Overcoming Complications of Polypropylene Prolapse Meshes: Development of Novel Elastomeric Auxetic Devices

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PROJECT SUMMARY Pelvic organ prolapse (POP) is a common, costly condition in women with a lifetime risk of surgical repair of 12.6%. Of those undergoing a native tissue repair, 40% will fail by 2 years prompting surgeons to turn to biomaterials, most commonly polypropylene mesh. Unfortunately, POP meshes are abdominal hernia meshes that have been remarketed under 510K applications for POP repair and, thus, were never designed specifically for the vagina. Our studies show that implantation with polypropylene mesh leads to degeneration, atrophy and loss of function of the vagina. The high material stiffness of polypropylene dictates that meshes manufactured from this polymer are knitted, leading to a device that undergoes pore collapse, wrinkling, and permanent deformation -- all contributing to increased mesh burden, a heightened foreign body response, and poor outcomes. We hypothesize that a mesh generated from an elastomeric polymer with a material stiffness on the same order of magnitude as that of the vagina, a geometry that favors stable pores, and minimal wrinkling with tensioning will be associated with a more favorable host response than current polypropylene prolapse meshes. Here we are proposing to develop and evaluate a mesh synthesized from polycarbonate-urethane (PCU), an elastomer with an inherent stiffness similar to that of vagina but that is also sufficiently tough to meet physiologic loading demands. The mesh is designed with auxetic pores; meaning they expand instead of contract with loading. In addition, the mesh can be 3D printed, permitting us to fine tune the in-plane geometry and thickness, and allow for non-rotational junctions, thereby reducing wrinkling and permanent deformation. Specifically, our goal in this application is to delineate the impact of our choice for the stiffness of PCU on the host response to the mesh because this choice will impact the amount of material necessary to achieve structural support and strength equivalent to that of polypropylene mesh. The amount of material contributes directly to the magnitude of the host response, but can also obviate or enhance mechanical behaviors, e.g. wrinkling, in the device that feedback into the host response. Thus, in moving this device forward for eventual use in humans, we will study how our design choices independently impact the host response to the material and the mechanics of the mesh by: (Aim 1) implanting small units of the mesh with varied material stiffness, fiber width and mesh thickness on the vagina without tensioning and loading, and (Aim 2) utilizing computational modeling and ex vivo tests to determine the impact of the same design choices on the mechanical behavior of the full length mesh with loading. In Aim 3, we will study how choices that balance the host response to the material with those resulting from the mechanics of the mesh collectively contribute to the overall host response to a mesh that is implanted on tension by sacrocolpopexy in a validated animal model as compared to conventional polypropylene mesh. In this way, the device developed in this proposal has high potential for markedly improving outcomes in POP surgical repair.