Effect of microneedles shape on skin penetration and transdermal drug administration

Microneedle (MN) patches are highly efficient and versatile tools for transdermal drug administration, in particular for pain-free, self-medication and rapid local applications. Diffraction ultraviolet (UV) light lithography offers an advanced method in fabricating poly(ethylene glycol)-based MNs with different shapes, by changing both the UV-light exposure time and photomask design. The exposure time interval is limited at obtaining conical structures with aspect ratio < 1:3, otherwise MNs exhibit reduced fracture load and poor indentation ability, not suitable for practical application. Therefore, this work is focused on a systematic analysis of the MN's base shapes effects on the structural characteristics, skin penetration and drug delivery. Analyzing four different base shapes (circle, triangle, square and star), it has been found that the number of vertices in the polygon base heavily affects these properties. The star-like MNs reveal the most efficient skin penetration ability (equal to 40 % of -their length), due to the edges action on the skin during the perforation. Furthermore, the quantification of the drug delivered by the MNs through ex-vivo porcine skin shows that the amounts of small molecules released over 24 h by star-like MNs coated by local anesthetic (Lidocaine) and an anti-inflammatory (Diclofenac epolamine) drugs are 1.5× and 2× higher than the circular-MNs, respectively.