Hierarchically Structured Functionalized Polymer Monoliths Via Two-Photon Polymerization for Miniaturized HPLC Separation Columns

Miniaturization of liquid chromatography (LC) systems offers numerous advantages. Nevertheless, miniaturized LC is still not widely used. Here, we present the additive manufacturing of hierarchically structured macro- and mesoporous functionalized polymer monoliths and their application for miniaturized reversed-phase chromatographic separations. A CAD-predesigned macroporous structure was generated by 3D printing of a repetitive design of Schoen gyroids from a photoresin via two-photon polymerization. For this, a photoresin formulation was developed containing a porogenic solvent to induce the formation of mesopores and a hydrophobic monomer to achieve a surface functionality suitable for reversed-phase chromatography. This strategy enables independent tuning of macropore geometry and mesoporosity, which is not readily achievable by conventional polymer monolith synthesis. Successful fabrication of hierarchically structured polymer monoliths was demonstrated by scanning electron microscopy and nano-computed tomography. The monolithic stationary phase was connected to a microfluidic system, and chromatographic separation of the nonpolar analytes naphthalene and fluoranthene was demonstrated. This highlights the applicability of the hierarchically structured porous functionalized polymer monolith as a reversed-phase stationary phase.