Exploring molecular and mechanical gradients in structural bioscaffolds.
Exploring molecular and mechanical gradients in structural bioscaffolds.
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DOI：
10.1021/bi049380h
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发表时间：
2004-06
期刊：
影响因子：
2.9
通讯作者：
J. Waite;H. Lichtenegger;G. Stucky;P. Hansma
中科院分区：
文献类型：
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作者：
J. Waite;H. Lichtenegger;G. Stucky;P. Hansma
大多数生物体都是由具有适应性功能的硬组织和软组织组合而成的。尽管用硬支架加强软原生质有明显的优势，但这种复合材料会在两者相遇的地方产生巨大的机械应力。尽管人们对自然界如何缓解这些压力知之甚少，但人们普遍认为，关于硬/软界面分子适应性的基本见解可能会深刻影响我们对生物材料的看法。基于两个非细胞组织，贻贝足丝和多毛类颌骨，最近的研究表明，一个自然的策略，以尽量减少相邻的硬组织和软组织之间的界面应力似乎是创建一个“模糊”的边界，这避免了机械性能的突然变化。相反，有一个渐进的机械变化，伴随着从僵硬到柔软的超越，反之亦然。在深海丝中，实现这种逐渐机械变化的生化介质涉及到基于胶原的自组装嵌段共聚物的巧妙使用。存在三种不同的二嵌段共聚物类型，其中一种嵌段总是胶原性的，而另一种可以是弹性蛋白样（软的）、无定形聚甘氨酸（中间体）或丝样（硬的）。通过在分泌细胞中递增滴定表达这三种蛋白质，其滴定表型与它们的位置有关。因此，准确地反映了每条线的组成，远端细胞主要分泌丝-和聚甘氨酸-胶原二嵌段，而近端细胞分泌弹性蛋白-和聚甘氨酸-胶原二嵌段。那些介于两者之间的细胞表现出胶原蛋白与丝或弹性蛋白块的渐变。自发自组装似乎是由pH触发的金属结合组氨酸（HIS）丰富的序列在氨基和羧基末端的二嵌段。在多毛类颌骨，HIS丰富的序列扩展到一个主要的块域。组氨酸在远端尖端附近以超过20摩尔%占优势，并且在近端基部附近减少至约5摩尔%。组氨酸的丰度与过渡金属含量（Zn或Cu）以及通过纳米压痕测定的硬度直接相关。EXAFS分析的下巴表明，过渡金属，如锌直接绑定到组氨酸配体，并可能作为交联剂。
Most organisms consist of a functionally adaptive assemblage of hard and soft tissues. Despite the obvious advantages of reinforcing soft protoplasm with a hard scaffold, such composites can lead to tremendous mechanical stresses where the two meet. Although little is known about how nature relieves these stresses, it is generally agreed that fundamental insights about molecular adaptation at hard/soft interfaces could profoundly influence how we think about biomaterials. Based on two noncellular tissues, mussel byssus and polychaete jaws, recent studies suggest that one natural strategy to minimize interfacial stresses between adjoining stiff and soft tissue appears to be the creation of a "fuzzy" boundary, which avoids abrupt changes in mechanical properties. Instead there is a gradual mechanical change that accompanies the transcendence from stiff to soft and vice versa. In byssal threads, the biochemical medium for achieving such a gradual mechanical change involves the elegant use of collagen-based self-assembling block copolymers. There are three distinct diblock copolymer types in which one block is always collagenous, whereas the other can be either elastin-like (soft), amorphous polyglycine (intermediate), or silk-like (stiff). Gradients of these are made by an incrementally titrated expression of the three proteins in secretory cells the titration phenotype of which is linked to their location. Thus, reflecting exactly the composition of each thread, the distal cells secrete primarily the silk- and polyglycine-collagen diblocks, whereas the proximal cells secrete the elastin- and polyglycine-collagen diblocks. Those cells in between exhibit gradations of collagens with silk or elastin blocks. Spontaneous self-assembly appears to be by pH triggered metal binding by histidine (HIS)-rich sequences at both the amino and carboxy termini of the diblocks. In the polychaete jaws, HIS-rich sequences are expanded into a major block domain. Histidine predominates at over 20 mol % near the distal tip and diminishes to about 5 mol % near the proximal base. The abundance of histidine is directly correlated to transition metal content (Zn or Cu) as well as hardness determined by nanoindentation. EXAFS analyses of the jaws indicate that transition metals such as Zn are directly bound to histidine ligands and may serve as cross-linkers.