Polymers and polymer composites have been widely used in tremendous engineering fields because of their advantages including light weight, good processibility, chemical stability in any atmospheric conditions, etc. However, long term durability and reliability of polymeric materials are still problematic when they serve for structural application. Exposure to harsh environment would easily lead to degradations of polymeric components. Comparatively, micro cracking is one of the fatal deteriorations generated in service, which would bring about catastrophic failure of the materials and hence significantly shorten lifetimes of the structures. Since the damages deep inside materials are difficult to be perceived and to repair in particular the materials had better to have the ability of self-healing. in fact, many naturally occurring portions in animals and plants are provided with such function in the case of healing of a skin wound, for example, the defect is temporarily plugged with a fibrin clot, which is infiltrated by inflammatory cells, fibroblasts, and a dense capillary plexus of new granulation tissue. Subsequently, proliferation of fibroblasts with new collagen synthesis and tissue remodeling of the scar become the key steps For haling of a broken bone, similar processes are conducted, including internal bleeding forming a fibrin clot, development of unorganized fiber mesh, calcification of fibrous cartilage, conversion of classification into fibrous bone and lamellar bone. Clearly, the natural healing in living bodies depends on rapid transportation of repair substance to the injured part and reconstruction of the tissues. Having been inspired by these findings, continuous efforts are now being made to mimic natural materials and to integrate self-healing capability into polymers and polymer composites. The progress has opened an era of new intelligent materials. On the whole, researches in this field are still in the infancy. More and more scientists and companies are interested in different aspects of the topic. innovative measures and new knowledge of the related mechanisms are constantly emerging The encyclopedia is intended for use in graduate and undergraduate courses, but practicing engineers and researchers in industry and academe will also find it a useful reference.
