Recent advances in the design of polymeric microneedles for transdermal drug delivery and biosensing

Microneedles is an efficient and minimally-invasive approach of transdermal drug delivery and extraction of skin interstitial fluid. Compared to solid microneedles made of silicon, metals and ceramics, polymeric microneedles have attracted extensive attentions due to their excellent biocompatibility, biodegradability and nontoxicity. They are ease to fabricate in large scale and load drugs with high amounts. More importantly, polymers with different degradation profiles, swelling properties, and responses to biological/physical stimulis can be employed to fabricate polymeric microneedles with different mechanical properties and performance. This review provides the guideline of the selection of polymers and the corresponding fabrication methods for the polymeric microneedles while summarizing their recent application in drug delivery and fluid extraction. It should be noted that although polymeric microneedles can achieve efficient transdermal delivery of drugs, their wide applications were limited by their unsatisfactory transdermal therapeutic efficiency. Delivery of nanomedicines that incorporates drugs into functional nanoparticles/capsules can address this problem and thus may be an interesting direction in the future.