Influence of Light Exposure Time on the Vat Photopolymerization of Methacrylated PVA Microneedles

Microneedles (MNs) provide a minimally invasive substitute for hypodermic injections, making them a revolutionary breakthrough in transdermal medication delivery. However, high prices and geometric limitations frequently restrict traditional fabrication techniques like micromolding. This work investigates the use of high-precision vat photopolymerization 3D printing to create hydrogel-forming microneedle arrays from poly-(vinyl alcohol) (PVA). By modification of PVA with methacrylic anhydride to methacrylated PVA (MPVA) and using lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) as a biocompatible photoinitiator, we created a photo-cross-linkable bioink. This study examined the effects of three different UV light exposure periods (30, 50, and 70 s) on the mechanical integrity, thermal stability, and morphological fidelity of the MPVA MNs in order to optimize the photopolymerization kinetics. The effective grafting of methacrylate groups onto the PVA backbone was verified by chemical analysis using FT-IR and NMR spectroscopies. A crucial trade-off was discovered by mechanical compression testing and scanning electron microscopy (SEM): while short exposure intervals (30 s) produced sharp but mechanically brittle structures, lengthy exposure times (70 s) produced strong but geometrically dull needles. The best processing window was found to be 50 s, which produced microneedles with enough mechanical stiffness. These results were further supported by differential scanning calorimetry (DSC), which demonstrated that longer exposure times improve the cross-linking density and heat stability of the polymer network. Parafilm-based insertion testing confirmed the functional penetration capability of MPVA-50 arrays, validating the optimized exposure condition as suitable for transdermal application These findings show that Vat photopolymerization printing of MPVA is a reliable, scalable, and adjustable technique for creating transdermal delivery systems.