of HOXA11, collagen type I, collagen type III, MMP2, and MMP9 in USLs of women with and without POP. Expression of HOXA11 and both collagens was dramatically decreased while MMP2 was increased in women with POP. Constitutive expression of Hoxa11 in murine fibroblasts resulted in significantly increased expression of collagen type III and decreased expression of MMP2. These results identified HOXA11 as an essential gene for the development of the USL and suggested that women with POP might have weakened connective tissue due to changes in a signaling pathway involving HOXA11, collagen type III, and MMP2.