The Effect of Menopause on Vaginal Tissue Mechanics: A Brief Review

Often called "the change of life," menopause affects every part of a woman's body. As the sex hormones decrease, the reproductive organs experience the most remarkable changes, with the vagina becoming thinner, drier, and less elastic. Despite the important implications of these changes in genitourinary conditions, there are only a few experimental studies that focus on quantifying the effect of menopause on the mechanical properties of the vagina. These studies are mostly conducted using uniaxial tests on strips of vaginal tissues isolated from rats, rabbits, and sheep and, in only a few cases, from humans. The purpose of this article is to present a systematic review of experimental protocols, methods, and results that are currently published on how menopause alters the mechanical behavior of the vagina. This review will enable new investigators in the biomechanics field to identify important gaps and frame research questions that inform the design of new treatment options for menopausal symptoms.

Two-Year Preclinical Evaluation of Long-Term Absorbable Poly-4-hydroxybutyrate Scaffold for Surgical Correction of Pelvic Organ Prolapse

INTRODUCTION AND HYPOTHESIS

Fully absorbable implants may be an alternative to permanent meshes in the correction pf pelvic organ prolapse (POP) as they may reduce adverse events by promoting tissue regeneration and collagen metabolism. This study was aimed at evaluating the long-term host and biomechanical response to a fully absorbable poly-4-hydroxybutyrate (P4HB) scaffold in comparison with polypropylene (PP) mesh.

METHODS

Poly-4-hydroxybutyrate scaffold (n = 16) and PP mesh (n = 16) were surgically implanted in the posterior vaginal wall of parous female Dohne Merino sheep. Vaginal explants were evaluated in terms of gross necropsy, host response (immune response, collagen deposition, tissue regeneration), biomechanics, and degradation of P4HB at 12 and 24 months post-implantation.

RESULTS

Gross necropsy revealed no infection or fluid collection using P4HB or PP. At 12 months, exposures were observed with both P4HB (3 out of 8) and PP (4 out of 8), whereas at 24 months, exposures were observed only with PP (4 out of 8). The tensile stiffness of the P4HB explants was maintained over time despite complete absorption of P4HB. The collagen amount of the vaginal tissue after P4HB implantation increased over time and was significantly higher than PP at 24 months. P4HB scaffolds exhibited significantly lower myofibroblast differentiation than PP meshes at 24 months.

CONCLUSIONS

The P4HB scaffold allowed for gradual load transfer to the vaginal wall and resulted in mechanically self-sufficient tissue. P4HB scaffold had a more favorable host response than PP mesh, with higher collagen content, lower myofibroblastic differentiation, and no exposures at 24 months. P4HB scaffolds have potential as an alternative to permanent implants in treating POP.

Next generation 3D-printed intravaginal ring for prevention of HIV and unintended pregnancy

Globally, there are 20 million adolescent girls and young women living with HIV who have limited access to long-acting, effective, women-controlled preventative methods. Additionally, although there are many contraceptive methods available, globally, half of all pregnancies remain unintended. Here we report the first 3D-printed multipurpose prevention technology (MPT) intravaginal ring (IVR) for HIV prevention and contraception. We utilized continuous liquid interface production (CLIP™) to fabricate MPT IVRs in a biocompatible silicone-based resin. Etonogestrel (ENG), ethinyl estradiol (EE), and islatravir (ISL) were loaded into the silicone poly(urethane) IVR in a controlled single step drug loading process driven by absorption. ENG/EE/ISL IVR promoted sustained release of drugs for 150 days in vitro and 14 days in sheep. There were no adverse MPT IVR-related findings of cervicovaginal toxicity or changes in vaginal biopsies or microbiome community profiles evaluated in sheep. Furthermore, ISL IVR in macaques promoted sustained release for 28 days with ISL-triphosphate levels above the established pharmacokinetic benchmark of 50-100 fmol/106 PBMCs. The ISL IVR was found to be safe and well tolerated in the macaques with no observed mucosal cytokine changes or alterations in peripheral CD4 T-cell populations. Collectively, the proposed MPT IVR has potential to expand preventative choices for young women and girls.

