Review of patents on microneedle applicators

Transdermal drug delivery offers certain advantages over conventional oral or parenteral administration. However, transdermal delivery is not available to many promising therapeutic agents, especially high molecular weight hydrophilic compounds. This is due to the excellent barrier property of the superficial skin layer, the stratum corneum (SC). Only drugs with very specific physicochemical properties (molecular weight < 500 Da, adequate lipophilicity, and low melting point) can be successfully administered transdermally. Of the several active approaches used to enhance the transport of drugs through the SC, the use of microneedles (MNs) has recently been shown to be very promising and has attracted considerable attention by researchers from both industry and academia. MNs, when used to puncture skin, will by-pass the SC and create transient aqueous transport pathways of micron dimensions and enhance the transdermal permeability. However, for effective performance of these MNs in drug delivery applications, irrespective of the type, material, height and density, it is imperative that they penetrate into the skin with the greatest possible accuracy and reproducibility. Due to the inherent elasticity and irregular surface topography of the skin, it remains a major challenge to the reproducibility of MN penetration. Therefore, in order to achieve uniform and reproducible MN penetration into skin, an external source of assistance could be very useful. Accordingly, this review deals with various innovative applicator designs developed by industry and research centres in the context of effective application of MN arrays for transdermal drug delivery, as disclosed in the recent patent literature.