Mechanical and in vitro biological properties of uniform and graded Cobalt-chrome lattice structures in orthopedic implants.

Human bones are biological examples of functionally graded lattice capable to withstand large in vivo loading and allowing optimal stress distribution. Disruption of bone integrity may require biocompatible implants capable to restore the original bone structure and properties. This study aimed at comparing mechanical properties and biological behavior in vitro of uniform (POR-FIX) and graded (POR-VAR) Cobalt-chrome alloy lattice structures manufactured via Selective Laser Melting. In compression, the POR-VAR equivalent maximum stress was about 2.5 times lower than that of the POR-FIX. According to the DIC analysis, the graded lattice structures showed a stratified deformation associated to unit cells variation. At each timepoint, osteoblast cells were observed to colonize the surface and the first layer of both scaffolds. Cell activity was always significantly higher in the POR-VAR (p < 0.0005). In terms of gene expression, the OPG/RANKL ratio increased significantly over time (p < 0.0005) whereas IL1ß and COX2 significantly decreased (7 day vs 1 day; p < 0.0005) in both scaffolds. Both uniform- and graded-porosity scaffolds provided a suitable environment for osteoblasts colonization and proliferation, but graded structures seem to represent a better solution to improve stress distribution between implant and bone of orthopedic implants.

CoCr porous scaffolds manufactured via selective laser melting in orthopedics: Topographical, mechanical, and biological characterization.

Over the last decade, advances in additive manufacturing have allowed to obtain complex 3D porous lattice in materials suitable for orthopedic applications. Whereas 3D-melted titanium alloys have been extensively investigated, little is the current knowledge on the feasibility of bone-replicating CoCr porous scaffolds manufactured via selective laser melting (SLM). Moreover, the effect of topography on bone cells viability and proliferation has not been fully explored yet. Small cylindrical porous lattices were modeled from micro-CT images of human trabecular bone, and from the repetition of spherical-hollow and body-centered cubic unit cells, and manufactured via SLM from CoCr powder. Macro- and microcharacterization of the porous samples were assessed using optical microscope, micro-CT, and SEM. The scaffolds mechanical properties, measured via ISO testing, compared well with those of the human bone. Osteoblast-like cells proliferation and viability were assessed in vitro, and compared to those cultured on a standard nonporous implant-to-bone interface, showing steady increase on all geometries over time. SEM analysis confirmed the quality of cells morphology, spread, and organization on all lattices. The SLM process appeared not to alter the biocompatibility of CoCr; however, 15-100 µm irregularities and macroalterations were observed in the porous scaffolds with respect to the 3D nominal models. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 2343-2353, 2019.