3D Printed Hollow Microneedles for Dermal and Transdermal Drug Delivery: Design, Fabrication, Application, and Perspective.

Hollow microneedles (HMNs) offer a transformative solution for topical diagnosis and therapeutic applications due to the unique challenges addressed by their ability to adjust dosing and their integration capabilities in the context of microfluidic and microelectronic devices. To fabricate HMN devices, 3D printing has been introduced as an advanced manufacturing technology in fabricating high-resolution micro- and nanofeatures overcoming the inferior capabilities of traditional manufacturing technologies such as lithography, etching, and laser fabrication in producing sophisticated devices. In this paper, a comprehensive review of recent advancements in the utilization of 3D printing technology for developing HMN devices is provided. The current fabrication technologies are summarized. In addition, design, fabrication, and testing considerations for generating HMN devices are summarized. Various applications, including drug delivery, sensing, and recording, along with integrated devices necessary for these applications are highlighted. Finally, the limitations of the current approaches are discussed, and the future of HMN devices fabricated by the 3D printing technology is proposed. In summary, this Review provides insight into the current status of 3D printed HMN devices and a roadmap for developing HMNs including design criteria, fabrication considerations, postprocessing approaches, and required testing for device functionality evaluation.