Tensile properties of commonly used prolapse meshes

In Vitro and In Vivo Drug Release from a Nano-Hydroxyapatite Reinforced Resorbable Nanofibrous Scaffold for Treating Female Pelvic Organ Prolapse

Pelvic prolapse stands as a substantial medical concern, notably impacting a significant segment of the population, predominantly women. This condition, characterized by the descent of pelvic organs, such as the uterus, bladder, or rectum, from their normal positions, can lead to a range of distressing symptoms, including pelvic pressure, urinary incontinence, and discomfort during intercourse. Clinical challenges abound in the treatment landscape of pelvic prolapse, stemming from its multifactorial etiology and the diverse array of symptoms experienced by affected individuals. Current treatment options, while offering relief to some extent, often fall short in addressing the full spectrum of symptoms and may pose risks of complications or recurrence. Consequently, there exists a palpable need for innovative solutions that can provide more effective, durable, and patient-tailored interventions for pelvic prolapse. We manufactured an integrated polycaprolactone (PCL) mesh, reinforced with nano-hydroxyapatite (nHA), along with drug-eluting poly(lactic-co-glycolic acid) (PLGA) nanofibers for a prolapse scaffold. This aims to offer a promising avenue for enhanced treatment outcomes and improved quality of life for individuals grappling with pelvic prolapse. Solution extrusion additive manufacturing and electrospinning methods were utilized to prepare the nHA filled PCL mesh and drug-incorporated PLGA nanofibers, respectively. The pharmaceuticals employed included metronidazole, ketorolac, bleomycin, and estrone. Properties of fabricated resorbable scaffolds were assessed. The in vitro release characteristics of various pharmaceuticals from the meshes/nanofibers were evaluated. Furthermore, the in vivo drug elution pattern was also estimated on a rat model. The empirical data show that nHA reinforced PCL mesh exhibited superior mechanical strength to virgin PCL mesh. Electrospun resorbable nanofibers possessed diameters ranging from 85 to 540 nm, and released effective metronidazole, ketorolac, bleomycin, and estradiol, respectively, for 9, 30, 3, and over 30 days in vitro. Further, the mesh/nanofiber scaffolds also liberated high drug levels at the target site for more than 28 days in vivo, while the drug concentrations in blood remained low. This discovery suggests that resorbable scaffold can serve as a viable option for treating female pelvic organ prolapse.

A reliable and replicable test protocol for the mechanical evaluation of synthetic meshes

Despite the worldwide spread of surgical meshes in abdominal and inguinal surgery repair, the lack of specific standards for mechanical characterization of synthetic meshes, used in hernia repair and urogynecologic surgery, makes performance comparison between prostheses undoubtedly difficult. This consequently leads to the absence of acknowledged specifications about the mechanical requirements that synthetic meshes should achieve in order to avoid patient discomfort or hernia recurrences. The aim of this study is to provide a rigorous test protocol for the mechanical comparison between surgical meshes having the same intended use. The test protocol is composed of three quasi-static test methods: (1) ball burst test, (2) uniaxial tensile test, and (3) suture retention test. For each test, post-processing procedures are proposed to compute relevant mechanical parameters from the raw data. Some of the computed parameters, indeed, could be more suitable for comparison with physiological conditions (e.g., membrane strain and anisotropy), while others (e.g., uniaxial tension at rupture and suture retention strength) are reported as they provide useful mechanical information and could be convenient for comparisons between devices. The proposed test protocol was applied on 14 polypropylene meshes, 3 composite meshes, and 6 urogynecologic devices to verify its universal applicability towards meshes of different types and produced by various manufacturers, and its repeatability in terms of coefficient of variation. The test protocol resulted easily applicable to all the tested surgical meshes with intra-subject variability characterized by coefficient of variations settled around 0.05. Its use within other laboratories could allow the determination of the inter-subject variability assessing its repeatability among users of alternative universal testing machines.

Complications Reported to the Food and Drug Administration: A Cross-sectional Comparison of Urogynecologic Meshes

IMPORTANCE

The U.S. Food and Drug Administration uses the Manufacturer and User Facility Device Experience database to evaluate the safety of urogynecologic meshes; however, reports on individual meshes have not been characterized.

OBJECTIVE

The aim of the study was to compare complications among available urogynecologic meshes reported to the Manufacturer and User Facility Device Experience database.

STUDY DESIGN

This study is a cross-sectional analysis of medical device reports (MDRs) of urogynecologic mesh from January 2004 to March 2019, using the Reed Tech Navigator (LexisNexis), which codes MDRs. The percentage of reports containing specific complaints (not an adverse event rate) were compared with χ 2 tests with Dunn-Sidak correction. Correlations with time on market, mesh weight, stiffness, and porosity were determined.

RESULTS

The 34,485 reports examined included 6 transvaginal meshes, 4 sacrocolpopexy meshes, and 10 midurethral slings. Most reported events were pain, erosion, and infection. For transvaginal prolapse, less than 10% of Uphold Lite (Boston Scientific) reports contained pain or erosion versus greater than 90% of Prolift/Prolift+M (Ethicon, P < 0.001). For sacrocolpopexy mesh, greater than 90% of Gynemesh (Ethicon; Prolift in vaginal form) reports included erosion and pain versus less than 60% for Artisyn (Ethicon), Restorelle (Colpoplast), and Upsylon (Boston Scientific, P < 0.0001). For slings, Gynecare TVT Obturator had the highest proportion of erosion and pain complaints. Heavier sling meshes had more reports. When Ascend (Caldera Medical), an outlier with only 5 reports, was excluded, transvaginal mesh stiffness correlated strongly with number of reports. For transvaginal meshes, number of reports correlated with time on market (ρ = 0.8, P = 0.04).

