Pubertal Bone Matrix Microparticles Support Rapid Generation of Mini‐Bone Organoids and Minimally‐Invasive Injection in Repairing Bone Defect

Abstract Existing stem cell‐based bone substitutes (SCBS) developed for repairing critical‐sized bone defects have several shortcomings, such as inconvenience for minimally‐invasive implantation, hard‐to‐completely fill defects, and insufficient osteogenesis of implanted stem cells. Mini‐bone organoids (mBOs), a new type of SCBS, show great potential to solve these shortcomings. Herein, after unveiling postnatal developmental dynamics of vertebra, vertebra in puberty shows superior osteogenesis and angiogenesis, thus selected as source tissue for decellularization, then fabricating into bone matrix microparticles (named pBM‐MPs) as cultivation matrix. The pBM‐MPs harbor osteo‐forming and biomimetic characteristics as well as functions of angiogenesis and anti‐senescence. Furthermore, a new cultivation pattern is developed for rapidly generating mBOs, namely cultivating a subpopulation of BMSCs showing strong osteogenic potential (named Osteo‐BMSCs) on the surface of pBM‐MPs undergoing FGF2‐stimulated early proliferation followed by BMP2‐induced late osteogenesis. In the presence of pBM‐MPs and Osteo‐BMSCs, the resulting mBOs exhibit similarities to native bone in terms of osteocyte phenotype, bony extracellular matrix and hold paracrine functions in angiogenesis and osteogenesis. Minimally‐invasive injection of the mBOs into rat femoral defect accelerates defect repair, indicating that this organoid serves as off‐the‐shelf substitute to completely fill defect even directly replace autologous bone, and paracrine units enhancing endogenous osteo‐formation.