Antioxidant and antibacterial properties of transition metals and metal oxides for medical uses: mechanisms, design strategies, and biomedical perspectives

This review provides a critical and integrative analysis of transition metal and metal oxide NPs as emerging multifunctional platforms for biomedical applications, with particular emphasis on their dual antioxidant and antibacterial properties. Beyond conventional descriptive approaches, we systematically correlate physicochemical parameters, including particle size, morphology, surface charge, crystallinity, and functionalization, with biological performance, thereby establishing clear structure-activity relationships governing therapeutic efficacy and biosafety. Key transition metals such as Ag, Cu, Se, Ti, Zn, and Fe, along with their oxides, are examined in terms of their mechanistic pathways, including reactive oxygen species (ROS) modulation, metal ion release, membrane disruption, and enzyme-mimetic antioxidant activity. Recent advances in synthesis strategies, particularly green and bioinspired methods, are highlighted as enabling routes for improving biocompatibility, stability, and targeted functionality. Importantly, this review critically discusses the dual role of ROS in mediating both antibacterial action and oxidative stress regulation, offering a unified framework for designing balanced nano-therapeutics. Comparative analyses reveal that materials with strong antibacterial activity often exhibit weaker intrinsic antioxidant capacity, underscoring the need for rational design of hybrid or multifunctional nanoplatforms. Furthermore, key challenges related to cytotoxicity, long-term biosafety, microbial resistance, and clinical translation are comprehensively evaluated. Strategies such as surface engineering, controlled ion release, and synergistic combinations with conventional antibiotics are proposed to overcome these limitations. By bridging fundamental mechanisms with applied biomedical perspectives, this review provides actionable insights for the next generation of safe, effective, and clinically translatable metal-based nanomaterials.