CONCLUSIONS

Individual meshes have different properties with different complication profiles, which should inform mesh development and use. Gynemesh MDRs included pain and erosion more frequently than others. Comprehensive registries are needed.

In-plane and out-of-plane deformations of gilt utero-sacral ligaments

The uterosacral ligaments (USLs) are supportive structures of the uterus and apical vagina. The mechanical function of these ligaments within the pelvic floor is crucial not only in normal physiological conditions but also in reconstructive surgeries for pelvic organ prolapse. Discrepancies in their anatomical and histological description exist in the literature, but such discrepancies are likely due to large variations of these structures. This makes mechanical testing very challenging, requiring the development of advanced methods for characterizing their mechanical properties. This study proposes the use of planar biaxial testing, digital image correlation (DIC), and optical coherence tomography (OCT) to quantify the deformations of the USLs, both in-plane and out-of-plane. Using the gilts as an animal model, the USLs were found to deform significantly less in their main direction (MD) of in vivo loading than in the direction perpendicular to it (PD) at increasing equibiaxial stresses. Under constant equibiaxial loading, the USLs deform over time equally, at comparable rates in both the MD and PD. The thickness of the USLs decreases as the equibiaxial loading increases but, under constant equibiaxial loading, the thickness increases in some specimens and decreases in others. These findings could contribute to the design of new mesh materials that augment the support function of USLs as well as noninvasive diagnostic tools for evaluating the integrity of the USLs.

Exosome-Induced Vaginal Tissue Regeneration in a Porcine Mesh Exposure Model

OBJECTIVES

The purpose of this study was to explore the utility of an injectable purified exosome product derived from human apheresis blood to (1) augment surgical closure of vaginal mesh exposures, and (2) serve as a stand-alone therapy for vaginal mesh exposure.

METHODS

Sixteen polypropylene meshes (1×1-3×3 cm) were implanted in the vaginas of 7 Yorkshire-crossed pigs by urogynecologic surgeons (day 0). On day 7, group 1 underwent surgical intervention via vaginal tissue suture reclosure with (n=2 pigs, n=4 meshes) or without (n=2 pigs, n=4 meshes) exosome injection; group 2 underwent medical intervention with an exosome injection (n=3, n=8 meshes). One animal in group 2 was given oral 2'-deoxy-5-ethynyluridine to track cellular regeneration. Euthansia occurred at 5 weeks.

RESULTS

Mesh exposures treated with surgical closure alone experienced reexposure of the mesh. Exosome treatment with or without surgical closure resulted in partial to full mesh exposure resolution up to 3×3 cm. Exosome-treated tissues had significantly thicker regenerated epithelial tissue (208 μm exosomes-only and 217 μm surgery+exosomes, versus 80 μm for surgery-only; P < 0.05); evaluation of 2'-deoxy-5-ethynyluridine confirmed de novo regeneration throughout the epithelium and underlying tissues. Capillary density was significantly higher in the surgery+exosomes group (P = 0.03). Surgery-only tissues had a higher inflammatory and fibrosis response as compared with exosome-treated tissues.

CONCLUSIONS

In this pilot study, exosome treatment augmented healing in the setting of vaginal mesh exposure, reducing the incidence of mesh reexposure after suture closure and decreasing the area of mesh exposure through de novo tissue regeneration after exosome injection only. Further study of varied local tissue conditions and mesh configurations is warranted.

In-vitro Characterization of a Hernia Mesh Featuring a Nanostructured Coating

Abdominal hernia repair is a frequently performed surgical procedure worldwide. Currently, the use of polypropylene (PP) surgical meshes for the repair of abdominal hernias constitutes the primary surgical approach, being widely accepted as superior to primary suture repair. Surgical meshes act as a reinforcement for the weakened or damaged tissues and support tissue restoration. However, implanted meshes could suffer from poor integration with the surrounding tissues. In this context, the present study describes the preliminary evaluation of a PCL-Gel-based nanofibrous coating as an element to develop a multicomponent hernia mesh device (meshPCL-Gel) that could overcome this limitation thanks to the presence of a nanostructured biomimetic substrate for enhanced cell attachment and new tissue formation. Through the electrospinning technique, a commercial PP hernia mesh was coated with a nanofibrous membrane from a polycaprolactone (PCL) and gelatin (Gel) blend (PCL-Gel). Resulting PCL-Gel nanofibers were homogeneous and defect-free, with an average diameter of 0.15 ± 0.04 μm. The presence of Gel decreased PCL hydrophobicity, so that membranes average water contact angle dropped from 138.9 ± 1.1° (PCL) to 99.9 ± 21.6°, while it slightly influenced mechanical properties, which remained comparable to those of PCL (E = 15.7 ± 2.7 MPa, σ R = 7.7 ± 0.6 ε R = 118.8 ± 13.2%). Hydrolytic and enzymatic degradation was conducted on PCL-Gel up to 28 days, with maximum weight losses around 20 and 40%, respectively. The meshPCL-Gel device was obtained with few simple steps, with no influences on the original mechanical properties of the bare mesh, and good stability under physiological conditions. The biocompatibility of meshPCL-Gel was assessed by culturing BJ human fibroblasts on the device, up to 7 days. After 24 h, cells adhered to the nanofibrous substrate, and after 72 h their metabolic activity was about 70% with respect to control cells. The absence of detectable lactate dehydrogenase in the culture medium indicated that no necrosis induction occurred. Hence, the developed nanostructured coating provided the meshPCL-Gel device with chemical and topographical cues similar to the native extracellular matrix ones, that could be exploited for enhancing the biological response and, consequently, mesh integration, in abdominal wall hernia repair.

