The dissolving microneedle (DMN) patch is a transdermal delivery system, containing arrays of micro-sized polymeric needles capable of encapsulating therapeutic drugs within their matrix and releasing them into the skin. However, the elastic properties of the skin prevent DMNs from complete insertion and accurate delivery of encapsulated compounds into the skin. Moreover, the adhesive materials used in patches may cause skin irritation, inflammation, and redness. Therefore, we developed a patchless, micro-pillar integrated DMN (P-DMN) that is simple to fabricate and enhances transdermal drug delivery compared with traditional DMN patches. The micro-pillars were made of polymethyl methacrylate at a height of 300 μm and a base diameter of 500 μm. To fabricate P-DMNs, we employed hyaluronic acid, which is a widely used derma filler and plays a role in tissue re-epithelialization. We demonstrate that utilizing P-DMNs significantly improves the delivery efficiency of an encapsulated drug surrogate (91.83% ± 7.75%) compared with traditional DMNs (64.86% ± 8.17%). Interestingly, P-DMNs remarkably increase the skin penetration accuracy rate of encapsulated drugs, up to 97.78% ± 2.22%, compared with 44.44% ± 7.85% in traditional DMNs. Our findings suggest that P-DMNs could serve as a highly accurate and efficient platform for transdermal delivery of various types of micro- and macro-biomolecules.

Alopecia, characterized by hair follicle blockage and hair loss, disrupts the normal cycle of hair growth. Although not a life-threatening condition, a growing body of evidence suggests that the psychological state of individuals experiencing alopecia can be highly influenced. Despite considerable research on hair loss treatment, interest in micro-pigmentation has increased in recent decades. Micro-pigmentation is an effective method to camouflage the visual contrast between the scalp and hair strands. However, the localization, intensity and dimension of microdots depend highly upon the physician performing the implantation. Incorrectly localized microdots within the skin may lead to patchy or faded micro-pigmentation. To overcome the limitations of conventional micro-pigmentation, we aimed to develop micro-pigment-encapsulated biodegradable microneedles (PBMs), capable of accurately implanting pigments below the epithelial-dermal junction of the scalp in a minimally invasive manner. A tissue interlocking microneedle technique was utilized to fabricate double-layered PBMs over a biodegradable flexible sheet, which could be washed off post-implantation. We confirmed that the intensity, dimension and insertion depth of 1000 μm-long PBMs was maintained on pig cadaver skin over time. This study suggested that the developed PBMs would serve as an attractive platform for scalp micro-pigmentation in the future.