Recent Advances in Hafnium Oxide Nanomaterials: From Controlled Synthesis, Structure, and Surface Engineering to Biomedical Applications

ABSTRACT Hafnium oxide (HfO 2 ) nanoparticles (NPs), derived from a rare‐metal element, have gained increasing attention as a versatile class of functional nanostructures with unique optical, dielectric, and surface properties that enable diverse biomedical applications. As a representative rare‐metal oxide, HfO 2 NPs with well‐defined architectures offer advantageous features such as a high atomic number, chemical inertness, tunable morphology, biocompatibility, and exceptional stability for integration with other functional materials. Significant advances have been achieved in controlling crystalline phases, improving scalability, and tailoring optoelectronic and surface characteristics. However, their exploration in biomedical fields remains limited and fragmented. This review discusses the key principles of controlled synthesis, interfacial functionalization, and toxicity evaluation of HfO 2 NPs. Emphasis is placed on their emerging biomedical applications, including bioimaging, radiosensitization, drug delivery, and multimodal theranostic integration. Attention is also given to hybrid systems combining HfO 2 NPs with polymers, metal oxides, metal–organic frameworks, and two‐dimensional nanomaterials, where interfacial synergies underpin enhanced therapeutic efficacy, diagnostic contrast, and safety. Finally, this review concludes with challenges, opportunities, and future directions, proposing strategies to establish reproducible, scalable, and high‐performance rare‐metal oxide platforms for next‐generation biomedical and functional technologies. It aims to provide a comprehensive roadmap linking the synthesis, properties, and applications of HfO 2 nanomaterials, positioning them as a model rare‐metal oxide system to bridge the gap between nanomaterial design and clinical translation in nanomedicine.