Historic transvaginal meshes and procedures: what did my patient have done?

PURPOSE OF REVIEW

Transvaginal mesh kits were widely used to treat pelvic organ prolapse for over a 10-year period in the early 2000s. Due to safety concerns and FDA regulations, these mesh kits are no longer available for use. Thus, current Obstetricians and Gynecologists are likely to encounter these meshes, but may have no previous experience or exposure to the devices making it difficult to adequately monitor, counsel, and care for patients that underwent these types of procedures. This review highlights the most commonly used transvaginal mesh kit types, provides insight into signs and symptoms related to transvaginal mesh complications, and provides guidance for management of mesh complications.

RECENT FINDINGS

Not all transvaginal mesh will give rise to a complication. If complications do occur, treatment options range from conservative observation to total mesh excision. Management must be customized to an individual patient's needs and goals.

SUMMARY

Transvaginal mesh kits promised increased durability of surgical repair for pelvic organ prolapse. Safety concerns over time caused these kits to no longer be available for use. Practicing Obstetricians and Gynecologists should be aware of the history of transvaginal mesh and the signs and symptoms of mesh complications.

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.

Electrospun nanofiber mesh with fibroblast growth factor and stem cells for pelvic floor repair

Surgical outcome following pelvic organ prolapse (POP) repair needs improvement. We suggest a new approach based on a tissue-engineering strategy. In vivo, the regenerative potential of an electrospun biodegradable polycaprolactone (PCL) mesh was studied. Six different biodegradable PCL meshes were evaluated in a full-thickness abdominal wall defect model in 84 rats. The rats were assigned into three groups: (1) hollow fiber PCL meshes delivering two dosages of basic fibroblast growth factor (bFGF), (2) solid fiber PCL meshes with and without bFGF, and (3) solid fiber PCL meshes delivering connective tissue growth factor (CTGF) and rat mesenchymal stem cells (rMSC). After 8 and 24 weeks, we performed a histological evaluation, quantitative analysis of protein content, and the gene expression of collagen-I and collagen-III, and an assessment of the biomechanical properties of the explanted meshes. Multiple complications were observed except from the solid PCL-CTGF mesh delivering rMSC. Hollow PCL meshes were completely degraded after 24 weeks resulting in herniation of the mesh area, whereas the solid fiber meshes were intact and provided biomechanical reinforcement to the weakened abdominal wall. The solid PCL-CTGF mesh delivering rMSC demonstrated improved biomechanical properties after 8 and 24 weeks compared to muscle fascia. These meshes enhanced biomechanical and biochemical properties, demonstrating a great potential of combining tissue engineering with stem cells as a new therapeutic strategy for POP repair. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:48-55, 2020.

Exploring the basic science of prolapse meshes

PURPOSE OF REVIEW

Polypropylene mesh has been widely used in the surgical repair of pelvic organ prolapse. However, low but persistent rates of complications related to mesh, most commonly mesh exposure and pain, have hampered its use. Complications are higher following transvaginal implantation prompting the Food and Drug Administration to release two public health notifications warning of complications associated with transvaginal mesh use (PHN 2008 and 2011) and to upclassify transvaginal prolapse meshes from Class II to Class III devices. Although there have been numerous studies to determine the incidence and management of mesh complications as well as impact on quality of life, few studies have focused on mechanisms.

RECENT FINDINGS

In this review, we summarize the current understanding of how mesh textile properties and mechanical behavior impact vaginal structure and function, as well as the local immune response. We also discuss how mesh properties change in response to loading.

SUMMARY

We highlight a few areas of current and future research to emphasize collaborative strategies that incorporate basic science research to improve patient outcomes.

Effect of mesh width on apical support after sacrocolpopexy

INTRODUCTION AND HYPOTHESIS

We evaluated the effect of polypropylene mesh width on vaginal apical support, mesh elongation, and mesh tensile strength for abdominal sacrocolpopexy.

METHODS

Abdominal sacrocolpopexy was performed on ten cadavers using pieces of polypropylene mesh of width 1, 2, and 3 cm. Weights of 1, 2, 3, and 4 kg were sequentially applied to the vagina. The total distance moved by the vaginal apex, and the amount of stretch of the intervening mesh segment between the sacrum and the vagina were recorded for each width. The failure strengths of additional single and double layer sets of each width were also tested using a tensiometer. Data were analyzed with analysis of variance using a random effects model.

