Evolution of 3D-Printed Microneedles toward Closed-Loop Theranostic Platforms

Advancements in biomedical interfaces increasingly demand technologies that can seamlessly bridge the gap between biological tissues and therapeutic systems. Microneedle (MN) technology has emerged as a minimally invasive platform for transdermal drug delivery (TDD) and biosensing, offering tunable geometries, efficient skin penetration, and reduced patient discomfort. However, the inherent limitations of conventional microfabrication techniques in terms of structural complexity, multi-material compatibility, and functional modularization have markedly constrained the development of next-generation biomedical systems. In recent years, 3-dimensional (3D) printing has positioned itself as a highly promising additive manufacturing (AM) technology, offering exceptional design freedom and high-resolution fabrication capabilities for the development of MN platforms with embedded microchannels and integrated multifunctionality. Herein, a comprehensive analysis of recent progress in 3D-printed MNs is provided, with emphasis placed on advances in architectural innovations, intelligent system integration, and their expanding applications in personalized drug delivery and intelligent theranostic platforms. Furthermore, an in-depth examination of the core challenges hindering the clinical translation of 3D-printed MNs, particularly regarding manufacturing processes, material selection, and standardization requirements, is presented, offering a forward-looking perspective on the paradigm shift of MNs from passive delivery terminals to active, closed-loop health platforms.