Experimental study and constitutive modeling of the viscoelastic mechanical properties of the human prolapsed vaginal tissue

Puerarin-Loaded Electrospun Patches with Anti-Inflammatory and Pro-Collagen Synthesis Properties for Pelvic Floor Reconstruction

Pelvic organ prolapse (POP) is one of the most common pelvic floor dysfunction disorders worldwide. The weakening of pelvic connective tissues initiated by excessive collagen degradation is a leading cause of POP. However, the patches currently used in the clinic trigger an unfavorable inflammatory response, which often leads to implantation failure and the inability to simultaneously reverse progressive collagen degradation. Therefore, to overcome the present challenges, a new strategy is applied by introducing puerarin (Pue) into poly(l-lactic acid) (PLLA) using electrospinning technology. PLLA improves the mechanical properties of the patch, while Pue offers intrinsic anti-inflammatory and pro-collagen synthesis effects. The results show that Pue is released from PLLA@Pue in a sustained manner for more than 20 days, with a total release rate exceeding 80%. The PLLA@Pue electrospun patches also show good biocompatibility and low cytotoxicity. The excellent anti-inflammatory and pro-collagen synthesis properties of the PLLA@Pue patch are demonstrated both in vitro in H2O2-stimulated mouse fibroblasts and in vivo in rat abdominal wall muscle defects. Therefore, it is believed that this multifunctional electrospun patch integrating anti-inflammatory and pro-collagen synthesis properties can overcome the limitations of traditional patches and has great prospects for efficient pelvic floor reconstruction.

Finite element analysis of female pelvic organ prolapse mechanism: current landscape and future opportunities

The prevalence of pelvic organ prolapse (POP) has been steadily increasing over the years, rendering it a pressing global health concern that significantly impacts women's physical and mental wellbeing as well as their overall quality of life. With the advancement of three-dimensional reconstruction and computer simulation techniques for pelvic floor structures, research on POP has progressively shifted toward a biomechanical focus. Finite element (FE) analysis is an established tool to analyze the biomechanics of complex systems. With the advancement of computer technology, an increasing number of researchers are now employing FE analysis to investigate the pathogenesis of POP in women. There is a considerable number of research on the female pelvic FE analysis and to date there has been less review of this technique. In this review article, we summarized the current research status of FE analysis in various types of POP diseases and provided a detailed explanation of the issues and future development in pelvic floor disorders. Currently, the application of FE analysis in POP is still in its exploratory stage and has inherent limitations. Through continuous development and optimization of various technologies, this technique can be employed with greater accuracy to depict the true functional state of the pelvic floor, thereby enhancing the supplementation of the POP mechanism from the perspective of computer biomechanics.

The influence of the combined impairments and apical mesh surgery on the biomechanical behavior of the pelvic floor system

Objective: The prolapse mechanism of multifactorial impairment of the female pelvic floor system and the mechanics of the pelvic floor after apical suspension surgery are not yet understood, so we developed biomechanical models of the pelvic floor for the normal physiological state (0°) and 90° pathological state. Methods: Under different types and levels of the impairments and uterosacral suspensions, the possible changes in the morphometric characteristics and the mechanical characteristics of suspension and support functions were simulated based on the biomechanical models of the pelvic floor. Results: After the combined impairments, the descending displacement of the pelvic floor cervix and the stress and displacement of the perineal body reached maximum values. After surgical mesh implantation, the stresses of the normal pelvic floor were concentrated on the uterine fundus, cervix, and top of the bladder and the stresses of the 90° pathological state pelvic floor were concentrated on the uterine fundus, uterine body, cervix, middle of the posterior vaginal wall, and bottom of the perineal body. Conclusion: After the combined impairments, the biomechanical support of the bladder and sacrococcyx in the anterior (0°) and 90° pathological state pelvic floor system is diminished, the anterior vaginal wall dislodges from the external vaginal opening, and the posterior vaginal wall forms "kneeling" profiles. The pelvic floor system may evolve with a tendency toward the cervical prolapse with anterior and posterior vaginal wall prolapse and eventually prolapse. After surgical mesh implantation, the cervical position can be better restored; however, the load of combined impairment of the pelvic floor is mainly borne by the surgical mesh suspension, the biomechanical support function of pelvic floor organs and sacrococcyx was not repaired by the physiological structure, and the results of uterosacral suspension alone may be poor.