Comparative anatomy of the ovine and human pelvis for laparoscopic sacrocolpopexy: evaluating the effectiveness of the ovine model

INTRODUCTION AND HYPOTHESIS

Laparoscopic sacrocolpopexy (LSC) is a functional reconstructive surgery used to treat pelvic organ prolapse (POP) in middle-aged women. Although LSC is widely used, its implementation is hindered by perceived technical difficulties and surgical learning curves. Surgeons require adequate experience with LSC prior to performing the procedure on patients to improve their quality of life. This study is aimed at demonstrating the effectiveness of the ovine model (OM) for training and research in LSC, while also comparing anatomical differences between ovine and human models during the procedure.

METHODS

The animal model and training were provided by the Jesús Usón Minimally Invasive Surgery Centre. Urologists and gynecologists with experience in LSC participated in a course and their findings were recorded and documented.

RESULTS

Differences in patient positioning, trocar placement, and reperitonealization were identified between the ovine and human models. Hysterectomy is always performed in the ovine model, whereas it is not mandatory in humans. There are also differences in the dissection of the levator ani muscle and attachment point of the posterior mesh to the uterus between the two models. Despite differences in some areas, the ovine pelvic structure and vagina are similar in size to those of humans.

CONCLUSIONS

The ovine model is a valuable tool for surgeons in their learning curve for LSC, allowing for safe and effective practice prior to performing the procedure on patients. The use of the OM can help to improve the quality of life for women affected by pelvic organ prolapse.

Current practice in animal models for pelvic floor dysfunction

INTRODUCTION AND HYPOTHESIS

The objective was to explore the current practice of using animal models for female pelvic floor dysfunction (PFD).

METHODS

By applying PFD and animal models as the keywords, we made a computerized search using PubMed, Ovid-Medline and Ovid-Embase from 2000 to 2022. The publications on the construction and application of animal models for PFD were included, and the results are presented in narrative text.

RESULTS

Studies on PFD primarily use rodents, large quadrupeds, and nonhuman primates (NHPs). NHPs are closest to humans in anatomy and biomechanics of the pelvic floor, followed by large quadrupeds and rodents. Rodents are more suitable for studying molecular mechanism, histopathology of PFD, and mesh immune rejection. Large quadrupeds are adaptable to the study of pelvic floor biomechanics and the development of new surgical instruments for PFD. NHPs are suitable for studying the occurrence and pathogenesis of pelvic organ prolapse. Among modeling methods, violent destruction of pelvic floor muscles, regulation of hormone levels, and denervation were used to simulate the occurrence of PFD. Gene knockout can be used to study both the pathogenesis of PFD and the efficacy of treatments. Other methods such as abdominal wall defect, vaginal defect, and in vitro organ bath system are more frequently used to observe wound healing after surgery and to verify the efficacy of treatments.

CONCLUSIONS

The rat is currently the most applicable animal type for numerous modeling methods. Vaginal dilation is the most widely used modeling method for research on the pathogenesis, pathological changes, and treatment of PFD.

