In this study, the unit cell approach, which has previously been demonstrated as a method of manufacturing porous components suitable for use as orthopedic implants, has been further developed to include randomized structures. These random structures may aid the bone in-growth process because of their similarity in appearance to trabecular bone and are shown to carry legacy properties that can be related back to the original unit cell on which they are ultimately based. In addition to this, it has been shown that randomization improves the mechanical properties of regular unit cell structures, resulting in anticipated improvements to both implant functionality and longevity. The study also evaluates the effect that a post process sinter cycle has on the components, outlines the improved mechanical properties that are attainable, and also the changes in both the macro and microstructure that occur.
Aims The purpose of this study was to evaluate the biological fixation of a 3D printed porous implant, with and without different hydroxyapatite (HA) coatings, in a canine model. Materials and Methods A canine transcortical model was used to evaluate the characteristics of bone ingrowth of Ti6Al4V cylindrical implants fabricated using laser rapid manufacturing (LRM). At four and 12 weeks post-implantation, we performed histological analysis and mechanical push-out testing on three groups of implants: a HA-free control (LRM), LRM with precipitated HA (LRM-PA), and LRM with plasma-sprayed HA (LRM-PSHA). Results Substantial bone ingrowth was observed in all LRM implants, with and without HA, at both time periods. Bone ingrowth increased from 42% to 52% at four weeks, to 60% to 65% at 12 weeks. Mechanical tests indicated a minimum shear fixation strength of 20 MPa to 24 MPa at four weeks, and 34 MPa to 40 MPa at 12 weeks. There was no significant difference in the amount of bone ingrowth or in the shear strength between the three implant types at either time period. Conclusion At four and 12 weeks, the 3D printed porous implants exhibited consistent bone ingrowth and high mechanical shear strength. Based on the results of this study, we confirmed the suitability of this novel new additive manufacturing porous material for biological fixation by bone ingrowth. Cite this article: Bone Joint J 2019;101-B(6 Supple B):62–67.
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