Photothermal Coating on Zinc Alloy for Controlled Biodegradation and Improved Osseointegration

Zinc (Zn) and its alloys are promising biomaterials for orthopedic applications due to their degradability and mechanical properties. Zn²⁺ plays a crucial role in bone formation, but excessive early release may cause cytotoxicity and inhibit osseointegration. To solve this, we developed a near-infrared (NIR) light-controlled polycaprolactone/copper-sulfur (PCL/CuS) coating that slows degradation and enhances osseointegration of Zn alloys. The zinc-lithium (Zn-Li) substrate is encapsulated with PCL, reducing Zn²⁺ release and maintaing biocompatibility. Controlled Zn²⁺ release and mild photothermal therapy via CuS nanoparticles promoted osteogenesis. In vitro studies demonstrated enhanced cell proliferation and osteogenic differentiation. In vivo Micro-Computed Tomography (Micro-CT), Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), and immunohistochemical analyses confirmed improved osseointegration. Mechanistic studies using RNA sequencing and Western blotting revealed that the coating promotes osteogenesis by activating the Wnt/β-catenin and inhibiting NF-κB pathways. This NIR light-controlled PCL/CuS coating successfully regulates Zn alloy degradation, enhances osseointegration via controlled Zn²⁺ release and mild photothermal therapy effct, presenting a promising avenue for orthopedic biomaterials.