Graft-related complications and biaxial tensiometry following experimental vaginal implantation of flat mesh of variable dimensions

Evaluation of Electrospun Poly-4-Hydroxybutyrate as Biofunctional and Degradable Scaffold for Pelvic Organ Prolapse in a Vaginal Sheep Model

Pelvic organ prolapse (POP) affects many women, especially after menopause. POP occurs due to the descent of weakened supportive tissue. Current prolapse surgeries have high failure rates, due to disturbed wound healing caused by lower tissue regeneration and estrogen depletion. Absorbable poly-4-hydroxybutyrate (P4HB) knit implants exhibited improved cell and tissue response leading to less complications from prolapse surgery. This study aims to enhance wound healing and improve surgical outcomes by using an electrospun (ES) P4HB scaffold (ES P4HB) that emulates natural tissue structure. Further 17β-estradiol (E2)-a prominent wound healing factor-is incorporated into the scaffold (ES P4HB-E2). Parous Dohne Merino sheep underwent posterior vaginal wall implantation of either P4HB (n = 6) or 17β-estradiol relasing P4HB-E2 (n = 6) scaffolds, or underwent native tissue repair (NTR) (n = 4). Vaginal explants were compared for short-term host response in terms of gross necropsy, histomorphology, biomechanics, tissue-integration, and degradation of P4HB at 3-months post-implantation. Both scaffolds show promising results with enhanced mechanical properties and increased macrophage infiltration compared to NTR, but without differences between scaffolds. Thus, it seems electrospun P4HB scaffolds already improve tissue integration and healing. Further long-term studies are needed before these scaffolds can be used in clinical practice.

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

INTRODUCTION AND HYPOTHESIS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Hutmacher D, Medeiros Savi F. 3D-Printed Medical-Grade Polycaprolactone (mPCL) Scaffold for the Surgical Treatment of Vaginal Prolapse and Abdominal Hernias

The expected outcome after a scaffold augmented hernia repair is the regeneration of a tissue composition strong enough to sustain biomechanical function over long periods. It is hypothesised that melt electrowriting (MEW) medical-grade polycaprolactone (mPCL) scaffolds loaded with platelet-rich plasma (PRP) will enhance soft tissue regeneration in fascial defects in abdominal and vaginal sheep models. A pre-clinical evaluation of vaginal and abdominal hernia reconstruction using mPCL mesh scaffolds and polypropylene (PP) meshes was undertaken using an ovine model. Each sheep was implanted with both a PP mesh (control group), and a mPCL mesh loaded with PRP (experimental group) in both abdominal and vaginal sites. Mechanical properties of the tissue-mesh complexes were assessed with plunger tests. Tissue responses to the implanted meshes were evaluated via histology, immunohistochemistry and histomorphometry. At 6 months post-surgery, the mPCL mesh was less stiff than the PP mesh, but stiffer than the native tissue, while showing equitable collagen and vascular ingrowth when compared to PP mesh. The results of this pilot study were supportive of mPCL as a safe and effective biodegradable scaffold for hernia and vaginal prolapse repair, hence a full-scale long-term study (over 24-36 months) with an adequate sample size is recommended.

Mesh Deformation: a mechanism underlying polypropylene prolapse mesh complications in vivo

Polypropylene meshes used in pelvic organ prolapse (POP) repair are hampered by complications. Most POP meshes are highly unstable after tensioning ex vivo, as evidenced by marked deformations (pore collapse and wrinkling) that result in altered structural properties and material burden. By intentionally introducing collapsed pores and wrinkles into a mesh that normally has open pores and remains relatively flat after implantation, we reproduce mesh complications in vivo. To do this, meshes were implanted onto the vagina of rhesus macaques in nondeformed (flat) vs deformed (pore collapse +/- wrinkles) configurations and placed on tension. Twelve weeks later, animals with deformed meshes had two complications, 1) mesh exposure through the vaginal epithelium, and 2) myofibroblast proliferation with fibrosis - a mechanism of pain. The overarching response to deformed mesh was vaginal thinning associated with accelerated apoptosis, reduced collagen content, increased proteolysis, deterioration of mechanical integrity, and loss of contractile function consistent with stress shielding - a precursor to mesh exposure. Regional differences were observed, however, with some areas demonstrating myofibroblast proliferation and matrix deposition. Variable mechanical cues imposed by deformed meshes likely induce these two disparate responses. Utilizing meshes associated with uniform stresses on the vagina by remaining flat with open pores after tensioning is critical to improving outcomes. STATEMENT OF SIGNIFICANCE: Pain and exposure are the two most reported complications associated with the use of polypropylene mesh in urogynecologic procedures. Most meshes have unstable geometries as evidenced by pore collapse and wrinkling after tensioning ex vivo, recapitulating what is observed in meshes excised from women with complications in vivo. We demonstrate that collapsed pores and wrinkling results in two distinct responses 1) mesh exposure associated with tissue degradation and atrophy and 2) myofibroblast proliferation and matrix deposition consistent with fibrosis, a tissue response associated with pain. In conclusion, mesh deformation leads to areas of tissue degradation and myofibroblast proliferation, the likely mechanisms of mesh exposure and pain, respectively. These data corroborate that mesh implantation in a flat configuration with open pores is a critical factor for reducing complications in mesh-augmented surgeries.

