Lattice structures are a prime candidate for applications in the medical implant industry due to their versatile mechanical behaviour, which can be tailored to meet specific patient needs and reduce stress shielding, while enabling the natural flow of body fluids. In this work, the mechanical properties of metallic lattices made of five different unit cell types, Cubic (C), Truncated Octahedron (TO), Truncated Cubic (TC), Rhombicuboctahedron (RCO), and Rhombitruncated Cuboctahedron (RTCO), were evaluated under uniaxial compression at three different relative densities, 5%, 15%, and 45%. The evaluation was experimental, and it was compared with previous and new finite element simulations. Specimens for the experimental tests were fabricated in stainless steel 316L by laser powder bed fusion, and stress–strain curves were obtained for the different lattices. The combination of the test results with a critical interpretation of the deformation mechanisms allowed us to confirm that two unit cell types, TO and RTCO, are stable for the whole range of relative densities evaluated. The other three unit cells exhibit more unpredictable behaviour, either due to manufacturing defects or limitations, or because their unstable compression behaviour leads to bucking. For these reasons, TO and RTCO unit cell types are mechanically more adequate for applications in the medical implant industry.

Laser powder bed fusion (L-PBF) is one of the most promising additive manufacturing technologies for creating customised 316L Stainless Steel (SS) implants with biomimetic characteristics, controlled porosity, and optimal structural and functional properties. However, the behaviour of as-fabricated 3D 316L SS structures without any surface finishing in environments that simulate body fluids remains largely unknown. To address this knowledge gap, the present study investigates the surface characteristics, the internal porosity, the corrosion in simulated body fluid (SBF), and the mechanical properties of as-fabricated 316L SS structures manufactured by L-PBF with rhombitruncated cuboctahedron (RTCO) unit cells with two distinct relative densities (10 and 35%). The microstructural analysis confirmed that the RTCO structure has a pure austenitic phase with a roughness of ~20 µm and a fine cellular morphology. The micro-CT revealed the presence of keyholes and a lack of fusion pores in both RTCO structures. Despite the difference in the internal porosity, the mechanical properties of both structures remain within the range of bone tissue and in line with the Gibson and Ashby model. Additionally, the as-fabricated RTCO structures demonstrated passive corrosion behaviour in the SBF solution. Thus, as-fabricated porous structures are promising biomaterials for implants due to their suitable surface roughness, mechanical properties, and corrosion resistance, facilitating bone tissue growth.

Metaphyseal sleeves help maintain long term stability and reduce revision rate for aseptic loosening in total knee arthroplasty (TKA) revision. However, their performance regarding bone remodeling is still poorly known for the long term. This study aimed to investigate the impact of metaphyseal sleeves on the bone remodeling of the tibia. Five finite element models of a female tibia with different implant configurations (regarding stem length and metaphyseal sleeve application) were developed. Loading conditions included joint reaction force, muscle, and tibia-fibula loads from 6 instances of the gait cycle. The bone remodeling model applied was adapted to the subject under analysis by selecting the bone remodeling parameters that best replicated the bone density distribution of the tibia estimated from the CT data. Changes in bone density after TKA were evaluated in 8 regions of interest. Global bone loss ranged from -31.16%, in 115 mm stemmed configurations, to -20.93%, in 75 mm stemmed configurations. Apart from the lateral and posterior regions in the proximal tibia, whose bone loss reduced and increased, respectively, due to the incorporation of a metaphyseal sleeve, changes in bone density were similar with and without a metaphyseal sleeve for each stem length. The results suggest that bone remodeling of the tibia is not critically affected by the incorporation of metaphyseal sleeves. Considering that sleeves are believed to present a favorable clinical outcome in stability and osseointegration, reducing the revision rate for aseptic loosening, their advantages seem to outweigh their disadvantages regarding bone remodeling.

The present work evaluates the surface roughness of lattice structures produced in AISI 316 stainless steel, with laser powder bed fusion (LPBF). To this end, five lattice types were evaluated, namely cubic (C), truncated octahedron (TO), truncated cubic (TC), rhombicuboctahedron (RCO) and rhombitruncated cuboctahedron (RTCO) to determine the average roughness Sa by profilometry. For comparison, the surface roughness of a bulk specimen was also measured. The average roughness was Sa=7.3 mm for the bulk specimen, for the C and TC arrangements it was around 11 mm, while for configurations RCO, RTCO and TO it was in the range 18-22 mm, meaning that surface roughness increases for more complex structures. Values of Sa around 10-25 mm are reported in the literature for parts fabricated by LPBF for medical implants. If complex lattice arrangements are required, a study of the printing parameters is relevant, to achieve scaffolds with improved biomechanical performance.

Metal additive manufacturing (AM) offers promising advancements in producing implants with complex geometry for biomedical applications, where accuracy and near-net-shape production are essential. Metal AM by laser powder bed fusion (PBF-LB) is a promising route to produce biodegradable iron implants made of complex lattice structures. However, processing windows for pure iron remain poorly defined. This work focuses on optimizing PBF-LB parameters for pure iron using a design of experiments (DoE) approach on bulk samples of different geometries to evaluate different parameters. Hatch laser power, scanning speed, hatch distance and point distance were varied and their effect on porosity, surface roughness and dimensional accuracy was evaluated. This was followed by the fabrication of rhombitruncated cuboctahedron (RTCO) lattice structures with the best parameters previously defined for the bulk samples. The best parameter set (hatch laser power 180 W, scanning speed 600 mm/s, hatch distance 110 µm and point distance 12 µm, corresponding to a volumetric energy density of 90.9 J/mm³) produced bulk samples with a porosity as low as 0.07% (99.93% density) measured in polished sections. Using these parameters, RTCO lattices with designed relative densities of 10.28%, 35.29% and 65.16% were successfully manufactured with small geometric deviations and good control of strut thickness and relative density. The results of this study define a robust PBF-LB processing window for pure iron and demonstrate the feasibility of producing geometrically controlled, biodegradable iron lattice structures suitable for future load-bearing biomedical applications.