Cross-linked xenogenic collagen implantation in the sheep model for vaginal surgery

Development of a cellulose-based prosthetic mesh for pelvic organ prolapse treatment: In vivo long-term evaluation in an ewe vagina model

The use of vaginal surgical mesh to treat pelvic organ prolapse (POP) has been associated with high rates of mesh-related complications. In the present study, we prepared new kinds of meshes based on bacterial cellulose (BC) and collagen-coated BC (BCCOL) using a laser cutting method and perforation technique. The mechanical properties of pre-implanted BC meshes, including breaking strength, suture strength and rigidity, were equal to or exceeded those of available clinically used polypropylene meshes. An in vitro cellular assay revealed that BCCOL meshes exhibited enhanced biocompatibility by increasing collagen secretion and cell adhesion. Both BC and BCCOL meshes only caused weak inflammation and were surrounded by newly formed connective tissue composed of type I collagen after implantation in a rabbit subcutaneous model for one week, demonstrating that the novel mesh is fully biocompatible and can integrate into surrounding tissues. Furthermore, a long-term (ninety days) ewe vaginal implantation model was used to evaluate foreign body reactions and suitability of BC and BCCOL meshes as vaginal meshes. The results showed that the tissue surrounding the BC meshes returned to its original physiology as muscle tissue, indicating the excellent integration of BC meshes into the surrounding tissues without triggering severe local inflammatory response post-implantation. The collagen coating appeared to induce a chronic inflammatory response due to glutaraldehyde remnants. The present exploratory research demonstrated that the developed BC mesh might be a suitable candidate for treating POP.

Rabbit as an animal model for the study of biological grafts in pelvic floor dysfunctions

The aims of this study were to evaluate the feasibility of the New Zealand White (NZW) rabbit for studying implanted biomaterials in pelvic reconstructive surgery; and to compare the occurrence of graft-related complications of a commercial polypropylene (PP) mesh and new developed human dermal matrix implanted at vaginal and abdominal level. 20 white female NZW rabbits were randomized into two groups, experimental group (human acellular dermal matrices-hADM-graft) and control group (commercial PP graft). In each animal, grafts were surgically implanted subcutaneously in the abdominal wall and in the vaginal submucosa layer for 180 days. The graft segments were then removed and the surgical and clinical results were analyzed. The main surgical challenges during graft implantation were: (a) an adequate vaginal exposure while maintaining the integrity of the vaginal mucosa layer; (b) to keep aseptic conditions; (c) to locate and dissect the breast vein abdominal surgery; and (d) to withdraw blood samples from the ear artery. The most abnormal findings during the explant surgery were found in the PP group (33% of vaginal mesh extrusion) in comparison with the hADM group (0% of vaginal graft extrusion), p = 0.015. Interestingly, macroscopic observation showed that the integration of the vaginal grafts was more common in the hADM group (40%) than in the PP group, in which the vaginal mesh was identified in 100% of the animals (p = 0.014). The NZW rabbit is a good model for assessing materials to be used as grafts for pelvic reconstructive surgery and vaginal surgery. Animals are easily managed during the procedures, including surgical intervention and vaginal mucosa approach. Additionally, hADM is associated with fewer clinical complications, as well as better macroscopic tissue integration, compared to PP mesh.

Immunochemical analysis on polypropylene mesh: does mesh size make a difference?

INTRODUCTION AND HYPOTHESIS

The aim of the study is to demonstrate the impact of the size of implanted mesh in relation to its immunohistochemical reaction implanted into animal models.

METHODS

An experimental study utilizing 54 female Sprague Dawley (SD) rats was divided into five groups: control, sham, and study groups (mesh-small [M-S], mesh-medium [M-M], mesh-large [M-L]). The M-S group used a mesh size of 0.2 × 0.2 cm, the M-M group a mesh size of 0.5 × 0.5 cm, and the M-L a mesh size of 0.7 × 1.0 cm. The sham group underwent vaginal dissection with no mesh implantation. The rats were sacrificed using isoflurane overdose on days 7 and 30. The mesh with the surrounding vaginal and bladder wall tissues were removed and processed for histochemical and western blot analysis.