Development and in vitro investigation of a biodegradable mesh for the treatment of stress urinary incontinence

Introduction and hypothesis

The use of polypropylene (PP) mesh for stress urinary incontinence (SUI) surgery has declined because of safety concerns. The aim of this study is to evaluate a biodegradable polycaprolactone (PCL) mesh and a PCL composite mesh tissue engineered with human uterine fibroblasts (HUFs) for SUI surgery by comparing mechanical properties and in vitro biocompatibility to commercially available PP and porcine dermis (PD).

Methods

The mechanical properties of four scaffold materials were evaluated: PCL, PCL-collagen-hyaluronic acid composite, acellular porcine dermal collagen (PD) (Pelvicol™) and polypropylene (Gynecare TVT™ Exact®). HUFs were seeded on separate scaffolds. After 7 and 14 days scaffolds were assessed for metabolic activity and cell proliferation using Alamar Blue, Live/Dead and PicoGreen assays. Soluble collagen production was evaluated using a Sircol assay.

Results

PCL and the composite scaffold reached ultimate tensile strength (UTS) values closest to healthy pelvic floor tissue (PCL = 1.19 MPa; composite = 1.13 MPa; pelvic floor = 0.79 MPa; Lei et al. Int Urogynecol J Pelvic Floor Dysfunct. 18(6):603-7, 2007). Cells on PCL showed significantly greater cell viability than PP at day 7 (p < 0.0001). At D14 the composite scaffold showed significantly greater cell viability than PP (p = 0.0006). PCL was the best performing scaffold for soluble collagen production at day 14 (106.1 μg versus 13.04 μg for PP, p = 0.0173).

Conclusions

We have designed a biodegradable PCL mesh and a composite mesh which demonstrate better biocompatibility than PP and mechanical properties closer to that of healthy pelvic floor tissue. This in vitro study provides promising evidence that these two implants should be evaluated in animal and human trials.

Design, mechanical and degradation requirements of biodegradable metal mesh for pelvic floor reconstruction

Pelvic organ prolapse (POP) is the herniation of surrounding tissue and organs into the vagina and or rectum, and is a result of weakening of pelvic floor muscles, connective tissue,...

Host-biomaterial interactions in mesh complications after pelvic floor reconstructive surgery

Polypropylene (PPL) mesh is widely used in pelvic floor reconstructive surgery for prolapse and stress urinary incontinence. However, some women, particularly those treated using transvaginal PPL mesh placement for prolapse, experience intractable pain and mesh exposure or extrusion. Explanted tissue from patients with complications following transvaginal implantation of mesh is typified by a dense fibrous capsule with an immune cell-rich infiltrate, suggesting that the host immune response has a role in transvaginal PPL mesh complications through the separate contributions of the host (patient), the biological niche within which the material is implanted and biomaterial properties of the mesh. This immune response might be strongly influenced by both the baseline inflammatory status of the patient, surgical technique and experience, and the unique hormonal, immune and microbial tissue niche of the vagina. Mesh porosity, surface area and stiffness also might have an effect on the immune and tissue response to transvaginal mesh placement. Thus, a regulatory pathway is needed for mesh development that recognizes the roles of host and biological factors in driving the immune response to mesh, as well as mandatory mesh registries and the longitudinal surveillance of patients.

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.

Evaluation of the histological and biomechanical properties of poly-4-hydroxybutyrate scaffold for pelvic organ prolapse, compared with polypropylene mesh in a rabbit model

INTRODUCTION AND HYPOTHESIS

Poly-4-hydroxybutyrate (P4HB) is a biopolymer produced by Escherichia coli K12 bacteria. P4HB is fully resorbed in vivo by 18-24 months post-implantation. The aim of this study is to evaluate P4HB in the rabbit abdomen and vagina to determine that the biomechanical and histological properties are similar to the standard polypropylene mesh. Our hypothesis is that the histological and biomechanical properties of a fully absorbable graft will be similar to a lightweight polypropylene (PP) mesh when implanted in rabbit vagina and abdomen.

METHODS

Sixteen (n = 16) female New Zealand White (retired breeder) rabbits were equally divided between two time points (3 and 9 months). A total of 17 rabbits were used owing to one death secondary to suspected cardiomyopathy. P4HB scaffold and PP mesh were subcutaneously and peri-vaginally implanted into the rabbit abdomen and vagina respectively. All rabbits had both posterior and anterior vaginal implants, and half of the rabbits had four abdominal implants in addition to the vaginal implants. The abdominal implants were 4.5 cm long × 1.5 cm wide whereas the vaginal implants were 1.5 cm long × 0.5 cm wide. At 3 and 9 months, gross necropsy was performed and samples were obtained, sectioned, stained and evaluated via histological analysis. Specimens were assessed for host inflammatory response, neovascularization, elastin content, and collagen deposition/maturation. Specimens were also biomechanically evaluated via uniaxial tensile test to determine the stiffness, ultimate tensile strength and load at ultimate tensile strength of the device/tissue composite.

