Learning from evolutionary optimisation: what are toughening mechanisms good for in dentine, a nonrepairing bone tissue?
Learning from evolutionary optimisation: what are toughening mechanisms good for in dentine, a nonrepairing bone tissue?
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从进化优化中学习：对于牙本质（一种不可修复的骨组织）来说，增韧机制有什么好处？
DOI：
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发表时间：
2016
影响因子：
3.4
通讯作者：
C. Fleck
中科院分区：
文献类型：
--
作者：
P. Zaslansky;J. Currey;C. Fleck
牙齿中发现的主要物质是牙本质，一种骨样组织，布满微米大小的小管，没有活细胞。它为牙釉质外耐磨层提供支撑，并表现出有助于抗裂的增韧机制。然而，与大多数骨组织不同的是，牙本质不会重塑，因此任何累积的损伤都不会“自我修复”。由于控制损伤和组织替换是大多数骨骼中发现的阻止裂纹的微观结构的主要原因，因此没有生物修复能力的增韧机制的出现令人费解。在这里，我们考虑这样一种观点，即牙本质可能因强度而过度设计，因为它必须弥补细胞介导的愈合机制的缺乏。根据我们自己和文献报道的观察结果，包括准静态和疲劳特性，根据牙齿进化的功能条件讨论了牙本质设计原则。我们的结论是，牙本质对于日常循环负荷只是稍微过度设计，因为通常的咀嚼应力可能接近其耐力强度。内置的增韧机制构成了进化上的好处，因为它们可以防止罕见的过载事件期间发生灾难性故障，这在我们的狩猎采集祖先时代可能非常有利。从仿生学的角度来看，了解进化过度设计的程度可能有助于优化用于承载的仿生结构。
The main mass of material found in teeth is dentine, a bone-like tissue, riddled with micron-sized tubules and devoid of living cells. It provides support to the outer wear-resistant layer of enamel, and exhibits toughening mechanisms which contribute to crack resistance. And yet unlike most bone tissues, dentine does not remodel and consequently any accumulated damage does not ‘self repair’. Because damage containment followed by tissue replacement is a prime reason for the crack-arresting microstructures found in most bones, the occurrence of toughening mechanisms without the biological capability to repair is puzzling. Here we consider the notion that dentine might be overdesigned for strength, because it has to compensate for the lack of cell-mediated healing mechanisms. Based on our own and on literature-reported observations, including quasistatic and fatigue properties, dentine design principles are discussed in light of the functional conditions under which teeth evolved. We conclude that dentine is only slightly overdesigned for everyday cyclic loading because usual mastication stresses may come close to its endurance strength. The in-built toughening mechanisms constitute an evolutionary benefit because they prevent catastrophic failure during rare overload events, which was probably very advantageous in our hunter gatherer ancestor times. From a bio-inspired perspective, understanding the extent of evolutionary overdesign might be useful for optimising biomimetic structures used for load bearing.
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