科技资讯:医学技术 蚕丝的妙用

由于高温容易导致药效降低，因此，如何在炎热的气候中保持药品（尤其是疫苗）的药效一直是一个难题。为了保证药效，人们不得不沿着一条“低温链”把药品从一个冰箱转移到另一个冰箱，直至送抵相应的诊所。然而，使用冰箱一方面成本太高，另一方面，在一些贫困地区常常没有电力供应。（有些地区虽然有电，但是电力不稳定）。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彻底失效。

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.

一些疫苗能通过冷冻干燥的方式进行保存，但尽管如此，如果没有冰箱，这些疫苗的存活时间也非常有限。因而，人们一直希望能够发明出能在高温天气中保存药物和疫苗的方法。马萨诸塞州塔夫茨的David Kaplan认为他已经找到了一个解决办法。简单地来说，David Kaplan和他的同事研究出了一种将药物包裹在蚕丝小袋中的方法，通过这种方法，能将药物与热量几乎完全隔绝开来。

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《科学研究院学报》中介绍了他们的技术方法。他们使用的原料是人们制作几乎任何丝绸产品都要用到的东西——蚕茧。他们们将蚕茧放入煮沸的碳酸钠溶液中加热，从而分离出他们想要的物质——一种称作丝心蛋白的蛋白质，而剩下的丝胶则被去除。他们将丝心蛋白用盐处理后，与需要保存的药物进行混合，之后将混合物平铺成薄膜，最后将其冻干。制作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.

这种新的方法确实能有效的保存那些易变质的药物——由于药物中的分子被固定，无法展开，因而药效就得以保持。同时，和普通的冷冻干燥法相比，这种方法方法也能更有效的减少药物中残存水分。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。

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，即使已使用冷冻干燥法处理过的MMR疫苗也会分解。在此环境中保存6个月后，疫苗药效降低至原来的60%到75%。将疫苗放在45℃的环境中（该温度并不常见，但在热带地区仍然存在）保存同样的时间后，疫苗已完全失效。然而使用Kaplan的方法进行保存的疫苗在六个月后依然保持了约85%药效，且丝毫不受温度的影响。

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.

研究者们又在人们经常使用的四环素和盘尼西林上进行了同样的实验，结果也不出意料。将四环素保存在普通溶液中并置于体温环境，四个星期后药效已损失80%，但用蚕丝薄膜进行保存的四环素未收任何影响。不仅如此，，由于丝心蛋白对人体不会产生伤害（蚕丝常被用于伤口的缝合），因此不用担心会产生不良的副作用。在接种疫苗时，只需将蚕丝小袋放入水中溶解，即可取出疫苗，即使有少量蚕丝混入疫苗中也不必担心。

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.

虽然用新方法保存的疫苗和抗生素还未在人体中进行过试验（人体试验将是研究者们下一步的计划），但如果药物能够起效，这种新的储存方法将在许多极度贫困的地区发挥巨大作用，减少不必要的死亡。