RESULTS

The mean (standard error of the mean) maximum distance moved by the vaginal apex was 4.63 cm (0.37 cm) for the 1 cm mesh compared to 3.67 cm (0.26 cm) and 2.73 cm (0.14 cm) for the 2 and 3 cm meshes, respectively (P < 0.0001). The 1 cm width ruptured during testing in four of the ten cadavers. The results were similar for mesh elongation, with the 1 cm mesh stretching the most and the 3 cm mesh stretching the least. Mesh failure loads for double-layer mesh were 52.9 N (2.5 N), 124.4 N (2.7 N), and 201.2 N (4.5 N) for the 1, 2, and 3 cm meshes, respectively, and were higher than the failure loads for single mesh (P < 0.001).

CONCLUSIONS

In a cadaver model, increasing mesh width is associated with better vaginal apical support, less mesh elongation, and higher failure loads. Mesh widths of 2-3 cm provide sufficient repair strength for sacrocolpopexy.

Textile properties of synthetic prolapse mesh in response to uniaxial loading

BACKGROUND

Although synthetic mesh is associated with superior anatomic outcomes for the repair of pelvic organ prolapse, the benefits of mesh have been questioned because of the relatively high complication rates. To date, the mechanisms that result in such complications are poorly understood, yet the textile characteristics of mesh products are believed to play an important role. Interestingly, the pore diameter of synthetic mesh has been shown to impact the host response after hernia repair greatly, and such findings have served as design criteria for prolapse meshes, with larger pores viewed as more favorable. Although pore size and porosity are well-characterized before implantation, the changes in these textile properties after implantation are unclear; the application of mechanical forces has the potential to greatly alter pore geometries in vivo. Understanding the impact of mechanical loading on the textile properties of mesh is essential for the development of more effective devices for prolapse repair.

OBJECTIVE

The objective of this study was to determine the effect of tensile loading and pore orientation on mesh porosity and pore dimensions.

STUDY DESIGN

In this study, the porosity and pore diameter of 4 currently available prolapse meshes were examined in response to uniaxial tensile loads of 0.1, 5, and 10 N while mimicking clinical loading conditions. The textile properties were compared with those observed for the unloaded mesh. Meshes included Gynemesh PS (Ethicon, Somerville, NJ), UltraPro (Artisyn; Ethicon), Restorelle (Coloplast, Minneapolis, MN), and Alyte Y-mesh (Bard, Covington, GA). In addition to the various pore geometries, 3 orientations of Restorelle (0-, 5-, 45-degree offset) and 2 orientations of UltraPro (0-, 90-degree offset) were examined.

RESULTS

In response to uniaxial loading, both porosity and pore diameter dramatically decreased for most mesh products. The application of 5 N led to reductions in porosity for nearly all groups, with values decreasing by as much as 87% (P < .05). On loading to 10 N of force, nearly all mesh products that were tested were found to have porosities that approached 0% and 0 pores with diameters >1 mm.

CONCLUSION

In this study, it was shown that the pore size of current prolapse meshes dramatically decreases in response to mechanical loading. These findings suggest that prolapse meshes, which are more likely to experience tensile forces in vivo relative to hernia repair meshes, have pores that are unfavorable for tissue integration after surgical tensioning and/or loading in urogynecologic surgeries. Such decreases in pore geometry support the hypothesis that regional increases in the concentration of mesh leads to an enhanced local foreign body response. Although pore deformation in transvaginal meshes requires further characterization, the findings presented here provide a mechanical understanding that can be used to recognize potential areas of concern for complex mesh geometries. Understanding mesh mechanics in response to surgical and in vivo loading conditions may provide improved design criteria for mesh and a refinement of surgical techniques, ultimately leading to better patient outcomes.

Biomechanical, Topological and Chemical Features That Influence the Implant Success of an Urogynecological Mesh: A Review

Synthetic meshes are normally used to treat several diseases in the field of urogynecological surgery. Not-optimal selection of mesh and/or its not-correct implant may increase patient's pain and discomfort. The knowledge of mechanical behaviour and topological and chemical properties of a mesh plays a fundamental role to minimize patient's suffering and maximize the implant success. We analysed several papers reporting the meshes application for urogynecological pathologies, to extrapolate the principal parameters that normally are used to characterise the biomechanical, topological, and chemical properties, and to verify their influence on implant success. In this way we want demonstrate that, knowing these features, it is possible to foresee the success of a mesh implant. This review shows that the application of a mesh strictly depends on elastic modulus, failure load, porosity and pore size, filament diameter, polymer weight, and crystallinity. To increase the success of the implant and to help choice of optimal mesh for a clinical need, two indexes have been proposed for comparing, in an easier way, the mechanical performance of different commercially available meshes.

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.

Diaphragm Repair with a Novel Cross-Linked Collagen Biomaterial in a Growing Rabbit Model

Background

Neonates with congenital diaphragmatic hernia and large defects often require patch closure. Acellular collagen matrices (ACM) have been suggested as an alternative to synthetic durable patches as they are remodeled by the host or could also be used for tissue engineering purposes.

Materials and Methods

2.0x1.0 cm diaphragmatic defects were created in 6-weeks old New-Zealand white rabbits. We compared reconstruction with a purpose-designed cross-linked ACM (Matricel) to 4-layer non-cross-linked small intestinal submucosa (SIS) and a 1-layer synthetic Dual Mesh (Gore-Tex). Unoperated animals or animals undergoing primary closure (4/0 polyglecaprone) served as age-matched controls. 60 (n = 25) resp. 90 (n = 17) days later, animals underwent chest x-ray and obduction for gross examination of explants, scoring of adhesion and inflammatory response. Also, uniaxial tensiometry was done, comparing explants to contralateral native diaphragmatic tissue.

