Research Papers

Preventing Mesh Pore Collapse by Designing Mesh Pores With Auxetic Geometries: A Comprehensive Evaluation Via Computational Modeling

[+] Author and Article Information
Katrina M. Knight

Department of Bioengineering,
Musculoskeletal Research Center,
University of Pittsburgh,
405 Center for Bioengineering
300 Technology Drive,
Pittsburgh, PA 15219
e-mail: kmk144@pitt.edu

Pamela A. Moalli

Department of Obstetrics and Gynecology and
Reproductive Sciences,
Magee-Womens Research Institute,
Magee Womens Hospital,
University of Pittsburgh,
204 Craft Avenue,
Pittsburgh, PA 15213
e-mail: moalpa@mail.magee.edu

Steven D. Abramowitch

Department of Bioengineering,
Musculoskeletal Research Center,
University of Pittsburgh,
Magee-Womens Research Institute,
Magee-Womens Hospital,
University of Pittsburgh,
309 Center for Bioengineering
300 Technology Drive,
Pittsburgh, PA 15219
e-mail: sdast9@pitt.edu

1Corresponding author.

Manuscript received August 22, 2017; final manuscript received January 8, 2018; published online March 1, 2018. Assoc. Editor: Jeffrey Ruberti.

J Biomech Eng 140(5), 051005 (Mar 01, 2018) (8 pages) Paper No: BIO-17-1379; doi: 10.1115/1.4039058 History: Received August 22, 2017; Revised January 08, 2018

Pelvic organ prolapse (POP) meshes are exposed to predominately tensile loading conditions in vivo that can lead to pore collapse by 70–90%, decreasing overall porosity and providing a plausible mechanism for the contraction/shrinkage of mesh observed following implantation. To prevent pore collapse, we proposed to design synthetic meshes with a macrostructure that results in auxetic behavior, the pores expand laterally, instead of contracting when loaded. Such behavior can be achieved with a range of auxetic structures/geometries. This study utilized finite element analysis (FEA) to assess the behavior of mesh models with eight auxetic pore geometries subjected to uniaxial loading to evaluate their potential to allow for pore expansion while simultaneously providing resistance to tensile loading. Overall, substituting auxetic geometries for standard pore geometries yielded more pore expansion, but often at the expense of increased model elongation, with two of the eight auxetics not able to maintain pore expansion at higher levels of tension. Meshes with stable pore geometries that remain open with loading will afford the ingrowth of host tissue into the pores and improved integration of the mesh. Given the demonstrated ability of auxetic geometries to allow for pore size maintenance (and pore expansion), auxetically designed meshes have the potential to significantly impact surgical outcomes and decrease the likelihood of major mesh-related complications.

Copyright © 2018 by ASME
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Fig. 1

Schematic of a sacrocolpopexy in which the mesh is attached to the anterior and posterior walls of the vagina and fixed to the sacrum. In vivo intra-abdominal pressure exerts a downward force on the pelvic organs. This results in a tensile force along the longitudinal axis of the mesh.

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Fig. 2

Orthographic frontal plain views of three-dimensional auxetic CAD models with eight different auxetic pore geometries. Note the models pictured represent only a portion of the total length of the CAD models utilized in the FEA.

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Fig. 3

Standard CAD models (top images) were created with square, diamond, and hexagon shaped pores, which are commonly used pore shapes for commercial synthetic meshes (bottom images). Note, the outlined shapes (in bold) in the commercial images represent the geometry that was used to create the respective CAD model. Actual images of mesh (bottom images) are 10 mm × 10 mm.

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Fig. 4

Finite element simulation of the square pore model with a Neo-Hookean material (Neo-Hookean, triangle) was able to accurately capture the ex vivo, nonlinear load-elongation behavior of Restorelle uniaxially loaded to 3 N (experimental, diamond)

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Fig. 5

To simulate a uniaxial tensile test, the bottom edge of the models was fixed in translation and rotation, while the top edge was fixed to a rigid body

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Fig. 6

FEA results at 0 N and 3 N for the standard models. The pores of the square model (SQ) remained relatively open, whereas the pores of the diamond (D) and hexagon(a) (Ha) models collapsed resulting in model contraction. RE = relative elongation.

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Fig. 7

FEA results at 0 N and 3 N for the bowtie (B), spiral (S), hexagon(b) (Hb), and square grid (SG) auxetic models. Pore expansion is apparent for all models pictured. RE = relative elongation.

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Fig. 8

FEA results at 0 N and 3 N for the triangle (T), chiral hexagon (CH), square chiral(a) (SCa), and square chiral(b) (SCb) auxetic models. The triangles and circles within these models all contracted. RE = relative elongation.

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Fig. 9

Relative lateral contraction results with increasing tension for both the standard and auxetic models. As anticipated, the relative lateral contraction was positive for the nonauxetic models for all levels of tension. Initially, the relative lateral contraction was negative for all auxetic models. However, at 1.5 N and 2.4 N, the relative lateral contraction was positive (and remained positive) for the triangle and chiral hexagon models, respectively. A positive value indicates model contraction, and a negative value indicates expansion.




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