A novel characterisation approach to reveal the mechano-chemical effects of oxidation and dynamic distension on polypropylene surgical mesh

Abstract

Polypropylene (PP) surgical mesh, used successfully for the surgical repair of abdominal hernias, is associated with serious clinical complications when used in the pelvic floor for repair of stress urinary incontinence or support of pelvic organ prolapse. While manufacturers claim that the material is inert and non-degradable, there is a growing body of evidence that asserts PP fibres are subject to oxidative damage and indeed explanted material from patients suffering with clinical complications has shown some evidence of fibre cracking and oxidation. It has been proposed that a pathological cellular response to the surgical mesh contributes to the medical complications; however, the mechanisms that trigger the specific host response against the material are not well understood. Specifically, this study was constructed to investigate the mechano-chemical effects of oxidation and dynamic distension on polypropylene surgical mesh. To do this we used a novel advanced spectroscopical characterisation technique, secondary electron hyperspectral imaging (SEHI), which is based on the collection of secondary electron emission spectra in a scanning electron microscope (SEM) to reveal mechanical-chemical reactions within PP meshes.

Fig. 1. Annotated images of the experimental set up of the TC-3 load bioreactor (Ebers Medical Technology SL, Zaragoza, Spain).

Fig. 2. Stress–strain curves of Gynemesh (top) and Restorelle (bottom) after; (left) 5%, 25% and 50% dynamic distention for 6 hours; (middle) 25% dynamic distention in dH₂O or H₂O₂ for 3 days; and (right) 14 days incubation at 60 °C within dH₂O or H₂O₂; all in comparison to that of the control material.

Fig. 3. Young's modulus of Gynemesh (left) and Restorelle (right) after; 5%, 25% and 50% dynamic distention for 6 hours, 25% dynamic distention within dH₂O or H₂O₂ for 3 days, and 14 days incubation at 60 °C within dH₂O or H₂O₂ in comparison to that of the control material. Mean ± SD (N = 3).

Fig. 4. Secondary electron spectra for Gynemesh (n = 4) (A), (C) and (E) and Restorelle (n = 4) (B), (D) and (F) after dynamic distention at varying degrees (A) and (B), after treatment combining 25% dynamic distention with H₂O₂ (C) and (D) and after treatment with H₂O₂ alone (E) and (F).

Fig. 5. SEHI images generated from automated SEHI colouring of cross sectioned Gynemesh after 25% mechanical distention with 3% H₂O₂ treatment (A) and (B) and Gynemesh – no treatment (C) and (D). Red regions symbolise high molecular order, green regions symbolize CH_x, and blue region indicate (CO, COO, OH) oxidation products.

Fig. 6. (A) Oxidation of Gynemesh samples characterized by means of XPS depth profiling (sputter time in seconds (s)), three levels of oxidation are indicated by step of 5% change, area X indicates potentially higher oxidation of the samples before the analysis, inset: XPS image of C 1s for Gynemesh after 25% mechanical distention with 3% H₂O₂ treatment. (B) SE images of Gynemesh after 25% mechanical distention with 3% H₂O₂ treatment, Gynemesh after 25% mechanical distention and inset SE image of control non treated Gynemesh. (C) SEHI images generated from automated SEHI colouring of Gynemesh after 25% mechanical distention with 3% H₂O₂ treatment. SEHI image shows formation of cracks of the Gynemesh after treatment.

Fig. 7. (A) SEM images of the surface of Gynemesh after 25% mechanical distention with 3% H₂O₂ treatment. Image shows material degradation of the surface of the material. (B) Secondary electron (SE) spectra for Gynemesh after 25% mechanical distention with 3% H₂O₂ treatment, with SE spectra taken from two regions of the surface; red area region showing strong emission in molecular order range (0–1.4 eV) when compared to that of the black area region whose emissions are consistent with the typical surface emissions of the material.

Fig. 8. Schematic of study experimental steps and findings.

Fig. 9. (A) (a)–(e) presents transmission optical micrographs for samples of PP with stretching speed values 0.35, 0.41, 0.45, 0.52 and 0.66 cm s⁻¹, respectively. Reproduced and rescaled from under the Creative Commons Attribution International License (CC BY) http://creativecommons.org/licenses/by/4.0/. (B) Contour map of |k_max| for representative Gynemesh (a)–(c) and Restorelle (d)–(f) samples at 10 N. Boundary conditions (BCs) 1, 2, and 3 are represented by (a) and (d), (b) and (e), and (c) and (f) respectively. Solid black lines represent the direction of k_max. Reprinted from with permission from Elsevier.