• Metallic microneedles (MMNs) offer superior mechanical properties, machinability, and biocompatibility compared to silicon, polymer, and ceramic counterparts, enabling painless and efficient skin penetration.
• MMNs are classified by structure (in-plane/out-of-plane) and internal/surface design (solid, hollow, coated, porous), each tailored for specific applications.
• Fabrication technologies for MMNs include cutting tool machining, non-traditional machining, etching, hot-forming, and additive manufacturing, each with distinct advantages and limitations.
• MMNs show significant promise in drug delivery, disease diagnosis, and cosmetology, but challenges remain in fabrication scalability, cost, and long-term safety, guiding future research directions.