After the Nozzle: Post-Printing Maturation, Failure Modes, and Use-Point Assessment of Cell-Laden Extrusion-Bioprinted Hydrogel Constructs.

Cell-laden hydrogel bioinks for extrusion bioprinting are commonly evaluated by precursor rheology, extrusion behavior, and immediate shape fidelity, yet these measures do not establish whether printed constructs remain stable and functional during culture or tissue maturation. This review examines the post-printing evolution of cell-laden extrusion-printed hydrogel constructs, prioritizing direct evidence from cell-laden prints and using acellular prints and bulk hydrogels only to clarify mechanisms. Maturation is organized into immediate stabilization, network evolution and environmental equilibration, and long-term remodeling. Crosslinking, hydration, ion exchange, stress relaxation, degradation, cellular contraction, and matrix deposition may support maturation or cause structural, mechanical, interfacial, transport, and biofunctional failure. We propose a conceptual, research-oriented use-point assessment framework that compares each construct with relevant reference states and application-specific requirements after stabilization, during culture, and before intended use. The framework links the earliest observed critical deviation to relevant measurements, targeted redesign, and reassessment under the same conditions. A cartilage construct illustrates sequential evaluation of geometry, wet-state mechanics, cell distribution, and matrix formation. Current evidence is limited by inconsistent assessment times, incomplete reporting, and few integrated longitudinal studies. Future work should standardize maturation histories, model construct trajectories, and prospectively validate product-specific criteria. Evaluation should focus on the complete cell-laden extrusion-printed construct at its intended use point rather than on the freshly printed filament.