Repairing the female pelvic floor: when good enough is not good enough

Where are we in 2024 in the development of materials for surgical treatment of pelvic organ prolapse and stress urinary incontinence?

PURPOSE OF REVIEW

There is a long history of implantation of absorbable and nonabsorbable materials to treat stress urinary incontinence (SUI) and pelvic organ prolapse (POP). The focus of this review is to review the development of new materials for use in the surgical management of both pelvic conditions following an unacceptable level of severe complications in the use of polypropylene mesh (PPM). We discuss current concepts relating to the development of new materials with particular reference to our experience with polyurethane mesh.

RECENT FINDINGS

Our review highlights the strategies that manufacturers and researchers are employing to improve PPM using collagen gels and stem cells, or to find alternatives. We conclude that current preclinical safety testing is inadequate, and the field requires better in vivo testing. Specifically, we highlight novel techniques demonstrating the degradation of polypropylene potentially elucidating the link between PPM degradation and induction of inflammation leading to adverse side effects.

SUMMARY

This field badly needs innovation in developing new materials and in testing these to ensure materials will benefit patients. A collaboration between materials scientists and clinicians is needed to facilitate the translation of basic research and preclinical testing into patient benefit for the treatment of SUI and POP.

Uncovering the relationship between macrophages and polypropylene surgical mesh

Currently, in vitro testing examines the cytotoxicity of biomaterials but fails to consider how materials respond to mechanical forces and the immune response to them; both are crucial for successful long-term implantation. A notable example of this failure is polypropylene mid-urethral mesh used in the treatment of stress urinary incontinence (SUI). The mesh was largely successful in abdominal hernia repair but produced significant complications when repurposed to treat SUI. Developing more physiologically relevant in vitro test models would allow more physiologically relevant data to be collected about how biomaterials will interact with the body. This study investigates the effects of mechanochemical distress (a combination of oxidation and mechanical distention) on polypropylene mesh surfaces and the effect this has on macrophage gene expression. Surface topology of the mesh was characterised using SEM and AFM; ATR-FTIR, EDX and Raman spectroscopy was applied to detect surface oxidation and structural molecular alterations. Uniaxial mechanical testing was performed to reveal any bulk mechanical changes. RT-qPCR of selected pro-fibrotic and pro-inflammatory genes was carried out on macrophages cultured on control and mechanochemically distressed PP mesh. Following exposure to mechanochemical distress the mesh surface was observed to crack and craze and helical defects were detected in the polymer backbone. Surface oxidation of the mesh was seen after macrophage attachment for 7 days. These changes in mesh surface triggered modified gene expression in macrophages. Pro-fibrotic and pro-inflammatory genes were upregulated after macrophages were cultured on mechanochemically distressed mesh, whereas the same genes were down-regulated in macrophages exposed to control mesh. This study highlights the relationship between macrophages and polypropylene surgical mesh, thus offering more insight into the fate of an implanted material than existing in vitro testing.

Estradiol-17β [E2] stimulates wound healing in a 3D in vitro tissue-engineered vaginal wound model

Childbirth contributes to common pelvic floor problems requiring reconstructive surgery in postmenopausal women. Our aim was to develop a tissue-engineered vaginal wound model to investigate wound healing and the contribution of estradiol to pelvic tissue repair. Partial thickness scalpel wounds were made in tissue models based on decellularized sheep vaginal matrices cultured with primary sheep vaginal epithelial cells and fibroblasts. Models were cultured at an airliquid interface (ALI) for 3 weeks with and without estradiol-17β [E₂]. Results showed that E₂ significantly increased wound healing and epithelial maturation. Also, E₂ led to collagen reorganization after only 14 days with collagen fibers more regularly aligned and compactly arranged Additionally, E₂ significantly downregulated α-SMA expression which is involved in fibrotic tissue formation. This model allows one to investigate multiple steps in vaginal wound healing and could be a useful tool in developing therapies for improved tissue healing after reconstructive pelvic floor surgery.

Recent advances in pelvic floor repair

Stress urinary incontinence (SUI) and pelvic organ prolapse (POP) are conditions which result in significant physical, mental and social consequences for women worldwide. The high rates of recurrence reported with primary repair for POP led to the use of synthetic mesh to augment repairs in both primary and secondary cases following failed previous POP repair. The widely reported, unacceptably high rates of complications associated with the use of synthetic, transvaginal mesh in pelvic floor repair have severely limited the treatment options that surgeons can offer. This article summarises the recent advances in pelvic floor repair, such as improved quantification and modelling of the biomechanics of the pelvic floor and the developing technology within the field of tissue engineering for treatment of SUI/POP, including biomaterials and cell-based therapies. Finally, we will discuss the issues surrounding the commercial introduction of synthetic mesh for use within the pelvic floor and what lessons can be learned for the future as well as the current guidance surrounding treatment for SUI/POP.

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.