Hollow microneedles as a flexible dosing control solution for transdermal drug delivery.

Microneedles, small needle-like structures typically less than 1000 μm in length, are effective tools for transporting substances across biological barriers via minimally invasive pathways. Various microelectromechanical system (MEMS) processes enable the production of different types of microneedles, including solid, coated, dissolving, hydrogel, and hollow microneedles, each tailored to specific drug and fluid delivery mechanisms. Among these, hollow microneedles stand out for their ability to offer flexible dosage control adaptable to varying drug formulations, making them particularly promising for transdermal drug delivery systems. This review examines the fabrication processes of hollow microneedles, highlights the advantages of their hollow structure for medical applications, and discusses the key factors influencing their performance. Finally, it proposes directions for advancing these technologies in both industrial and research settings.