In the quest to heal wounds without leaving a scar， researchers have looked at some 3，000 treatments. Many have not lived up to expectations， and none can induce repair that leaves the skin in pristine condition. Now U. S. and British scientists have come up with three different recipes for advanced bandages that jump-start the repair of injured skin but then break down， leaving behind only healed tissue. Such biodegradable scaffolds eliminate the need to change dressings， cut the risk of infection and improve the odds of scarless healing.

When skin is injured the weave-like structure of collagen fibers， the skin's glue， is destroyed. Tominimize blood loss and infection， the body opts for a quick fix: it marshals cells called fibroblasts， which lay down thin， linear strips of replacement collagen. When skin cells grow on the replacement collagen， they produce pale， less flexible material. Avoiding this scar tissue means getting the body to rebuild the complex fibrous structure of the original.

An aggressive， active therapy relies on tissue cultured in the lab for use as a temporary patch. Organogenesis in Canton， Mass， and Advanced Tissue Sciences in La Jolla， Calif. both depend on foreskin from circumcised newborns. The foreskin cells are grown on substrates， resulting in layered matrices that secrete growth factors. But the costly engineered tissue would be inappropriate for smaller sores that may heal naturally with just the right kind of dressing.

Ronald A. Coffee， a University of Oxford biochemist and president of the Oxford-based biotech company Electrosols， has a spray- on dressing he hopes will encourage normal skin growth immediately after an injury. The spray consists of a synthetic polymer mixed with ethanol and placed in a small， high-tech dispenser that could be mistaken for a prop on the set of Star Trek. An applied electrical field charges the mixture， a step \"that turns out to be the key to the whole thing\"， Coffee notes. Because the wounds is at a far lower electrical potential than the polymer is， the solution is attracted to the skin and flies out through a tiny nozzle， producing fine， light fibers， each of them two microns in diameter.

The fibers have the same charge， so they repel one another and regularly space themselves like a textile weave. The collagen- forming fibroblasts， however， are attracted to the charged fibers. The woven pattern of the fibers makes the difference; the cells use it as a road map to re-create the original collagen structure. Coffee believes that controlling the formation of collagen in this way will lead to normal skin growth instead of scarring.

The inventors predict that spray-on fibers could treat everything from minor cuts to third-degree burns， and because the device is so small it could easily be carried by paramedics and kept in first-aid kits. Coffee is confident the fiberswill work， although he admits that thus far only one human patient， a colleague at the company， has successfully used the spray. The technique has potential， but animal and human trials are needed to determine how the spray works in the body， points out Mark W. J. Ferguson， an expert in wound healing at the University of Manchester. \"A person's immune system can demolish and reabsorb the scaffold before the cells have a chance to migrate on it\"， he says. The scaffolds could also cause infiammation， which would interfere with scarless healing.

If the spray-on method flops in clinical trials， a less futuristic treatment might work; a three-layer dressing incorporating chitosan- a fiber derived from crab shells， 350 million pounds of which are discarded in the U.S. annually. Applied to the skin， the scaffold pro- vides a base for cell growth. It encourages cells to grow back only from the edges of the chitosan layer， thus preventing renegade cells from erupting below the wound， which would contribute to scar formation.

The dressing， which is being developed at North Carolina State University， also incorporates two other layers: a starch-derived polymer， which transports away pus and protects the wound as the chitosan breaks down， and an outer cotton gauze， which can be changed as needed without bother to the wound. The body eventually absorbs both the chitosan and polymer layers， leaving behind intact skin.

To make the dressing， the researchers grind crab shells to a fine powder and mix it with chemicals to convert the base material， chitin， into chitosan. They then pour the resulting viscous liquid onto Teflon sheets to create a thin film. In addition to its healing abilities， chitosan has natural infection-fighting properties: fungi， viruses and other microbes seem unable to live on it. The team also hopes to streamline manufacturing and to design a second-layer polymer that will allow delivery of medications to the injured skin.

So far results are positive， based on studies in pigs. But， as with the spray-on fibers， clinical trials are needed to see how well the dressing performs on human skin， and Gupta says it will be several more years before consumers see it on pharmacy shelves.

There is a high-tech scaffold that's commercially available now， and it comes from a source as unexpected as crab shells: the small intestines of pigs. Ten years ago Purdue University scientists isolated the layer of tissue called small intestinal submucosa， or SIS， and found that it had unusual healing properties. It contains a complex matrix of collagen， growth factors and other proteins that， when applied to a wound， functions as a natural framework that prompts the body to build new tissue with little or no scarring. It has already been used in humans to cure chronic sores and to treat severe skin injuries that might otherwise result in amputation.

OaSIS is easy to make and doesn't cost much; the small intestine is a throwaway product from pork production， and a single pig can donate up to 90 feet of it. The isolated SIS material is first washed and sterilized; then unwanted surrounding cells are stripped away before it is freeze-dried. The result resembles parchment paper. Applied to a wound， it stimulated new blood vessels to form creating a pipeline that can nourish the newly implanted scaffold ( chronic sores are often caused by poor circulation). As the new tissue grows， the body dismantles the intestine-derived material replaces it with the same tissue type there originally.