RESULTS

No abdominal mesh exposures were noted. A comparable number of asymptomatic partial vaginal exposures were observed at 3 months (P4HB: n = 3; PP: n = 2) and 9 months (P4HB: n = 3; PP: n = 2) respectively. Histological analysis of specimens showed comparable results in the P4HB and PP groups at 3 and 9 months post-implantation. Although no acute inflammation was seen, chronic inflammation was demonstrated in all specimens. Elastic fibers were present in the 3-month vaginal PP and P4HB specimens, but were not seen again. There was an increase in type I/III collagen noted over time. Biomechanical evaluation of the vaginal mesh tissue complex showed ultimate tensile strength was not significantly different between P4HB and PP groups at 3 (P = 0.625) and 9 months (P = 0.250) respectively.

CONCLUSIONS

P4HB scaffold may represent a fully absorbable alternative to permanent mesh for pelvic organ prolapse (POP) repair.

Pelvic organ prolapse meshes: Can they preserve the physiological behavior?

Implants for the cure of female genital prolapse still show numerous complications cases that sometimes have dramatic consequences. These implants must be improved to provide physiological support and restore the normal functionalities of the pelvic area. Besides the trend towards lighter meshes, a better understanding of the in vivo role and impact of the mesh implantation is required. This work investigates the mechanical impact of meshes after implantation with regards to the behavior of the native tissues. Three meshes were studied to assess their mechanical and biological impact on the native tissues. An animal study was conducted on rats. Four groups (n = 17/group) underwent surgery. Rats were implanted on the abdominal wall with one of the three polypropylene knitted mesh (one mesh/group). The last group served as control and underwent the same surgery without any mesh implantation. Post-operative complications, contraction, mechanical rigidities, and residual deformation after cyclic loading were collected. Non-parametric statistical comparisons were performed (Kruskal-Wallis) to observe potential differences between implanted and control groups. Mechanical characterization showed that one of the three meshes did not alter the mechanical behavior of the native tissues. On the contrary, the two others drastically increased the rigidities and were also associated with clinical complications. All of the meshes seem to reduce the geometrical lengthening of the biological tissues that comes with repetitive loads. Mechanical aspects might play a key role in the compatibility of the mesh in vivo. One of the three materials that were implanted during an animal study seems to provide better support and adapt more properly to the physiological behavior of the native tissues.

Animal experimental research assessing urogynecologic surgical mesh implants: Outcome measures describing the host response, a systematic review and meta-analysis

Aim

Before the introduction of new biomaterials for prolapse surgery, animal studies on the host response are required. Unfortunately, large variation in study design hampers obtaining an overview of the safety and efficacy, and translation to clinical practice. Our aim is to systematically review the literature on all outcome measures describing the host response in animal studies assessing the biocompatibility of urogynecologic surgical mesh implants for prolapse surgery. Furthermore, by meta‐analysis, we aim to assess the effect of implantation and compare this to control animals receiving sham surgery or native tissue repair.

Methods

We performed a systematic search from inception to August 2020. Since this is an explorative study we included original, controlled, and noncontrolled animal studies describing any host response to the implant. Quantitative outcome measures reported ≥10 times in ≥2 articles were eligible for meta‐analysis.

Results

Fifty articles were included in the qualitative synthesis and 36 articles were eligible for meta‐analysis. In total, 154 outcome measures were defined and classified into (1) histomorphology, (2) biomechanics and, (3) macroscopic morphology. Animals with vaginal implants demonstrated significantly increased M1 and M2 macrophages, MMP‐2, neovascularization, TNF‐α, and stiffness, and lower vaginal contractility compared to control animals.

Conclusion

The host response significantly differs in animals after vaginal mesh implantation compared to control animals, both pro‐ and anti‐inflammatory. However, we observed a paucity in the uniformity of reported outcomes. For future animal studies, we propose the development of a core outcome set, which ideally predicts the host response in women.

Biodegradable materials for surgical management of stress urinary incontinence: A narrative review

Stress urinary incontinence (SUI) was managed with techniques such as colposuspension, autologous fascia sling and urethral bulking agents. The introduction of the mid-urethral polypropylene (PP) sling in the 1990s led to a significant and rapid global change in SUI surgery. The synthetic non-degradable PP sling had superior results to traditional SUI procedures but its use has now declined due to significant complications such as pain and mesh erosion. These complications are attributed to its poor biocompatibility and integration into vaginal tissues. The efficacy of PP was extrapolated from studies on abdominal wall repair and it is now clear that integration of implanted materials in the pelvic floor differs from the abdominal wall. With PP prohibited in some jurisdictions, female patients with SUI have few management options. In the present review we summarise recent advances in SUI surgery and evaluate potential alternatives to PP slings with a particular focus on degradable materials. Allograft and xenograft materials demonstrate good biocompatibility but have yielded suboptimal cure rates. Tissue engineered synthetic degradable materials outperform unmodified synthetic degradable materials in terms of biomechanics and cell support. Synthetic tissue engineered degradable materials show promising results from in vitro studies and future research should focus on animal and human trials in this field.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Comparison of Biaxial Biomechanical Properties of Post-menopausal Human Prolapsed and Non-prolapsed Uterosacral Ligament