RESULTS

There is a significant increase in IL-1 and TNF-α immunoreactivity in the M-M and M-L groups on day 7 when compared with the sham group with p values of 0.001 and < 0.001 respectively. M-L showed significantly higher immunoreactivity to TNF-α persisting until day 30. All study groups presented a significantly higher immunoreactivity to MMP-2 and NGF on day 7. However, reactivity to NGF does not persist to day 30 in all groups. Immunoreactivity to CD 31 on days 7 and 30 appears significantly greater in the M-M and M-L groups, with the reaction in the M-L group continuing until day 30.

CONCLUSION

Mesh size is directly proportional to the inflammatory reaction in the host tissue. The prolonged inflammatory process leads to delayed tissue remodeling and angiogenesis, which could delay mesh-tissue integration.

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

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

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

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

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

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

New Zealand white rabbit: a novel model for prolapse mesh implantation via a lumbar colpopexy

INTRODUCTION AND HYPOTHESIS

New Zealand white rabbits are an inexpensive large-animal model. This study explored the rabbit as a model for mesh-augmented colpopexy using the intra-abdominal vagina. We hypothesized that polypropylene mesh would negatively impact rabbit vaginal smooth muscle (VSM) morphology and contractile function, similar to the nonhuman primate (NHP)-the established model for prolapse mesh evaluation.

METHODS

Restorelle was implanted onto the vagina of ten rabbits via lumbar colpopexy after a hysterectomy. Ten rabbits served as sham. Twelve weeks post-implantation, the vagina was excised and VSM morphology and vaginal contractility were assessed. Outcome measures were compared using independent samples t and Mann-Whitney U tests with a Bonferroni correction, where appropriate. Results from the rabbits were compared with published NHP data.

RESULTS

Animals had similar age, parity and BMI. VSM was 18% thinner after Restorelle implantation, P = 0.027. Vaginal contractility was 43% decreased in response to 120 mM KCl (P = 0.003), similar to the 46% reduction observed in the NHP vagina implanted with Restorelle (P = 0.027). Three meshes wrinkled in vivo, resulting in dramatic thinning of the underlying vagina in the area of the mesh causing a mesh exposure.

CONCLUSIONS

Polypropylene mesh negatively impacts VSM morphology and vaginal contractility in the rabbit, similar to the NHP, suggesting that the rabbit may serve as an alternative large-animal model. The vaginal thinning and appearance of a mesh exposure in the area of a mesh wrinkle suggest the rabbit may also serve as a model for understanding the pathophysiology of mesh exposure.

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.

Safety and efficacy of non-absorbable mesh in contemporary gynaecological surgery

Mesh-augmented pelvic floor surgery evolved to address the limitations of native tissue repair in reconstructive surgery. The development of the synthetic mid-urethral tape signalled a revolution in the treatment of stress urinary incontinence, whilst the use of mesh in abdominal apical prolapse repair may confer benefits over native tissue alternatives. However, these procedures can be associated with mesh-specific complications, underlining the need for shared decision-making between physicians and patients prior to mesh surgery.

Transvaginal non-absorbable mesh implants for pelvic organ prolapse are associated with a high risk of serious adverse events, leading to withdrawal or restricted use in many countries. Increased scrutiny has led to growing concerns about complications associated with all types of mesh-augmented reconstructive surgery, attracting widespread media attention.

National and international reports have been commissioned examining the safety and efficacy of mesh surgery in gynaecology. They have all highlighted systemic failures in the development, regulation and clinical adoption of medical devices. The widespread application of novel devices prior to the availability of reliable safety and efficacy data, and delayed recognition of adverse events, is of serious concern. Notwithstanding, the available data continue to support a role for mesh augmentation. This review outlines the evolution of gynaecological mesh, the safety and efficacy of pelvic floor surgery using non-absorbable mesh materials, and an overview of specific complications.

