Self-healing materials are substances that are able to repair structural cracks or other damage automatically, an ability that can greatly extend the usable life of a product, and in some cases help to protect people from harm. Many self repairing products have been inspired by biological processes that permit living bodies to heal. By observing natural healing activity on a microscopic level, scientists have develop multiple methods to replicate this beneficial ability in man-made substances. There are several different types of self-healing products, and multiple approaches can be used to create these materials. Regardless of the structure, self repairing objects are all designed to function without requiring human intervention.
One type of self repairing product is known as a microencapsulated system. These self-healing materials are specifically engineered to fix minuscule cracks that occur in polymers. This damage, sometimes called "microcracking," can be caused by mechanical wear or thermal stress. Microencapsulated materials contain a chemical agent that is formulated to rebuild and reinforce the polymer structure. A layer of epoxy contains these reinforcing chemicals within tiny pockets, and the agent begins to spread when structural damage causes the small capsules to rupture.
Microvascular systems are another variety of self-healing materials. Like microencapsulated solutions, this type of material uses a healing agent that is kept contained until needed. Instead of being uniformly spread throughout a surface within tiny capsules, however, the helpful chemicals are placed in artificial "veins" or channels that honeycomb the material. This vein-like structure allows chemicals to be continuously pumped into a cracked area, which helps prevent ongoing damage.
A third method that can be used to create self-healing materials employs mechanochemically active polymers. This approach is similar to the way that human bones begin to repair themselves after breaking. With this method, polymers are created which contain clusters of molecules call as "mechanophores." These clusters are naturally prone to connect with other similar molecules. When a polymer is impacted by stress, the embedded mechanophores form a structural link, much like two pieces of Velcro® fasteners being forced together.
Self-healing materials have many practical applications. Scientists have experimented with spacecraft surfaces that automatically seal dangerous ruptures caused by meteoroid strikes or space debris. Airplanes can also benefit from these substances, and can benefit from resistance to cracks on the control surfaces. These types of materials may also be used in synthetic rubber-like products, in order to prevent wear and improve tread life.