Optimization of Two-Photon Polymerization for Fabrication of High-Density Micropatterned Contact Interfaces

Two-photon polymerization (2PP) enables the fabrication of polymeric microstructures with complex three-dimensional geometries and sub-micrometer resolution, providing new opportunities for engineering microscale contact interfaces. In such interfaces, the geometry, spacing, and mechanical properties of surface microstructures can strongly influence their deformation and mechanical response under contact loading. Therefore, reliable control of the fabricated microstructure is essential for developing functional and reproducible contact interfaces.

In this work, a systematic optimization of 2PP was performed to fabricate large-area, high-density micropatterned surfaces with controlled geometrical and mechanical characteristics. Using a Nanoscribe Photonic Professional GT2 system and IP-Visio photoresist, four fabrication strategies combining different CAD geometries and laser writing approaches, namely solid and contour trajectories, were investigated. The influence of key printing parameters, including writing speed, hatching distance, slicing distance, and hatching strategy, was evaluated through morphological characterization and scanning electron microscopy.

The optimized fabrication conditions enabled the production of approximately 4 × 4 mm² surfaces containing nearly 48,000 hexagonal micropillars arranged in a dense periodic lattice, with improved dimensional accuracy and uniform inter-pillar spacing. The resulting micropatterned structures were validated as biomimetic scaffolds for culture of human ARPE-19 retinal pigment epithelium cells. The analysis demonstrated that micropatterned interfaces have superior performance with respect to flat controls (not micropatterned) in terms of cell adhesion, proliferation and differentiation with possible applications in the treatment of retinal detachment.

Further studies have been conducted to assess the influence of fabrication parameter on mechanical response of micrometric pillars, obtained by 2PP comparing the behavior of three different resins. Microcompression tests revealed that tiny details in design and fabrication strongly alter the contact stiffness in indentation tests supporting the importance of controlling microstructure geometry and fabrication parameters for obtaining reproducible mechanical responses of microscale contacts.