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.

Two-dimensional biomechanical finite element modeling of the pelvic floor and prolapse

We developed the pelvic floor model in physiological and pathological states to understand the changes of biomechanical axis and support that may occur from the normal physiological state to the prolapse pathological state of the pelvic floor. Based on the physiological state model of the pelvic floor, we model the uterus to the pathological state position by balancing intra-abdominal pressure (IAP) and uterine pathological position load. Under combined impairments, we compared the patterns of changes in pelvic floor biomechanics that may be induced by different uterine morphological characteristic positions under different IAP. The orientation of the uterine orifice gradually changes from the sacrococcygeal direction to the vertical downward of vaginal orifice, and a large downward prolapse displacement occurs, and the posterior vaginal wall shows "kneeling" profile with posterior wall bulging prolapse. When the abdominal pressure value was 148.1 cmH₂O, the descent displacement of the cervix in the normal and pathological pelvic floor system was 11.94, 20, 21.83 and 19.06 mm in the healthy state, and 13.63, 21.67, 22.94 and 19.38 mm in the combined impairment, respectively. The above suggests a maximum cervical descent displacement of the uterus in the anomalous 90° position, with possible cervical-uterine prolapse as well as prolapse of the posterior vaginal wall. The combined forces of the pelvic floor point in the direction of vertical downward prolapse of the vaginal orifice, and the biomechanical support of the bladder and sacrococcygeal bone gradually diminishes, which may exacerbate the soft tissue impairments and biomechanical imbalances of the pelvic floor to occur of POP disease.

History-Dependent Deformations of Rat Vaginas under Inflation

The vagina is a highly inhomogeneous, anisotropic, and viscoelastic organ that undergoes significant deformations in vivo. The mechanical attributes of this organ facilitate important physiological functions during menstruation, intercourse, and birthing. Despite the crucial mechanical role that the vagina plays within the female reproductive system, the deformations that the organ can sustain over time under constant pressure, in both the longitudinal direction (LD) and circumferential direction (CD), have not been fully characterized. This experimental study focuses on quantifying the creep properties of the vagina via ex vivo inflation testing using the rat as animal model. Toward this end, rat vaginas were subjected to three consecutively increasing constant luminal pressures (28 kPa, 55 kPa, and 83 kPa) using a custom-built experimental setup and the resulting inhomogeneous deformations were measured using the digital image correlation (DIC) method. The vagina was found to deform significantly more in the CD than the LD at any constant pressure, suggesting that the organ primarily adapts to constant pressures by significantly changing the diameter rather that the length. The change in deformation over time (i.e., creep) was significantly higher during the 1st inflation test at a constant pressure of 28 kPa than over the 2nd and 3rd inflation tests at constant pressures of 55 kPa and 83 kPa, respectively. The findings of this study on the mechanical behavior of the vagina could serve to advance our limited knowledge about the physiology and pathophysiology of this important reproductive organ.

