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Stiffening under pressure [复制链接]

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发表于 2009-3-6 08:59 |只看该作者 |倒序浏览 |打印
JANMEY/MACMILLAN
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4 {6 g) y9 X( Q+ A* g+ rNetworks of biological filaments have just enough flexibility to stiffen as they are strained, according to findings from Cornelis Storm, Paul Janmey (University of Pennsylvania, Philadelphia, PA), and colleagues.
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Natural networks, such as collagen gels or cytoskeletal webs, have the ability to increase their stiffness with increasing strain. This unique feature is an advantage over most synthetic fibers. If blood vessels were made of rubber tubing, for example, the pressure from a heart beat would vastly increase vessel diameter. But collagen's nonlinear elasticity prevents such a drastic endothelial deformation.
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- M- O, O  y4 H$ MThis ability is usually explained by the heterogeneous nature of biological gels〞perhaps tauter filaments take over at increasing strains. But in vitro measurements by Storm et al. now show that uniform biopolymer gels also exhibit nonlinear elasticity. The authors then produced a mathematical model that explains this behavior based on the characteristics of the individual polymer filaments within a cross-linked network." A6 E7 H! d# Q

8 [: w% `9 `: ^& f( O"We show that strain stiffening comes about automatically because of the semiflexible nature of the chains in the biomaterials," says Janmey. "They're not exactly straight, but they're not randomly highly coiled either." That flexibility allows for short range movement under mild strain, but under greater strain the filaments reach the end of their leash and stop extending. Slightly stiffer polymers (actin, collagen), with shorter leashes, stop extending at lower strains. Softer gels, such as intermediate filaments, take larger deformations before they stiffen.
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The model makes certain assumptions that might not hold true in vivo. For one, networks were assumed to form randomly. But Arp2/3 complexes, for instance, bias actin filament branching at specific angles. Additionally, cross-links were assumed to stay put under strain, although they are probably labile in cells. Determining the effects of these variations on strain stiffening will require further modeling.% f2 H% s* M  X- o7 ^, M& k; ~7 N
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Beyond biological interests, the findings might also prove useful to engineers. "If you wanted to make a material that stiffens as you deform it," says Janmey, "filaments as stiff as intermediate filaments would create a new type of  polymer."6 n' ?3 T3 V! R9 T, U0 S2 R3 Q

8 j% B& t6 @0 z  yReference:
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Storm, C., et al. 2005. Nature. 435:191–194.(Unlike polyacrylamide (black), natural n)

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沙发
发表于 2015-5-23 13:42 |只看该作者
我的啦嘿嘿  

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藤椅
发表于 2015-5-30 13:30 |只看该作者
在线等在线等  

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板凳
发表于 2015-6-16 12:25 |只看该作者
干细胞之家微信公众号
昨天没来看了 ~~  

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报纸
发表于 2015-6-24 13:27 |只看该作者
原来这样也可以  

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地板
发表于 2015-6-27 17:34 |只看该作者
这个贴不错!!!!!  

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发表于 2015-6-29 19:55 |只看该作者
顶你一下,好贴要顶!  

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发表于 2015-7-19 11:27 |只看该作者
哈哈,这么多的人都回了,我敢不回吗?赶快回一个,很好的,我喜欢  

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发表于 2015-9-3 17:10 |只看该作者
羊水干细胞

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发表于 2015-9-4 22:38 |只看该作者
不错不错.,..我喜欢  
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