Results

Overall weight nearly doubled from 1,554±242 g at surgery to 2,837±265 g at obduction (+84%). X-rays did show rare elevation of the left diaphragm (SIS = 1, Gore-Tex = 1, unoperated control = 1), but no herniation of abdominal organs. 56% of SIS and 10% of Matricel patches degraded with visceral bulging in four (SIS = 3, Matricel = 1). Adhesion scores were limited: 0.5 (Matricel) to 1 (SIS, Gore-Tex) to the left lung (p = 0.008) and 2.5 (Gore-Tex), 3 (SIS) and 4 (Matricel) to the liver (p<0.0001). Tensiometry revealed a reduced bursting strength but normal compliance for SIS. Compliance was reduced in Matricel and Gore-Tex (p<0.01). Inflammatory response was characterized by a more polymorphonuclear cell (SIS) resp. macrophage (Matricel) type of infiltrate (p<0.05). Fibrosis was similar for all groups, except there was less mature collagen deposited to Gore-Tex implants (p<0.05).

Conclusions

Matricel induced a macrophage-dominated inflammatory response, more adhesions, had appropriate strength but a lesser compliance compared to native tissue. The herein investigated ACM is not a viable option for CDH repair.

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.

The impact of boundary conditions on surface curvature of polypropylene mesh in response to uniaxial loading

Exposure following pelvic organ prolapse repair has been observationally associated with wrinkling of the implanted mesh. The purpose of this study was to quantify the impact of variable boundary conditions on the out-of-plane deformations of mesh subjected to tensile loading. Using photogrammetry and surface curvature analyses, deformed geometries were accessed for two commercially available products. Relative to standard clamping methods, the amount of out-of-plane deformation significantly increased when point loads were introduced to simulate suture fixation in-vivo. These data support the hypothesis that regional increases in the concentration of mesh potentially enhance the host׳s foreign body response, leading to exposure.

Varying degrees of nonlinear mechanical behavior arising from geometric differences of urogynecological meshes

Synthetic polypropylene meshes were designed to restore pelvic organ support for women suffering from pelvic organ prolapse; however, the FDA released two notifications regarding potential complications associated with mesh implantation. Our aim was to characterize the structural properties of Restorelle and UltraPro subjected to uniaxial tension along perpendicular directions, and then model the tensile behavior of these meshes utilizing a co-rotational finite element model, with an imbedded linear or fiber-recruitment local stress-strain relationship. Both meshes exhibited a highly nonlinear stress-strain behavior; Restorelle had no significant differences between the two perpendicular directions, while UltraPro had a 93% difference in the low (initial) stiffness (p=0.009) between loading directions. Our model predicted that early alignment of the mesh segments in the loading direction and subsequent stretching could explain the observed nonlinear tensile behavior. However, a nonlinear stress-strain response in the stretching regime, that may be inherent to the mesh segment, was required to better capture experimental results. Utilizing a nonlinear fiber recruitment model with two parameters A and B, we observed improved agreement between the simulations and the experimental results. An inverse analysis found A=120 MPa and B=1.75 for Restorelle (RMSE=0.36). This approach yielded A=30 MPa and B=3.5 for UltraPro along one direction (RMSE=0.652), while the perpendicular orientation resulted in A=130 MPa and B=4.75 (RMSE=4.36). From the uniaxial protocol, Restorelle was found to have little variance in structural properties along these two perpendicular directions; however, UltraPro was found to behave anisotropically.

Characterizing the ex vivo mechanical properties of synthetic polypropylene surgical mesh

The use of synthetic polypropylene mesh for hernia surgical repair and the correction of female pelvic organ prolapse have been controversial due to increasing post-operative complications, including mesh erosion, chronic pain, infection and support failure. These morbidities may be related to a mismatch of mechanical properties between soft tissues and the mesh. The aim of this study was to gain a better understanding of the biomechanical behavior of Prolene polypropylene mesh (Ethicon, Sommerville, NJ, USA), which is widely used for a variety of surgical repair procedures. The stiffness and permanent deformation of Prolene mesh were compared in different directions by performing uniaxial tensile failure tests, cyclic and creep tests at simulated physiological loads in the coursewise (0°), walewise (90°) and the diagonal (45°) directions. Failure tests suggest that the mechanical properties of the mesh is anisotropic; with response at 0° being the most compliant while 90° was the stiffest. Irreversible deformation and viscoelastic behavior were observed in both cyclic and creep tests. The anisotropic property may be relevant to the placement of mesh in surgery to maximize long term mesh performance. The considerable permanent deformation may be associated with an increased risk of post-operative support failure.

Mesh contraction: in vivo documentation of changes in apparent surface area utilizing meshes visible on magnetic resonance imaging in the rabbit abdominal wall model

INTRODUCTION AND HYPOTHESIS

Our aim was to analyze the apparent contraction of meshes in vivo after abdominal wall reconstruction and evaluate histological and biomechanical properties after explantation.

