A Review on Microneedle-Based Transdermal Drug and Vaccine Delivery: Design, Fabrication, and Emerging Applications

Transdermal drug delivery systems (TDDS) have emerged as an effective alternative to conventional drug administration routes due to their ability to bypass gastrointestinal degradation and hepatic first-pass metabolism while improving patient compliance. However, the outermost layer of the skin, the stratum corneum, acts as a major barrier limiting the delivery of many therapeutic agents, particularly macromolecules such as proteins, peptides, and vaccines. Microneedle technology has been developed as an innovative approach to overcome this limitation by creating microscopic channels in the skin that allow efficient drug transport with minimal pain and tissue damage. Microneedles are micron-sized needle arrays capable of penetrating the stratum corneum without reaching deeper nerve endings, enabling painless and minimally invasive drug administration. Various types of microneedles have been developed, including solid, hollow, coated, dissolving, and hydrogel-forming microneedles, each designed for specific drug delivery strategies. Among these, dissolving polymer microneedle patches have gained significant attention due to their ability to encapsulate drugs or vaccines and dissolve completely within the skin, eliminating biohazardous sharps waste. This review discusses the design, fabrication methods, and material composition of microneedles, along with their applications in transdermal drug and vaccine delivery. Special emphasis is given to dissolving polymer microneedle patches for influenza and COVID-19 vaccination, highlighting their ability to induce strong immune responses by targeting antigen-presenting cells in the skin. In addition, the advantages, limitations, and future prospects of microneedle-based delivery systems are addressed. Overall, microneedle technology represents a promising platform for safe, efficient, and patient-friendly transdermal therapeutic delivery.