Secondary urethral sphincter function of the rabbit pelvic and perineal muscles

Perineal and pelvic floor muscles play an important role in continence by providing mechanical support to pelvic organs. It is also known that the pubococcygeus muscle (PcM) contracts in the storage phase and is inactive during voiding, while the bulbospongiosus muscle (BsM) is active during the voiding phase. Recent evidence suggested an additional role of these muscles in supporting urethral closure in rabbits. However, the individual role of perineal and pelvic muscles as urethral sphincters is not well-defined. Here we evaluated the individual, sequential and synergistic roles of the PcM and BsM in assisting urethral closure and defined the optimal electrical stimulation parameters that can effectively contract these muscles and increase the urethral pressure (P _ura ) in young nulliparous animals (n = 11). Unilateral stimulation of either the BsM or PcM at 40 Hz induced modest increases in average P _ura (0.23 ± 0.10 and 0.07 ± 0.04 mmHg, respectively). Investigation on the changes in P _ura evoked by stimulation frequencies between 5 and 60 Hz show that sequential contralateral PcM-BsM activation at 40 Hz induced a 2-fold average P _ura increase (0.23 ± 0.07 mmHg) compared to that evoked by PcM stimulation. Simultaneous activation of PcM and BsM at 40 Hz also showed an increased average P _ura (0.26 ± 0.04 mmHg), with a 2-fold increase in average P _ura observed during the unilateral sequential PcM-BsM stimulation at 40 Hz (0.69 ± 0.2 mmHg). Finally, stimulation at 40 Hz of the bulbospongiosus nerve (BsN) induced an approximate 4-fold increase in average P _ura (0.87 ± 0.44 mmHg; p < 0.04) compared to that elicited by BsM stimulation, confirming that direct nerve stimulation is more effective. Together, this study shows that in the female rabbit, both perineal and pelvic muscles support of the urethral function during continence, and that unilateral stimulation of the BsN at 40-60 Hz is sufficient to achieve maximal secondary sphincter activity. The results also support the potential clinical value of neuromodulation of pelvic and perineal nerves as bioelectronic therapy for stress urinary incontinence.

Validation of an ovine vesicovaginal fistula model

INTRODUCTION AND HYPOTHESIS

A representative, large animal model of vesicovaginal fistulas is needed for the training of surgeons and for the development of new surgical techniques and materials for obstetric fistula repair.

METHODS

The safety, feasibility, and reproducibility of vesicovaginal fistula creation were studied in 4 adult female sheep. A 1-cm fistula was created between the vagina and the bladder through a transvaginal approach. The defect was allowed to heal for 8 weeks and the animals were then euthanized. The primary outcome was the fistula patency. Secondary outcomes were fistula size, urogenital dimensions, urodynamic evaluation, histology (inflammation, vascularization, collagen deposition) and biomechanical characteristics of the fistula edge (stress at break, maximum elongation, and stiffness).

RESULTS

The transvaginal creation of a vesicovaginal fistula was safe. All animals survived the surgical procedure and follow-up period, without complications. Three of the four animals demonstrated a patent vesicovaginal fistula after 8 weeks. Baseline data are provided of the urogenital dimensions and the urodynamic, histological, and biomechanical characteristics of the model.

CONCLUSIONS

The ewe is a safe, feasible, and reproducible model for vesicovaginal fistulas. The model can help to study new techniques and materials to boost surgical innovation for vesicovaginal fistula repair.

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.

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.

An overview of de novo bone generation in animal models

Some of the earliest success in de novo tissue generation was in bone tissue, and advances, facilitated by the use of endogenous and exogenous progenitor cells, continue unabated. The concept of one health promotes shared discoveries among medical disciplines to overcome health challenges that afflict numerous species. Carefully selected animal models are vital to development and translation of targeted therapies that improve the health and well-being of humans and animals alike. While inherent differences among species limit direct translation of scientific knowledge between them, rapid progress in ex vivo and in vivo de novo tissue generation is propelling revolutionary innovation to reality among all musculoskeletal specialties. This review contains a comparison of bone deposition among species and descriptions of animal models of bone restoration designed to replicate a multitude of bone injuries and pathology, including impaired osteogenic capacity.

The ewe as an animal model of vaginal atrophy and vaginal Er:YAG laser application

OBJECTIVE

In sheep of reproductive age, we aimed to document decrease in epithelial thickness, glycogen amount, and other vaginal changes after castration and the effect of Er:YAG laser as used clinically.

METHODS

On day 0, 16 sheep underwent ovariectomy. They were randomized to sham or three vaginal Er:YAG laser applications at monthly intervals. Primary outcome was vaginal epithelial thickness (d60, d71, d73, d77, and d160). Secondary outcomes included indicators of atrophy (vaginal health index = VHI), pH, cytology, morphology at the above time points, microcirculation focal depth (FD; d70 and d160), and at sacrifice (d160) vaginal dimensions and active and passive biomechanical testing.

