An opportunity is offered by porous structures as implants in medical applications and arthroplasties because their mechanical and physical properties can be tuned to match patient-specific needs. For ex vivo research, there is merit in using 3D models instead of 2D layers in tissue engineering to recapitulate cell growth in microenvironments that are similar to native tissue, because this narrows the gulf between in vitro tests and clinical translation. [1] Titanium and its alloys have been researched extensively because of their biocompatibility, high strength, low wear, and corrosion resistance (due to the passivating oxide layer spontaneously formed on the surface [2] ). When embodied as porous structures, they offer mechanical properties that can match those of cortical and trabecular bone, [3] avoiding stress shielding and biomechanical failure. Porous scaffolds must be conducive to osseointegration by means of providing channels and interconnected pores for nutrient distribution, [4] networks for cellular proliferation, differentiation and maturation, and ultimately for bone healing. [5] Much work has explored different pore architectures and sizes and routes by which they can be physically realized. Advances in computer-aided design (CAD), multiphysics modeling, [6] and additive manufacturing (AM) technology have allowed the definition of a design space to digitally test manufacturability boundaries for porous structures with the desired physical, mechanical, and permeability properties that can enhance biological behavior. [7] Techniques such as selective laser melting (SLM) or electron beam melting (EBM) have been demonstrated as practical processing routes to achieve both parametric and nonparametric designs, ordered or random, using metals. With regard to parametric designs, triply periodic minimal surface (TPMS) structures [8] have received attention in recent years as AM managed to realize the manufacture of these topologies that offer mechanical superiority due to a uniformly distributed load transfer, free of discontinuities and self-intersecting elements, and

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In this study, Ti-(0-30 wt.%)Nb alloys developed from elemental powders were fabricated by the Selective Laser Melting (SLM) process. Compositional homogeneity, microstructure and mechanical performance were investigated as a function of energy density. The proportion of un-melted Nb particles and isolated pore count reduced with increasing energy density, while Ti allotropic content (i.e. α’, α” and β) varied with energy density due to in-situ alloying. Increasing the Nb content led to the stabilisation of the α” and β phases. The mechanical properties were similar to those compositions manufactured using casting methods, without further post processing. The addition of 20Nb (wt.%) and using an energy density of 230 J/mm3 resulted in a Young’s Modulus of 65.2 ± 1.8 GPa, a yield strength of 769 ± 36 MPa and a microstructure of predominantly α” martensite. This strength to stiffness ratio (33% higher than Ti-10Nb and 22% higher than Ti-30Nb), is attributed to in-situ alloying that promotes solid solution strengthening and homogenisation. These alloys are strong contenders as materials suitable for implantable load-bearing orthopaedic applications.

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The cover illustrates the difficulty in predicting properties in selective laser melted metals. The presence of "satellite particles", inherent to the manufacturing process, creates discrepancies between the CAD model and the as‐manufactured scaffold, manifested in a departure of actual properties from those predicted. When these structures are used as implants in regenerative medicine, that roughness also impacts cell behaviour. Further details can be found in article number http://doi.wiley.com/10.1002/adem.202100527 by Carmen Torres‐Sanchez and co‐workers.