The transfer of pig viruses to humans is unlikely. \"Porcine products have a good history with humans; pig skin has been used for years to treat burns\"， points out Purdue biomedical engineer Stephen F. Badylak. Some patients， though， may be allergic to pig products.

Biodegradable scaffolds might not win the healing race， but if they live up to their promise， at least there won't be a scar in sight.

WordsExpressions

1． questn．尋求，探求，研究

2． live up to phr．符合，不辜負(fù)希望

3． induce v．引起，導(dǎo)致

4． pristineadj．原來的，未被破壞的

5． recipyn．調(diào)制法，烹飪法，食譜

6． jump-startv．助推起動

7． biodegradableadj．可降解的

8． scaffaldn．腳手架，建筑架

9． dressingn．敷料，包扎，處理

10． oddsn．機(jī)會，可能性

11． collagenn．膠原（蛋白）

12． opt for v．選擇

13． marshalv．排列，安排，整理

14． fibroblastn．成纖維細(xì)胞

15．organogenesisn．器官再生

16．foreskinn．包皮

17. circumcisev．環(huán)剖包皮，行禮

18．substraten．底層，下層，基礎(chǔ)

19．matricesn．團(tuán)體，基層，基質(zhì)

20．secrete v．分泌

21．sprayv．噴射，噴涂

22．syntheticadj．合成的，人造的

23．polymern．聚合物

24．ethanoln．乙醇

25．dispensern．分配器

26．nozzlen．噴嘴

27．micronn．微米

28．make the difference phr. 有重要影響，起重要作用

29．parameldicn．護(hù)理人員，醫(yī)療輔助人員

30．first-aid kit n．急救箱(包)

31．inflammationn．炎癥

32．flop v.砸鍋，徹底失敗

33．renegadeadj．反抗傳統(tǒng)的，叛逆的，變節(jié)的

34．pusn．膿

35．chitinn．甲殼質(zhì)，聚乙酰氨基萄糖

36．chitosann．聚氨基葡糖

37．fungin．菌，菌類

38．intestinen．腸

39．matrixn．母體，基體，基層，基質(zhì)

40．a(chǎn)mputationn．截肢

41．dsmantlev．去掉…覆蓋物，拆除

在探索如何治療傷口而不留疤痕的過程中專家們已在近三千的病人進(jìn)行了試驗，其中許多并未達(dá)到預(yù)期效果，而且沒有一例能使受傷的皮膚完全恢復(fù)到原來的狀態(tài)?，F(xiàn)在美、英科學(xué)家已發(fā)明了三種不同的高級繃帶，能加速受傷皮膚的修復(fù)過程，然后繃帶本身慢慢自行降解，只留下完好如初的皮膚。有了這種可自行分解的繃帶就不必要經(jīng)常更換繃帶，減少了感染機(jī)會，大大增加了不留疤痕而復(fù)原的機(jī)會。

一旦受傷，皮膚的膠原纖維組織及膠質(zhì)均會遭到損傷。為最大限度減少血液的流失和感染，受傷者身體會本能地做出及時處理，如重新排列其成纖維細(xì)胞。這種細(xì)胞可以制造出厚厚而細(xì)長的新膠原蛋白。新皮在膠原蛋白上生長時會生出一種色澤蒼白，不很柔韌的結(jié)疤組織。要避免結(jié)疤產(chǎn)生就要使身體重新長出受傷前那種有錯綜結(jié)構(gòu)的纖維狀組織。

專家們有一個積極、大膽的想法，他們寄希望于在實驗室中培育出一種組織，做為臨時修補(bǔ)手段貼在傷口之上。馬薩諸塞州坎頓市的器官培育研究所和加利福尼亞州拉·約拉的高級組織研究所的研究工作都需用新生兒施割禮后的包皮。因為包皮細(xì)胞可在培養(yǎng)基上繼續(xù)生長，形成層層的基層，并能分泌出生長素。然而這種昂貴的人工培育皮膚并不適于那些小的瘡傷，包扎處理后，它們是可以自愈的。

羅那爾多·柯菲是牛津大學(xué)的生物化學(xué)家，同時也是設(shè)在牛津的Electrosols生物技術(shù)公司的經(jīng)理。他發(fā)明了噴涂敷藥法以期促使創(chuàng)傷面新皮膚的正常再生。這種噴劑是一種摻有乙醇的聚合物，被置于一個不大而精密中分配器中。這個分配器很像電影《星球大戰(zhàn)》中道具飛船帶噴咀的推進(jìn)器，用一外加電場對混合溶液充電?？路平忉屨f：“這是很關(guān)鍵的一步”。因為創(chuàng)傷面的電勢遠(yuǎn)遠(yuǎn)低于溶液的電勢，所以器內(nèi)的溶液被吸向皮膚，從一個極小的噴咀中噴出，形成又輕又細(xì)的纖維，每個直徑僅有兩微米。

