Functional PEO layers on magnesium alloys: innovative polymer-free drug-eluting stents

In this research, thin layers of magnesium oxide (MgO) were formed on the surface of biodegradable AZ91 magnesium alloys through a plasma electrolytic oxidation (PEO) process. A betamethasone sodium phosphate (BSP) layer was further deposited onto the magnesium oxide coatings through a dip-coating process. The microscopic observations indicated that the pores and the cracks of the PEO coating were sealed by BSP layers. The corrosion resistance and surface reactivity behaviors of the uncoated and coated samples were evaluated by electrochemical tests and immersing in a simulated body fluid solution, respectively. The results showed that the impedance module of the PEO/BSP coating was 300 times higher than the impedance module of the PEO coating, related to the barrier BSP layer formed in the defects and pores of the sealed samples. The proposed design could play an important role in the surface activity and release behavior of polymer-free drug-eluting stents to overcome the inflammation at the site of action.