One-step digital printing of microneedle array via self-focusing photo polymerization

The interest in microneedles is currently increasing due to their user-friendliness. However, the resource-intensive nature of conventional fabrication methodologies, such as photolithography and layer-by-layer 3D printing, restrain their application in high-dose drug delivery systems. This paper presents a novel one-step fabrication method for high-aspect-ratio microneedle arrays. The methodology integrates self-focusing photo polymerisation with digital light processing. In this approach, changes in the refractive index before and after photo polymerisation was leveraged to enable the single-exposure fabrication of microneedles with sharp tips and controllable geometries. Grayscale image projection was used to enable localised control over structural height and spacing, facilitating capillary-driven aggregation of microneedles and the formation of microcavities capable of accommodating high drug loads. Mechanical testing and in vitro experiments conducted using porcine skin confirmed both the penetration strength and the delivery of vitamin B12 without structural damage. Furthermore, internal light-guiding properties embedded in the microneedles enable localised optical delivery for potential phototherapeutic applications. Thus, the proposed technique allows rapid, maskless manufacturing with flexible customisation of microneedle designs tailored to specific drug doses or skin conditions. This fabrication strategy holds promise for applications in transdermal drug delivery, personalised therapy, and dermatological light treatment.