RESULTS

Menopausal changes between 60 and 160 days after ovariectomy included a progressive decrease in epithelial thickness, in VHI, FD, glycogen, elastin content and vasculature, and an increase in pH and collagen content. In lasered animals, the first day a few white macroscopic foci were visible and an increase in pH was measured. Both disappeared within 3 days. Seven days after laser the epithelial thickness increased. At sacrifice (d160), there were no differences between sham and laser group in vaginal dimensions, morphometry, mitotic and apoptotic activity, active contractility, vaginal compliance, except for a lower blood vessel density in the lamina propria of the midvagina in the laser group.

CONCLUSIONS

In reproductive sheep, ovariectomy induces vaginal atrophy evidenced in different outcome measurements. Vaginal Er:YAG laser induced visual impact, a short-term increase in epithelial thickness yet no long-term changes compared to sham therapy in menopausal controls.

Vaginal Er:YAG laser application in the menopausal ewe model: a randomised estrogen and sham-controlled trial

OBJECTIVE

To describe effects of non-ablative erbium-doped:yttrium-aluminium-garnet (Er:YAG) laser on vaginal atrophy induced by iatrogenic menopause in the ewe.

DESIGN

Animal experimental, randomised, sham and estrogen-treatment controlled study with blinding for primary outcome.

SETTING

KU Leuven, Belgium.

SAMPLE

Twenty-four ewes.

METHODS

Menopause was surgically induced, after which the ewes were randomised to three groups receiving vaginal Er:YAG laser application three times, with a 1-month interval; three sham manipulations with a 1-month interval; or estrogen replacement and sham manipulations. At given intervals, ewes were clinically examined and vaginal wall biopsies were taken. Vaginal compliance was determined by passive biomechanical testing from explants taken at autopsy.

MAIN OUTCOME MEASURES

Vaginal epithelial thickness (primary), composition of the lamina propria (collagen, elastin, glycogen and vessel content), vaginal compliance, clinical signs.

RESULTS

Animals exposed to Er:YAG laser application and sham manipulation, but not to estrogens, displayed a significant and comparable increase in vaginal epithelial thickness between baseline and 7 days after the third application (69% and 67%, respectively, both P < 0.0008). In laser-treated ewes, temporary vaginal discharge and limited thermal injury were observed. Estrogen-substituted ewes displayed a more prominent increase in epithelial thickness (202%; P < 0.0001) and higher vaginal compliance (P < 0.05). None of the interventions induced changes in the lamina propria.

CONCLUSIONS

Vaginal Er:YAG laser has comparable effect to sham manipulation in menopausal ewes.

TWEETABLE ABSTRACT

Vaginal Er:YAG laser has comparable effect to sham manipulation in menopausal ewes #LASER #GSM #RCT.

A three-dimensional pelvimetric assessment on pelvic cavity of gazelle (Gazella subgutturosa) by computed tomography

The gazelles (Gazella subgutturosa), which are at the risk of extinction and are legally protected, have a cultural and aesthetic value in Turkey. It becomes incredibly important to increase their numbers in order to ensure their survival. In this context, it is required to examine thoroughly the pelvic cavity which contains reproductive organs and is used as the birth canal, as well. This study was conducted to determine the pelvimetric data of the gazelles by scanning their pelvic cavity via a multidetector computed tomography (MDCT) and preparing three-dimensional models of the pelvic cavity. Twelve adult (6 females, 6 males) gazelle carcasses were used in the study. After the pelvic cavity was scanned using the MDCT device with 64 detectors at 80 kV, 200 mA, 639 mGY and 0.625 mm cross-section thickness, the MDCT images were obtained. The three-dimensional models of the images obtained using MIMICS 20.1 (The Materialise Group, Leuven, Belgium) program were prepared. Pelvimetric measurements of the pelvic cavity were taken using these models. It was determined based on the pelvimetric examinations that there was a significant difference between the female and male gazelles in terms of conjugate diameter, vertical diameter, intermediate traversal diameter, and cranial and medial transverse diameter data at p < .05. Also, there was a significant difference in their data related to caudal transverse diameter and ischial arch at p < .01. Consequently, it is thought that the use of pelvimetric values belonging to the pelvic cavity of gazelles would reveal the sexual dimorphism of the species and its differences with other species and would contribute to clinical sciences.

