Additive manufacturing of Trabecular Titanium orthopedic implants
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Introduction Orthopedic implants such as hip, knee, and shoulder replacements are subjected to great challenges during their use:1 Cyclic loads, sliding wear, and the human body ambient are demanding factors for the materials employed. This has allowed research for new materials with better performance to flourish over the past 50 years. One of the critical success factors for prosthetic implants is called osseointegration and is responsible for long-term implant fixation. Having a good bone response leads to less risk of implant detachment or loosening. Osseointegration is related to both cell attachment and proliferation, and involves a large number of biological factors. However, the success of bone response in prosthetic implant osseointegration processes largely depends on the surface properties of the applied material.2 A large body of research has been carried out to improve biological responses of the human body to biomaterials, mainly related to enhancing the adhesion of bone osteoblasts, which are the cells responsible for bone formation, to the implant surface.2–6 The development of highly porous surfaces and scaffolds to mimic the so-called trabecular structure of cancellous bone (a network of spongy tissue found, for example, at the core of bones) is of great interest, and its successful application is demonstrated by clinical evidence.7,8 There is a large body of scientific literature on the ability of natural bone to
re-grow within narrow porosities of cellular solids and metal foams, designed to be as close as possible to the trabecular porous structure of natural bone.3,7,8 All of these efforts have led to the creation of a number of technologies used by the orthopedic implant industry toward the creation of novel porous surfaces to be in contact with bone, such as vacuum plasma spray (VPS), chemical vapor deposition, and lowtemperature arc vapor deposition. Despite overall positive clinical outcomes, enhancing implant surface complexity resulted in some drawbacks, such as porous layer detachment from the substrate, corrosion phenomena, and implant loosening.9–11 This propelled further research seeking the optimal technologies and porous structures to be employed. Pore size and porosity play critical roles in the formation of new bone tissue. In fact, a minimum pore size of 300 µm appears to be necessary in order to improve osseointegration. Further, it has been found that the growth of osteoblast is quicker in 600 µm diameter holes than other diameters, ranging from 300 to 1000 µm.7 In addition, bone response can be enhanced by surface roughness as well. It has been demonstrated that microtexturing (10–50 μm) enhances the osseointegration properties of the scaffold, such that comparable levels of bone ingrowth can be obtained even with different pore diameters and porosity.12,13 It has to be considered, however, that porosity and roughness affect the mechanical
Marco Regis, Lima Corporate, Italy; [email protected] Elia Marin, Chemistry, Physics, and Ambient Department, University of Udi
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