Evaluation of the corrosion of magnets in hydrocephalus shunt valve coated in epoxy resin

Abstract Hydrocephalus remains a complex neurosurgical pathology requiring permanent cerebrospinal fluid (CSF) shunting. This work explores the characteristics of polymer resins, intended to isolate and stabilize the micromagnets of the pressure and flow adjustment mechanism. The polymeric disc containing the micromagnets play a critical role in the functional stability and safety of programmable valves with magnetic mechanism: any failure of the coating can lead to corrosion phenomena and ion diffusion in the CSF. It has a diameter of 5.5 mm and on it are positioned 10 magnets with a diameter of 2 mm. However, corrosion phenomena and electrochemical interactions between the magnets and LCS represent a potential risk of ion release (Co, Sm, Nd, B) and toxicity in CFS. The study focuses on the nature of coating resins, by several techniques electrochemical using rotating electrode, by impedance (EIE), Nielsen-Tuccillo tests and cations release on encapsulated magnets. Three resins were evaluated: Stycast 1266, Stycast 1267 and Loctite( M D A). The encapsulated magnets are of CoSm and CoNd Fe B nature. All tests reveal an ion exchange permeability between electrolyte NaCl 9 g/l is the coated magnets after three days of immersion. All three resins shift the polarisation curves into the domain of 10 – 10 A/cm Degradations by corrosion phenomena on the surfaces of magnets were found in the Stycast 1266 by the Nielsen-Tuccillo test after 30 days of immersion. The extraction kinetic tests were carried out for 30, 60 and 90 days. The Stycast 1267 releases cobalt mainly in the first 60 days, at approximately 0.8 µg/l. The Loctite series a level of about 0.15 µ/l is observed for 60 days, then cobalt release increases to 1.2 µg/l after 90 days. The Stycast 1267 releases Nyodymium up to a concentration that could reach 0.6 µg.l/1. The release of Nyodymium from the Loctite series is at the detection limit < 0.2 6 g/l after 90 days. Future generations of valves, integrating electronic sensors and wireless telemetry, will have to take these constraints into account to ensure their long-term reliability and biocompatibility.