Uterosacral ligaments (USLs) provide structural support to the female pelvic floor, and a loss of USL structural integrity or biomechanical function may induce pelvic organ prolapse (POP). Alterations in extracellular matrix composition and organization dictate USL mechanical function. Changes in USL microstructure and corresponding mechanical properties, however, are not fully understood, nor is it understood how microstructure and mechanics change with onset and progression of POP. This is due, in part, as USL properties are primarily characterized along a single direction (uniaxial test), whereas the USL is loaded in multiple directions simultaneously within the body. Biaxial testing permits the acquisition of biomechanical data from two axes simultaneously, and thus simulates a more physiologic assessment compared to the traditional uniaxial testing. Therefore, the objective of this study was to quantify the biaxial biomechanical properties and histological composition of the USL in post-menopausal women with and without POP at various stages. Potential correlations between tissue microstructural composition and mechanical function were also examined. Tangential modulus was lower and peak stretch higher in POP III/IV compared to non-POP and POP I/II in the main in vivo loading direction; however, no significant differences in mechanical properties were observed in the perpendicular loading direction. Collagen content positively correlated to tangential modulus in the main in vivo loading direction (r = 0.5, p = 0.02) and negatively correlated with the peak stretch in both the main in vivo (r = -0.5, p = 0.02) and perpendicular loading directions (r = -0.3, p = 0.05). However, no statistically significant differences in USL composition were observed, which may be due to the small sample size and high variability of small sections of human tissues. These results provide first step towards understanding what microstructural and mechanical changes may occur in the USL with POP onset and progression. Such information may provide important future insights into the development of new surgical reconstruction techniques and graft materials for POP treatment.

Stress Urinary Incontinence and Pelvic Organ Prolapse: Biologic Graft Materials Revisited

Symptomatic stress urinary incontinence (SUI) and pelvic organ prolapse (POP) refractory to conservative management with pelvic floor muscle training or vaginal pessaries may warrant surgical intervention with different forms of biologic or synthetic material. However, in recent years, several global regulatory agencies have issued health warnings and recalled several mesh products due to an increase in complications such as mesh erosion, infection, chronic pain, and perioperative bleeding. At present, current surgical treatment strategies for SUI and POP are aimed at developing biological graft materials with similar mechanical properties to established synthetic meshes, but with improved tissue integration and minimal host response. This narrative review aims to highlight recent studies related to the development of biomimetic and biologic graft materials as alternatives to traditional synthetic materials for SUI/POP repair in female patients. We also investigate complications and technical limitations associated with synthetic mesh and biological biomaterials in conventional SUI and POP surgery. Our findings demonstrate that newly developed biologic grafts have a lower incidence of adverse events compared to synthetic biomaterials. However there remains a significant disparity between success in preclinical trials and long-term clinical translation. Further characterization on the optimal structural, integrative, and mechanical properties of biological grafts is required before they can be reliably introduced into clinical practice for SUI and POP surgery. Impact statement Our review article aims to outline the clinical history of developments and controversies associated with the use of synthetic mesh materials in the surgical treatment of stress urinary incontinence and pelvic organ prolapse, as well as highlighting recent advancements in the area of biological graft materials and their potential importance in an area that remains an enduring issue for patients and clinicians alike. This article aims to provide a concise summary of previous controversies in the field of urinary incontinence, while evaluating the future of potential biomaterials in this field.

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

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

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.

Improving the biocompatibility of biomaterial constructs and constructs delivering cells for the pelvic floor

PURPOSE OF REVIEW

Interactions between biomaterials and biomaterial-delivering cells and the host tissues are complexly affected by the material itself, the ultrastructure of the overall construct and cells and other bioactive factors involved. The aim of this review is to review the current understanding on the definitions of biocompatibility and current advances in improving biocompatability of tissue-engineered constructs.

RECENT FINDINGS

Some synthetic materials are associated with more foreign body reactions compared with natural materials; however, they allow fabrication of materials with a great diversity of physical and mechanical properties. Material design strategies can be tailored to mimic the natural extracellular matrix topography. There are also advancements in the pharmacological functionalization of materials with improved angiogenic potential that can lead to better tissue response. Stem cells are also used to improve the tissue response of tissue-engineered materials; however, the recent regulations on regenerative medicine products necessitate significant regulatory approval processes for these.

SUMMARY

The biggest challenge faced in translation of tissue-engineered constructs into clinical practice relates to their engraftment and poor tissue integration into the challenging wound bed of the pelvic floor. Biocompatibility of tissue engineered constructs can theoretically be improved by the incorporation of bioactive agents, such as vitamins C or oestradiol.

Complications related to use of mesh implants in surgical treatment of stress urinary incontinence and pelvic organ prolapse: infection or inflammation?

The surgical mesh material used in the surgical treatment of stress urinary incontinence (SUI) and pelvic organ prolapse (POP) in women is associated with significant complications in some women. This has recently become a public health issue with involvement of national parliaments and regulatory bodies. The occurrence of mesh complications is thought to be a result of multifactorial processes involving problems related to the material design, the surgical techniques used and disease, and patient-related factors. However, the infectious complications and mesh–tissue interactions are least studied. The aim of this article is to review any previous clinical and basic scientific evidence about the contribution of infectious and inflammatory processes to the occurrence of mesh-related complications in SUI and POP. A literature search for the relevant publications without any time limits was performed on the Medline database. There is evidence to show that vaginal meshes are associated with an unfavourable host response at the site of implantation. The underlying mechanisms leading to this type of host response is not completely clear. Mesh contamination with vaginal flora during surgical implantation can be a factor modifying the host response if there is a subclinical infection that can trigger a sustained inflammation. More basic science research is required to identify the biological mechanisms causing a sustained inflammation at the mesh–tissue interface that can then lead to contraction, mesh erosion, and pain.

