Infection-Resistant Alloys for Implants

Implant-associated infection remains one of the leading causes of failure in orthopaedics, imposing substantial clinical and economic burdens despite advances in surgical techniques and antibiotic therapy. Conventional infection management strategies, including systemic antibiotics, local drug delivery, surface coatings, and physical surface modifications, primarily provide short-term protection. These approaches fail to deliver sustained antibacterial performance over the long service life expected for load-bearing implants. This review critically evaluates existing antibacterial strategies, highlighting their mechanisms, advantages, and translational limitations. Particular emphasis is placed on the fundamental shortcomings of surface-based approaches and external stimulus-responsive systems in long-term clinical scenarios. Building on these insights, the emerging paradigm of bulk antibacterial alloy design for infection-resistant implants is discussed. Copper, silver, and zinc are widely accepted antibacterial elements; however, they cannot be used as standalone bulk materials because they do not independently meet the mechanical, corrosion, and biocompatibility requirements of metallic implants. Among them, silver is limited by elution-driven activity and cytotoxicity concerns, zinc exhibits relatively weaker antibacterial efficacy, while copper offers a favorable balance of antibacterial performance, alloyability, and structural compatibility. Copper-, silver-, and zinc-containing alloy systems are systematically examined with respect to antibacterial efficacy, cytocompatibility, corrosion behavior, and mechanical integrity. Copper-added alloys, which offer broad-spectrum antibacterial activity through contact killing and controlled ion release while preserving structural performance when appropriately alloyed, are extensively discussed. Finally, future directions are outlined, including biodegradable antibacterial metals, multi-functional alloy design, and data-driven alloy optimisation strategies, providing a roadmap toward clinically viable, long-term infection-resistant implant materials.