Retardation and self-repair of erosion pits by a two-stage barrier on bioactive-glass/layered double hydroxide coating of biomedical magnesium alloys

• Published in: Surface & coatings technology 2021-01, Vol.405, p.126562, Article 126562
• Main Authors: Ouyang, Jianglin, Hong, Xiaozhe, Gao, Yan
• Format: Article
• Language: English
• Subjects: Biological activity; Calcium ions; Containers; Corrosion currents; Corrosion potential; Corrosion prevention; Corrosion tests; Degradation; Degradation retarding; Drug delivery systems; Electrochemical corrosion; Fluorapatite; Fluorides; Hydroxides; Ingestion; Ion exchange; LDH-container layer; Magnesium alloy; Magnesium alloys; Magnesium base alloys; Magnesium fluorides; Mineralization; Orthopedics; Pits; Protective coatings; Self-repairing; Sol-gel processes; Spin coating
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126562

Magnesium alloys for orthopedic applications are mainly restricted by their rapid degradation and undesirable surface mineralization. A hierarchical layered double hydroxide (LDH)/bioactive-glass (Bg) coating was constructed via in-situ hydrothermal growth to obtain LDH-container layer on magnesium alloys, and then a sol-gel spin-coating method to cover an outer bioactive-glass layer. The ion-exchange capacity of LDH-container layer was studied by stimuli-triggered release experiment. The results show that alkaline environment is conducive to the ingestion of aggressive chlorides accompanied fluoride-releasing, and this ion-exchange process reached equilibrium after 40 h. Electrochemical corrosion tests manifested that the LDH-container layer delayed the corrosion onset, declined the corrosion current by two orders of magnitude and positively shifted the corrosion potential of 1.15 V. Furthermore, corrosion degradation and mineralization evolution in vitro revealed that a well-defined self-repairing effect and collaborative mineralization were obtained when the LDH-container pre-encapsulated with fluoride and coupled with bioactive-glass. Specifically, the self-repairing was achieved by a local re-deposition of the degradation products Mg2+ and dissolved Ca2+ with the displaced F− to form stable magnesium fluoride or fluorapatite in the erosion pits. This intelligent two-stage strategy, based on physical protective barrier and self-repairing the eroded pits by re-depositing of bone-like minerals, progressively retarded rapid degradation and simultaneously facilitated remineralization. The strategy described herein provides a versatile route for designing smart corrosion protection coatings or targeting drug delivery systems. Schematic representation of a two-stage barrier strategy to retard magnesium alloy degradation. For this intelligent anti-erosion strategy, both corrosion degradation and biomineralization are taken into account: harmful corrosive aggressor are replaced by beneficial corrosion inhibitors, and unfavorable degradation products are converted into beneficial bone-like minerals. A hierarchical layered double hydroxide (LDH)/bioactive-glass (Bg) coating was constructed as a physical protective barrier and self-repairing coating, in which the LDH-container layer acted as a corrosive aggressor barrier/‘transfer station’ for inhibitors and the bioactive-glass layer assisted displaced inhibitors to repair the erosion pits. Firstly, the LDH-conta