科学美国人60秒 SSS 头发的力量超乎想象（在线收听）

This is Scientific American's 60-second Science, I'm Susanne Bard.

这里是科学美国人——60秒科学系列，我是苏珊娜·巴德。

All mammals have hair—commonly called fur when it's on your cat or a koala. And the thickness of individual hairs varies from species to species. For example, elephant hairs are more than four times thicker than a strand from an adult human.

所有哺乳动物都有毛发，猫咪或考拉身上的通常被称为“毛”。个体毛发的粗细程度因物种而不同。例如，大象毛发比成年人头发粗四倍。

"Normally, when the animal is larger, the hair tends to be thicker."

“通常，动物体型越大，其毛发往往越粗。”

University of California, San Diego, materials scientist Wen Yang. She's interested in how biological structures like hair hold up under stress. That interest comes from a desire to design better synthetic materials.

加州大学圣地亚哥分校的材料科学家杨文（音译）说到。她感兴趣的是毛发这种生物结构如何在压力下保持完好。这种兴趣来自于设计出更优合成材料的渴望。

Yang's team tested the tensile strength of hair from eight different mammal species, including humans. They subjected those hairs to increasing levels of tension until the fibers broke. The researchers assumed that thick hair—from giraffes, elephants and boars, for example, would be more robust. But they were wrong.

杨的团队测试了包括人类在内的八种哺乳动物毛发的抗张强度。他们让这些毛发承受越来越强的张力，直到纤维断裂。研究人员原本以为长颈鹿、大象和野猪身上的粗密毛发会更加结实。但他们想错了。

"Interestingly, we find the thinner hair, actually, is stronger."

“有趣的是，我们发现毛发越细越结实。”

In fact, adult human hair was some of the strongest in the study. And children's hair—the thinnest of all—was even more durable.

事实上，在这项研究中，成人头发的强度位居前列。而最细的儿童头发则更加紧固。

Yang's team took a closer look at the hair with a scanning electron microscope. All hair is made of the protein keratin. The microscope views revealed specific patterns of breakage in the keratin fibers, which are composed of a protective outer cuticle and an inner cortex that provides strength.

杨的团队用扫描电子显微镜仔细观察了这些毛发。所有毛发都由角蛋白构成。显微镜观察发现了角蛋白纤维的特殊断裂模式，而角蛋白纤维由保护性的外角质层和提供强度的内部皮层组成。

The microscope images showed that the cortex of thicker hair tends to snap when broken, leaving a clean, even break. But the inner cortex of thinner hair breaks off less evenly. Yang compares the process to what happens when a powerful gust of wind blows a tree down. In those cases, the trunk tends to shear at an angle. And that kind of break is a sign of strength—it actually takes more tension to cause shearing than a clean break.

显微镜图像显示，较粗毛发的皮层在被折断时时容易断裂，留下干净平整的直茬。但较细毛发的内部皮层断裂茬口并不平整。杨将这一过程比作一股强风吹倒大树。在这种情况下，树干往往以一定角度断裂。这种断裂是一种力量的标志，相比干脆的断裂，这种断裂需要消耗更多张力。

The researchers found that the cutoff point between these two types of breakage was about 200 micrometers—about two and a half times thicker than human hair.

研究人员发现，这两种断裂之间的分界值大约是200微米，约比人类的头发粗2.5倍。

The study is in the journal Matter.

这项研究发表在《物质》期刊上。

Yang is now attempting to mimic the complex structure of hair in the lab with 3-D printing. Once the technology is perfected down to the nanoscale, these artificial fibers could be used to create a variety of strong materials for use in construction or even rescue operations—such as nearly indestructible ropes.

杨现在正尝试在实验室里用三维打印来模拟毛发的复合结构。一旦这项技术完善到纳米级，这些人造纤维就可以用来制造各种坚固的材料，用于建筑甚至救援行动，比如制作几乎不会损坏的绳索。

Until then, we'll just have to be content with the knowledge that fewer than 1,000 human hairs can support an entire person's weight. Think of all the strength that's left on the hair salon floor.

到那时，我们就要满足于一种知识，即不到1000根人类头发就可以支撑一个人的体重。想想美发店地板上留下的力量吧。

Thanks for listening for Scientific American's 60-second Science. I'm Susanne Bard.

谢谢大家收听科学美国人——60秒科学。我是苏珊娜·巴德。