科技資訊:醫學技術 蠶絲的妙用

KEEPING drugs, and particularly vaccines, potent in tropical climes is a challenge. Heat tends to damage them. Such medicines have therefore to be moved from one refrigerator to another, along what is referred to as a cold chain, until they arrive at the clinics where they are to be administered. Fridges, however, are expensive. They also require electricity, which is not always available-or is available only unreliably-in the poorer parts of the world. As a consequence, breaks in cold chains are estimated by the World Health Organisation to destroy almost half of the vaccines produced around the world.

由於高溫容易導致藥效降低，因此，如何在炎熱的氣候中保持藥品（尤其是疫苗）的藥效一直是一個難題。爲了保證藥效，人們不得不沿着一條“低溫鏈”把藥品從一個冰箱轉移到另一個冰箱，直至送抵相應的診所。然而，使用冰箱一方面成本太高，另一方面，在一些貧困地區常常沒有電力供應。（有些地區雖然有電，但是電力不穩定）。世界衛生組織預計，若低溫鏈斷裂，全世界近一半的疫苗都將徹底失效。

Some vaccines can be freeze-dried, which helps. But even when treated in this way, their lifetime out of the fridge is limited. Ways of keeping drugs and vaccines stable at tropical temperatures would therefore be welcome. And David Kaplan of Tufts University, in Massachusetts, thinks he has found one. Put simply, he and his colleagues have worked out how to pack medicines into tiny silk pouches, in a manner that makes them almost indifferent to heat.

一些疫苗能通過冷凍乾燥的方式進行保存，但儘管如此，如果沒有冰箱，這些疫苗的存活時間也非常有限。因而，人們一直希望能夠發明出能在高溫天氣中保存藥物和疫苗的方法。馬薩諸塞州塔夫茨大學的David Kaplan認爲他已經找到了一個解決辦法。簡單地來說，David Kaplan和他的同事研究出了一種將藥物包裹在蠶絲小袋中的方法，通過這種方法，能將藥物與熱量幾乎完全隔絕開來。

Dr Kaplan and his team describe their technique in a recent issue of Proceedings of the National Academy of Sciences. They start with silkworm cocoons-the raw material for almost all silk production. They boil the cocoons in a solution of sodium carbonate to separate a protein called fibroin, which is the one they want, from another, called sericin, which they do not. They treat the fibroin with salt, then mix it with the substance to be preserved and spread the result out as films, before freeze-drying it. The resulting films consist of a fibroin matrix filled with tiny pockets a few hundred nanometres (billionths of a metre) across. These pockets contain the medicine.

Kaplan博士和他的小組在最近一期美國《國家科學研究院學報》中介紹了他們的技術方法。他們使用的原料是人們製作幾乎任何絲綢產品都要用到的東西——蠶繭。他們們將蠶繭放入煮沸的碳酸鈉溶液中加熱，從而分離出他們想要的物質——一種稱作絲心蛋白的蛋白質，而剩下的絲膠則被去除。他們將絲心蛋白用鹽處理後，與需要保存的藥物進行混合，之後將混合物平鋪成薄膜，最後將其凍幹。製作完成的薄膜以絲心蛋白爲基質，上面佈滿了直徑只有幾百納米（十億分之一米）的小袋，而藥物就儲存在這些小袋裏。

Packaging delicate medicines in this way does, indeed, help preserve them. It immobilises the molecules, preventing them from unfolding and thus losing their potency. It also minimises residual moisture even better than normal freeze-drying. Dr Kaplan and his team demonstrated the effectiveness of their new technique by trying it out on the MMR (measles, mumps and rubella) vaccine.

這種新的方法確實能有效的保存那些易變質的藥物——由於藥物中的分子被固定，無法展開，因而藥效就得以保持。同時，和普通的冷凍乾燥法相比，這種方法方法也能更有效的減少藥物中殘存水分。Kaplan博士和他的小組在MMR疫苗（麻疹、腮腺炎和風疹的聯合疫苗）上實驗了他們的方法，結果證明，該方法十分有效。

Prolonged storage at just 25°C will cause even the freeze-dried version of MMR to break down. After six months it retains only 60-75% of its potency. If kept for that length of time at 45°C (extreme, but not unknown in the tropics) it is practically worthless. When stored using Dr Kaplan’s silk sheets, however, it was still about 85% potent after six months, regardless of temperature.

在25℃的環境中，當儲存時間過長時，即使已使用冷凍乾燥法處理過的MMR疫苗也會分解。在此環境中保存6個月後，疫苗藥效降低至原來的60%到75%。將疫苗放在45℃的環境中（該溫度並不常見，但在熱帶地區仍然存在）保存同樣的時間後，疫苗已完全失效。然而使用Kaplan的方法進行保存的疫苗在六個月後依然保持了約85%藥效，且絲毫不受溫度的影響。

When the researchers tried the same trick with tetracycline, a commonly prescribed antibiotic, they got similar results. Tetracycline stored at body temperature lost 80% of its potency after four weeks in ordinary solution, but lost none when stored in silk films. The new technique also worked with penicillin. Moreover, fibroin is harmless to people-silk is, after all, often used in sutures-so there is little risk of adverse side-effects. It probably does not matter if some silk gets into a vaccine when it is dissolved in water prior to inoculation.

研究者們又在人們經常使用的四環素和盤尼西林上進行了同樣的實驗，結果也不出意料。將四環素保存在普通溶液中並置於體溫環境，四個星期後藥效已損失80%，但用蠶絲薄膜進行保存的四環素未收任何影響。不僅如此，，由於絲心蛋白對人體不會產生傷害（蠶絲常被用於傷口的縫合），因此不用擔心會產生不良的副作用。在接種疫苗時，只需將蠶絲小袋放入水中溶解，即可取出疫苗，即使有少量蠶絲混入疫苗中也不必擔心。

That said, the vaccines and antibiotics stored in this new way have yet to be tested on people. That is the next step. But if they work, this new trick will help save lives being needlessly lost in some of the poorest parts of the world.

雖然用新方法保存的疫苗和抗生素還未在人體中進行過試驗（人體試驗將是研究者們下一步的計劃），但如果藥物能夠起效，這種新的儲存方法將在許多極度貧困的地區發揮巨大作用，減少不必要的死亡。