A biomechanical study of the birth position: a natural struggle between mother and fetus

Birth trauma affects millions of women and infants worldwide. Levator ani muscle avulsions can be responsible for long-term morbidity, associated with 13-36% of women who deliver vaginally. Pelvic floor injuries are enhanced by fetal malposition, namely persistent occipito-posterior (OP) position, estimated to affect 1.8-12.9% of pregnancies. Neonates delivered in persistent OP position are associated with an increased risk for adverse outcomes. The main goal of this work was to evaluate the impact of distinct fetal positions on both mother and fetus. Therefore, a finite element model of the fetal head and maternal structures was used to perform childbirth simulations with the fetus in the occipito-anterior (OA) and OP position of the vertex presentation, considering a flexible-sacrum maternal position. Results demonstrated that the pelvic floor muscles' stretch was similar in both cases. The maximum principal stresses were higher for the OP position, and the coccyx rotation reached maximums of 2.17[Formula: see text] and 0.98[Formula: see text] for the OP and OA positions, respectively. Concerning the fetal head, results showed noteworthy differences in the variation of diameters between the two positions. The molding index is higher for the OA position, with a maximum of 1.87. The main conclusions indicate that an OP position can be more harmful to the pelvic floor and pelvic bones from a biomechanical point of view. On the other side, an OP position can be favorable to the fetus since fewer deformations were verified. This study demonstrates the importance of biomechanical analyses to further understand the mechanics of labor.

Investigation of Murine Vaginal Creep Response to Altered Mechanical Loads

The vagina is a viscoelastic fibromuscular organ that provides support to the pelvic organs. The viscoelastic properties of the vagina are understudied but may be critical for pelvic stability. Most studies evaluate vaginal viscoelasticity under a single uniaxial load; however, the vagina is subjected to dynamic multiaxial loading in the body. It is unknown how varied multiaxial loading conditions affect vaginal viscoelastic behavior and which microstructural processes dictate the viscoelastic response. Therefore, the objective was to develop methods using extension-inflation protocols to quantify vaginal viscoelastic creep under various circumferential and axial loads. Then, the protocol was applied to quantify vaginal creep and collagen microstructure in the fibulin-5 wildtype and haploinsufficient vaginas. To evaluate pressure-dependent creep, the fibulin-5 wildtype and haploinsufficient vaginas (n = 7/genotype) were subjected to various constant pressures at the physiologic length for 100 s. For axial length-dependent creep, the vaginas (n = 7/genotype) were extended to various fixed axial lengths then subjected to the mean in vivo pressure for 100 s. Second-harmonic generation imaging was performed to quantify collagen fiber organization and undulation (n = 3/genotype). Increased pressure significantly increased creep strain in the wildtype, but not the haploinsufficient vagina. The axial length did not significantly affect the creep rate or strain in both genotypes. Collagen undulation varied through the depth of the subepithelium but not between genotypes. These findings suggest that the creep response to loading may vary with biological processes and pathologies, therefore, evaluating vaginal creep under various circumferential loads may be important to understand vaginal function.

Mesenchymal stem cell-based bioengineered constructs enhance vaginal repair in ovariectomized rhesus monkeys

Transvaginal meshes repair for treating pelvic organ prolapse (POP) was halted by the U. S. Food and Drug Administration (FDA) because they can lead to severe complications. Therefore, investigations of new therapeutic strategies are urgently needed. Cell-based regenerative therapy holds great promise for the repair and restoration of damaged tissue. Here, we generated a bioengineered graft by seeding human umbilical cord mesenchymal stem cells (HUMSCs) on bioscaffolds to reconstruct the damaged vagina. In the in vitro study, HUMSCs proliferated well and the density was appropriate after 5 days of culture. Besides, we demonstrated that the differentiation potential of HUMSCs was maintained with external growth factor stimulation. The complete transcriptomic profile of HUMSCs revealed that HUMSCs cultured on grafts produced significantly higher levels of proangiogenic cytokines than cells cultured in tissue culture plates (TCPs). Three months after implantation of the bioengineered grafts into ovariectomized (OVX) rhesus monkeys via sacrocolpopexy, extracellular matrix reorganization, large muscle bundle formation, angiogenesis and, mechanical properties of the vagina were enhanced. To our knowledge, this is the first demonstration of the utility of stem cell-based bioengineered grafts for repairing damaged vaginal tissue in rhesus monkeys. These results elucidate a new approach for vagina repair and provide new ideas for treating POP.

