Advancements in transdermal drug delivery using microneedles: technological and material perspective

The concept of a microneedle patch (MNP) for transdermal delivery emerged in the 1970s. This review provides a detailed examination of the manufacturing methods, materials, designs, advantages and recent advancements in MN-mediated transcutaneous drug delivery. MNPs consist of an array of micron-sized projections that can painlessly deliver drugs across the skin or mucosa by bypassing the stratum corneum. MNPs can be fabricated in various designs, including solid, hollow, coated, dissolving and hydrogel-forming using materials such as silicon, polymers (e.g., chitosan, hyaluronic acid, sodium alginate, Eudragit, polycaprolactone, polyvinyl alcohol), sugars (e.g., maltose, trehalose, xylitol), ceramics (e.g., alumina, brushite, zirconia), metals (e.g., titanium, nickel, stainless steel and glass (e.g., silica, borosilicate). MNs can be produced through techniques like micromoulding, lithography, thermal drawing and three-dimensional printing. During recent years, micromoulding has emerged as the most widely employed method for preparing MNPs due to its cost effectiveness and ease of operation. MNPs efficiently deliver a wide range of therapeutic substances from small molecules to macromolecules, proteins and vaccines across the skin. Recently, the therapeutic moieties have been encapsulated in different nanosystems and then embedded into MNPs to enhance the dermal deposition and drug stability. MNPs have also been utilised for diagnostic, theragnostic (e.g., stimulus-responsive drug delivery), sampling and therapy monitoring purposes. In recent years, MN technology has been combined with other techniques such as electroporation, sonophoresis and iontophoresis to further enhance transdermal permeation. The advantages of MN-based systems such as self-application and minimal pain suggest that MNPs could be ideal candidates for drug and vaccine administration particularly in paediatric and geriatric populations.