Figure 2.

Diagrams showing various microneedle drug delivery approaches. (A) Solid microneedles, for skin pretreatment to create microchannels, followed by the application of transdermal patch; (B) coated microneedles, for deposition of drug formulations into the skin, followed by removal of microneedles; (C) dissolving microneedles, incorporated into the substrate of microneedles, remaining in the skin and dissolving over time to release the drugs; and (D) hollow microneedles, for inserted into the skin and continuous infusion of the drug through the created microchannels [56]. (Adapted from Ref. [56]).