Post-implantation alterations of polypropylene in the human.

PURPOSE: We reviewed the mechanisms by which polypropylene mesh changes after implantation in the human body.
MATERIALS AND METHODS: The existing polymer and medical literature was reviewed regarding polypropylene, including its chemical characteristics, and compositional and physical properties, which undergo alteration after implantation at various human body locations. We also reviewed the changes in those physical properties that were demonstrable in explanted specimens.
RESULTS: Polypropylene in mesh form is commonly considered inert and without adverse reactions after implantation in humans. The literature suggests otherwise with reports of various degrees of degradation, including depolymerization, cross-linking, oxidative degradation by free radicals, additive leaching, hydrolysis, stress cracking and mesh shrinkage along with infection, chronic inflammation and the stimulation of sclerosis. Many substances added to polypropylene for various purposes during manufacture behave as toxic substances that are released during the degradation process. The material may also absorb various substances. These alterations in the chemical structure of polypropylene are responsible for visibly demonstrable fiber changes, resulting in the loss of structural integrity through material embrittlement. The heat of manufacturing polypropylene fibers begins the degradation process, which is augmented by the post-production heat used to flatten the mesh to prevent curling and attach anchoring appendages.
CONCLUSION: Based on available evidence the polypropylene used for surgical treatment of various structural defects is not inert after implantation in the human body. The quest for the perfect mesh must continue.