Department of Mechanical Engineering, Villanova University, 800 Lancaster Avenue, Villanova, PA, 19085, USA.
Biomech Model Mechanobiol. 2018 Oct;17(5):1415-1428. doi: 10.1007/s10237-018-1035-6. Epub 2018 May 28.
The recent studies have shown that long-term bisphosphonate use may result in a number of mechanical alterations in the bone tissue including a reduction in compositional heterogeneity and an increase in microcrack density. There are limited number of experimental and computational studies in the literature that evaluated how these modifications affect crack initiation and propagation in cortical bone. Therefore, in this study, the entire crack growth process including initiation and propagation was simulated at the microscale by using the cohesive extended finite element method. Models with homogeneous and heterogeneous material properties (represented at the microscale capturing the variability in material property values and their distribution) as well as different microcrack density and microstructure were compared. The results showed that initiation fracture resistance was higher in models with homogeneous material properties compared to heterogeneous ones, whereas an opposite trend was observed in propagation fracture resistance. The increase in material heterogeneity level up to 10 different material property sets increased the propagation fracture resistance beyond which a decrease was observed while still remaining higher than the homogeneous material distribution. The simulation results also showed that the total osteonal area influenced crack propagation and the local osteonal area near the initial crack affected the crack initiation behavior. In addition, the initiation fracture resistance was higher in models representing bisphosphonate treated bone (low material heterogeneity, high microcrack density) compared to untreated bone models (high material heterogeneity, low microcrack density), whereas an opposite trend was observed at later stages of crack growth. In summary, the results demonstrated that tissue material heterogeneity, microstructure, and microcrack density influenced crack initiation and propagation differently. The findings also elucidate how possible modifications in material heterogeneity and microcrack density due to bisphosphonate treatment may influence the initiation and propagation fracture resistance of cortical bone.
最近的研究表明，长期使用双膦酸盐可能会导致骨组织发生多种力学改变，包括组成异质性降低和微裂纹密度增加。文献中仅有少数实验和计算研究评估了这些改变如何影响皮质骨中的裂纹起始和扩展。因此，在这项研究中，使用内聚扩展有限元法在微尺度上模拟了整个裂纹扩展过程，包括起始和扩展。比较了具有均匀和非均匀材料特性的模型（在微尺度上表示，捕捉材料特性值及其分布的可变性）以及不同的微裂纹密度和微观结构。结果表明，与非均匀材料特性模型相比，具有均匀材料特性模型的起始断裂阻力更高，而在扩展断裂阻力方面则相反。材料非均匀性水平增加到 10 种不同的材料特性集，增加了扩展断裂阻力，超过这一水平后，阻力会下降，但仍高于均匀材料分布。模拟结果还表明，总骨单位面积影响裂纹扩展，初始裂纹附近的局部骨单位面积影响裂纹起始行为。此外，与未处理骨模型相比，代表双膦酸盐处理骨（低材料非均匀性、高微裂纹密度）的模型的起始断裂阻力更高，而在裂纹扩展的后期阶段则相反。总之，结果表明，组织材料异质性、微观结构和微裂纹密度对裂纹起始和扩展的影响不同。这些发现还阐明了由于双膦酸盐治疗可能导致的材料异质性和微裂纹密度的变化如何影响皮质骨的起始和扩展断裂阻力。
