Environment-dependent degradation pathways of pure zinc induced by acid-alkali surface chemistry

Pure zinc (Zn) is a promising candidate for biodegradable metallic implants; however, its degradation behaviour in physiological environments is highly sensitive to interfacial chemistry, often resulting in non-uniform and environment-dependent corrosion responses that complicate controlled tissue regeneration. This study introduces a simple two-step chemical modification, consisting of acid etching followed by alkaline treatment, to tailor the early-stage degradation behaviour of pure Zn. The degradation behaviour of untreated and treated Zn was systematically evaluated in Hanks' balanced salt (HBSS), 0.85 wt% NaCl and 10 mM Tris-HCl solutions at 37 °C. Electrochemical measurements, immersion tests and surface characterisation studies were conducted. The results show that the combined acid-alkali treatment did not merely accelerate degradation, but altered the dominant degradation pathways in a strongly media-dependent manner. In HBSS, chemically treated Zn promoted the formation of Ca/P-rich surface layers, which was associated with more moderate and spatially homogeneous degradation behaviour, whereas chloride- and buffer-dominated environments favoured film destabilisation or enhanced dissolution. These findings demonstrate that surface chemistry can be used to control environment-specific degradation pathways of pure Zn without alloying, providing a new design strategy for biodegradable Zn-based implants.