Harnessing Hydrothermal Treatments to Control Magnesium Alloy Degradation for Bioresorbable Implants: A Comprehensive Evaluation of Bath Chemistry Effect

Magnesium alloys have been recently recognized as promising materials for temporary orthopedic applications, thanks to their biocompatibility, nontoxicity and biodegradability, combined with bone-like mechanical properties; nevertheless, their clinical viability is still hindered by their excessively rapid corrosion in physiological environments. In this context, hydrothermal surface modification offers a simple and inexpensive option to form thick ceramic conversion films capable of protecting magnesium and delaying the initial stages of corrosion. In this study, magnesium samples were hydrothermally treated in various aqueous baths to systematically assess the influence of their chemistry on the resulting coating features. The obtained coatings were characterized in terms of physicochemical properties, electrochemical corrosion behavior in SBF, and long-term degradation with volumetric loss quantification by µ-CT. The results highlighted how corrosion resistance is dictated by coating uniformity rather than thickness. Moreover, XRD analyses revealed that all the best-performing coatings contained a stable magnesium oxide phase in addition to magnesium hydroxide, a feature absent in less protective films. A simple sodium nitrate solution was found to produce the most protective layer, showing the lowest volumetric losses after immersion testing.