Engineering Tunable Microneedle Arrays Through Visible Light-Mediated PET-RAFT 3D Printing

3D printing has enabled the development of patient-specific drug delivery systems and medical devices. Here, we report the fabrication of microneedle arrays using visible light-mediated photoinduced electron/energy-transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization via digital light processing (DLP) 3D printing. A series of formulations based on poly(ethylene glycol) diacrylate (PEGDA), N,N-dimethylacrylamide (DMA), and the RAFT agent 2-(n-butyltrithiocarbonate)-propionic acid (BTPA) were systematically investigated by varying formulation composition and exposure conditions to evaluate their effects on printability and material properties. The results show that both formulation composition and exposure time influence the successful fabrication of stable microneedle structures. Optimized formulations produced well-defined microneedle arrays with tunable mechanical properties, exhibiting Young's modulus values of 6-13 MPa and fracture forces of 0.15-0.38 N per needle, exceeding the threshold required for skin penetration. Controlled insertion tests, supported by optical microscopy and optical coherence tomography (OCT), confirmed effective penetration without structural failure. In addition, drug-loaded microneedles demonstrated rapid hydration and diffusion-controlled release while maintaining comparable mechanical integrity after drug incorporation. In vitro biocompatibility studies using human dermal fibroblasts showed no statistically significant reduction in cell viability or metabolic activity following exposure to the printed microneedles. Collectively, these findings demonstrate the potential of visible light-mediated PET-RAFT DLP printing for the fabrication of mechanically robust and functionally tunable microneedle systems for transdermal drug delivery.