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.

Biomimetic implants for pelvic floor repair

BACKGROUND

Polypropylene implants are used for the reconstructive surgery of urogynaecological disorders like pelvic organ prolapse, but severe complications associated with their use have been reported. There is evidence that surface properties and a difference in mechanical stiffness between the implant and the host tissue contribute to these adverse events. Electrospinning is an innovative engineering alternative that provides a biomimetic microstructure for implants, resulting in a different mechano-biological performance.

AIM

The main objective of this review is to inform about the potential of electrospun matrices as an alternative modality for pelvic floor repair.

METHODS

Publications with the following studies of electrospun matrices were reviewed: (i) the technique; (ii) in vitro use for soft tissue engineering; (iii) in vivo use for reconstruction of soft tissues in animals; and (iv) clinical use in humans.

RESULTS

Electrospun matrices provide a synthetic mimic of natural extracellular matrix (ECM), favoring cellular attachment, proliferation and matrix deposition, through which a proper, low-inflammatory tissue-implant interaction can be established. Electrospun sheets can also be created with sufficient mechanical strength and stiffness for usage in prolapse surgery.

CONCLUSION

Electrospun matrices mimic the structural topography of the extracellular matrix and can be functionalized for better biological performance. As such, they have great potential for the next generation of urogynecological implants. However, their long-term safety and efficacy must still be established in vivo.

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.

Comparing different tissue-engineered repair materials for the treatment of pelvic organ prolapse and urinary incontinence: which material is better?

INTRODUCTION AND HYPOTHESIS

Synthetic non-absorbable meshes are widely used to augment surgical repair of pelvic organ prolapse (POP) and stress urinary incontinence (SUI), but these meshes are associated with serious complications. This study compares the attachment and extracellular matrix (ECM) production of adipose-derived stem cells (ADSCs) on different biodegradable nanomaterials to develop tissue engineered repair materials.

METHODS

Rat ADSCs were isolated and cultured on electrospun poly-L-lactic acid (PLA) and electrospun poly(L-lactide)-trimethylene carbonate-gycolide (PLTG) terpolymers for 1 and 2 weeks. Samples were tested for cell proliferation (cell counting kit-8), microstructure, and morphology (scanning electron microscopy), production of ECM components (immunostaining for collagen I, collagen III, and elastin) and biomechanical properties (uniaxial tensile methods).

RESULTS

The ADSCs showed good attachment and proliferation on both PLA and PLTG scaffolds. The production of collagen I and collagen III on both scaffolds was greater at 14 days than at 7 days and was greater on PLTG scaffolds than on PLA scaffolds, but these differences were not significant. The addition of ADSCs onto scaffolds led to a significant increase in the biomechanical properties of both PLA and PLTG scaffolds compared with unseeded scaffolds.

CONCLUSION

These data support the use of both PLA and PLTG as tissue-engineered repair materials for POP or SUI.

Oestradiol-releasing Biodegradable Mesh Stimulates Collagen Production and Angiogenesis: An Approach to Improving Biomaterial Integration in Pelvic Floor Repair

BACKGROUND

Polypropylene meshes cause severe complications in some patients. Materials that are biomechanically compatible and can better integrate into host tissues are urgently needed.

OBJECTIVE

To design an oestradiol-releasing electrospun poly-l-lactic acid (PLA) mesh and evaluate its ability to stimulate new extracellular matrix and new blood vessel formation.

DESIGN, SETTING, AND PARTICIPANTS

Human adipose derived mesenchymal cells (ADMSC) were isolated from fat. PLA meshes with micro- to nano-sized fibres containing 1%, 5%, and 10% oestradiol were constructed and used for in vitro and in vivo experiments.

INTERVENTION

The angiogenic potential of the fibrous meshes was evaluated using an in vivo chorioallantoic membrane and an in vitro chick aortic arch assays.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Oestradiol release was measured fluorometrically. The effect of fibrous meshes on proliferation and extracellular matrix (ECM) production of ADMSC was assessed using immunohistology. Mechanical properties were tested using a tensiometer.

RESULTS AND LIMITATIONS

The ultrastructure of the mesh was not affected by the inclusion of oestradiol and mechanical properties were only slightly modified. Oestradiol was released from PLA meshes over a 5-mo period. ADMSCs cultured on oestradiol-releasing PLA meshes produced more ECM involving collagen I, collagen III, and elastin. Oestradiol-releasing meshes doubled new blood vessel formation in the chorioallantoic membrane assay (p=0.001) and outgrowth of pro-angiogenic cells in the aortic arch assay (p=0.001). Further studies in longer-term animal models are required to confirm these results.

CONCLUSIONS

Oestradiol-releasing PLA meshes increase ECM production and stimulate angiogenesis. As such, they are promising candidate materials to be used in pelvic floor repair and to improve the initial healing phase of a repair material following implantation.

