Polydopamine-modified metal-organic frameworks nanoparticles enhance the corrosion resistance and bioactivity of polycaprolactone coating on high-purity magnesium

Biodegradable magnesium (Mg) and its alloys exhibit excellent biocompatibility and mechanical compatibility, demonstrating tremendous potential for applications in orthopedics. However, the rapid degradation rate has limited their clinical application. Polycaprolactone (PCL) is commonly employed as a polymer coating to impede the rapid degradation of Mg. Unfortunately, its long-term anti-corrosion capability and bioactivity are inadequate. To address these issues, polydopamine (PDA)-modified zeolitic imidazolate framework-8 (PZIF-8) bioactive nanoparticles are fabricated and incorporated into the PCL coating. The PZIF-8 particles, featuring catechol motifs, can enhance the compactness of the PCL coating, reduce its defects, and possess biomineralization ability, thereby effectively improving its anti-corrosive and bioactive properties. Moreover, the active substances released from the degradation of the PZIF-8 particles such as Zn2+ and PDA are beneficial for osteogenesis. The corrosion tests indicate that the corrosion current density of PCL-treated sample decreases by more than one order of magnitude and the amount of H2 released decreases from 0.23 ± 0.12 to 0.08 ± 0.08 ml cm−2 after doping with the PZIF-8. Furthermore, the improved corrosion resistance and released PDA and Zn2+ from the coating can promote osteogenic differentiation by up-regulating the expression of alkaline phosphatase activity, related osteogenic genes, and proteins. In addition, in vivo implantation experiments in rabbit femur defects further offer strong evidence that the doping of PZIF-8 nanoparticles accelerates bone reconstruction of the PCL coating. In summary, this work implies a new strategy to fabricate a PCL-based coating on Mg-based implants by introducing the PZIF-8 particles for orthopedic applications.