Fabrication and characterization of dissolving microneedles combining digital light processing and vacuum compression molding technique for the transdermal delivery of rivastigmine

Abstract

Dissolving microneedles (MNs) are promising transdermal drug delivery systems that can effectively increase the absorption of the drugs. They bypass the first layer of the skin, the stratum corneum (SC) and deliver the drugs directly into the dermis, by dissolving inside the interstitial fluid and releasing the active. The traditional ways of MN fabrication involve primarily micromolding, which basically uses silicone molds. Drugs and polymer mixture solutions are poured into these molds and after drying the MN arrays are carefully removed. In the present study, a novel molding process was employed to fabricate dissolving MNs containing rivastigmine (RIV). RIV is available as an oral tablet and a transdermal patch. The patch (Exelon®), used for managing Alzheimer’s symptoms in mild to moderate dementia, releases only about 50 % of its drug content, raising concerns about dose wastage, environmental impact, and patient costs. Thus, RIV was selected as the model drug to fabricate MNs by combining to novel processes, Digital Light Processing and Free-D Molding, a Vacuum Compression Molding (VCM) Technique provided by MeltPrep®. The developed arrays were evaluated regarding their physiochemical characteristics and their ability to penetrate the skin without breaking or creating fragments, as they can withstand forces up to 600 N. The MNs were visualized using optical microscopy, SEM, and CLSM to examine their geometry, surface and length (0.708 mm). Permeability studies verified that the MNs can increase significantly RIV transportation across the skin, up to 9-fold. Histological analysis was conducted to ensure that the produced MNs are safe for transdermal applications. Overall, the present study suggests that Free-D molding, a combination of 3D printing and VCM can produce dissolving MN arrays that are effective and safe for transdermal applications.