Kang Heesuk, Hollister Scott J, La Marca Frank, Park Paul, Lin Chia-Ying
J Biomech Eng. 2013 Oct 1;135(10):101013-8. doi: 10.1115/1.4025102.
Biodegradable cages have received increasing attention for their use in spinal procedures involving interbody fusion to resolve complications associated with the use of nondegradable cages, such as stress shielding and long-term foreign body reaction. However, the relatively weak initial material strength compared to permanent materials and subsequent reduction due to degradation may be problematic. To design a porous biodegradable interbody fusion cage for a preclinical large animal study that can withstand physiological loads while possessing sufficient interconnected porosity for bony bridging and fusion, we developed a multiscale topology optimization technique. Topology optimization at the macroscopic scale provides optimal structural layout that ensures mechanical strength, while optimally designed microstructures, which replace the macroscopic material layout, ensure maximum permeability. Optimally designed cages were fabricated using solid, freeform fabrication of poly(ε-caprolactone) mixed with hydroxyapatite. Compression tests revealed that the yield strength of optimized fusion cages was two times that of typical human lumbar spine loads. Computational analysis further confirmed the mechanical integrity within the human lumbar spine, although the pore structure locally underwent higher stress than yield stress. This optimization technique may be utilized to balance the complex requirements of load-bearing, stress shielding, and interconnected porosity when using biodegradable materials for fusion cages.
可生物降解椎间融合器在涉及椎体间融合的脊柱手术中的应用日益受到关注，以解决使用不可降解椎间融合器相关的并发症，如应力遮挡和长期异物反应。然而，与永久性材料相比，其初始材料强度相对较弱，且随后会因降解而降低，这可能存在问题。为了设计一种用于临床前大型动物研究的多孔可生物降解椎间融合器，该融合器能够承受生理负荷，同时具有足够的连通孔隙率以实现骨桥接和融合，我们开发了一种多尺度拓扑优化技术。宏观尺度的拓扑优化提供了确保机械强度的最佳结构布局，而替代宏观材料布局的优化设计微观结构则确保了最大渗透性。使用聚（ε-己内酯）与羟基磷灰石的固体自由成型制造工艺制备了优化设计的椎间融合器。压缩试验表明，优化后的融合器的屈服强度是典型人体腰椎负荷的两倍。计算分析进一步证实了其在人体腰椎内的机械完整性，尽管孔隙结构局部承受的应力高于屈服应力。当使用可生物降解材料制造融合器时，这种优化技术可用于平衡承重、应力遮挡和连通孔隙率等复杂要求。