Investigating the birth-related caudal maternal pelvic floor muscle injury: The consequences of low cycle fatigue damage

BACKGROUND

One of the major causes of pelvic organ prolapse is pelvic muscle injury sustained during a vaginal delivery. The most common site of this injury is where the pubovisceral muscle takes origin from the pubic bone. We hypothesized that it is possible for low-cycle material fatigue to occur at the origin of the pubovisceral muscle under the large repetitive loads associated with pushing during the second stage of a difficult labor.

PURPOSE

The main goal was to test if the origin of the pubovisceral muscle accumulates material damage under sub-maximal cyclic tensile loading and identify any microscopic evidence of such damage.

METHODS

Twenty origins of the ishiococcygeous muscle (homologous to the pubovisceral muscle in women) were dissected from female sheep pelvises. Four specimens were stretched to failure to characterize the failure properties of the specimens. Thirteen specimens were then subjected to relaxation and subsequent fatigue tests, while three specimens remained as untested controls. Histology was performed to check for microscopic damage accumulation.

RESULTS

The fatigue stress-time curves showed continuous stress softening, a sign of material damage accumulation. Histology confirmed the presence of accumulated microdamage in the form of kinked muscle fibers and muscle fiber disruption in the areas with higher deformation, namely in the muscle near the musculotendinous junction.

CONCLUSIONS

The origin of ovine ishiococcygeous muscle can accumulate damage under sub-maximal repetitive loading. The damage appears in the muscle near the musculotendinous junction and was sufficient to negatively affect the macroscopic mechanical properties of the specimens.

The histological microstructure and in vitro mechanical properties of pregnant and postmenopausal ewe perineal body

OBJECTIVE

The mechanical properties and microstructure of the perineal body are important for the improvement of numerical models of pelvic organs. We determined the mechanical parameters and volume fractions of the ewe perineal body as an animal model.

METHODS

The 39 specimens of 13 pregnant swifter ewes delivering by cesarean section (aged 2 years, weight 61.2 ± 6.2 kg (mean ± standard deviation) and 24 specimens of 8 postmenopausal swifter ewes 150 days after surgical ovariectomy (aged 7 years, 58.6 ± 4.6 kg)) were loaded uniaxially to determine Young's moduli of elasticity in the small (E0) and large (E1) deformation regions, and ultimate stresses and strains. The 63 adjacent tissue samples were processed histologically to assess volume fractions of smooth and skeletal muscle, adipose cells, elastin, and type I collagen using a stereological point testing grid. We compared the structural and mechanical differences along the ewe perineal body, and between pregnant and postmenopausal groups.

RESULTS

The pregnant/postmenopausal perineal body was composed of smooth muscle (12/14%; median), skeletal muscle (12/16%), collagen (10/23%), elastin (8/7%), and adipose cells (6/6%). The E0 was 37/11 kPa (median), E1 was 0.97/1.04 MPa, ultimate stress was 0.55/0.59 MPa, and ultimate strain was 0.90/0.87 for pregnant/postmenopausal perineal body. The perineal body showed a structural and mechanical stability across the sites. The pregnant ewes had a higher amount of skeletal muscle, higher E0, and a less amount of collagen when compared with postmenopausal ewes.

CONCLUSIONS

The data can be used as input for models simulating vaginal delivery, pelvic floor prolapsed, or dysfunction.

The importance of developing relevant animal models to assess existing and new materials

PURPOSE OF REVIEW

We summarize the recent literature on the use of different animal models for testing existing and new materials for treatment of pelvic organ prolapse.

