Drawing lithography for the fabrication of 3D microneedle structures. In the glass transition, parameters for the onset of drawing lithography are shear viscosity (ηs), processability (P) and initial planar extensional viscosity (ηiE). In extensional deformation of drawing lithography, parameters are tensile stress (τE), apparent extensional viscosity (η_appE) and surface tension (σ) (Reproduced with permission from reference 57).

Over the last number of years, a significant body of evidence has shown the benefit of using dissolving microneedles (DMNs) for transdermal drug delivery. These devices are prepared from a wide range of materials such as sugars and polymers. DMNs are mainly fabricated by micromolding, photopolymerization, drawing lithography and droplet-airborne blowing. In this review, we have focused on the advances made in the field in recent years using a representative set of studies. Although the list of studies is not exhaustive, they highlight the challenges encountered such as the need to increase mechanical strength as well as medication dose while ensuring fast release of the active ingredient. DMNs can be used to delivery low molecular drugs as well as peptides, proteins and other high molecular weight compounds.