Embedded cell-only bioprinting to engineer structurally aligned meniscal fibrocartilage

This study investigated whether external geometric confinement can be used to guide collagen organization in engineered meniscal fibrocartilage. Mesenchymal stem/stromal cells were first cast in non-adhesive agarose channels, where they formed fibrocartilaginous tissues with collagen aligned parallel to the long axis of the boundary. The concept was then translated into an embedded cell-only bioprinting platform, where MSC-only bioinks were printed into a methacrylated xanthan gum support bath to generate filaments of different widths. Narrower 250 μm filaments produced the most uniform collagen alignment throughout the construct and also supported enhanced fibrocartilaginous matrix formation compared with wider filaments. Mechanistic studies showed that inhibiting YAP or ROCK disrupted cytoskeletal and nuclear alignment, yet collagen remained highly aligned, suggesting that boundary-induced collagen organization can be maintained even when these mechanotransduction pathways are suppressed. The strategy was then scaled to create anisotropic fibrocartilage sheets and circumferential meniscus-like constructs with collagen following the printing path. Overall, the study establishes embedded cell-only bioprinting with geometric confinement as a scalable way to engineer meniscal grafts with more biomimetic collagen architecture.