METHODS

Nine New Zealand female rabbits underwent repair of two full-thickness 25 × 30-mm midline defects in the upper and lower parts of the abdomen. These were primarily overlaid by 35 × 40-mm implants of a polyvinylidene fluoride (PVDF) DynaMesh (n = 6) or polypropylene meshes Ultrapro (n = 6) and Marlex (n = 6). Edges of the meshes were secured with iron(II,III) oxide (Fe(3)O(4))-loaded PVDF sutures. Magnetic resonance images (MRIs) were taken at days 2, 30 and 90 after implantation. The perimeter of the mesh was traced using a 3D spline curve. The apparent surface area or the area within the PVDF sutures was compared with the initial size using the one-sample t test. A two-way repeat analysis of variance (ANOVA) was used to compare the apparent surface area over time and between groups.

RESULTS

PVDF meshes and sutures with Fe(3)O(4) could be well visualized on MRI. DynaMesh and Marlex each had a 17 % decrease in apparent surface area by day 2 (p < 0.001 and p = 0.001), respectively, which persisted after day 90. Whereas there was a decrease in apparent surface area in Ultrapro, it did not reach significance until day 90 (p = 0.01). Overall, the apparent surface area decreased 21 % in all meshes by day 90. No differences in histological or biomechanical properties were observed at day 90.

CONCLUSIONS

There was a reduction in the apparent surface area between implantation and day 2, indicating that most mesh deformation occurs prior to tissue in-growth.

Characterisation of clinical and newly fabricated meshes for pelvic organ prolapse repair

Clinical meshes used in pelvic organ prolapse (POP) repair are predominantly manufactured from monofilament polypropylene (PP). Complications from the use of these meshes in transvaginal kits, including mesh exposure and pain, have prompted two public health notifications by the FDA. The aim of this study was to compare several clinical PP POP meshes to new fabricated POP meshes, knitted from alternative polymers, for their mechanical properties using standard and clinically relevant multi-axial testing methods. Five new meshes were warp knitted to different architectures and weights from polyamide and polyetheretherketone monofilaments. A composite mesh of a polyamide mesh incorporating a gelatin layer was also fabricated to enable the potential delivery of cells on these meshes. Meshes were assessed for their structural characteristics and mechanical properties, using uniaxial stiffness, permanent strain, bending rigidity and multi-axial burst strength methods. Results were compared to three clinical urogynaecological polypropylene meshes: Polyform®, Gynemesh(TM)PS, and IntePro®. New fabricated meshes were uniaxially less stiff (less than 0.24 N/mm and 1.20 N/mm in toe and linear regions, respectively) than the Gynemesh (0.48 N/mm and 2.08 N/mm in toe and linear regions, respectively) and IntePro (0.57 N/mm in toe region) clinical meshes, with the gelatin coated PA mesh exhibiting lower permanent strain than Polyform clinical mesh (8.1% vs. 23.5%). New meshes had lower burst stiffness than Polyform (less than 16.9 N/mm for new meshes and 26.6N/mm for Polyform). Within the new mesh prototypes, the PA meshes, either uncoated (4.7-5.7 μN m) or with gelatin coating (16.7 μN m) possessed lower bending rigidity than both Polyform and Gynemesh (46.2 μN m and 36.4 μN m, respectively). The new fabricated mesh designs were of similar architecture, but with some improved mechanical properties, compared to clinical POP meshes. Multi-axial analysis of new and clinical mesh designs provides greater discriminatory power in analysing mesh mechanical properties for clinical applications.

Vaginal degeneration following implantation of synthetic mesh with increased stiffness

OBJECTIVE

To compare the impact of the prototype prolapse mesh Gynemesh PS with that of two new-generation lower stiffness meshes, UltraPro and SmartMesh, on vaginal morphology and structural composition.

DESIGN

A mechanistic study employing a nonhuman primate model.

SETTING

Magee-Womens Research Institute at the University of Pittsburgh.

POPULATION

Parous rhesus macaques, with similar age, weight, parity and Pelvic Organ Prolapse-Questionnaire scores.

METHODS

Following Institutional Animal Care Use Committee approval, 50 rhesus macaques were implanted with Gynemesh PS (n = 12), UltraPro with its blue line perpendicular to the longitudinal axis of vagina (n = 10), UltraPro with its blue line parallel to the longitudinal axis of vagina (n = 8) or SmartMesh (n = 8) via sacrocolpopexy following hysterectomy. Sham-operated animals (n = 12) served as controls.

MAIN OUTCOME MEASURES

The mesh-vagina complex was removed after 12 weeks and analysed for histomorphology, in situ cell apoptosis, total collagen, elastin, glycosaminoglycan content and total collagenase activity. Appropriate statistics and correlation analyses were performed accordingly.

RESULTS

Relative to sham and the two lower stiffness meshes, Gynemesh PS had the greatest negative impact on vaginal histomorphology and composition. Compared with sham, implantation with Gynemesh PS caused substantial thinning of the smooth muscle layer (1557 ± 499 μm versus 866 ± 210 μm, P = 0.02), increased apoptosis particularly in the area of the mesh fibres (P = 0.01), decreased collagen and elastin content (20%, P = 0.03 and 43%, P = 0.02, respectively) and increased total collagenase activity (135%, P = 0.01). Glycosaminoglycan, a marker of tissue injury, was highest with Gynemesh PS compared with sham and other meshes (P = 0.01).

CONCLUSION

Mesh implantation with the stiffer mesh Gynemesh PS induced a maladaptive remodelling response consistent with vaginal degeneration.

