Photothermal-controlled ICG@ZIF-8/PLGA coating to modify the degradation behavior and biocompatibility of Zn-Li alloy for bone implants

Biodegradable Zn alloy have recently gained considerable attention for use in bone implants considering their biodegradability, attractive mechanical properties, and bioactivity. However, excessive corrosion of Zn alloy at the early stage of implantation may cause severe cytotoxicity, resulting in insufficient osseointegration, which hinders the clinical use of the Zn alloy. In this study, we designed a photothermal-controlled degradative hybrid coating as corrosion-protective barrier with the intention of preventing Zn ion burst release during the early stages of implantation and regaining the alloy's corrosion advantage later on. The coating consisting of Zeolite imidazole skeleton-encapsulated indocyanine green core-shell structured nanoparticles and polylactic coglycolic acid (ICG@ZIF-8/PLGA) on pristine Zn-0.8 (wt.%) Li (ZL) alloy. The electrochemical test results indicated that coating ZL with ICG@ZIF-8/PLGA might effectively reduce its corrosion current density (icorr) from 2.48 × 1 0 −5 A•cm−2 to 2.10 × 1 0 −8 A•cm−2. After near-infrared light irradiation, ICG@ZIF-8 heated PLGA coating to reach Tg, so that the coating was degrading, and the icorr of coated ZL alloy decreased to 2.50 × 1 0 −7 A•cm−2, thus restoring corrosion advantage. Both in vitro and in vivo investigations showed that coated ZL alloy had acceptable biocompatibility. Overall, the development of the photothermally controlled coating improved the Zn alloy's resistance to corrosion and allowed for the adjustment of the coated ZL alloy's rate of degradation through the use of 808 nm NIR laser irradiation.