Predicting the output dimensions, porosity and elastic modulus of additive manufactured biomaterial structures targeting orthopedic implants

Abstract

SLM accuracy for fabricating porous materials is a noteworthy hindrance when aiming to obtain biomaterial cellular structures owing precise geometry, porosity, open-cells dimension and mechanical properties as outcomes. This study provides a comprehensive characterization of seventeen biomaterial Ti6Al4V-based structures in which experimental and numerical investigations (compression stress-strain tests) were carried out. Mono-material Ti6Al4V cellular structures and multi-material Ti6Al4V-PEEK cellular structures were designed, produced by SLM and characterized targeting orthopedic implants. In this work, the differences between the CAD design and the as-produced Ti6Al4V-based structures were obtained from image analysis and were used to develop predictive models. The results showed that dimensional deviations inherent to SLM fabrication are systematically found for different dimensional ranges. The present study proposes several mathematical models, having high coefficients of determination, that estimate the real dimensions, porosity and elastic modulus of Ti6Al4V-based cellular structures as function of the CAD model. Moreover, numerical analysis was performed to estimate the octahedral shear strain for correlating with bone mechanostat theory limits. The developed models can help engineers to design and obtain near-net shape SLM biomaterials matching the desired geometry, open-cells dimensions, porosity and elastic modulus. The obtained results show that by using these AM structures design it is possible to fabricate components exhibiting a strain and elastic modulus that complies with that of bone, thus being suitable for orthopedic implants.

Multi-material NiTi-PEEK hybrid cellular structures by Selective Laser Melting and Hot Pressing: Tribological characterization

“…By analyzing mono-material cellular structures some deviations between the real dimensions obtained for open-cell sizes and wall thicknesses and the ones designed in the CAD model are observed, with these structures displaying lower open-cell sizes and higher wall thicknesses. This phenomenon, already reported in literature, is typical of SLM process and is related with powder related aspects and partial melting of powder particles near the laser melted zones [6,39,41,43,44].…”

“…Firstly, it is important to highlight that adjusted CAD designs were modeled for each group by substituting the designed dimensions by the real dimensions (open-cell and thickness) that were measured after SLM fabrication. More details on these differences between CAD design and SLM fabricated parts can be found in literature [38][39][40][41][42]. From the "adjusted CAD model" of each group, the initial volume of the specimen was taken from the software and, subsequently, the wear track that was previously designed in 3D (considering the collected width and length of the track) was imported.…”

Selective Laser Melting of Ti6Al4V sub-millimetric cellular structures: Prediction of dimensional deviations and mechanical performance

“…Considering the five types of structures (SP1 to SP5), on average, the open-cell sizes are ≈105 μm lower and the wall sizes are ≈99 μm higher comparing to the model CAD dimensions. In fact, it is important to highlight that these deviations were found for all the investigated structures indicating that these dissimilarities are inherent to SLM technique, as reported in several studies (Arabnejad et al, 2016;Bartolomeu et al, 2017bBartolomeu et al, , 2019bBartolomeu et al, , 2020aRan et al, 2018). In literature several studies can be found indicating that the fabrication of sub-millimetric porous structures by SLM leads to ≈100 μm smaller open-cells and ≈100 μm thicker walls (Bagheri et al, 2017;Yan et al, 2012;Arabnejad et al, 2016;Dallago et al, 2019b).…”

Additive manufacturing of NiTi-Ti6Al4V multi-material cellular structures targeting orthopedic implants

“…However, in several applications such as orthopedic implants, components should incorporate distinct materials in different beneficial positions for achieving high-efficient and long-term solutions [38,39] . Several studies have been reported involving the SLM production of Ti6Al4V dense or cellular structures parts and some on Ti6Al4V-based multi-material structures [11,[40][41][42][43][44] . Some studies can be found in literature where AM is used to fabricate multimaterial Ti6Al4V-based components such as Ti6Al4V-Invar, Ti6Al4V-Stainless Steel, Ti6Al4V-Inconel 718, Ti6Al4V-Al12Si [36,[45][46][47] .…”

“…Currently, biomedical cellular structured materials are in great demand once these materials can provide, simultaneously, adequate mechanical properties (strength and stiffness), physical and morphological properties, as well as a suitable ecosystem for cell seeding and bone ingrowth [41,42,44,48,49] . SLM technique has been used to produce mono-material Ti6Al4V and NiTi cellular structures for lowering the implant-bone stiffness mismatch [41,[50][51][52][53] .…”