Department of Biomaterials Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, 700-8525, Japan.
Dental School, Okayama University, Advanced Research Center for Oral and Craniofacial Sciences, Okayama, 700-8525, Japan.
Adv Biol (Weinh). 2022 Nov;6(11):e2200076. doi: 10.1002/adbi.202200076. Epub 2022 Jul 20.
Bone apatite crystals grow in clusters, but the microstructure of these clusters is unknown. This study compares the structural and compositional differences between bone apatite clusters formed in intramembranous (IO) and endochondral ossification (EO). Calvaria (IO) and femurs (EO) are isolated from mice at embryonic days (E) 14.5 to 15.5 and post-natal days (P) 6 to 7, respectively. Results show that the initially formed bone apatite clusters in EO (≅1.2 µm ) are >10 times larger than those in IO (≅0.1 µm ), without significant changes in ion composition. In IO (E14.5 calvarium), early minerals are formed inside matrix vesicles (MVs). In contrast, in EO (P6 femur epiphysis), no MVs are observed, and chondrocyte-derived plasma membrane nanofragments (PMNFs) are the nucleation site for mineralization. Apatite cluster size difference is linked with the different nucleation sites. Moreover, an alkaline pH and slow P supply into a Ca-rich microenvironment are suggested to facilitate apatite cluster growth, as demonstrated in a biomimetic mineralization system. Together, the results reveal for the first time the distinct and exquisite microstructures of bone apatite clusters in IO and EO, and provide insightful inspirations for the design of more efficient materials for bone tissue engineering and repair.
骨磷灰石晶体呈簇状生长，但这些簇的微观结构尚不清楚。本研究比较了在膜内（IO）和软骨内骨化（EO）中形成的骨磷灰石簇的结构和组成差异。分别从胚胎期 14.5 至 15.5 天（E）和出生后 6 至 7 天（P）的小鼠的颅顶骨（IO）和股骨（EO）中分离出这些组织。结果表明，EO 中最初形成的骨磷灰石簇（≅1.2 μm）比 IO 中的大 10 倍以上（≅0.1 μm），但其离子组成没有明显变化。在 IO（E14.5 颅顶骨）中，早期矿物质在基质小泡（MVs）内形成。相比之下，在 EO（P6 股骨骨骺）中，未观察到 MVs，且软骨细胞来源的质膜纳米片段（PMNFs）是矿化的成核位点。磷灰石簇大小的差异与不同的成核位点有关。此外，在仿生矿化体系中，碱性 pH 值和缓慢的 P 供应进入富含 Ca 的微环境被认为有利于磷灰石簇的生长。综上所述，这些结果首次揭示了 IO 和 EO 中骨磷灰石簇的独特而精细的微观结构，为设计更有效的骨组织工程和修复材料提供了有价值的启示。
