面向3D打印可变模量金属假体的微结构设计

Microstructure Design for 3D Printed Metal Prosthesis of Adjustable Modulus

为了解决假体与骨的弹性模量存在较大差异而造成应力遮挡的问题,基于3D打印在制造多孔微结构的优势,将假体设计为多孔结构能有效降低模量,缓解应力遮挡。但是,如何优化微结构几何参数以实现假体模量的最佳匹配仍然没有得到解决。因此,提出了一种面向3D打印的可变模量金属假体的微结构设计方法,旨在获得与宿主骨模量相匹配又具有可加工性的生物型假体。针对体心立方单元(BCC)和增强体心立方单元(RBCC),采用有限元法计算了两种多孔单元沿轴向、面对角线和体对角线方向的弹性模量,建立了单元弹性模量与支柱直径的函数关系,分析了单元各向异性随支柱直径变化的规律,研究了棱边直径和单元尺寸对单元弹性模量的影响。结果表明:在加工精度范围内,通过减小支柱直径能实现单元等效弹性模量与骨模量一致性要求;在各向同性上BCC单元要优于RBCC单元,而且增大棱边直径有助于提高单元各向同性;由于BCC单元能实现相邻不同模量的单元界面连续拼接,故选用BCC单元构建模量可调的假体,可变模量范围为15.9~100 GPa。该设计方法可用于构建具有模量梯度结构的生物假体,以实现关节应力最优分布。

In order to avoid the stress shielding caused by the difference of elastic modulus between human bone and the prosthetic implant, porous design can be effective to reduce the effectively modulus of the prostheses. However, how to optimize the microstructure geometric parameters for better matching with the bone tissue has not been solved yet. By taking the advantages of 3D printing technology on customized microstructure manufacture, a design method to adjust the modulus of the metal prosthetic for better matching with the bone tissue is proposed in this study, to obtain satisfactory and manufacturable prosthesis by 3D printing. The elastic modulus of two porous lattices along the edge direction, surface diagonal and body diagonal have been calculated individually by implementing the finite element method （FEM）. Thereafter the functional relationship between the equivalent elastic modulus and the strut diameter has been established. The anisotropy characteristics of the microstructure has been analyzed along with the change of the strut diameter, and the influence of the edge diameter and the lattice size on the elastic modulus has been investigated as well. Within the limitation of manufacturing capacity of metal 3D printing, the calculated equivalent elastic modulus of the prosthesis were found to be consistent with those of the human bone by reducing the strut diameter. The body-centered cubic （BCC） is superior to reinforced body-centered cubic （RBCC） in terms of the isotropy characteristics. The BCC unit implementing successfully interface connection of adjacent and different modulus lattice can be used to construct prosthesis of adjustable modulus, and the allowable range of elastic modulus is 15.9-100 GPa. The proposed method can be applied to build prosthesis with gradient modulus gradient in order to achieve the optimized stress distribution within the joints.