蛋殼比金屬還要堅硬小雞如何破殼而出英語美文

It’s been a tough one to crack, but scientists say they have zoomed in, to an unprecedented degree, on the structure of shells surrounding chicken embryos, revealing how they change to allow young birds to hatch.

科學家説他們以前所未有的程度對蛋殼的結構進行放大並進一步瞭解，揭示了它們如何改變以允許幼雞孵化。

Before being laid, bird eggs form a hard calcium-rich shell with three main layers. While it was already known that these thin from the innermost out as a chick grows in preparation for hatching – with calcium from the shell being incorporated into its skeleton in the process – quite what happens at the molecular scale has been something of a mystery.

雞蛋離開母體時蛋殼富含鈣質，蛋殼有3層構造，小雞在蛋殼中一點點成長起來，在這個過程中，蛋殼由內到外變薄，來自蛋殼的鈣質也會被小雞的骨骼吸收。但在分子尺度上這一過程至今還是祕密，到底是怎麼發生的呢?

Now scientists say they have discovered that eggshells have a nanostructure, and that it appears to play a key role in the strength of the shell.

現在科學家們説他們已經發現蛋殼具有納米結構，並且它似乎在貝殼強度方面起着關鍵作用。

“Everybody thinks eggshells are fragile – [when] we’re careful, we ‘walk on eggshells’ – but in fact, for their thinness they are extremely strong, harder than some metals,” said Prof Marc McKee, a coauthor of the study from McGill University in Canada. “We are really understanding now at the almost molecular scale how an eggshell is assembled and how it dissolves.”

“每個人都認為蛋殼很脆弱，當我們小心翼翼，我們走在蛋殼上時，但事實上，由於它們的纖薄，它們比一些金屬更堅硬，更硬，”該研究的合着者來自加拿大麥吉爾大學馬克麥基教授説。 “我們正在瞭解蛋殼的組裝方式和分解過程。”

Writing in the journal Science Advances, McKee and colleagues describe how they probed the issue by focusing on the role of a protein known as osteopontin. This substance is found throughout the eggshell and was already thought to be important in organising the structure of its minerals.

McKee及其同事在“科學進展”雜誌上撰文，並描述他們如何通過關注骨橋蛋白這一蛋白質的作用來探討這個問題。這種物質在整個蛋殼中均可發現，並已被認為是組織其礦物結構的重要組成部分。

“Something as different as an eggshell and a tooth and a bone, they all have this protein,” said McKee. “We think it is proteins like that that help guide the mineralisation process to give these tissues their properties.”

“像蛋殼，牙齒和骨頭那樣不同的東西，它們都含有這種蛋白質，”麥基説。“我們認為這些蛋白質能夠輔助礦化過程，並賦予這些組織特性。”

Using a number of microscopy techniques, as well as a cutting-edge method known as focused-ion beam for preparing thin sections of the eggshell, the team found that all of the layers appear to be formed from an array of tiny areas packed with a crystalline calcium-containing mineral.

通過採用許多顯微鏡技術，以及稱為聚焦離子束的尖端方法來製備蛋殼薄片，該團隊發現所有層都是由一系列小區域的結晶含鈣礦物構成。

The team also found the areas are smaller and more closely arranged in the outer layer, with the nanostructure becoming larger towards the inner layers. Levels of osteopontin were found to be lowest in the innermost eggshell layer.

研究小組還發現，外層的面積更小，排列更緊密，納米結構朝內層方向變大。同時發現骨橋蛋白含量水平在最內層的`蛋殼層中最低。

“The third discovery was that the outside of the shell is harder as it has the smallest [nanostructure] and then you move inwards and it gets a little bit softer,” said McKee.

“第三個發現是，外殼的外部更硬，因為它具有最小的納米結構，然後你向內移動，它就會變得更柔軟一點，”麥基説。

The team say the upshot is that osteopontin seems to form a sort of scaffold that guides the arrangement of calcium-containing mineral, generating a nanostructure that affects the hardness of the eggshell layer.

該團隊説，骨橋蛋白似乎形成一種指導含鈣礦物排列的支架，從而產生影響蛋殼層硬度的納米結構。

McKee says the theory is backed up by experiments in the lab.

麥基説這個理論是由實驗室試驗支持的。

“If you don’t put in the protein in the test tube you get a big giant calcite [calcium carbonate] crystal like you’d find in a museum. If you throw in the protein, it slows the process down, it gets embedded inside that crystal and it generates a very similar nanostructure property in those synthetic crystals and they have increased hardness,” said McKee. Higher concentrations of osteopontin were found to produce a smaller nanostructure.

“如果你不把蛋白質放進試管裏，你會得到一個巨大的方解石(碳酸鈣)晶體，就像你在博物館裏找到的那樣。如果你投入蛋白質，它減緩了整個過程，它嵌入到晶體內部，它在這些合成晶體中產生非常類似的納米結構性質，並且提高硬度，“McKee説。較高濃度的骨橋蛋白能夠產生較小的納米結構。

The team then turned from the eggs that wind up on our breakfast tables to looking at the structure of chicken eggs that had been fertilised and incubated for 15 days. While the nanostructure of the outermost of the three eggshell layers remained unchanged, the nanostructure of the inner layers had become smaller in size. That, said McKee, is a result of calcium carbonate being dissolved in acidic conditions and used in the chick’s skeleton, and the process might be aided by the nanostructure increasing the surface area of the calcium-containing mineral.

然後團隊從早餐桌上的雞蛋轉向查看已經受精並孵育15天的雞蛋的結構。雖然三個蛋殼層最外層的納米結構保持不變，但內層的納米結構尺寸變的更小。McKee説，這是碳酸鈣在酸性條件下溶解並用於小雞骨骼成長的結果，並且該過程可能為納米結構提高含鈣礦物表面積提供幫助。

The upshot is that the shell weakens, allowing it to crack and the chick to hatch.

這樣的結果是殼被削弱了，使得小雞孵化，蛋殼破裂成為可能。

While the role of other proteins in the structure of eggshell layers has yet to be unpicked, McKee said the latest findings could prove useful in the design of new human-made materials.

雖然其他蛋白質在蛋殼層結構中的作用尚未被揭露，但McKee説最新的發現可能在新型人造材料的設計中具有指導作用。

“When you think about it, we should be making materials that are inspired by nature and by biology because, boy, it is really hard to beat hundreds of millions of years of evolution in perfecting something,” he said.

“當你思考這個問題時，我們應該尋求來自於大自然和生物學的材料，從中獲取設計材料的靈感，因為這些經歷了數億年的進化是東西可以説是近乎完美的”他説。