Rare‐Earth Doped Hydroxyapatite Nanoparticles for Biomedical Applications: A Comprehensive Review From Bone Regeneration to Cancer Theranostics

Rare-earth element (REE)-doped hydroxyapatite nanoparticles (HAp-NPs) have emerged as multifunctional bioceramics with significant potential across diverse biomedical fields, owing to their excellent biocompatibility, bioactivity, and tunable physicochemical properties. Recent advances in the doping of HAp-NPs with lanthanide ions have expanded their functionality, enabling innovative applications in bone tissue engineering, targeted drug delivery, cancer therapy, dentistry, and biomedical imaging. This review provides a comprehensive assessment of the synthesis strategies and surface modification techniques, utilizing both natural and synthetic precursors, for REE-doped HAp-NPs. Particular attention is given to the role of individual REE dopants (e.g., La³⁺, Ce³⁺, Pr³⁺, Eu³⁺, Gd³⁺, Er³⁺, Sm³⁺, Nd³⁺, Dy³⁺, Tb³⁺, Yb³⁺, and Y³⁺) in modulating the luminescent, antibacterial, osteoconductive, and drug-delivery properties of HAp-NPs. Furthermore, the theranostic potential of these nanomaterials is examined, emphasizing their low cytotoxicity, high loading capacity, efficient cellular uptake, and advanced imaging capabilities. Collectively, REE-doped HAp-NPs represent a versatile and promising platform for the development of next-generation nanomedicines, with broad implications for precision therapy and regenerative medicine.