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.

Study on the Generalized Formulations with the Aim to Reproduce the Viscoelastic Dynamic Behavior of Polymers

Appropriate modelling of the real behavior of viscoelastic materials is of fundamental importance for correct studies and analyses of structures and components where such materials are employed. In this paper, the potential to employ a generalized Maxwell model and the relative fraction derivative model is studied with the aim to reproduce the experimental behavior of viscoelastic materials. For both models, the advantage of using the pole-zero formulation is demonstrated and a specifically constrained identification procedure to obtain the optimum parameters set is illustrated. Particular emphasis is given on the ability of the models to adequately fit the experimental data with a minimum number of parameters, addressing the possible computational issues. The question arises about the minimum number of experimental data necessary to estimate the material behavior in a wide frequency range, demonstrating that accurate results can be obtained by knowing only the data of the upper and low frequency plateaus plus the ones at the loss tangent peak.

Biaxial Stress Relaxation of Vaginal Tissue in Pubertal Gilts

Pelvic organ prolapse (POP) is a condition characterized by displacement of the vagina from its normal anatomical position leading to symptoms such as incontinence, physical discomfort, and poor self-image. Conservative treatment has shown limited success and surgical procedures, including the use of mesh, often lead to severe complications. To improve the current treatment methods for prolapse, the viscoelastic properties of vaginal tissue need to be characterized. We determined the biaxial stress relaxation response of vaginal tissue isolated from healthy pubertal gilts. Square specimens (n = 20) with sides aligned along the longitudinal directions (LD) and circumferential direction (CD) of the vagina were biaxially displaced up to 5 N. The specimens were then kept at the displacements corresponding to 5 N for 20 min in both the LD and CD, and the corresponding strains were measured using digital image correlation (DIC). The stresses in the LD and CD were found to decrease by 49.91 ± 5.81% and 46.22 ± 5.54% after 20 min, respectively. The strain in the LD and CD increased slightly from 0.080 ± 0.054 to 0.091 ± 0.064 and 0.050 ± 0.039 to 0.058 ± 0.047, respectively, but these changes were not significant (p > 0.01). By using the Peleg model, the initial decay rate and the asymptotic stress during stress relaxation were found to be significantly higher in the LD than in the CD (p≪0.001), suggesting higher stress relaxation in the LD. These findings may have implications for improving current surgical mesh, mechanical devices, and physical therapy used for prolapse treatment.

A new nonlinear viscoelastic model and mathematical solution of solids for improving prediction accuracy

We developed an innovative material nonlinear viscoelastic model with physical mechanism and mathematical solution to improve existing ones. The relaxation modulus transits from the glassy stage to the rubbery stage through a time-dependent viscosity in a continuous spectrum considering the nonlinear strain hardening. Experimental results of differential solid materials including asphalt concrete, agarose gel, vaginal tissue, polymer, agar, bone, spider silk, and hydrogel demonstrate that the developed model is superior to generalized Maxwell model or Prony series for more accurate prediction outside of the range for data fitting while using much less model parameters. Numerical simulation results indicate that the new model has improved accuracy. It is stable numerically, and does not reduce computation speed. Therefore, the model may be used to simulate a broad range of viscoelastic solids for predicting experimental data and responses with improved accuracy.

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.

Managing female pelvic floor disorders: a medical device review and appraisal

Pelvic floor disorders (PFDs) will affect most women during their lifetime. Sequelae such as pelvic organ prolapse, stress urinary incontinence, chronic pain and dyspareunia significantly impact overall quality of life. Interventions to manage or eliminate symptoms from PFDs aim to restore support of the pelvic floor. Pessaries have been used to mechanically counteract PFDs for thousands of years, but do not offer a cure. By contrast, surgically implanted grafts or mesh offer patients a more permanent resolution but have been in wide use within the pelvis for less than 30 years. In this perspective review, we provide an overview of the main theories underpinning PFD pathogenesis and the animal models used to investigate it. We highlight the clinical outcomes of mesh and grafts before exploring studies performed to elucidate tissue level effects and bioengineering considerations. Considering recent turmoil surrounding transvaginal mesh, the role of pessaries, an impermanent method, is examined as a means to address patients with PFDs.