PATIENT SUMMARY

In this study, we designed a tissue engineered material to be used to support weakened pelvic floor tissues in women to avoid the complications associated with current surgical mesh. Our results showed that this material can stimulate new blood vessel formation in simple chick assays and tissue production in vitro. Both properties should help with the integration of this material into patients' tissues and merit further study in physiologically relevant animal models.

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.

Developing Repair Materials for Stress Urinary Incontinence to Withstand Dynamic Distension

BACKGROUND

Polypropylene mesh used as a mid-urethral sling is associated with severe clinical complications in a significant minority of patients. Current in vitro mechanical testing shows that polypropylene responds inadequately to mechanical distension and is also poor at supporting cell proliferation.

AIMS AND OBJECTIVES

Our objective therefore is to produce materials with more appropriate mechanical properties for use as a sling material but which can also support cell integration.

METHODS

Scaffolds of two polyurethanes (PU), poly-L-lactic acid (PLA) and co-polymers of the two were produced by electrospinning. Mechanical properties of materials were assessed and compared to polypropylene. The interaction of adipose derived stem cells (ADSC) with the scaffolds was also assessed. Uniaxial tensiometry of scaffolds was performed before and after seven days of cyclical distension. Cell penetration (using DAPI and a fluorescent red cell tracker dye), viability (AlamarBlue assay) and total collagen production (Sirius red assay) were measured for ADSC cultured on scaffolds.

RESULTS

Polypropylene was stronger than polyurethanes and PLA. However, polypropylene mesh deformed plastically after 7 days of sustained cyclical distention, while polyurethanes maintained their elasticity. Scaffolds of PU containing PLA were weaker and stiffer than PU or polypropylene but were significantly better than PU scaffolds alone at supporting ADSC.

CONCLUSIONS

Therefore, prolonged mechanical distension in vitro causes polypropylene to fail. Materials with more appropriate mechanical properties for use as sling materials can be produced using PU. Combining PLA with PU greatly improves interaction of cells with this material.

Changes in pelvic organ prolapse mesh mechanical properties following implantation in rats

BACKGROUND

Pelvic organ prolapse (POP) is a multifactorial disease that manifests as the herniation of the pelvic organs into the vagina. Surgical methods for prolapse repair involve the use of a synthetic polypropylene mesh. The use of this mesh has led to significantly higher anatomical success rates compared with native tissue repairs, and therefore, despite recent warnings by the Food and Drug Administration regarding the use of vaginal mesh, the number of POP mesh surgeries has increased over the last few years. However, mesh implantation is associated with higher postsurgery complications, including pain and erosion, with higher consecutive rates of reoperation when placed vaginally. Little is known on how the mechanical properties of the implanted mesh itself change in vivo. It is assumed that the mechanical properties of these meshes remain unchanged, with any differences in mechanical properties of the formed mesh-tissue complex attributed to the attached tissue alone. It is likely that any changes in mesh mechanical properties that do occur in vivo will have an impact on the biomechanical properties of the formed mesh-tissue complex.

OBJECTIVE

The objective of the study was to assess changes in the multiaxial mechanical properties of synthetic clinical prolapse meshes implanted abdominally for up to 90 days, using a rat model. Another objective of the study was to assess the biomechanical properties of the formed mesh-tissue complex following implantation.

STUDY DESIGN

Three nondegradable polypropylene clinical synthetic mesh types for prolapse repair (Gynemesh PS, Polyform Lite, and Restorelle) and a partially degradable polypropylene/polyglecaprone mesh (UltraPro) were mechanically assessed before and after implantation (n = 5/ mesh type) in Sprague Dawley rats for 30 (Gynemesh PS, Polyform Lite, and Restorelle) and 90 (UltraPro and Polyform Lite) days. Stiffness and permanent extension following cyclic loading, and breaking load, of the preimplanted mesh types, explanted mesh-tissue complexes, and explanted meshes were assessed using a multi-axial (ball-burst) method.

RESULTS

The 4 clinical meshes varied from each other in weight, thickness, porosity, and pore size and showed significant differences in stiffness and breaking load before implantation. Following 30 days of implantation, the mechanical properties of some mesh types altered, with significant decreases in mesh stiffness and breaking load, and increased permanent extension. After 90 days these changes were more obvious, with significant decreases in stiffness and breaking load and increased permanent extension. Similar biomechanical properties of formed mesh-tissue complexes were observed for mesh types of different preimplant stiffness and structure after 90 days implantation.

CONCLUSION

This is the first study to report on intrinsic changes in the mechanical properties of implanted meshes and how these changes have an impact on the estimated tissue contribution of the formed mesh-tissue complex. Decreased mesh stiffness, strength, and increased permanent extension following 90 days of implantation increase the biomechanical contribution of the attached tissue of the formed mesh-tissue complex more than previously thought. This needs to be considered when using meshes for prolapse repair.

Mobility and stress analysis of different surgical simulations during a sacral colpopexy, using a finite element model of the pelvic system

INTRODUCTION AND HYPOTHESIS

We aim to analyze the combined influence of the size of the mesh, the number of sutures, the combined use of an anterior and posterior mesh, and the tension applied to the promontory, on the mobility of the pelvic organs and on the sutures, using a Finite Element (FE) model of the female pelvic system during abdominal sacral colpopexy.

