ORTHOPAEDICS AND ADDITIVE MANUFACTURING: DOES IT ALL ADD UP?

Advancements in 3D printing, known as additive manufacturing (AM), has allowed for the production of highly porous Trabecular Metals (TM) that aim to ‘mimic’ human bone allowing bony in-growth. AM is being increasingly used to produce acetabular implants with a TM surface aiming to create a well-fixed component, reducing the rate of aseptic loosening. There remains much debate over the optimum design of these TMs, however, many ‘off the shelf’ implants already exist and are widely used in arthroplasty surgery. From the limited data published on these products there is a wide variation in their structural properties, namely pore size, shape and porosity, as well as variations in the manufacturing process. This highlighted the need for a study that can better evaluate, and potentially predict, the ‘real world’ performance of these developing materials to allow for accurate pre-clinical analysis, as well as direct comparisons between those implants already available. 5 commonly available acetabular cups, all produced by AM were cut into multiple samples. (Lima Delta TT, Adler Fixa-Ti-Por, Zimmer-Biomet G7 Osseo-Ti, Smith & Nephew Redapt, Stryker Trident II). The samples were imaged with scanning electron microscopy and micro-CT to evaluate their trabecular structure and surface finish. Human bone marrow stem cells (HBMSCs) were then seeded onto these samples, cultured and fixed for analysis. Further imaging was performed to visualise the HBMSCs on the trabecular surface, demonstrating the differences in attachment and proliferation across the different acetabular cups. Subsequent biomolecular analysis compared cell viability, proliferation and early markers of osteointergration across the different implants. Image analysis highlighted key differences in the structural design of the implants and demonstrated how the HBMSCs interacted with these TM surfaces. Biochemical analysis showed a statistically significant difference (P≤0.05) in the early osteogenic response of HBMSCs cultured on the different implants. These results show a significant variance in the response of HBMSCs to each surface design/structure across the implants. Whilst difficult to draw precise conclusions on the long-term performance of each implant this shows that the variation in TM design has an impact on HBMSC function.