Nitroxide‐Mediated Photo‐Polymerization: A Swiss Army Knife for Microfluidic Design

ABSTRACT Microfluidic systems have attracted growing interest from both academic and industrial communities, particularly for medical and pharmaceutical applications. While 3D printing (3DP) offers an attractive route for the rapid prototyping of such devices, it often suffers from limitations such as inert surface chemistry, poor functionalisation, and challenging sealing procedures. In this work, we demonstrate the use of nitroxide‐mediated photopolymerisation (NMP2) implemented in a Digital Light Processing (DLP) platform as a versatile approach to print and assemble polymer‐based microstructures for microfluidic applications. By designing a tailored photocurable resin, NMP2 enables the fabrication of base (P1) layers embedding nitroxide moieties that subsequently initiate a truly surface‐initiated polymerisation of neat monomers (P2) arbitrarily chosen among the acrylate family. This strategy allows the straightforward and rapid formation of DLP‐patterned P2 features — including pillar arrays, Y‐shaped circuits (e.g., with 200 µm channels width), and microfluidic geometries — simply by spreading unmodified monomers on preformed P1 substrates, with no need for additional photoinitiator. Moreover, this process enables the direct sealing of P2 layers with polymeric P1 covers, providing a glue‐free and annealing‐free welding method that prevents clogging and ensures robust bonding. The demonstrated versatility and functional compatibility of NMP2 with the wide chemical variety of acrylate monomers are expected to significantly expand the scope of DLP photostructuring for the fabrication of next‐generation microfluidic systems.