Effects of the unit cell topology on the compression properties of porous Co-Cr scaffolds fabricated via selective laser melting

Abstract

Purpose Selective laser melting (SLM) is an additive manufacturing process suitable for fabricating metal porous scaffolds. The unit cell topology is a significant factor that determines the mechanical property of porous scaffolds. Therefore, the purpose of this paper is to evaluate the effects of unit cell topology on the compression properties of porous Cobalt–chromium (Co-Cr) scaffolds fabricated by SLM using finite element (FE) and experimental measurement methods. Design/methodology/approach The Co-Cr alloy porous scaffolds constructed in four different topologies, i.e. cubic close packed (CCP), face-centered cubic (FCC), body-centered cubic (BCC) and spherical hollow cubic (SHC), were designed and fabricated via SLM process. FE simulations and compression tests were performed to evaluate the effects of unit cell topology on the compression properties of SLM-processed porous scaffolds. Findings The Mises stress predicted by FE simulations showed that different unit cell topologies resulted in distinct stress distributions on the bearing struts of scaffolds, whereas the unit cell size directly determined the stress value. Comparisons on the stress results for four topologies showed that the FCC unit cell has the minimum stress concentration due to its inclined bearing struts and horizontal arms. Simulations and experiments both indicated that the compression modulus and strengths of FCC, BCC, SHC, CCP scaffolds with the same cell size presented in a descending order. These distinct compression behaviors were correlated with the corresponding mechanics response on bearing struts. Two failure mechanisms, cracking and collapse, were found through the results of compression tests, and the influence of topological designs on the failure was analyzed and discussed. Finally, the cell initial response of the SLM-processed Co-Cr scaffold was tested through the in vitro cell culture experiment. Originality/value A focus and concern on the compression properties of SLM-processed porous scaffolds was presented from a new perspective of unit cell topology. It provides some new knowledge to the structure optimization of porous scaffolds for load-bearing bone implants.

CoCr porous scaffolds manufactured via selective laser melting in orthopedics: Topographical, mechanical, and biological characterization

“…The effect of laser‐sintered CoCr implants on bone growth was previously reported using nonporous structures, or in porous scaffolds using electron beam melting technology only . More recently, the effect of different unit cells topologies on the mechanical properties of SLM‐processed CoCr porous scaffolds has been reported . The topological design was found to be responsible for 10‐fold differences in mechanical properties, whereas the material type for up to twofold differences .…”

“…28 More recently, the effect of different unit cells topologies on the mechanical properties of SLM-processed CoCr porous scaffolds has been reported. 29,30 The topological design was found to be responsible for 10-fold differences in mechanical properties, whereas the material type for up to twofold differences. 29 While initial biological response to osteoblast-like cells 30 and the antibacterial properties of silk fibroin coatings have also been reported by the same authors, 31 the current knowledge on the biological response and topographical effects of 3D-printed CoCr lattices on osseointegration 28 is still relatively poor.…”

Review of defects in lattice structures manufactured by powder bed fusion

“…6.1). Other supporting comments on the texture of lattice surfaces can be found elsewhere [11,36,37,41,57,58,68,71,73,[80][81][82][83][84][85][86][87]].…”

“…Hildebrand and Rüegsegger [99] highlight additional parameters useful for characterising lattice structures with XCT, for example the ratio of surface area to volume which could allow for a comparison of attached particles in multiple samples. Dimensional measurements have been performed using XCT [98,100], SEM [11,13,68,69,73,[85][86][87][101][102][103] and optical microscopy [25,36,63,75,76,[104][105][106]. It is also relatively common to use Vernier callipers for the measurement of outer dimensions (for example, lattice diameter, length, width) [74,103,104,107].…”

Fatigue performance of additively manufactured meta-biomaterials: The effects of topology and material type

“…The main concerns of the previous studies have been to investigate the effects of the topological characteristics of the porous structure on their fatigue response, and as a result the performance comparisons have been made between porous structures with different topological designs but made from the same bulk materials (e.g. steel [29,30], magnesium [31,32], titanium [33][34][35], Co-Cr [36,37]). Therefore, it is currently not clear what the effects of material type on the normalized S-N curve are.…”