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

Biodegradable Zn alloy has recently gained attention for use in bone implants considering its 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 Zn alloy. In this study, we designed a photothermally controlled degradative hybrid coating as a 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 consists 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 can effectively reduce its corrosion current density (i_corr) from 2.48 × 10^-5 A·cm^-2 to 2.10 × 10^-8 A·cm^-2. After near-infrared (NIR) light irradiation, ICG@ZIF-8 heated PLGA coating to reach Tg, causing the coating to degrade and the i_corr of the coated ZL alloy decreased to 2.50 × 10^-7 A·cm^-2, thus restoring corrosion advantage. Both in vitro and in vivo investigations showed that the coated ZL alloy had acceptable biocompatibility. Overall, the developed photothermally controlled coating improved the Zn alloy's resistance to corrosion and allowed for the adjustment of the Zn alloy's degradation rate through 808-nm NIR light irradiation.