In Vitro Corrosion Assessment of the Essure? Medical Device in Saline, Simulated Inflammatory Solution and Neutral Buffered Formalin

The Essure (R) permanent contraceptive implant, comprised of four alloys (nickel-titanium, 316L stainless steel, platinum-iridium, and tin-silver solder) and Dacron (PET) fibers, has been approved for use in the US for about two decades. However, little has been published on this implant's biomaterials performance, and as this implant gains interest in terms of in vivo performance, methods of implant post-retrieval storage also need to be assessed. This study investigated the electrochemical properties and ion release profile of Essure (R) during storage in phosphate buffered saline (PBS), 10 mM H 2 O 2 /PBS, a simulated inflammatory solution, and 10% neutral buffered formalin (NBF) to investigate the corrosion behavior and metal ion release. First, a galvanic test method was used to measure the galvanic interactions between alloys within the device. Second, an ion-release study over 107 days was performed. Ions were measured using inductively-coupled plasma mass spectrometry and the implants were assessed using digital optical microscopy, scanning electron microscopy, and energy dispersive x-ray spectrometry. The tin-silver (SnAg) solder continuously corroded in PBS and H 2 O 2 /PBS. In the presence of H 2 O 2 , nickel and titanium ions were released from the nickel-titanium (NiTi) coil, whereas release of these ions was minimal in PBS alone. Overall, corrosion of the SnAg solder, which holds the NiTi and 316L SS together, was significant in both PBS and H 2 O 2 /PBS and may result in loss of connection of the NiTi and 316L stainless steel portions of the implant. Storage in NBF exhibited very low corrosion rates for all alloys and low levels of ion release were observed indicating that formalin storage minimally affects the implant's corrosion status. Statement of significance The Essure (R) device is an FDA premarket-approved female permanent sterilization device containing four different metal alloys and poly(ethylene terephthalate) polymer fibers. Significant concerns related to this device have been raised by the FDA since its introduction in 2002. This study is the first published in vitro work to specifically assess the corrosion mechanisms in this multi-alloy device and the role of dif-ferent solution environments, including formalin storage, inorganic physiological saline and a simulated inflammatory condition. Significant evidence of corrosion of the tin-silver solder is documented, the re-lease of Ni and Ti under simulated inflammatory conditions, and the relative inertness of storage of these implants in neutral buffered saline is presented. The tin-silver corrosion corroborates recent clinical evi-dence of tin corrosion products in tissues adjacent to these devices in vivo.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

This study investigated the corrosion behavior and metal ion release of the Essure (R) permanent contraceptive implant during storage in different solutions. The results showed that the tin-silver solder corroded continuously in phosphate buffered saline and hydrogen peroxide solution, while the corrosion was minimal in formalin storage. This study provides important insights into the long-term performance and safety of the Essure (R) implant.