Max Planck Institute of Colloids and Interfaces, Department of Biomaterials, Research Campus Golm, 14424 Potsdam, Germany; Berlin-Brandenburg School for Regenerative Therapies (BSRT), Charité - Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany.
Max Planck Institute of Colloids and Interfaces, Department of Biomaterials, Research Campus Golm, 14424 Potsdam, Germany.
J Mech Behav Biomed Mater. 2018 Jan;77:258-266. doi: 10.1016/j.jmbbm.2017.08.022. Epub 2017 Aug 31.
All hierarchical levels in bone are known to contribute to its mechanical behavior. The basic building block is the mineralized collagen fibril which is assembled into larger structures with varying fibrillar organization. The collagen organization increases from unordered woven bone in the callus which is gradually replaced by higher ordered lamellar bone during bone development and healing and finally results in cortical lamellar bone with highest degree of organization. The structural and mechanical description of these organizational motifs is not yet complete. We investigated a femoral osteotomy mouse model and analyzed newly formed callus tissue and mature lamellar bone in the cortex. This model exhibits three bone types with different fibrillar organization: (i) woven, (ii) moderate lamellar and (iii) lamellar. Using high resolution synchrotron small angle X-ray scattering in combination with back-scattered electron imaging we characterized the ultrastructure of the different regions in terms of degree of mineralization, averaged mineral particle thickness and mineral particle orientation. We further used microindentation to correlate hardness, induced crack lengths and crack patterns with the bone ultrastructure. The newly formed callus tissue contains highly mineralized woven bone islands, featuring thick but poorly ordered mineral particles. Such islands are surrounded by layers of lamellar bone with a low mineralization level and thin but well aligned particles. Callus tissue shows lower hardness values and longer cracks than the cortex. Callus woven bone exhibits shorter cracks than callus lamellar bone. However, the poorly mineralized callus lamellar bone shows crack propagation mechanisms similar to cortical bone due to its very similar lamellar organization and high degree of mineral particle orientation. In conclusion we demonstrate that woven and increasingly higher oriented lamellar bone do not only differ in collagen fibril organization, but also that the amount, orientation and different shape of mineral particles are also likely to contribute to the reduced mechanical competence of woven as compared to lamellar bone. This may explain why many organisms replace less organized bone types with higher organized ones.
所有骨的层次结构都被认为对其力学性能有贡献。基本结构单元是矿化的胶原原纤维，它被组装成具有不同纤维组织的更大结构。胶原组织从在愈伤组织中无序的编织骨逐渐增加，在骨发育和愈合过程中逐渐被更高有序的板层骨取代，最终形成具有最高组织程度的皮质板层骨。这些组织图案的结构和力学描述尚不完全。我们研究了股骨切开术小鼠模型，并分析了新形成的愈伤组织和皮质中的成熟板层骨。该模型表现出三种具有不同纤维组织的骨类型：（i）编织骨、（ii）中等板层骨和（iii）板层骨。我们使用高分辨率同步加速器小角 X 射线散射结合背散射电子成像，从矿化程度、平均矿化颗粒厚度和矿化颗粒取向的角度对不同区域的超微结构进行了表征。我们进一步使用微压痕将硬度、诱导裂纹长度和裂纹模式与骨超微结构相关联。新形成的愈伤组织包含高度矿化的编织骨岛，其特征为厚但无序排列的矿化颗粒。这种岛被矿化程度较低、颗粒较薄但排列较好的板层骨层包围。愈伤组织的硬度值和裂纹长度比皮质组织低。愈伤组织编织骨的裂纹长度比愈伤组织板层骨短。然而，由于其非常相似的板层组织和高度的矿化颗粒取向，矿化程度较低的愈伤组织板层骨表现出与皮质骨相似的裂纹扩展机制。总之，我们证明编织骨和排列方向逐渐增加的板层骨不仅在胶原原纤维组织上有所不同，而且矿化颗粒的数量、取向和不同形状也可能导致编织骨的力学性能不如板层骨。这可能解释了为什么许多生物体用更有序的骨类型取代不太有序的骨类型。
