Novel Approach in Design of Multi-Scale Porous Metamaterials Using Laser Powder Bed Fusion

Multi-scale porous metamaterials can be fabricated via laser powder bed fusion (LPBF) and deployed in the next generation of Ti-alloy spinal implants. Furthermore, metallic porous structures can be augmented with a photopolymer resin, using tomographic volumetric additive manufacturing (TVAM) to achieve biomimetic structures and performance. The motivation behind this work is to address stress-shielding effects, which remains an ongoing challenge in metallic implants and occurs due to the mismatch of mechanical properties between the implant and human bone. Common alloys used for implants such as Ti-6Al-4V, SS316L and CoCr are magnitudes stronger and stiffer than bone, which can cause issues such as implant loosening and failure due to the stress-shielding effect. Strategically introducing voids into implant structures can help with tailoring mechanical properties of these alloys to improve biocompatibility. Lattices manufactured using LPBF have been extensively studied for this application, however, they are still unable to reach the target mechanical properties of human bone. This study leverages LPBF processing parameters to create strategic voids, a novel approach to manufacturing porous materials for implant applications tackling the stress-shielding effect. Process-driven porous structures are created by altering parameters in the LPBF process, such as hatch spacing and rotation angle. This results in structures with broad ranges of porosities (0% - 70%) and pore morphologies (stochastic and columnar). Multi-scale porous structures can be designed by combining the process-driven and deterministic lattice approaches, resulting in a structure with various surface textures, pore sizes and mechanical properties. Mechanical testing of deterministic (latticed), process-driven (stochastic) and a combination of the two porous structures have been conducted, and results show differences in mechanical response depending on the architecture. This work highlights the ability to tailor the response of porous structures through design and manufacturing to bridge the gap in performance requirements of spinal implants.