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In recent years, transdermal drug delivery based on microneedles (MNs) technology has received extensive attention, which offers a safer and painless alternative to hypodermic needle injections. They can pierce the stratum corneum and deliver drugs to the epidermis and dermis-structures of skin, showing prominent properties such as minimally invasiveness, bypassing first-pass metabolism, and can be self-administered. A range of materials has been used to fabricate MNs, such as silicon, metal, glass, and polymers. Among them, polymer MNs have gained increasing attention from pharmaceutical and cosmetic companies as one of the promising drug delivery methods. MN products have recently become available on the market, and some of them are under evaluation for efficacy and safety. This paper focuses on the current state of polymer MNs in drug transdermal delivery. The materials and methods for the fabrication of polymer MNs and their drug administration are described. The recent progress of polymer MNs for treatment of cancer, vaccine delivery, blood glucose regulation, androgenetic alopecia, obesity, tissue healing, myocardial infarction, and gout are reviewed. The challenges of MNs technology are summarized and the future development trend of MNs is also prospected., (© 2022 Wiley-VCH GmbH.)

[Display omitted] • Polymer microneedles (MNs) have been prepared for transdermal delivery of drugs. • Free Met and Met-loaded BGNs were encapsulated into MNs for a sustained drug release. • MNs with integration of free and loaded Met exhibit a significant hypoglycemic effect. Transdermal delivery provides a suitable and painless self-administration for diabetic patients. In this work, the polymer microneedles (MNs) integrated with mesoporous bioactive glass nanoparticles (BGNs) for transdermal delivery of metformin (Met) have been developed for regulation of blood glucose levels (BGLs) on diabetic rats. The obtained MNs system contains free Met and Met-loaded BGNs (Met/BGNs) for independently controlling the kinetics of anti-diabetic drug during the treatment. Once these MNs are penetrated into the skin, the free Met is firstly released due to the swelling and degradation of matrix material of MNs. And then the loaded Met is slowly seep through the microchannels of BGNs to form a sustained drug release behaviors and a better hypoglycemic effect, suggesting the potential of this new transdermal delivery system as substitutes for multiple daily injections. [ABSTRACT FROM AUTHOR]