Electromagnetic Valves for Cerebrospinal Fluid Bypass: Corrosion Evaluation of Magnets Embedded in Epoxy Resins

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 LCS. 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, Pt and Fe) and toxicity in LCS. The study focuses on the nature of coating resins, by several techniques. Electrochemical measurements using rotating electrode technology, and by impedance (EIE), through Nielsen-Tuccillo tests and release kinetic tests on encapsulated magnets. Three resins were evaluated: Stycast 1266, Stycast 1267 and Loctite Medical Device Adhesives. The encapsulated magnets are of CoSmCo 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 sweeping polarisation curves into the domain of 10-7 – 10-12 A/cm2 Degradations by corrosion phenomena on the surfaces of magnets were found in the case of 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 series Stycast 1267 releases cobalt mainly in the first 60 days, then we note un niveau qui est établi à environ 0,8 µg /l. The Loctite series a level of about 0.15 µg/l is observed for 60 days, then cobalt release increases to 1.2 µg/l after 90 days. The Stycast 1267 series 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 long-term reliability and biocompatibility in their functional environment.