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Abstract: Background Dense titanium (Ti) fusion cages have been commonly used in transforaminal lumbar interbody fusion. However, the stiffness mismatch between cages and adjacent bone endplates increases the risk of stress shielding and cage subsidence. Methods The current study presents a multiscale optimization approach for porous Ti fusion cage development, including microscale topology optimization based on homogenization theory that obtains a unit cell with prescribed mechanical properties, and macroscale topology optimization that determines the layout of framework structure over the porous cage while maintaining the desired stiffness. The biomechanical performance of the designed porous cage is assessed using numerical simulations of fusion surgery. selective laser melting is employed to assists with fabricating the designed porous structure and porous cage. Results The simulations demonstrate that the designed porous cage increases the strain energy density of bone grafts and decreases the peak stress on bone endplates. The mechanical and morphological discrepancies between the as-designed and fabricated porous structures are also described. Conclusion From the perspective of biomechanics, it is demonstrated that the designed porous cage contributes to reducing the risk of stress shielding and cage subsidence. The optimization of processing parameters and post-treatments are required to fabricate the designed porous cage. The present multiscale optimization approach can be extended to the development of cages with other shapes or materials and further types of orthopedic implants.

山东大学万熠等 | 指定力学性能的多孔椎间融合器多尺度设计及生物力学性能评价

本研究论文聚焦指定力学性能的多孔椎间融合器多尺度设计及生物力学性能评价。钛合金融合器已广泛用于经椎间孔腰椎融合术，但融合器和相邻骨性终板之间的刚度差异增加了融合器的应力遮挡效应和沉降的风险。本研究提出一种多孔钛合金融合器多尺度优化设计方法，包括基于均匀化理论的微观拓扑优化，用于获取具有指定力学性能的单胞，宏观拓扑优化用于确定多孔钛合金融合器上框架结构的布局，并维持融合器所需的刚度。仿真结果表明，多孔融合器增加了填充骨的应变能密度，降低了骨性终板上的峰值应力。从生物力学角度来看，设计的多孔融合器有助于降低融合器的应力遮挡效应和沉降的风险。但是，多孔融合器的增材制造仍需要进一步优化工艺参数和后处理，以消除与设计的力学性能和形貌之间差异。该多尺度优化方法可以推广应用于其它类型的骨科植入物设计。

（论文的第一作者为山东大学机械工程学院博士研究生王宏卫；山东大学齐鲁医院骨科刘新宇主任为本研究做出了重要贡献；山东大学机械工程学院万熠教授为该文章的通讯作者）