Osteoconductive Lattice Microarchitecture for Optimized Bone Regeneration

Abstract

Selective laser melting (SLM) is one methodology to realize additive manufacturing and is mainly used to join metal powder in a layer-by-layer manner to produce a solid three-dimensional (3D) object. For bone tissue engineering purposes, scaffolds can readily be designed as 3D data model and realized with titanium known for its excellent osseointegration behavior. The microarchitecture, that is, design with submillimeter features, of additively manufactured scaffolds is in many cases a lattice structure. This study aimed to apply SLM that allows a high degree of microarchitectural freedom to generate lattice structures and to determine the optimal distance between rods and the optimal diameter of rods for osteoconduction (bone ingrowth into scaffolds) and bone regeneration. For the biological readout, diverse SLM-fabricated titanium implants were placed in the calvarium of rabbits and new bone formation and defect bridging were determined after 4 weeks of healing. The results from the middle section of the defects show that with a lattice microarchitecture, the optimal distance between titanium rods is around 0.8 mm and the optimal rod dimension is between 0.3 and 0.4 mm to optimize defect bridging and bone regeneration.

Reconsidering Osteoconduction in the Era of Additive Manufacturing

“…(c) Because the rods form squares, the diagonal of the most osteoconductive squares and the most osteoconductive pore diameter are almost identical (1.13 and 1.20 mm, respectively). 36,84 additive manufacturing in hand, further studies on the essence of osteoconduction in terms of microarchitecture and guiding cues can be undertaken in the future.…”

“…100 Here, in this review, we only looked at microarchitecture and osteoconduction, and defined certain microarchitectures to be highly osteoconductive in terms of bony defect bridging. 36,84 Since bony defect bridging is the key element in avoiding nonunions, and given the clinical and economic burden of treating nonunions, 101 there is an obvious need to develop bone substitutes with high osteoconductive properties in terms of osteoconductive microarchitectures.…”

“…For a rod distance of 0.8 mm, the defect was 90.83 -16.22% bridged, compared with a rod distance of 0.3 mm, where to only 57.50 -24.57% bony bridging occurred. 36 This suggests that bone ingrowth is significantly faster, and thus osteoconduction is optimized in wide-open microarchitectures compared with narrower counterparts, 36 and that the surface component overpowers osteoconduction in narrow structures. The results from narrow microarchitectures might be the reason for a definition of osteoconduction as provided in a previous study 15 : ''This term (osteoconduction) means that bone grows on a surface.''…”

“…The outcome of this study revealed that the most osteoconductive lattice architecture is one consisting of rods with a thickness of 0.3 mm at a distance of 0.8 mm from each other. 36 To test the material dependence of this finding, microarchitecturally identical titanium and TCP scaffolds were compared, and no difference in the ingrowth of bone was found. 99 This is reasonable because with pores wider than 0.5 mm bone grows between the rods (Fig.…”

Osteoconductive Microarchitecture of Bone Substitutes for Bone Regeneration Revisited

“…The unit cells ( Figure 1C ) to design the scaffolds are cubes of 1.0–2.0 mm length. We have chosen this design and adjusted it to the needs of the material and production methodology, since it resembles the design with the highest mechanical performance and high anisotropy, as previously reported for titanium scaffolds ( de Wild et al, 2016 , 2018 ; Rüegg et al, 2017 ). In the center of each unit cell a pore of 0.5–1.7 mm is located.…”