這些纖維狀溶液本身帶有相同的電荷，互相排斥，像布紋一樣，其紋理排列得極有規(guī)律。傷處能形成膠原蛋白的成纖維細(xì)胞則被吸向這些帶電纖維狀溶液。這層纖維溶液繃帶卻正是關(guān)鍵所任!人體的細(xì)胞以它為溫床長出自己新的膠原蛋白組織?？路普J(rèn)為用此種主方興未艾來控制膠原蛋白的生長將會使新皮無結(jié)疤之慮。

發(fā)明者們預(yù)言噴涂纖維繃帶無論是對輕微劃傷還是三級灼傷都同樣有療效。其裝置非常小巧，便于醫(yī)護(hù)人員隨身攜帶，放在急救箱中即可。柯菲承認(rèn)到目前為止只有他所在公司的一位同事成功地接受了噴涂治療，但他堅信纖維噴劑療法將會成功，這種技術(shù)很有前途。當(dāng)然，還需在動物和人身上繼續(xù)試驗以確定纖維噴劑對人體的影響。曼徹斯特大學(xué)創(chuàng)傷專家馬克·費(fèi)爾古森指出：“在新細(xì)胞在其之上生長，繁殖之前，人體的免疫系統(tǒng)有可能毀壞或吸收掉這一布狀纖維繃帶。這種繃帶也可能導(dǎo)致皮膚發(fā)炎，而炎癥將會影響無疤痊愈的效果?！?/p>

如果噴涂療法在臨床試驗中失敗的話，那么還有一種更現(xiàn)實可行些的治療方法：加有聚氨基葡糖的三層敷藥繃帶。聚氨基葡糖是一種取自螃蟹殼的纖維。每年有三億五千萬磅的蟹殼被人們廢棄掉。使用這種繃帶時，這一聚氨基葡糖層能為新細(xì)胞提供生長基地：它不但能促進(jìn)新細(xì)胞在其界面內(nèi)生長而且還能阻止創(chuàng)傷面下受傷細(xì)胞的滋長。而這些非正常細(xì)胞的滋長也可促生結(jié)疤的產(chǎn)生。

北卡羅來納大學(xué)研制的這種藥物繃帶還有另外兩層：一層是以淀粉為原料的聚合物組成，其作用是排濃，當(dāng)聚氨基葡糖分解時，還有保護(hù)創(chuàng)傷面的作用。再上一層是棉沙。它可以隨時更換而不至影響創(chuàng)傷面。這樣身體會逐漸吸收下面二層藥物而長出完好如初的新皮。

為制做敷藥繃帶的基層，專家們把蟹殼研磨成粉末狀，又加入一些化學(xué)制劑，將基層的聚乙酰氨基葡糖轉(zhuǎn)換成聚氨基葡糖。然后將此粘性溶液倒到特氟隆薄片上就形成了一層藥物薄膜。除了其愈合療效之外此藥膜還有抗感染功能：菌類，病毒和其他微生物都不能在其上生長。研究小組希望能提高制做效率并能讓第二層聚合藥物層也能直接向皮膚滲透藥物，從而進(jìn)一步改進(jìn)療效。

到目前為止，此藥在豬身上的試驗結(jié)果表明其療效是肯定的。但正如噴涂纖維繃帶療法一樣，還需由臨床試驗進(jìn)一步確定其在人體皮膚上的療效到底如何。藥物發(fā)明人古普塔說還需再過幾年，此藥才能供應(yīng)市場。

現(xiàn)在市場上出現(xiàn)了一種高科技的敷藥繃帶。像蟹殼原料一樣出人意料之外，其原料是豬小腸。十年前波爾都大學(xué)的科學(xué)家們分離出一種組織名叫小腸結(jié)膜(SIS)，他們發(fā)現(xiàn)其有不同尋常的愈合功效。它含有復(fù)雜的膠原蛋白基質(zhì)，生長素和其它蛋白質(zhì)。敷到傷口時，這層粘膜像天然框架一樣促使在其中的機(jī)體長出新組織，而幾乎不留疤痕。此種繃帶已被用來治療長期皮膚腫痛和嚴(yán)重到需截肢程度的皮膚創(chuàng)傷。

OaSIS制做簡便，成本不高：小腸是豬肉生產(chǎn)中的棄物。一只豬可提供九十尺小腸。先把分離中的小腸膜洗凈，消毒；把無用的表面細(xì)胞撥離開來加以冷凍。最終產(chǎn)品非常類似羊皮紙。將其敷在傷口上可以刺激新血管的形成，以便為新敷的生物繃帶提供營養(yǎng)（皮膚長期腫痛通常是由血液循環(huán)不良造成的）。當(dāng)新皮長出時，腸膜就會脫落，代之而起的是完好如初的新皮。

此療法導(dǎo)致感染豬病毒的機(jī)率極小。波爾都公司的生物醫(yī)學(xué)專家斯蒂芬·柏蒂拉克指出：“長期以來人們一直使用波爾都公司的制品；而且多年來豬皮一直被用來治療灼傷。”當(dāng)然，總會有些病人對豬制品藥物過敏。

生物降解繃帶在療傷藥品競爭中不敢說首屈一指，如果其功能真如廣告所宣傳的那樣，那么至少治愈的傷口不會留下疤痕是指日可待的。