A porous fibrous hyperelastic damage model for human periodontal ligament: Application of a microcomputerized tomography finite element model

The periodontal ligament (PDL) is a soft biological tissue that connects the tooth with the trabecular bone of the mandible. It plays a key role in load transmission and is primarily responsible for bone resorption and most common periodontal diseases. Although several numerical studies have analysed the biomechanical response of the PDL, most did not consider its porous fibrous structure, and only a few analysed damage to the PDL. This study presents an innovative numerical formulation of a porous fibrous hyperelastic damage material model for the PDL. The model considers two separate softening phenomena: fibre alignment during loading and fibre rupture. The parameters for the material model characterization were fitted using experimental data from the literature. Furthermore, the experimental tests used for characterization were computationally modelled to verify the material parameters. A finite element model of a portion of a human mandible, obtained by microcomputerized tomography, was developed, and the proposed constitutive model was implemented for the PDL. Our results confirm that damage to the PDL may occur mainly because of overpressure of the interstitial fluid, while large forces must be applied to damage the PDL fibrous network. Moreover, this study clarifies some aspects of the relationship between PDL damage and the bone remodelling process.

Anisotropy of the Passive and Active Rat Vagina Under Biaxial Loading

Pelvic organ prolapse, the descent of the pelvic organs from their normal anatomical position, is a common condition among women that is associated with mechanical alterations of the vaginal wall. In order to characterize the complex mechanical behavior of the vagina, we performed planar biaxial tests of vaginal specimens in both the passive (relaxed) and active (contracted) states. Specimens were isolated from virgin, female Long-Evans rats (n = 16) and simultaneously stretched along the longitudinal direction (LD) and circumferential direction (CD) of the vagina. Tissue contraction was induced by electric field stimulation (EFS) at incrementally increasing values of stretch and, subsequently, by KCl. On average, the vagina was stiffer in the CD than in the LD (p < 0.001). The mean maximum EFS-induced active stress was significantly higher in the CD than in the LD (p < 0.01). On the contrary, the mean KCl-induced active stress was lower in the CD than in the LD (p < 0.01). When comparing the mean maximum EFS-induced active stress to the mean KCl-induced active stress, no differences were found in the CD (p = 0.366) but, in the LD, the mean active stress was much higher in response to the KCl stimulation (p < 0.001). Collectively, these results suggest that the anisotropic behavior of the vaginal tissue is determined not only by collagen and smooth muscle fiber organization but also by the innervation.

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.

Viscous effects in pelvic floor muscles during childbirth: A numerical study

During vaginal delivery, women sustain stretching of their pelvic floor, risking tissue injury and adverse outcomes. Realistic numerical simulations of childbirth can help in the understanding of the pelvic floor mechanics and on the prevention of related disorders. In previous studies, biomechanical finite element simulations of a vaginal delivery have been performed disregarding the viscous effects present on all biological soft tissues. The inclusion of the viscoelastic behaviour is fundamental, since it allows to investigate rate-dependent responses. The present work uses a viscohyperelastic constitutive model to evaluate how the childbirth duration affects the efforts sustained by the pelvic floor during delivery. It was concluded that viscoelasticity adds a stiffness component that leads to higher forces comparing with the elastic response. Viscous solutions are rate dependent, and precipitous labours could be associated to higher efforts, while lower reaction forces were denoted for normal and prolonged labours, respectively. The existence of resting stages during labour demonstrated the capability of the tissue to relax and recover some of the initial properties, which helped to lower the forces and stresses involved. The present work represents a step further in achieving a robust non-invasive procedure, allowing to estimate how obstetrical factors influence labour and its outcomes.

