Recent advances of microneedles used towards stimuli-responsive drug delivery, disease theranostics, and bioinspired applications

Microneedles (MNs) as a minimally invasive tool have drawn increasing attention recently. They possess many prominent advantages, including pain-free, self-administration, and ease-of-disposal, when compared to the traditional administration tools. This review summarizes the latest developments of the MN technology and focuses on the advanced applications in stimuli-responsive drug delivery, disease theranostics, and bioinspired functions. Starting from a brief overview of different types of MNs based on their structures and materials, we then detail the fabrication strategies, including hot embossing, micro-molding, thermal-drawing lithography, magnetorheological lithography, laser-drilling, and the emerging 3D printing techniques. Later, the recent biomedical applications of these MNs are highlighted, including stimuli-responsive drug release for disease therapy, biosensing for disease diagnosis, and bioinspired applications.