RECENT FINDINGS

A wide spectrum of animal models is being used in urogynecology, both for the study of physiologic and pathophysiologic processes, training in surgical procedures, yet mainly to study the host response to implant materials. The quality of studies is variable, and procedures, read-outs, and reporting are not standardized. This makes comparison very difficult. The research community is experimenting with different knitting patterns, novel polymers, bioactivation, as well as resorbable rather than durable implants. Outcomes of the experiments are dependent on the location of implantation. Lighter polypropylene constructs seem to induce a less vigorous host response than elder heavier products. Modification of the surface yields contradictory findings. Resorbable acellular collagen matrices may be reintroduced as prophylactically inserted support structures.

SUMMARY

Although animal experimentation with novel candidate implants is advocated, there is a lack of standardization in reporting. The concept of resorbable construct is being revived, as durable materials have caused clinical graft-related complications. Large animal experiments seem to provide interesting and more comprehensive information, yet their use may be contested.

Predicting the mechanical response of the vaginal wall in ball burst tests based on histology

A histologically motivated (HM) coefficient that establishes a link between tissue's microstructure and material model through histological data is used in the prediction of the mechanical properties of vaginal tissue that is subjected to multiaxial loading conditions. Therefore, the material parameters were based on an HM coefficient obtained from tensile testing and histological data of comparable tissues. Uniaxial tensile test data and histological data were collected from three groups of sheep at different time points in their life cycle, including virgins, pregnant, and parous ewes. From this data, a correlation between material parameters and histological data was obtained. Spherical indentation (ball burst [BB]) tests were then performed in specimens with similar tissue structure. The histological data of these samples were used in conjunction with the correlations already established for the uniaxial samples data, to define the material parameters of the BB samples. Mechanical properties of the BB specimens were predicted through basic histology and using finite element modeling (FEM) simulations, without direct mechanical measurements. The predicted force and displacement values of the FEM simulation displayed a good correlation with the experimental (BB) testing results. No fitting of the BB results was performed. In this way, the use of uniaxial tests coupled with useful histological information offers a promising approach to predicting macroscopic material behavior under multiaxial loading conditions in biomechanics.

Composite mesh design for delivery of autologous mesenchymal stem cells influences mesh integration, exposure and biocompatibility in an ovine model of pelvic organ prolapse

The widespread use of synthetic transvaginal polypropylene mesh for treating Pelvic Organ Prolapse (POP) has been curtailed due to serious adverse effects highlighted in 2008 and 2011 FDA warnings and subsequent legal action. We are developing new synthetic mesh to deliver endometrial mesenchymal stem cells (eMSC) to improve mesh biocompatibility and restore strength to prolapsed vaginal tissue. Here we evaluated knitted polyamide (PA) mesh in an ovine multiparous model using transvaginal implantation and matched for the degree of POP. Polyamide mesh dip-coated in gelatin and stabilised with 0.5% glutaraldehyde (PA/G) were used either alone or seeded with autologous ovine eMSC (eMSC/PA/G), which resulted in substantial mesh folding, poor tissue integration and 42% mesh exposure in the ovine model. In contrast, a two-step insertion protocol, whereby the uncoated PA mesh was inserted transvaginally followed by application of autologous eMSC in a gelatin hydrogel onto the mesh and crosslinked with blue light (PA + eMSC/G), integrated well with little folding and no mesh exposure. The autologous ovine eMSC survived 30 days in vivo but had no effect on mesh integration. The stiff PA/G constructs provoked greater myofibroblast and inflammatory responses in the vaginal wall, disrupted the muscularis layer and reduced elastin fibres compared to PA + eMSC/G constructs. This study identified the superiority of a two-step protocol for implanting synthetic mesh in cellular compatible composite constructs and simpler surgical application, providing additional translational value.

