In situ synthesis of a zeolitic imidazolate framework coating on a Mg surface for pH-sensitive drug release

Mg alloys have become a new generation of biodegradable medical materials due to their good biocompatibility. However, their rapid corrosion rate in physiological environments and the mismatch between their degradation rate and tissue reconstruction pose challenges for clinical applications. To improve the corrosion resistance and biocompatibility of Mg alloys, drug-loaded corrosion resistant coating has gradually become a research hotspot. In this work, a uniform pH-responsive ZIF-14 coating was in situ synthesized on the surface of Mg alloy via a solvothermal method. Using rapamycin, an anti-restenosis drug, as a model compound, the drug release behavior and biocompatibility of the rapamycin-loaded ZIF-14 coating were evaluated under different pH conditions. ZIF-14 coating exhibited rapid drug release under both acidic and alkaline conditions. The rapamycin-loaded ZIF-14 coating effectively inhibited the excessive proliferation of smooth muscle cells, thereby preventing vascular restenosis after device implantation. Notably, theoretical calculations and experimental characterizations revealed that Zn²⁺ ions in ZIF-14 precursor solution can coordinate with both imidazole ligands and Mg from the substrate, leading to the formation of a stable ZIF precursor on Mg surface. In addition, ZIF-14 coating enhanced the corrosion resistance of Mg alloy, effectively prolonging its service life. This work provides a new strategy for the design of multifunctional smart coatings on Mg alloy surfaces and shows great potential for applications in biomedical Mg alloy implants. STATEMENT OF SIGNIFICANCE: This study presents a significant advancement in addressing the limitations of biodegradable Mg alloy stents by developing a uniform, and pH-responsive ZIF-14 coating via one-step in situ solvothermal synthesis. Integrating DFT calculations with experimental validation, this research elucidates the intricate coordination mechanism among Zn²⁺, imidazole ligands, and Mg, offering fundamental insights into MOFs growth on reactive metal surfaces. This coating exhibits dual-trigger pH-responsive drug release, accelerating drug release under both acidic (local inflammation) and alkaline (Mg corrosion) conditions, thus providing a smart solution for localized therapeutic intervention. Furthermore, this nanostructured coating enhances the corrosion resistance and biocompatibility of Mg alloy. This work proposes a strategy for designing multifunctional smart coatings on biodegradable implants, holding potential for biodegradable implants.