METHODS

We used a FE model of the female pelvic system, which allowed us to simulate the mobility of the pelvic system and to evaluate problems related to female prolapse. The meshes were added to the geometrical model and then transferred to computing software. This analysis allowed us to compare the stress and mobility during a thrust effort in different situations.

RESULTS

The bigger the mesh, the less mobility of both anterior and posterior organs there would be. This is accompanied by an increase in stress at the suture level. The combination of a posterior mesh with an anterior one decreases mobility and stress at the suture level. There is a particularly relevant stressing zone on the suture at the cervix. The increase in the number of sutures induces a decrease in the tension applied at each suture zone and has no impact on organ mobility.

CONCLUSION

Our model enables us to simulate and analyze an infinite number of surgical hypotheses. Even if these results are not validated at a clinical level, we can observe the importance of the association of both an anterior and a posterior mesh or the number of sutures.

Fixation of Light Weight Polypropylene Mesh with n-Butyl-2-cyanocrylate in Pelvic Floor Surgery: Experimental Design Approach in Sheep for Effectiveness Evaluation

Objective. The aim of this study was to find a proper experimental design and to evaluate n-butyl-2-cyanoacrylate (Histoacryl) as a fixation method for a light-weight and large pore PP mesh (Synthetic PP Mesh-1) using the sheep as an animal model. Methods. Posterior vaginal implantation by means of episiotomy was used to implant 8 ewes which were evaluated macroscopically and histologically at 3 months (n = 4) and 6 months (n = 4) post-surgery. In previous pilot studies anterior vaginal implantation was evaluated, as well as different synthetic mesh materials, sizes and fixation methods (n = 1 to 3) during three weeks. In all cases a clinical evaluation of the animal was performed. Results. A reduction in the mesh size (Synthetic PP Mesh-1) together with precise application of the surgical glue Histoacryl to fix the mesh yielded significantly better histocompatibility results (P < 0.01) compared to larger size or other fixation methods. Conclusion. The combination of Synthetic PP Mesh-1 with Histoacryl offered a high degree of graft integration without vaginal ulceration and a minimal foreign body reaction, being the sheep a proper animal model to test these types of medical devices.

Biomaterials for pelvic floor reconstructive surgery: how can we do better?

Stress urinary incontinence (SUI) and pelvic organ prolapse (POP) are major health issues that detrimentally impact the quality of life of millions of women worldwide. Surgical repair is an effective and durable treatment for both conditions. Over the past two decades there has been a trend to enforce or reinforce repairs with synthetic and biological materials. The determinants of surgical outcome are many, encompassing the physical and mechanical properties of the material used, and individual immune responses, as well surgical and constitutional factors. Of the current biomaterials in use none represents an ideal. Biomaterials that induce limited inflammatory response followed by constructive remodelling appear to have more long term success than biomaterials that induce chronic inflammation, fibrosis and encapsulation. In this review we draw upon published animal and human studies to characterize the changes biomaterials undergo after implantation and the typical host responses, placing these in the context of clinical outcomes.

Host reaction to vaginally inserted collagen containing polypropylene implants in sheep

OBJECTIVE

We aimed to characterize the effect of vaginal or abdominal mesh insertion and of different collagen augmentation of polypropylene mesh in a sheep model. Outcome measures were passive and active biomechanical properties and semiquantitative morphometry.

STUDY DESIGN

Forty-two Texel sheep were used: 6 were nonimplanted controls (n = 6), the rest were implanted with polypropylene mesh (n = 12; Avaulta Solo; Bard Medical, Covington, GA) or collagen-coated meshes: Avaulta Plus (n = 12; Bard Medical) and Ugytex (n = 12; Sofradim International, Trevoux, France). Through a single incision, the rectovaginal septum was dissected and a 35 × 35-mm mesh was sutured to the underlying tissues. Abdominally, a 50 × 50-mm mesh was laid over a primarily sutured full thickness 40-mm longitudinal incisional defect. Animals were explanted after 60 or 180 days (n = 6 per group). Outcome measures were passive biomechanics by biaxial tensiometry, active contractility of vaginal explants, and histologic evidence.

RESULTS

Vaginal explants were 2.4 times stiffer compared with native vaginal tissue (P < .001), but without differences in comfort zone stiffness or slope of the load-elongation in the physiologic range between the products that were tested. Collagen coating was associated with a 16-fold reduction in contractile force at 180 days, compared with native vaginal tissue, both for Avaulta Plus (P = .032) and Ugytex (P = .015). Abdominal explants were 1.3-times stiffer compared with native abdominal wall tissue (P < .001) and were 1.9-times stiffer compared with vaginal explants.

CONCLUSION

Vaginal mesh implantation yields less stiff explants compared with abdominal explants. Vaginal mesh implantation also alters the passive and active biomechanical properties compared with native vaginal tissues. Collagen matrices did not reduce the number of graft-related complications.