Linking hyperelastic theoretical models and experimental data of vaginal tissue through histological data

Mechanical characterization of living tissues and computer-based simulations related to medical issues, has become increasingly important to improve diagnostic processes and treatments evaluation. This work proposes a link between the mechanical testing and the material model predictions through histological data of vaginal tissue. Histological data was used to link tensile testing experiments with material-dependent parameters; the approach was adequate to capture the nonlinear response of ovine vaginal tissue over a large strain range. The experimental data obtained on a previous study, has two main components: tensile testing and histological analysis of the ovine vaginal tissue. Uniaxial tensile test data and histological data were collected from three sheep groups: virgins, pregnant and parous. The distal part of vaginal wall was selected since it is prone to tears induced by vaginal delivery. The HGO (Holzapfel-Gasser-Ogden) model parameters were fitted using a stochastic approach, namely the Simple Genetic Algorithm (SGA). The SGA was able to fit the experimental data successfully (R² > 0.986). The dimensionless coefficient ξ, was highly correlated with histological data. The ratio was seen to increase linearly with increasing collagen content. Coefficient ξ brings a new way of interpreting and understanding experimental data; it connects the nonlinear mechanical behaviour (tensile test) with tissue's morphology (histology). It can be used as an 'inverse' (approximate) method to estimate the mechanical properties without direct experimental measurements, through basic histology. In this context, the proposed methodology appears very promising in estimating the response of the tissue via histological information.

The effect of consecutive pregnancies on the ovine pelvic soft tissues: Link between biomechanical and histological components

BACKGROUND

Pelvic organ prolapse, various types of incontinence (urinary incontinence, defecatory dysfunction), chronic cystourethritis, and sexual dysfunctions remain between the most common disorders in urogynecology. Currently, it is believed that the nature and number of births plays a major role in their development. Moreover, after these events, pelvic floor tissues may not recover to their original statuses. The close anatomical relationship among the vaginal wall, bladder and rectum often contribute to the emergence of anatomical-functional failure of adjacent organs and systems.

BASIC PROCEDURES

The aim of this study was to investigate the effect of consecutive pregnancies on pelvic floor soft tissues, conducting biomechanical and histological analysis. Fifteen Swifter ewes: virgins, parous and pregnant were used. Samples, for uniaxial tension tests and histological analysis, were cut out from fresh tissue. A description of the mechanical properties of native tissue was obtained from the stress-strain curve. Histological samples were stained with Miller's Elastica staining and analyzed using ImageJ software. Collagen, elastin, and smooth muscle contents (%) were analyzed along the full wall thickness of the selected organs. The links between mechanical properties of the soft tissues and histological parameters were analyzed.

MAIN FINDINGS

Mechanically, vaginal wall tissue and cervix of pregnant sheep were more compliant. In contrast, bladder and rectum became stiffer and had the highest total collagen content. Parous sheep rectum and bladder were stiffer, compared to virgin sheep.

PRINCIPAL CONCLUSIONS

Tensile strength appears to be linked to total collagen content. Elastin and smooth muscle show a direct influence on tissue compliance.

Transvaginal Mesh Insertion in the Ovine Model

This protocol describes mesh insertion into the rectovaginal septum in sheep using a single vaginal incision technique, with and without the trocar-guided insertion of anchoring arms. Parous sheep underwent the dissection of the rectovaginal septum, followed by the insertion of an implant with or without four anchoring arms, both designed to fit the ovine anatomy. The anchoring arms were put in place using a trocar and an "outside-in" technique. The cranial arms were passed through the obturator, gracilis, and adductor magnus muscles. The caudal arms were fixed near the sacrotuberous ligament, through the coccygeus muscles. This technique allows for the mimicking of surgical procedures performed in women suffering from pelvic organ prolapse. The anatomical spaces and elements are easily identified. The most critical part of the procedure is the insertion of the cranial trocar, which can easily penetrate the peritoneal cavity or the surrounding pelvic organs. This can be avoided by a more extensive retroperitoneal dissection and by guiding the trocar more laterally. This approach is designed only for experimental testing of novel implants in large animal models, as trocar-guided insertion is currently not used clinically.