Transvaginal Mesh Insertion in the Ovine Model

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

Tissue response to collagen containing polypropylene meshes in an ovine vaginal repair model

Pelvic Organ Prolapse (POP) is the herniation of pelvic organs into the vagina. Despite broad acceptance of mesh use in POP surgical repair, the complication rate is unacceptable. We hypothesized that collagen-containing polypropylene (PP) mesh types could modulate mesh-tissue integration and reduce long-term inflammation, thereby reducing mesh-associated complications. This study compared the long-term tissue response to an unmodified PP mesh and two collagen containing meshes in an ovine model which has similar pelvic anatomy and vaginal size to human. Three commercially available macroporous PP meshes, uncoated PP mesh (Avaulta Solo) (PP), the same textile PP mesh layered with a sheet of cross-linked porcine acellular matrix (Avaulta Plus) (PP-ACM) and a different yet also macroporous PP (Sofradim) mesh coated with solubilized atelocollagen (Ugytex) (PP-sCOL) were implanted in the ovine vagina and tissue explanted after 60 and 180days. The macrophage phenotype and response to implanted meshes, and vascularity were quantified by immunostaining and morphometry. We quantified changes in extracellular matrix composition biochemically and collagen organisation and percentage area around the interface of the mesh implants by Sirius Red birefringence and morphometry. PP-ACM induced a more sustained inflammatory response, indicated by similar CD45(+) leukocytes but reduced CD163(+) M2 macrophages at 60days (P<0.05). PP-sCOL increased Von Willebrand Factor (vWF)-immunoreactive vessel profiles after 60days. At the micro-molecular level, collagen birefringence quantification revealed significantly fewer mature collagen fibrils (red, thick fibrils) at the mesh-tissue interface than control tissue for all mesh types (P<0.001) but still significantly greater than the proportion of immature (green thin fibrils) at 60days (P<0.05). The proportion of mature collagen fibrils increased with time around the mesh filaments, particularly those containing collagen. The total collagen percent area at the mesh interface was greatest around the PP-ACM mesh at 60days (P<0.05). By 180days the total mature and immature collagen fibres at the interface of the mesh filaments resembled that of native tissue. In particular, these results suggest that both meshes containing collagen evoke different types of tissue responses at different times during the healing response yet both ultimately lead to physiological tissue formation approaching that of normal tissue.

STATEMENT OF SIGNIFICANCE

Pelvic organ prolapse (POP) is the descent of the pelvic organs to the vagina. POP affects more than 25% of all women and the lifetime risk of undergoing POP surgery is 19%. Although synthetic polypropylene (PP) meshes have improved the outcome of the surgical treatment for POP, there was an unacceptable rate of adverse events including mesh exposure and contracture. It is hypothesized that coating the PP meshes with collagen would provide a protective effect by preventing severe mesh adhesions to the wound, resulting in a better controlled initial inflammatory response, and diminished risk of exposure. In this study we assessed the effect of two collagen-containing PP meshes on the long-term vaginal tissue response using new techniques to quantify these tissue responses.

In vivo response to polypropylene following implantation in animal models: a review of biocompatibility

INTRODUCTION AND HYPOTHESIS

Polypropylene is a material that is commonly used to treat pelvic floor conditions such as pelvic organ prolapse (POP) and stress urinary incontinence (SUI). Owing to the nature of complications experienced by some patients implanted with either incontinence or prolapse meshes, the biocompatibility of polypropylene has recently been questioned. This literature review considers the in vivo response to polypropylene following implantation in animal models. The specific areas explored in this review are material selection, impact of anatomical location, and the structure, weight and size of polypropylene mesh types.

METHODS

All relevant abstracts from original articles investigating the host response of mesh in vivo were reviewed. Papers were obtained and categorised into various mesh material types: polypropylene, polypropylene composites, and other synthetic and biologically derived mesh.

RESULTS

Polypropylene mesh fared well in comparison with other material types in terms of host response. It was found that a lightweight, large-pore mesh is the most appropriate structure.

CONCLUSION

The evidence reviewed shows that polypropylene evokes a less inflammatory or similar host response when compared with other materials used in mesh devices.