Bone regeneration procedures in clinics and bone tissue engineering stand on three pillars: osteoconduction, osteoinduction, and stem cells. In the last two decades, the focus in this field has been on osteoinduction, which is realized by the use of bone morphogenetic proteins and the application of mesenchymal stem cells to treat bone defects. However, osteoconduction was reduced to a surface phenomenon because the supposedly ideal pore size of osteoconductive scaffolds was identified in the 1990s as 0.3-0.5 mm in diameter, forcing bone formation to occur predominantly on the surface. Meanwhile, additive manufacturing has evolved as a new tool to realize designed microarchitectures in bone substitutes, thereby enabling us to study osteoconduction as a true three-dimensional phenomenon. Moreover, by additive manufacturing, wide-open porous scaffolds can be produced in which bone formation occurs distant to the surface at a superior bony defect-bridging rate enabled by highly osteoconductive pores 1.2 mm in diameter. This review provides a historical overview and an updated definition of osteoconduction and related terms. In addition, it shows how additive manufacturing can be instrumental in studying and optimizing osteoconduction of bone substitutes, and provides novel optimized features and boundaries of osteoconductive microarchitectures. Impact Statement This review updates the definition of osteoconduction and draws clear lines to discriminate between osteoconduction, osseointegration, and osteoinduction. Moreover, additively manufactured libraries of scaffolds revealed that: osteoconduction is more a three-dimensional than a surface phenomenon; microarchitecture dictates defect bridging, which is the measure for osteoconduction; pore diameter or the diagonal of lattice microarchitectures of osteoconductive bone substitutes should be ∼1.2 mm.

中文翻译：

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重新考虑增材制造时代的骨传导。

临床和骨组织工程中的骨再生程序基于三个支柱：骨传导，骨诱导和干细胞。在过去的二十年中，该领域的重点一直放在骨诱导上，这是通过使用骨形态发生蛋白和应用间充质干细胞治疗骨缺损来实现的。然而，骨传导减少为表面现象，因为骨传导支架的理想孔尺寸在1990年代被确定为直径为0.3-0.5 mm，从而迫使骨形成主要发生在表面上。同时，增材制造已发展成为一种新的工具，可以在骨替代物中实现设计的微结构，从而使我们能够将骨传导研究为一种真正的三维现象。而且，通过增材制造 可以制造全开式多孔支架，其中通过直径为1.2 mm的高度骨传导性孔，可以以较高的骨缺损率在远处远离表面形成骨形成。这篇综述提供了历史概述以及骨传导及其相关术语的更新定义。此外，它显示了增材制造如何在研究和优化骨替代物的骨传导中发挥作用，并提供了骨传导微体系结构的新颖的优化特征和边界。影响陈述该评论更新了骨传导的定义，并划清了界限以区分骨传导，骨整合和骨诱导。此外，加成制造的支架库显示：骨传导更多是三维而非表面现象；微结构决定了缺陷桥接，这是骨传导的措施；骨传导性骨替代物的孔直径或晶格微结构的对角线应为〜1.2 mm。