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

The properties of meshes used in reconstructive surgery affect the host response and biomechanical characteristics of the grafted tissue. Whereas durable synthetics induce a chronic inflammation, biological grafts are usually considered as more biocompatible. The location of implantation is another determinant of the host response: the vagina is a different environment with specific function and anatomy. Herein, we evaluated a cross-linked acellular collagen matrix (ACM), pretreated by the anti-calcification procedure ADAPT® in a sheep model for vaginal surgery. Ten sheep were implanted with a cross-linked ACM, and six controls were implanted with a polypropylene (PP; 56 g/m²) control. One implant was inserted in the lower rectovaginal septum, and one was used for abdominal wall defect reconstruction. Grafts were removed after 180 days; all graft-related complications were recorded, and explants underwent bi-axial tensiometry and contractility testing. Half of ACM-implanted animals had palpable induration in the vaginal implantation area, two of these also on the abdominal implant. One animal had a vaginal exposure. Vaginal ACMs were 63 % less stiff compared to abdominal ACM explants (p = 0.01) but comparable to vaginal PP explants. Seven anterior vaginal ACM explants showed areas of graft degradation on histology. There was no overall difference in vaginal contractility. Considering histologic degradation in the anterior vaginal implant as representative for the host, posterior ACM explants of animals with degradation had a 60 % reduced contractility as compared to PP (p = 0.048). Three abdominal implants showed histologic degradation; those were more compliant than non-degraded implants. Vaginal implantation with ACM was associated with graft-related complications (GRCs) and biomechanical properties comparable to PP. Partially degraded ACM had a decreased vaginal contractility.

Stem cell augmented mesh materials: an in vitro and in vivo study

INTRODUCTION AND HYPOTHESIS

To test in vitro and in vivo the capability of mesh materials to act as scaffolds for rat-derived mesenchymal stem cells (rMSCs) and to compare inflammatory response and collagen characteristics of implant materials, either seeded or not with rMSCs.

METHODS

rMSCs isolated from rat bone marrow were seeded and cultured in vitro on four different implant materials. Implants showing the best rMSC proliferation rate were selected for the in vivo experiment. Forty-eight adult female Sprague-Dawley rats were randomly divided into two treatment groups. The implant of interest-either seeded or not with rMSCs-was laid and fixed over the muscular abdominal wall. Main outcome measures were: in vitro, proliferation of rMSCs on selected materials; in vivo, the occurrence of topical complications, the evaluation of systemic and local inflammatory response and examination of the biomechanical properties of explants.

RESULTS

Surgisis and Pelvitex displayed the best cell growth in vitro. At 90 days in the rat model, rMSCs were related to a lower count of neutrophil cells for Pelvitex and a greater organisation and collagen amount for Surgisis. At 7 days Surgisis samples seeded with rMSCs displayed higher breaking force and stiffness.

CONCLUSIONS

The presence of rMSCs reduced the systemic inflammatory response on synthetic implants and improved collagen characteristics at the interface between biological grafts and native tissues. rMSCs enhanced the stripping force on biological explants.

Full thickness abdominal wall defect in growing rats as a model for congenital diaphragmatic hernia prosthetic repair

BACKGROUND

Large congenital diaphragmatic hernia may require prosthetic correction. Acellular collagen matrices were introduced to avoid complications owing to the use of synthetic patches. We tested 3 different ACM for reconstruction of an abdominal wall defect in an animal model that mimics the fast growth during infancy.

METHODS

Pelvisoft® (CR Bard, Covington, GA) and 2 investigational ACM were used for primary reconstruction of a full thickness abdominal wall defect. 3months-old rats (n=26) were allowed to survive for 90days after implantation. Anatomical, tensiometric and histological analyses were performed. Based on good outcomes, we did the same with 1month-old rats (n=54). Unoperated rats were used for obtaining reference tensiometric values of selected native tissues.

RESULTS

Major wound complications were exclusively observed in 1month-old rats. All explants in both groups thinned significantly (p<0.03) and had an elastic modulus increasing over time, far above that from native tissues at 90days of life. Both investigational ACM induced a more vigorous foreign body reaction than Pelvisoft(®).

CONCLUSIONS

The shift from 3 to 1month-old rats was associated with wound complications. Pelvisoft® showed a better biocompatibility than the 2 investigational ACM. Passive biomechanical properties of all explants were still not comparable to that of native tissues.

Optimal management of the critically ill: anaesthesia, monitoring, data capture, and point-of-care technological practices in ovine models of critical care

Animal models of critical illness are vital in biomedical research. They provide possibilities for the investigation of pathophysiological processes that may not otherwise be possible in humans. In order to be clinically applicable, the model should simulate the critical care situation realistically, including anaesthesia, monitoring, sampling, utilising appropriate personnel skill mix, and therapeutic interventions. There are limited data documenting the constitution of ideal technologically advanced large animal critical care practices and all the processes of the animal model. In this paper, we describe the procedure of animal preparation, anaesthesia induction and maintenance, physiologic monitoring, data capture, point-of-care technology, and animal aftercare that has been successfully used to study several novel ovine models of critical illness. The relevant investigations are on respiratory failure due to smoke inhalation, transfusion related acute lung injury, endotoxin-induced proteogenomic alterations, haemorrhagic shock, septic shock, brain death, cerebral microcirculation, and artificial heart studies. We have demonstrated the functionality of monitoring practices during anaesthesia required to provide a platform for undertaking systematic investigations in complex ovine models of critical illness.

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.