Embedded cell-only bioprinting to engineer structurally aligned meniscal fibrocartilage

This study developed an embedded cell-only bioprinting strategy to engineer fibrocartilage with collagen organization resembling the native knee meniscus. The authors first demonstrated that external geometric confinement could direct extracellular matrix organization by culturing mesenchymal stem/stromal cells within non-adhesive agarose channels. They then translated this concept to embedded bioprinting, depositing MSC-only bioink into a methacrylated xanthan gum support bath. Narrower 250 µm filaments produced the most consistent collagen alignment throughout the tissue depth and greater sGAG deposition per DNA than wider 580 and 1000 µm filaments. To investigate whether this organization depended on active cellular mechanotransduction, YAP and ROCK signaling were inhibited during culture. Inhibition disrupted cytoskeletal and nuclear alignment but did not eliminate collagen alignment or significantly alter Brillouin frequency shift, suggesting that geometric confinement itself can strongly influence extracellular matrix organization independently of these two pathways. The approach was then scaled to create anisotropic fibrocartilage sheets and meniscus-like constructs formed from circumferentially printed MSC lines. The engineered sheets developed a collagen-rich fibrocartilaginous phenotype and measurable tensile properties, while the meniscus-shaped constructs showed collagen alignment that followed the circumferential printing path. Overall, the study demonstrates that embedded cell-only bioprinting can use temporary geometric boundary cues to direct collagen architecture and generate more structurally biomimetic engineered meniscal fibrocartilage.