Polymeric Materials Research Group, Department of Materials Science and Engineering, Sharif University of Technology, Tehran, Iran.
J Biomech. 2012 Nov 15;45(16):2866-75. doi: 10.1016/j.jbiomech.2012.08.029. Epub 2012 Sep 15.
The performance of cellular solids in biomedical applications relies strongly on a detailed understanding of the effects of pore topology on mechanical properties. This study aims at characterizing the failure mechanism of scaffolds based on nodal connectivity (number of struts that meet in joints) and geometry of the pores. Plastic models of scaffolds having the same relative density but different cubic and trigonal unit cells were designed and then fabricated via three dimensional (3-D) printing. Unit cells were repeated in different arrangements in 3-D space. An in-situ imaging technique was utilized to study the progressive deformation of the scaffold models. Different nodal connectivities resulted in a wide range of compressive behaviors in scaffold models, from elastic-plastic to fully brittle. The Maxwell necessary criterion for rigidity was used to explain mechanical behavior of the scaffolds. Nodal connectivity of 4 satisfied Maxwell's criterion for rigidity in the examined structures. In a stress-strain curve of scaffolds with cubic unit cells and nodal connectivities of 3 and 4, pore deformation was observed after yielding. On the other hand, scaffolds with trigonal unit cells and nodal connectivities of 4 and 6, exhibited brittle behavior in the absence of pore deformation. These results highlight the role of nodal connectivity on failure mechanism and subsequently mechanical performance of scaffolds. This study reveals that appropriate pore geometry can provide sufficient condition for rigidity when Maxwell's necessary condition is satisfied. In addition, this study demonstrates that Maxwell's criterion can be used in pre-designing of pore geometries for scaffolds with distinct nodal connectivities.
细胞多孔固体在生物医学应用中的性能强烈依赖于对孔拓扑结构对力学性能的影响的深入理解。本研究旨在表征基于节点连通性（关节处相遇的支柱数量）和孔几何形状的支架的失效机制。设计了具有相同相对密度但具有不同立方和三角单胞的支架塑性模型，然后通过三维（3-D）打印制造。单元在 3-D 空间中以不同的排列方式重复。利用原位成像技术研究支架模型的渐进变形。不同的节点连通性导致支架模型的压缩行为范围很广，从弹塑性到完全脆性。使用 Maxwell 刚性必要准则来解释支架的力学行为。在所研究的结构中，节点连通性为 4 满足 Maxwell 刚性的必要准则。在具有立方单胞和节点连通性为 3 和 4 的支架的应力-应变曲线上，屈服后观察到孔变形。另一方面，具有三角单胞和节点连通性为 4 和 6 的支架表现出脆性行为，而没有孔变形。这些结果突出了节点连通性对支架失效机制和随后的力学性能的作用。本研究表明，当满足 Maxwell 必要条件时，适当的孔几何形状可以为刚性提供足够的条件。此外，本研究表明，Maxwell 准则可用于具有不同节点连通性的支架的孔几何形状的预设计。
