Optimising metallic microneedles for transdermal drug delivery: A multi-objective parameter optimisation approach via design of experiments in additive manufacturing

Transdermal drug delivery (TDD) systems offer a non-invasive and patient-friendly approach, yet conventional methods often encounter limitations with nucleic acid and large drug molecule delivery. Microneedles (MN) present a promising solution due to their painless and minimally invasive drug delivery capabilities. Recent progress in additive manufacturing (AM) has enabled the fabrication of metallic MN arrays with desirable therapeutic delivery properties. This study focused on optimising the 3D printing and post-processing of 316L stainless steel-based MN arrays to achieve ideal mechanical and geometrical properties for potential platform for TDD. Design of Experiments (DoE) methodology was employed to investigate the influence of printing and post-processing factors on the final MN array properties and identify the optimal parameters. Through comprehensive DoE studies, we established that a laser power of 65 W, speed of 650 mm/s, trace width of 0.09 mm, electropolishing time of 60 s, and current of 7 A could attain MN arrays with desirable geometrical and mechanical characteristics for potential platform for TDD. The optimised geometrical features meet the requirements for a painless micro-sized device, where the electropolished MNs demonstrate a 0.4 mm to 0.7 mm insertion withstood by forces ranging from 2.5 N to 7 N for porcine skin, synthetic tissue and parafilm, ensuring successful penetration without tip failure. These optimised solid metallic MN arrays provide a mechanically robust platform for future TDD strategies based on microchannel formation or drug-loaded surface coatings.