Effects of Reactive Oxygen Species on the Physical Properties of Polypropylene Surgical Mesh at Various Concentrations: a Model for Inflammatory Reaction as a Cause for Mesh Embrittlement and Failure

Jean Kurtz, BS1, Ben Rael2, Jesus Lerma2, Tariq Khraishi, PhD2, Timothy Perez, MD3, Edward Auyang, MD3. 1University of New Mexico School of Medicine, 2University of New Mexico Department of Mechanical Engineering, 3University of New Mexico Department of General Surgery

Hypothesis:

Surgical meshes made from modified polypropylene (PP) are used in a variety of procedures. Polypropylene mesh undergoes structural changes in the human body that alter its physical properties and contribute to post-operative complications. Oxidative degradation by reactive oxygen species (ROS) from the human inflammatory process may initiate cross-linking, depolymerization, and formation of a more quasi-crystallline quality. Stress cracking and fiber changes cause PP meshes to lose structural integrity and embrittle. Measurement of embrittlement in vivo is extremely difficult. In order to investigate the relationship between ROS and embrittlement, a basic laboratory environment was constructed in which PP mesh samples were exposed to various concentrations of ROS. Human inflammatory factors vary from individual to individual, and mesh failure has been associated with health, age, and disease state. For this reason, concentration of ROS was expected to be positively correlated to measured effect, and changes were anticipated at low, physiological concentrations.

Methods:

Medical-grade surgical mesh, Ethicon Ultrapro©, samples were prepared in dog-bone shapes and soaked in hydrogen peroxide solutions with concentration of 1M, 0.1 M, or 1 mM for 6 months. Tensile strength and elongation to failure were determined for 5-7 samples at each concentration using load displacement tensile testing (LDTT) and were compared to samples that remained unexposed to hydrogen peroxide (0 M). Observational alterations in fiber structure were explored using scanning electron microscopy (SEM).

Results:

LDTT yielded results for tensile strength and elongation to failure that were determined with 95% confidence interval (CI). For samples exposed to 0 M, tensile strength was 28.0 ± 2.4 lbs and elongation to failure was 2.0 ± 0.3 in. For samples exposed to 1 mM, tensile strength was 19.2 ± 1.1 lbs and the elongation to failure was 2.0 ± 0.1 in. For samples exposed to 0.1 M, tensile strength was 19.3 ± 1.6 lbs and elongation to failure was 1.9 ± 0.1 in. For samples exposed to 1 M, tensile strength was 20.7 ± 1.2 lbs and elongation to failure was 0.47 ± 0.02 in.

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SEM images of mesh exposed to ROS had fracture surfaces that appear similar to brittle materials. Pulled ends of 0 M mesh demonstrate blunted surfaces typical of non-rigid materials whereas pulled ends of 1 M mesh demonstrate a rough fracture surface typical of rigid materials.

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Conclusion:

The results demonstrated that small concentrations of ROS (1 mM) can decrease tensile strength by 31%. Concentrations on this order have been known to occur physiologically in humans. Results for samples exposed in 1 mM and 0.1 M solutions behaved similarly and yielded similar tensile strength at failure suggesting that the concentration of ROS does not correlate in a linear fashion to changes in physical property. Exposure to ROS and affect on tensile strength is not well correlated to concentration of the ROS. The samples exposed to 1 M environments were particularly rigid as demonstrated by LDTT and SEM imaging.

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