Measuring tissue displacement of the anterior vaginal wall using the novel aspiration technique in vivo

Little is known about the mechanical properties of pelvic floor structures and their role in the course and treatment of pelvic organ prolapse (POP). We hypothesize that in vivo mechanical properties of the vaginal wall are related to the appearance of POP and pre-and post-operative states. We used a suction device for intravaginal application, the aspiration device, to evaluate two in vivo mechanical parameters of the anterior vaginal wall, the load dependent tissue displacement and the initial displacement, by image analysis in pre- and post-menopausal women with (POP) and without (control) cystocele (POP: pre-menopausal: N = 6, post-menopausal: N = 19, control: pre-menopausal: N = 17, post-menopausal: N = 6). Mechanical parameters in women with and without cystocele and pre- and post-operative parameters were compared. Statistically significant differences were observed between the two mechanical parameters in pre- and post-operative states (P = 0.04, P = 0.03), but not between the parameters for women with and without cystocele (P = 0.92, P = 0.75). The mechanical behavior of pelvic floor structures is influenced by factors such as POP, age or estrogenization that are apparent at different length scales, which cannot be separated by the aspiration based biomechanical measurements. When comparing pre- and post-operative states of the same patient, a firmer tissue response was observed after intervention.

A biofidelic computational model of the female pelvic system to understand effect of bladder fill and progressive vaginal tissue stiffening due to prolapse on anterior vaginal wall

Treatment of anterior vaginal prolapse (AVP), suffered by over 500,000 women in the USA, is a challenge in urogynecology because of the poorly understood mechanics of AVP. Recently, computational modeling combined with finite element method has been used to model AVP through the study of pelvic floor muscle and connective tissue impairments on the anterior vaginal wall (AVW). Also, the effects of pelvic organ displacements on the AVW were studied numerically. In our current work, an MRI-based full-scale biofidelic computational model of the female pelvic system composed of the urinary bladder, vaginal canal, and the uterus was developed, and a novel finite element method framework was employed to simulate vaginal tissue stiffening and also bladder filling due to expansion for the first time. A mesh convergence study was conducted to choose a computationally efficient mesh, and a non-linear hyperelastic Yeoh's material model was adopted for the study. The AVW displacements, mechanical stresses, and strains were estimated at varying degrees of bladder fills and vaginal tissue stiffening. Both bladder filling and vaginal stiffening were found to increase the stress concentration on the AVW with varying trends, which have been discussed in detail in the paper. To our knowledge, this study is the first to estimate the individual and combined effects of bladder filling and vaginal tissue stiffening due to prolapse on the AVW. Copyright © 2016 John Wiley & Sons, Ltd.

Logarithmic rate based elasto-viscoplastic cyclic constitutive model for soft biological tissues

Based on the logarithmic rate and piecewise linearization theory, a thermodynamically consistent elasto-viscoplastic constitutive model is developed in the framework of finite deformations to describe the nonlinear time-dependent biomechanical performances of soft biological tissues, such as nonlinear anisotropic monotonic stress-strain responses, stress relaxation, creep and ratchetting. In the proposed model, the soft biological tissue is assumed as a typical composites consisting of an isotropic matrix and anisotropic fiber aggregation. Accordingly, the free energy function and stress tensor are divided into two parts related to the matrix and fiber aggregation, respectively. The nonlinear biomechanical responses of the tissues are described by the piecewise linearization theory with hypo-elastic relations of fiber aggregation. The evolution equations of viscoplasticity are formulated from the dissipation inequalities by the co-directionality hypotheses. The anisotropy is considered in the hypo-elastic relations and viscoplastic flow rules by introducing some material parameters dependent on the loading direction. Then the capability of the proposed model to describe the nonlinear time-dependent deformation of soft biological tissues is verified by comparing the predictions with the corresponding experimental results of three tissues. It is seen that the predicted monotonic stress-strain responses, stress relaxation, creep and ratchetting of soft biological tissues are in good agreement with the corresponding experimental ones.

