Research progress on detachable microneedles for advanced applications

Introduction Microneedles (MNs) have undergone great advances in transdermal drug delivery, and commercialized MN applications are currently available in vaccination and cosmetic products. Despite the development of MN technologies, common limitations of MN products still exist. Typical MN patches are applied to target tissues, where the substrate of an MN patch must remain until the drug is delivered, which reduces patients' compliance and hinders the applicability of the MN technique to many diseases in various tissues. MN research is ongoing to solve this issue. Areas covered Most recent MNs developed by combining various biomaterials with appropriate fabrication processes are detachable MNs (DeMNs). Because of advances in biomaterials and fabrication techniques, various DeMNs have been rapidly developed. In this review, we discuss four types of DeMN: substrate-separable, multi-layered, crack-inducing, and shell DeMN. These DeMNs deliver various therapeutic agents ranging from small- and large-molecular-weight drugs to proteins and even stem cells for regeneration therapy. Furthermore, DeMNs are applied to skin as well as non-transdermal tissues. Expert opinion It has become increasingly evident that novel MN technologies can be expected in terms of designs, fabrication methods, materials, and even possible application sites given the recent advances in DeMNs.