Optical Fiber-Assisted Bioprinting Enables Freeform Printing of Cell-Laden and Turbid Hydrogel Resins

Optical fiber-assisted printing (OFAP) was recently introduced as a straightforward light-based platform for the spatially controlled photopolymerization of hydrogel-based resins. Here, we extend this concept toward optical fiber-assisted bioprinting (OFAB) by processing cell-laden GelMA- and GelMA/PEGDA-based bioresins in a freeform embedded printing configuration. The system relies on a 405 nm LED-coupled optical fiber mounted on an automated 3D motion platform, enabling localized photocrosslinking directly within a resin bath. First, GelMA and GelMA/PEGDA formulations containing LAP and tartrazine were screened to evaluate the influence of light intensity, printing velocity, and material composition at the line width and curing depth. Single-line features with widths down to 70 ± 20 µm were obtained under optimized conditions, while more robust printing conditions yielded reproducible features in the range of 200–300 µm. Photorheological and rotational rheology measurements confirmed that the formulations provide both thermoresponsive support during printing and photocrosslinked stability after processing. The incorporation of L929 cells demonstrated high cytocompatibility for GelMA and GelMA/PEGDA 6000 Da formulations, with viabilities above 90% after 7 days for selected printed constructs. Importantly, increasing the cell concentration up to 1 × 10 ⁷ cells mL ⁻¹ did not prevent printing and reduced the extent of overcuring, suggesting that cell-induced turbidity can improve spatial confinement of polymerization in OFAB. Finally, a customized OFAB printer was developed to enable temperature-controlled processing and the fabrication of centimeter-scale 3D structures, including cell-laden constructs. Overall, this work establishes OFAB as an accessible and modular bioprinting strategy for cell-laden and optically turbid hydrogel resins, complementing existing light-based biofabrication approaches.