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.由于高温更容易造成药效减少，因此，如何在寒冷的气候中维持药品（特别是在是疫苗）的药效仍然是一个难题。为了确保药效，人们被迫沿着一条“低温链”把药品从一个冰箱移往到另一个冰箱，以后送抵适当的医院。然而，用于冰箱一方面成本太高，另一方面，在一些贫困地区经常没电力供应。（有些地区虽然有电，但是电力不平稳）。

世界卫生组织预计，若低温链断裂，全世界近一半的疫苗都将完全过热。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.一些疫苗能通过冷冻干燥的方式展开留存，但尽管如此，如果没冰箱，这些疫苗的存活时间也十分受限。

因而，人们仍然期望需要发明者出能在高温天气中留存药物和疫苗的方法。马萨诸塞州塔夫茨大学的David Kaplan指出他早已寻找了一个解决办法。

非常简单地来说，David Kaplan和他的同事研究出有了一种将药物包覆在蚕丝小袋中的方法，通过这种方法，能将药物与热量完全几乎阻隔出去。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博士和他的小组在最近一期美国《国家科学研究院学报》中讲解了他们的技术方法。他们用于的原料是人们制作完全任何丝绸产品都要中用的东西——蚕茧。

他们们将蚕茧放进浸泡的碳酸钠溶液中冷却，从而分离出他们想的物质——一种称为丝心蛋白的蛋白质，而只剩的丝胶则被除去。他们将丝心蛋白用盐处置后，与必须留存的药物展开混合，之后将混合物平铺成薄膜，最后将其冻干。制作已完成的薄膜以丝心蛋白为基质，上面布满了直径只有几百纳米（十亿分之一米）的小袋，而药物就储存在这些小袋里。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.这种新的方法显然能有效地的留存那些不易变质的药物——由于药物中的分子被相同，无法进行，因而药效就以求维持。

同时，和普通的冷冻干燥法比起，这种方法方法也能更加有效地的增加药物中仅存水分。Kaplan博士和他的小组在MMR疫苗（麻疹、腮腺炎和风疹的联合疫苗）上实验了他们的方法，结果证明，该方法十分有效地。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℃的环境中，当储存时间过长时，即使已用于冷冻干燥法处置过的MMR疫苗也不会分解成。在此环境中留存6个月后，疫苗药效减少至原本的60%到75%。

将疫苗放到45℃的环境中（该温度并不少见，但在热带地区依然不存在）留存某种程度的时间后，疫苗已几乎过热。然而用于Kaplan的方法展开留存的疫苗在六个月后仍然维持了大约85%药效，且丝毫不不受温度的影响。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.研究者们又在人们常常用于的四环素和盘尼西林上展开了某种程度的实验，结果也不来意料。

将四环素留存在普通溶液中并置放体温环境，四个星期后药效已损失80%，但用蚕丝薄膜展开留存的四环素续任何影响。不仅如此，，由于丝心蛋白对人体会产生损害（蚕丝经常被用作伤口的穿孔），因此不必担忧不会产生不当的副作用。在疫苗疫苗时，只需将蚕丝小袋放进水中沉淀，才可放入疫苗，即使有少量蚕丝混进疫苗中也不用担忧。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.虽然用新方法留存的疫苗和抗生素还并未在人体中展开过试验（人体试验将是研究者们下一步的计划），但如果药物需要较慢，这种新的储存方法将在许多极为贫穷的地区充分发挥巨大作用，增加不必要的丧生。

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