High-resolution bioprinting of complex bio-structures via engineering of the photopatterning approaches and adaptive segmentation.

Digital light processing (DLP) technology has significantly advanced various applications, including 3D bioprinting, through its precision and speed in creating detailed structures. While traditional DLP systems rely on light-emitting diodes (LEDs), their limited power spectral density, high etendue, and spectral inefficiency constrain their performance in resolution, dynamic range, printing time, and cell viability. This study proposes and evaluates a dual-laser DLP system to overcome these limitations and enhance bioprinting performance. The proposed dual-laser system resulted in a twofold increase in resolution and a twelvefold reduction in printing time compared to the LED system. The system's capability was evaluated by printing three distinct designs, achieving a maximum percentage error of 1.16% and a minimum of 0.02% in accurately reproducing complex structures. Further, the impact of exposure times (10-30 s) and light intensities (0.044-0.11 mW mm^-2) on the viability and morphology of 3T3 fibroblasts in GelMA and GelMA-poly(ethylene glycol) diacrylate (PEGDA) hydrogels is assessed. The findings reveal a clear relationship between longer exposure times and reduced cell viability. On day 7, samples exposed for extended periods exhibited the lowest metabolic activity and cell density, with differences of ∼40% between treatments. However, all samples show recovery by day 7, with GelMA samples exhibiting up to a sixfold increase in metabolic activity and GelMA-PEGDA samples showing up to a twofold increase. In contrast, light intensity variations had a lesser effect, with a maximum variation of 15% in cell viability. We introduced a segmented printing method to mitigate over-crosslinking and enhance the dynamic range, utilizing an adaptive segmentation control strategy. This method, demonstrated by printing a bronchial model with a 14.43x compression ratio, improved resolution and maintained cell viability up to 90% for GelMA and 85% for GelMA-PEGDA during 7 d of culture. The proposed dual-laser system and adaptive segmentation method were confirmed through successful prints with diverse bio-inks and complex structures, underscoring its advantages over traditional LED systems in advancing 3D bioprinting.