The progress of fabrication designs of polymeric microneedles and related biomedical applications

Microneedles (MNs) have been broadly used for transdermal delivery of a variety of drugs, ranging from small chemicals to biological macromolecules, due to the properties of increased drug permeability, minimal invasiveness and improved patient compliance. Despite these MNs can be made of different materials, such as metal, silicon, and glass, polymers have attracted the most attention as a microneedle (MN) matrix because of their excellent biocompatibility and biodegradability, which eliminates the requirement of MN removal after drug release. To satisfy different needs of transdermal drug delivery, polymeric MNs have been fabricated with several special designs. In this review, we summarize the advancement of the fabrication designs of polymeric MNs, including integrated MNs, two-segment MNs, core-shell or multi-layered MNs, and arrowhead MNs. The related biomedical applications of MNs with these different specific designs are also discussed. Finally, we provide our perspectives on the future development of polymeric MNs.