Microneedles for non-transdermal drug delivery: design strategies and current applications

Microneedles (MNs) are an innovative and viable option for drug delivery that offer the distinct advantages of minimal invasiveness, painlessness, stable drug loading, efficient drug permeation, and biocompatibility. MNs were first used to penetrate the skin surface and facilitate transcutaneous drug delivery with great success. Recent applications of MNs have extended to non-transdermal drug delivery, specifically, to various tissues and organs. This review captures the fabrication methods for MNs, discusses advanced design strategies for achieving controlled drug release, and summarizes current MN applications in delivering multiple therapeutic agents to the cardiovascular, digestive (e.g., oral cavity), reproductive, and central nervous systems. The findings in this review would contribute toward the improved designs of MN systems that can be modified according to purpose, including material selection, structural design, choice of fabrication methods, and tissue considerations, to determine the optimal therapeutic regimen for the target treatment area.