Micro-pillar tunnel stamp for enhanced transdermal delivery of topical drug formulations

Dissolving microneedles (DMNs), despite their minimally invasive drug administration, face challenges in skin insertion and drug-loading capacity, which lead to less effective drug delivery. The micro-pillar tunnel stamp (MPTS) was designed to enhance the transdermal delivery efficacy of externally provided topical formulations via the creation of microchannels. The tunnel and canal of the MPTS enable the simultaneous application of DMNs and topical drugs. The application of micro-pillar-polycaprolactone (MP-PCL), which is a DMN made of a slowly dissolving polymer, exhibited a drug permeation rate 1.3-fold and 2.6-fold higher than that of micro-pillar-hyaluronic acid (MP-HA), a DMN made of a rapidly dissolving polymer, and the topical group, respectively. The base diameter of MP-PCL was set to 700 μm for maximized delivery efficacy, achieving 2.8-fold higher L-ascorbic acid accumulation than that of the topical group. In vivo analysis showed that, compared to topical administration, MPTS-delivered lidocaine had 5-fold greater permeation and the MPTS-delivered group showed 1.25-fold higher skin residual amount, confirming enhanced delivery. Thus, the optimized MPTS system can be presented as an attractive alternative to overcome the limitations of the existing MN systems such as incomplete insertion and limited drug-loading capacity, enhancing the delivery of topical formulations in the transdermal market. STATEMENT OF SIGNIFICANCE: We developed a micro-pillar tunnel stamp (MPTS) to enhance the delivery of externally provided topical formulations. The functional tunnel and canal of the MPTS enabled the simultaneous application of a dissolving microneedle (DMN) array insertion and administration of external topical drugs. Upon insertion, the DMNs created skin microchannels that allowed the externally administered drug to diffuse. DMNs were fabricated using polycaprolactone (PCL), a slowly dissolving polymer, to maintain their structure inside the skin and prolong the opening duration of the microchannels. This system achieved significantly improved delivery of topically administered external drugs via integration with slowly dissolving DMNs, while offering the possibility of its development as a universal delivery system for various topical pharmaceuticals.