Biomechanical properties of synthetic surgical meshes for pelvic prolapse repair

Synthetic meshes are widely used for surgical repair of different kind of prolapses. In the light of the experience of abdominal wall repair, similar prostheses are currently used in the pelvic region, to restore physiological anatomy after organ prolapse into the vaginal wall, that represent a recurrent dysfunction. For this purpose, synthetic meshes are surgically positioned in contact with the anterior and/or posterior vaginal wall, to inferiorly support prolapsed organs. Nonetheless, while mesh implantation restores physiological anatomy, it is often associated with different complications in the vaginal region. These potentially dangerous effects induce the surgical community to reconsider the safety and efficacy of mesh transvaginal placement. For this purpose, the evaluation of state-of-the-art research may provide the basis for a comprehensive analysis of mesh compatibility and functionality. The aim of this work is to review synthetic surgical meshes for pelvic organs prolapse repair, taking into account the mechanics of mesh material and structure, and to relate them with pelvic and vaginal tissue biomechanics. Synthetic meshes are currently available in different chemical composition, fiber and textile conformations. Material and structural properties are key factors in determining mesh biochemical and mechanical compatibility in vivo. The most significant results on vaginal tissue and surgical meshes mechanical characterization are here reported and discussed. Moreover, computational models of the pelvic region, which could support the surgeon in the evaluation of mesh performances in physiological conditions, are recalled.

Influence of Geometry and Mechanical Properties on the Accuracy of Patient-Specific Simulation of Women Pelvic Floor

The woman pelvic system involves multiple organs, muscles, ligaments, and fasciae where different pathologies may occur. Here we are most interested in abnormal mobility, often caused by complex and not fully understood mechanisms. Computer simulation and modeling using the finite element (FE) method are the tools helping to better understand the pathological mobility, but of course patient-specific models are required to make contribution to patient care. These models require a good representation of the pelvic system geometry, information on the material properties, boundary conditions and loading. In this contribution we focus on the relative influence of the inaccuracies in geometry description and of uncertainty of patient-specific material properties of soft connective tissues. We conducted a comparative study using several constitutive behavior laws and variations in geometry description resulting from the imprecision of clinical imaging and image analysis. We find that geometry seems to have the dominant effect on the pelvic organ mobility simulation results. Provided that proper finite deformation non-linear FE solution procedures are used, the influence of the functional form of the constitutive law might be for practical purposes negligible. These last findings confirm similar results from the fields of modeling neurosurgery and abdominal aortic aneurysms.

Prosthetic Meshes for Repair of Hernia and Pelvic Organ Prolapse: Comparison of Biomechanical Properties

This study aims to compare the mechanical behavior of synthetic meshes used for pelvic organ prolapse (POP) and hernia repair. The analysis is based on a comprehensive experimental protocol, which included uniaxial and biaxial tension, cyclic loading and testing of meshes in dry conditions and embedded into an elastomer matrix. Implants are grouped as POP or hernia meshes, as indicated by the manufacturer, and their stiffness in different loading configurations, area density and porosity are compared. Hernia meshes might be expected to be stiffer, since they are implanted into a stiffer tissue (abdominal wall) than POP meshes (vaginal wall). Contrary to this, hernia meshes have a generally lower secant stiffness than POP meshes. For example, DynaMesh PRS, a POP mesh, is up to two orders of magnitude stiffer in all tested configurations than DynaMesh ENDOLAP, a hernia mesh. Additionally, lighter, large pore implants might be expected to be more compliant, which was shown to be generally not true. In particular, Restorelle, the lightest mesh with the largest pores, is less compliant in the tested configurations than Surgipro, the heaviest, small-pore implant. Our study raises the question of defining a meaningful design target for meshes in terms of mechanical biocompatibility.

