Porcelain-clay-inspired microsphere hydrogel bioink facilitates bone regeneration via immune-osteogenic regulation

High-quality regeneration of large bone defects depends on the coordinated integration of immunomodulation, osteogenic signal presentation, and structural support. However, conventional bioinks often struggle to simultaneously fulfill these key requirements, particularly in terms of the effective utilization of low-dose bone morphogenetic protein 2 (BMP-2) and matching biomechanical interfaces. Inspired by the shaping behavior of traditional porcelain clay, we developed a clay-like microsphere-based hydrogel bioink that integrates biomimetic immunomodulation, low-dose osteogenic factor delivery, and structural support within a single system. In this construct, mesenchymal stem cell membranes (MSCM) functionalized with mildly biotinylated BMP-2 served as the core bioactive interface and were further integrated onto the surface of chitosan microspheres (CSMP). These functionalized microspheres were subsequently assembled with a gelatin methacryloyl (GM) continuous phase to form a microsphere-composite hydrogel, termed BMP2@MSCM/CSMP + GM, which exhibited rheological and shaping characteristics similar to porcelain clay. Both in vitro and in vivo results demonstrated that this system synergistically optimizes the immune and osteogenic microenvironments, thereby promoting bone-related regenerative processes and achieving superior bone repair performance compared with the control groups. This strategy provides an integrated biomanufacturing approach for large bone defect repair by combining bioactive regulation and structural functionality within a single platform.