Mould-Free Microneedles in a Single Step: 3D Printing with Photopolymer Resins for Transdermal Delivery

Background: Digital light processing (DLP) 3D printing has emerged as a rapid alternative to labour-intensive micro-moulding for producing microneedle (MN) arrays, yet its use in biodegradable, dissolving MNs has been limited by proprietary, non-degradable resins. Methods: The current study proposed an innovative, biocompatible PEGDA-vinyl-pyrrolidone photo-resin with lithium phenyl(2,4,6-trimethylbenzoyl) phosphinate initiator, which systematically optimises its rheology and photo-reactivity for DLP printing. Resin formulations were evaluated through viscosity profiling, cure kinetics, FTIR, and ¹H NMR, and MN arrays were printed using a desktop DLP platform and characterised by optical microscopy, mechanical testing, thermal analysis, and dissolution studies. Results: A 40% PEGDA up-to 100% VP blend with 0.4% initiator was identified as providing rapid photopolymerisation, low shrinkage and complete vinyl conversion. Using a desktop DLP platform, 6 × 6 MN patches were printed in a single step without moulds and analysed by optical and scanning electron microscopy. The printed MNs reproduced CAD dimensions with <3% deviation, achieving a height of 1.40 ± 0.02 mm and a base thickness of 1.00 ± 0.01 mm, and showed a tip radius consistent with sharp penetration. Compression testing measured an array force of 32 N, corresponding to ~0.9 N per needle, exceeding the 0.2 N threshold for skin insertion. FTIR and ¹H NMR confirmed near-quantitative crosslinking, thermogravimetric and differential scanning calorimetry indicated stability at ambient conditions, and dissolution studies showed complete needle dissolution. Conclusions: An optimised PEGDA/VP resin yields geometrically precise, mechanically robust dissolving MNs in a single step, addressing the limitations of micro-moulding and paving the way for customisable, on-demand transdermal delivery of active molecules and biologics.