美研制出像皮肤一样可自愈的新塑料

据美国物理学家组织网近日报道，“一种新型塑料可模仿人体皮肤，当被划伤或割伤时会‘出血’变红以警示受伤，而创面触光后又可自愈合，这为飞机、汽车、手机、笔记本电脑和其他产品提供了理想的自修复表面。”这是美国南密西西比大学一个研究小组的科研人员在第243届美国化学协会全国会议及博览会上的描述。

塑料的应用已非常普遍，由于其结合了强度大、重量轻、耐腐蚀等多种优良特性于一身，可替代钢、铝、玻璃、纸等传统材料。然而，科学家也一直在努力修正这些随处可见的材料的一大缺点：许多塑料一旦被刮伤或破裂，修复会很困难或根本不可能。

自愈塑料已成为材料科学的圣杯。实现这一目标的方法之一是在裂痕或划伤处破开引晶塑料胶囊，其可释放出使伤痕愈合的化合物。另一种方法是使塑料经光、热或化学制剂等外部刺激而进行自修复。

这项研究的首席研究员马雷克教授说：“大自然赋予各种生物系统自我修复的能力，例如皮肤受伤后自愈和树干被切割后长出新树皮，还有一些虽看不到，但却在帮助我们维护生命和健康，像DNA（脱氧核糖核酸）用以修复基因遗传损伤的自愈系统。这种新型塑料可以模仿大自然中的这种能力，当受损时会显示红色警示信号，然后将其暴露于可见光或变化温度和pH值，可促其自我修复。”

该研究小组开发的塑料是用很小的分子链接或架“桥”于塑料化学物质上组成长链，当塑料被划伤或破裂，这些环节会被打破而改变形状，进而产生可见的颜色变化，裂口周围会出现红色斑点。而暴露在普通日光或灯光下或者pH值、温度发生变化时，其内“桥梁”会重建，损伤得以愈合，红色标记自行消除。

这种可显示受伤警告并具备自我修复能力的塑料可广泛应用于很多领域，例如汽车挡泥板上的划痕，可能只需将其暴露在强光下即可自行修复；飞机关键部件受损后裂缝边缘会显示出红色警示标记，便于工程师决定是用照灯的方式“治愈”损伤，还是进行完整的组件更换；此外还可能大量应用于战场上的武器系统。

新型塑料不像依靠嵌入式愈合化合物只能自修复一次，而是可以反复进行修复；同时相比许多其他塑料更为环保，因为其生产过程基于水性塑料，而不是依赖于潜在的有毒成分。该研究团队现正在引进其他技术来生产可以承受高温的塑料。

New plastics 'bleed' when cut or scratched — and then heal like human skin

new genre of plastics that mimic the human skin's ability to heal scratches and cuts offers the promise of endowing cell phones,laptops, cars and other products with self-repairing surfaces,scientists reported today. The team's lead researcher described the plastics, which change color to warn of wounds and heal themselves when exposed to light,here today at the 243rd National Meeting & Exposition of the American Chemical Society (ACS),the world's largest scientifi c society.

"Mother Nature has endowed all kinds of biological systems with the ability to repair themselves," explained Professor Marek W. Urban, Ph.D., who reported on the research. "Some we can see, like the skin healing and new bark forming in cuts on a tree trunk. Some are invisible,but help keep us alive and healthy,like the self-repair system that DNA uses to fix genetic damage to genes. Our new plastic tries to mimic nature, issuing a red signal when damaged and then renewing itself when exposed to visible light,temperature or pH changes."

Urban, who is with the University of Southern Mississippi in Hattiesburg foresees a wide range of potential applications for plastic with warn-and-selfrepair capabilities. Scratches in automobile fenders, for instance,might be repaired by simply exposing the fender to intense light.Critical structural parts in aircraft might warn of damage by turning red along cracks so that engineers could decide whether to shine the light and heal the damage or undertake a complete replacement of the component. And there could be a range of applications in batile fi eld weapons systems.

Plastics have become so common, replacing steel,aluminum, glass, paper and other traditional materials because they combine desirable properties such as strength, light weight and corrosion resistance. Hundreds of scientists around the world have been working, however, to remedy one of the downsides of these ubiquitous materials: Once many plastics get scratched or cracked, repairs can be diffi cult or impossible.

Self-healing plastics have become a Holy Grail of materials science. One approach to that goal involves seeding plastics with capsules that break open when cracked or scratched and release repairing compounds that heal scratches or cuts. Another is to make plastics that respond to an outside stimulus — like light, heat or a chemical agent — by repairing themselves.

Urban's group developed plastics with small molecular links or "bridges" that span the long chains of chemicals that compose plastic. When plastic is scratched or cracked, these links break and change shape. Urban tweaked them so that changes in shape produce a visible color change — a red splotch that forms around the defect. In the presence of ordinary sunlight or visible light from a light bulb, pH changes or temperature,the bridges reform, healing the damage and erasing the red mark.

Urban cited other advantages of the new plastic. Unlike selfhealing plastics that rely on embedded healing compounds that can self-repair only once, this plastic can heal itself over and over again. The material also is more environmentally friendly than many other plastics, with the process for producing the plastic water-based,rather than relying on potentially toxic ingredients. And his team now is working on incorporating the technology into plastics that can withstand high temperatures.