Biomechanical properties of vaginal tissue in women with pelvic organ prolapse

BACKGROUND/AIMS

To compare biomechanical properties of vaginal tissues between women with and without pelvic organ prolapse (POP) and investigate factors that may influence these properties.

METHODS

Forty patients submitted to POP surgery and 15 non-POP cadavers were evaluated. The tissue was excised from anterior and posterior middle third vagina. The biomechanical properties considered were stiffness (E) and maximum stress (S), and they were evaluated by means of uniaxial tension tests.

RESULTS

POP patients were associated with higher values of E (13.1 ± 0.8 vs. 9.5 ± 0.7 MPa; p < 0.001) and S (5.3 ± 0.5 vs. 3.2 ± 0.9 MPa; p < 0.001) in the anterior vaginal wall compared to the posterior wall. In contrast, non-POP women presented lower values of E (6.9 ± 1.1 vs. 10.5 ± 1.0 MPa; p = 0.01) and S (2.6 ± 0.4 vs. 3.5 ± 0.4 MPa; p = 0.043) in the anterior wall. The occurrence of POP was the only independent predictor of higher values of E and S in anterior vaginal samples (p = 0.003 and p = 0.008, respectively). Women with severe anterior vaginal prolapse presented higher levels of E and S in the anterior sample compared to those with lower POP stages (p = 0.001 and p = 0.01; respectively).

CONCLUSION

Women with POP present significant changes of biomechanical properties in the vagina.

Mechanical properties of cross-linked collagen meshes after human adipose derived stromal cells seeding

The main goal of this study was to evaluate the potential of collagen meshes derived from porcine dermis as scaffolds for repairing pelvic organ prolapses. Mechanical properties of collagen meshes with different cross-linking percentages before and after Adipose Derived Stromal Cells (ADSC) seeding were studied as well as the cell-scaffold interaction. Uniaxial tensile tests of the collagen meshes with three different cross-linking percentages (full-, partial-, and noncross-linked) were carried out along orthogonal directions. Their mechanical properties were studied with the same tests before and after seeding with human derived adipose stem cells (ADSC) after 1 and 7 days. Histological analyses were performed to determine adhesion and proliferation of ADSC. Significant differences in mechanical properties of the unseeded meshes were observed between each orthogonal direction independently of the cross-linking percentage. A better cell adhesion rate was observed in the cross-linked meshes. An increase in the mechanical properties after cell seeding was observed with a direct relation with the degree of cross-linking. All meshes analyzed showed a marked anisotropy that should be taken into account during the surgical procedure. The cross-linking treatment increased cell adhesion and the mechanical properties of the collagen meshes after seeding. These results suggest that the mechanical properties of this type of collagen mesh could be useful as scaffolds for repair of pelvic organ prolapse.

Depression and heart disease: therapeutic implications

The consequences of depression and coronary artery disease (CAD) were reviewed in the literature. The comorbidity of depression and CAD results in an increased cardiovascular mortality. We reviewed possible explanations for this increased morbidity, which include: toxicity of tricyclic antidepressants that can cause cardiac arrhythmias, abnormalities in platelet function leading to increased platelet aggregation due to abnormalities in serotonin in the platelet (an abnormality that possibly causes depression in the central nervous system), diffuse atherosclerosis causing central nervous system abnormalities including depression (vascular depression), as well as the possibility that depressed patients are less compliant with their medications and physician-directed health recommendations. Recent reports of selective serotonin reuptake inhibitors (SSRIs) causing a reduced cardiovascular mortality may be related to serotonin platelet abnormalities in depressed patients that are effectively treated by SSRIs (SADHART and ENRICHD trial). It is possible that these trials reveal a mechanism of depression that also effects platelet function and can be improved with SSRI therapy, suggesting a preferential therapeutic pathway for the treatment of depressed patients with CAD.