title: Varying degrees of nonlinear mechanical behavior arising from geometric differences of urogynecological meshes.
abstract: Synthetic polypropylene meshes were designed to restore pelvic organ support for women suffering from pelvic organ prolapse; however, the FDA released two notifications regarding potential complications associated with mesh implantation. Our aim was to characterize the structural properties of Restorelle and UltraPro subjected to uniaxial tension along perpendicular directions, and then model the tensile behavior of these meshes utilizing a co-rotational finite element model, with an imbedded linear or fiber-recruitment local stress-strain relationship. Both meshes exhibited a highly nonlinear stress-strain behavior; Restorelle had no significant differences between the two perpendicular directions, while UltraPro had a 93% difference in the low (initial) stiffness (p=0.009) between loading directions. Our model predicted that early alignment of the mesh segments in the loading direction and subsequent stretching could explain the observed nonlinear tensile behavior. However, a nonlinear stress-strain response in the stretching regime, that may be inherent to the mesh segment, was required to better capture experimental results. Utilizing a nonlinear fiber recruitment model with two parameters A and B, we observed improved agreement between the simulations and the experimental results. An inverse analysis found A=120 MPa and B=1.75 for Restorelle (RMSE=0.36). This approach yielded A=30 MPa and B=3.5 for UltraPro along one direction (RMSE=0.652), while the perpendicular orientation resulted in A=130 MPa and B=4.75 (RMSE=4.36). From the uniaxial protocol, Restorelle was found to have little variance in structural properties along these two perpendicular directions; however, UltraPro was found to behave anisotropically.
authors.affiliation: Musculoskeletal Research Center, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Feola
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Siladitya
authors.initials: S
authors.lastname: Pal
authors.affiliation: Magee-Womens Research Institute, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Pamela
authors.initials: P
authors.lastname: Moalli
authors.affiliation: Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA.
authors.forename: Spandan
authors.initials: S
authors.lastname: Maiti
authors.affiliation: Musculoskeletal Research Center, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, USA; Magee-Womens Research Institute, University of Pittsburgh, Pittsburgh, PA, USA. Electronic address: sdast9@pitt.edu.
authors.forename: Steven
authors.initials: S
authors.lastname: Abramowitch
mesh_terms: D016880:Anisotropy; D003198:Computer Simulation; D004548:Elasticity; D005260:Female; D020342:Finite Element Analysis; D006801:Humans; D008422:Materials Testing / Q000379:methods*; D011126:Polypropylenes / Q000737:chemistry; D011312:Pressure; D019736:Prostheses and Implants; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013526:Surgical Mesh; D013718:Tensile Strength
chemical_list: D011126:Polypropylenes
keywords: Co-rotational theorem; Finite element model; Prolapse mesh; Structural properties; Uniaxial tension