Droplet-confined anodization for defect-directed oxide repair: A review and perspective on mechanistic foundations, technological platforms, feasibility, and validation roadmap

Oxide layers are critical functional interfaces that determine the corrosion resistance, dielectric reliability, optical response, electronic behavior, catalytic activity, wear resistance, and biocompatibility of modern materials and devices. Even localized defects on oxide layers can accelerate degradation, disrupt functionality, and shorten its lifetime. Restoring damaged oxide regions is therefore important for maintaining structural integrity, recovering application-specific performance, and preventing progressive failure. In this review, we critically examine droplet-scale anodization as an emerging approach for the site-selective regeneration of damaged oxide films. By confining the electrolyte and electric field within micro- to millimeter-scale droplets, this method may enable oxide regrowth directly at defective regions while minimizing chemical consumption and limiting changes to surrounding intact surfaces. The review discusses the principal mechanisms that may contribute to localized healing, including field-assisted ionic migration, defect passivation, pore filling, oxide regrowth, and self-limiting growth. Material-specific opportunities and limitations are evaluated for aluminum, titanium, stainless steel, magnesium, and selected functional oxides. Current technological platforms, including open sessile droplets, scanning droplet cells, solution-flow microdroplet cells, electrolyte jets, and scanning-probe systems, are also assessed in terms of their potential for localized oxide repair. Although these systems have been widely investigated for oxide formation, patterning, and surface modification, direct demonstrations of functional oxide healing remain scarce. Major research gaps therefore persist in experimental validation, mechanistic understanding, process reproducibility, standardized recovery metrics, and long-term durability. A staged research roadmap is proposed to advance droplet-scale anodization from localized oxide fabrication toward reliable and experimentally validated oxide-layer repair systems.