Hollow Out-of-Plane Polymer Microneedles Made by Solvent Casting for Transdermal Drug Delivery

Although hollow microneedles have been proposed as an effective and convenient method for transdermal drug delivery, their expensive fabrication techniques to date have prevented their mass fabrication as a viable option. A novel method, based on solvent casting, is presented for inexpensive fabrication of hollow out-of-plane polymer microneedles. Microneedles are formed during a solvent evaporation process, which leaves a polymer layer around pillars in a prefabricated mold. The mold is fabricated using photolithography and can be used for consecutive solvent casting of microneedles. Arrays of microneedles with lengths up to 250 μm have been fabricated from clay-reinforced polyimide. Several mechanical tests were performed on solvent cast solid structures to find the optimum clay percentage in the polyimide that would lead to the highest compressive strength. The fabricated needles were tested for robustness, and it was observed that the needles were capable of withstanding on average compressive loads of up to 0.32 N. The suitability of the microneedles for skin penetration and drug delivery was demonstrated by injection of fluorescent beads into a skin sample.