Intelligent degradation of polymer coating on zinc alloy surface by near-infrared photothermal control

Zinc and its alloys are promising biodegradable metals for bone implants due to their biocompatibility and mechanical properties. However, zinc degradation can release excess zinc ions, causing cytotoxicity and inflammation. Photoresponsive materials, categorized as intelligent materials, possess the capability to convert absorbed light energy into thermal energy. Inspired by photothermal technology, we synthesized Zn-P/PCL@PPy composite coatings by incorporating varying amounts of polypyrrole (PPy) into Zn-5Ag-0.5Mg substrates using spin-coating. The sample morphology and composition were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction. The photothermal properties were assessed using differential scanning calorimetry, ultraviolet–visible spectrophotometry, and infrared thermal imaging. The corrosion resistance of the samples was evaluated through electrochemical impedance spectroscopy and in-vitro immersion tests. Furthermore, the cytocompatibility and antibacterial properties were examined via in-vitro cytotoxicity and bacteriostatic assays. PPy incorporation enhanced the polycaprolactone (PCL) photothermal absorption in the near-infrared (NIR) spectrum and reduced its glass transition temperature. An increased PPy content improved the coating hydrophilicity and corrosion resistance. NIR irradiation caused localized heating, forming microcracks and pores that allowed controlled corrosion ion infiltration and targeted degradation.