Mould-free microneedles in a single step: 3D printing with photopolymer resins for transdermal delivery

Digital light processing (DLP) 3D printing has emerged as a rapid alternative to la-bour intensive micro moulding for producing microneedle (MN) arrays, yet its use in biodegradable, dissolving MNs has been limited by proprietary, non degradable resins. 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. The resin viscosity, cure kinetics and spectral signatures were characterised, and a 40 % PEGDA up-to 100 % VP blend with 0.4 % initiator was identified as providing rapid photopol-ymerisation, low shrinkage and complete vinyl conversion. Using a desktop DLP plat-form, 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 dimen-sions 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 stabil-ity at ambient conditions, and dissolution studies showed complete needle dissolution. These results demonstrate that pixel aware DLP printing of 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.