Ordered micro-nano structures: synergistic integration of microneedles and photonic crystals for advanced biomedical...

Ordered micro-nano-superstructures are hierarchical assemblies composed of micro- and nanoscale building blocks that integrate multiple functions, in which individual components retain their intrinsic structural features while collectively generating emergent properties that cannot be achieved by single-scale structures alone. For example, the combination of microneedles and photonic crystals forms a superstructure in which the microscale needles provide mechanical penetration and biochemical sampling, while the nanoscale photonic crystals enable optical signal transduction, resulting in a unified system with synergistic capabilities. Microneedles (MNs) and photonic crystals (PCs) have attracted considerable attention for their applications in transdermal drug delivery and optical sensing, respectively. However, despite significant advancements, the field remains fragmented, with much of the research focused on isolated systems, often overlooking the complex relationships between structure, material properties, fabrication methods, and functional outcomes. Integrating these systems into multifunctional platforms remains challenging due to material compatibility, fabrication complexity, and functional tuning requirements. This review summarizes recent advances in ordered micro-nano-structured systems, focusing on MNs and PCs, and discusses their functions, biomedical applications, and prospects for hybridization.