Recent advances in microneedle designs and their applications in drug and cosmeceutical delivery

Transdermal drug delivery (TDD) was initially limited to fewer therapeutic agents due to the requirements of suitable physicochemical and biological properties for passage across the stratum corneum (SC) of the skin. However, with the advent of microneedles (MNs) technology, involving the creation of micron-sized conduits in the skin and other biological barriers, the barrier nature of the SC could be breached to deliver a broad spectrum of molecules, including micromolecules and macromolecules such as protein and peptide-based drugs, biomolecules and vaccines into the skin or systemic circulation. Not only that, but it is also capable of surpassing the biological barriers of the non-transdermal route such as ocular, oral, mucosal, vascular tissues, brain, gastrointestinal tract (GIT), ear, and cardiac tissues. MNs technology not only solves the problem associated with TDD but also offers potential advantages such as personalization of drug delivery systems (DDSs) leading to better patient compliance and patient adherence. The present review compiles basic types of MNs (solid, coated, dissolving, hollow and hydrogel MNs) and novel designs including bio-inspired MNs, separable MNs and recent advancements in the field of MNs design. This review also compiles the drug and cosmeceutical delivery across various routes such as transdermal and intradermal, ocular, oral cavity, vascular tissues, GIT, brain, ear, and heart. In addition, this review provides insight into nanoparticles in MNs, and three-dimensional (3D) and four-dimensional (4D) printing in MNs design along with the commercial MNs product.