Deterioration in biomechanical properties of the vagina following implantation of a high-stiffness prolapse mesh

OBJECTIVE

To define the impact of prolapse mesh on the biomechanical properties of the vagina by comparing the prototype Gynemesh PS (Ethicon) to two new-generation lower stiffness meshes, SmartMesh (Coloplast) and UltraPro (Ethicon).

DESIGN

A study employing a nonhuman primate model.

SETTING

University of Pittsburgh, PA, USA.

POPULATION

Forty-five parous rhesus macaques.

METHODS

Meshes were implanted via sacrocolpopexy after hysterectomy and compared with sham. Because its stiffness is highly directional, UltraPro was implanted in two directions: UltraPro Perpendicular (less stiff) and UltraPro Parallel (more stiff), with the indicated direction referring to the position of the blue orientation lines relative to the longitudinal axis of the vagina. The mesh-vaginal complex (MVC) was excised in toto after 3 months.

MAIN OUTCOME MEASURES

Active mechanical properties were quantified as the contractile force generated in the presence of 120 mmol/l KCl. Passive mechanical properties (a tissue's ability to resist an applied force) were measured using a multiaxial protocol.

RESULTS

Vaginal contractility decreased by 80% following implantation with the Gynemesh PS (P = 0.001), 48% after SmartMesh (P = 0.001), 68% after UltraPro Parallel (P = 0.001) and was highly variable after UltraPro Perpendicular (P = 0.16). The tissue contribution to the passive mechanical behaviour of the MVC was drastically reduced for Gynemesh PS (P = 0.003), but not for SmartMesh (P = 0.9) or UltraPro independent of the direction of implantation (P = 0.68 and P = 0.66, respectively).

CONCLUSIONS

Deterioration of the mechanical properties of the vagina was highest following implantation with the stiffest mesh, Gynemesh PS. Such a decrease associated with implantation of a device of increased stiffness is consistent with findings from other systems employing prostheses for support.

Tissue engineering as a potential alternative or adjunct to surgical reconstruction in treating pelvic organ prolapse

INTRODUCTION AND HYPOTHESIS

Cell-based tissue engineering strategies could potentially provide attractive alternatives to surgical reconstruction of native tissue or the use of surgical implants in treating pelvic organ prolapse (POP).

METHODS

Based on a search in PubMed, this review focuses on candidate cell types, scaffolds, and trophic factors used in studies examining cell-based tissue engineering strategies to treat POP, stress urinary incontinence (SUI), and the closely related field of hernias.

RESULTS

In contrast to the field of SUI, the use of cell-based tissue engineering strategies to treat POP are very sparsely explored, and only preclinical studies exist.

CONCLUSION

The available evidence suggests that the use of autologous muscle-derived cells, fibroblasts, or mesenchymal stem cells seeded on biocompatible, degradable, and potentially growth-promoting scaffolds could be an alternative to surgical reconstruction of native tissue or the use of conventional implants in treating POP. However, the vagina is a complex organ with great demands of functionality, and the perfect match of scaffold, cell, and trophic factor has yet to be found and tested in preclinical studies. Important issues such as safety and economy must also be addressed before this approach is ready for clinical studies.

Tissue engineering as a potential alternative or adjunct to surgical reconstruction in treating pelvic organ prolapse

INTRODUCTION AND HYPOTHESIS

Cell-based tissue engineering strategies could potentially provide attractive alternatives to surgical reconstruction of native tissue or the use of surgical implants in treating pelvic organ prolapse (POP).

METHODS

Based on a search in PubMed, this review focuses on candidate cell types, scaffolds, and trophic factors used in studies examining cell-based tissue engineering strategies to treat POP, stress urinary incontinence (SUI), and the closely related field of hernias.

RESULTS

In contrast to the field of SUI, the use of cell-based tissue engineering strategies to treat POP are very sparsely explored, and only preclinical studies exist.

CONCLUSION

The available evidence suggests that the use of autologous muscle-derived cells, fibroblasts, or mesenchymal stem cells seeded on biocompatible, degradable, and potentially growth-promoting scaffolds could be an alternative to surgical reconstruction of native tissue or the use of conventional implants in treating POP. However, the vagina is a complex organ with great demands of functionality, and the perfect match of scaffold, cell, and trophic factor has yet to be found and tested in preclinical studies. Important issues such as safety and economy must also be addressed before this approach is ready for clinical studies.

Characterizing the ex vivo textile and structural properties of synthetic prolapse mesh products

INTRODUCTION AND HYPOTHESIS

The use of polypropylene meshes for surgical repair of pelvic organ prolapse (POP) has been limited by complications, including mesh exposure, encapsulation, and pain. Numerous products are available with a wide array of textile and structural properties. It is thought that complications may be related, in part, to mesh structural properties. However, few descriptions of these properties exists to directly compare products. The aim of this study was to determine the textile and structural properties of five commonly used prolapse mesh products using a ball-burst failure protocol.

METHODS

Porosity, anisotropic index, and stiffness of Gynemesh PS (n = 8), the prototype polypropylene mesh for prolapse repair, was compared with four newer-generation mesh produces: UltraPro (n = 5), SmartMesh (n = 5), Novasilk (n = 5), and Polyform (n = 5).

