Development of Magnesium Alloy Stents with Layered Double Hydroxide Coating for Improved Corrosion Resistance and Biochemical Stability in AVF Applications

Background: Autologous arteriovenous fistula (AVF) is the most commonly used vascular access for end-stage renal disease patients. However, during the maturation process following AVF surgery, insufficient initial venous diameter often results in inadequate blood flow, leading to fistula maturation failure. Studies have indicated that implanting stents can enlarge the initial venous diameter and improve the success rate of AVF surgeries. However, stents made from metallic materials remain permanently in the body after implantation, posing risks such as in-stent restenosis. Methods: Our development and testing of magnesium alloy stents with a layered double hydroxide (LDH) coating to assist AVF maturation is presented in this paper. Firstly, AZ31 alloy was used as a benchmark to screen coating technologies, including anodizing, alkaline films, and LDH coatings. ZM21 tubes were then utilized to verify the transferability of optimized parameters across different substrates. Finally, the optimized coating was applied to ZM21 stents, followed by validation through in vitro degradation tests and biochemical simulations. Results: The results showed that LDH-coated AZ31 samples exhibited a 95% reduction in average corrosion rate compared to untreated samples. Additionally, the anion exchange property of the LDH layer effectively reduced the pH of the saline solution. Subsequently, LDH coatings were applied to ZM21 magnesium alloy stents, followed by in vitro degradation and biochemical simulation. Compared to untreated ZM21 stents, LDH-coated stents demonstrated a 94.9% reduction in average corrosion rate and significantly reduced the generation of soluble magnesium chloride, maintaining the solution pH below 8.0 and the Mg2+ concentration below 300 μg/mL. Conclusions: The results show LDH is the most effective corrosion-resistant coating and can control the degradation rate of magnesium alloy stents to enhance their support duration and biocompatibility.