RESULTS

SmartMesh was found to be the most porous, at 78 % ± 1.4 %. This value decreased by 21 % for Gynemesh PS (p < 0.001), 14 % for UltraPro and Novasilk (p < 0.001), and 28 % for Polyform (p < 0.001). Based on the knit pattern, SmartMesh and Polyform were the only products considered to be geometrically isotropic, whereas all other meshes were anisotropic. Comparing the structural properties of these meshes, Gynemesh PS and Polyform were the stiffest: 60 % and 42 % stiffer than SmartMesh (p < 0.001) and Novasilk (p < 0.001), respectively. However, no significant differences were found between these two mesh products and UltraPro.

CONCLUSIONS

Porosity, anisotropy, and biomechanical behavior of these five commonly used polypropylene mesh products were significantly different. This study provides baseline data for future implantation studies of prolapse mesh products.

Uniaxial biomechanical properties of seven different vaginally implanted meshes for pelvic organ prolapse

INTRODUCTION AND HYPOTHESIS

Recently, numerous type I macroporous polypropylene vaginal meshes have been introduced into the market with little known of their differences.

METHODS

Seven vaginal meshes were obtained and loaded to failure (n = 5/type). Additional cyclic loading determined permanent deformation with submaximal loading.

RESULTS

The load elongation curves demonstrated a bilinear response with lower stiffness (N/mm), followed by higher stiffness. Ascend™ was the stiffest mesh in both regions of the load elongation curve (0.72 and 1.66 N/mm) with the lowest transition to higher stiffness (13.4%). Polyform™ had the highest failure load (53.8 N) while Ultrapro™ had the lowest (7.83 N). Novasilk™ (89.4%) and Ultrapro™ (87.9%) had the highest relative elongations at mesh failure while Ascend™ had the lowest (40.2%). Ascend™ had the least relative elongation after three protocols of cyclic loading (3.0%, 9.8%, and 9.7%).

CONCLUSIONS

Current vaginal meshes demonstrate marked variation in biomechanical characteristics which may impact the in vivo behavior.

New measurements to compare soft tissue anchoring systems in pelvic floor surgery

Suburethral slings as well as different meshes are widely used treating stress urinary incontinence and prolaps in women. With the development of MiniSlings and special meshes using less alloplastic material anchorage systems become more important to keep devices in place and to put some tension especially on the MiniSlings. To date, there are many different systems of MiniSlings of different companies on the market which differ in the structure of the used meshes and anchors. A new objective measurement method to compare different properties of MiniSling systems (mesh and anchor) is presented in this article. Ballistic gelatine acts as soft tissue surrogate. Significant differences in parameters like pull-out strength of anchors or shrinkage of meshes under loading conditions have been determined. The form and size of the anchors as well as the structural stability of the meshes are decisive for a proper integration. The tested anchorings sytems showed markedly different mechanical function at their respective load bearing capacity. As the stable fixation of the device in tissue is a prerequisite for a permanet reinforcement, the proposed test system permits further optimisation of anchor and mesh devices to improve the success of the surgical treatment.

Persistence of polypropylene mesh anisotropy after implantation: an experimental study

OBJECTIVE

To determine whether anisotropy persisted after incorporation into the host, using a standardised rabbit model for abdominal wall reconstruction.

DESIGN

Investigator-initiated prospective-controlled experimental study.

SETTING

Centre for Surgical Technologies, Medical Faculty KU-Leuven.

SAMPLE

Fifteen New Zealand White rabbits.

METHODS

In each rabbit, four full thickness primarily repaired abdominal wall defects were covered by a 4 × 5-cm Prolift+M implant (Johnson & Johnson, Norderstedt, Germany), either with the stiffest (n = 6 rabbits) or most elastic (n = 6) direction parallel to the body axis. Prolift+M contains 32 g/m² polypropylene, reinforced with polyglecaprone fibres. Harvesting was performed after 30, 60 and 120 days (n = 2 each time-point). The abdominal wall of three unoperated rabbits was used as negative control.

MAIN OUTCOME MEASURES

Contraction, compliance and maximal strain and stress determined by uniaxial tensiometry.

RESULTS

Anisotropy properties persist at lower, more physiological displacements, but not at higher displacements. The stiffness of a mesh-augmented repair in the lower strain range remains above that of native tissue. Eventual mesh contraction was limited to 4.3%.

CONCLUSIONS

Anisotropic properties of Prolift+M persist in vivo and shrinkage is minimal. Compliance of mesh-augmented repair remains less than that of native tissue. The functional consequences of this remain to be studied.

The effect of source animal age upon extracellular matrix scaffold properties

Biologic scaffold materials composed of mammalian extracellular matrix (ECM) are commonly used for the repair and reconstruction of injured tissues. An important, but unexplored variable of biologic scaffolds is the age of the animal from which the ECM is prepared. The objective of the present study was to compare the structural, mechanical, and compositional properties of small intestinal submucosa (SIS)-ECM harvested from pigs that differed only in age. Degradation product bioactivity of these ECM materials was also examined. Results showed that there are distinct differences in each of these variables among the various age source ECM scaffolds. The strength and growth factors content of ECM from 3-week-old animals is less than that of ECM harvested from 12, 26 or >52-week-old animals. The elastic modulus of SIS-ECM for 3 week and >52-week-old source was less than that of the 12 and 26 week source. Degradation products from all age source ECMs were chemotactic for perivascular stem cells, with the 12 week source the most potent, while the oldest source caused the greatest increase in proliferation. In summary, distinct differences exist in the mechanical, structural, and biologic properties of SIS-ECM harvested from different aged animals.