When is the last time you got a cut or scraped your knee? You probably put a Band-Aid on it and promptly forgot about the wound, knowing that your body would take care of itself and begin the healing process almost immediately.
As human beings, we’re quite spoiled with the self-healing nature of our bodies, but we’re forced to manually fix almost everything else in our lives. Over time, it seems like every object in the world breaks down, so wouldn’t it be incredible if other materials were able to self-heal like our miraculous bodies?
Well, that dream is rapidly becoming a reality, thanks to the recent development of self-healing materials!
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What is a Self-Healing Material?
As the name implies, a self-healing material is any material that can repair itself without direct human interaction. Does that sound like magic? Well, a few decades ago, it would have been, but over the past 15 years, extensive research into self-healing material has produced some amazing results, and there are now many types of self-healing materials that just may change the world as we know it.
There are four main types of self-healing materials: embedded healing materials, the hollow tube approach, reversible polymers, and shape-memory materials. These classifications of materials are based on their method of repair. The most rudimentary form is also the easiest to understand.
Embedded Healing Materials
Some of the simplest self-healing materials are filled with microcapsules (tiny packets of material) that are embedded within the material. When a hairline or crack causes those monomer capsules to break, the replacement material essentially leaks out to seal the crack. The polymers that the material is made of will bind with those leaked monomers (polymers are just long chains of identical monomers). This rapid binding prevents any loss of integrity to the structure or material.
The major limitations to this method is the one-time nature of this fix, which can be an issue since the compromised portion of the material is almost certainly weaker than in its original form, albeit “repaired”.
Our bodies contain an incredibly complex network of blood vessels and capillaries that provide access to almost every millimeter of the body. This is why our body is able to heal so rapidly – a signal is sent reporting the damage, resources are sent to the problem spot, and chemical reactions can begin to start the healing process.
The hollow-tube approach of self-healing materials is quite similar – a micro-network of vascular channels is built into the material, and operates on a pressure principle. When part of the tube network is damaged, the pressure difference will autonomously cause “repair” material to be pumped through the hollow tubes to the spot that requires repair. This method takes slightly longer, but can fix much larger cracks, and can also work more than once, unlike the microcapsule approach.
Our research on polymers seems never-ending and one of the most curious discoveries has been polymers that basically “turn back time”. When they are forced out of shape or damaged in any way, some of these self-healing polymers only require a bit of heat and energy to snap those polymers back to their original orientation. Many times, the friction, stress, or direct impact that causes the damage to the material is enough to cause it to reform. The highly reactive ends of these “broken” polymers will be electrochemically attracted to one another and will gradually reform.
One of the more complex advancements in self-healing materials comes in the form of shape-memory materials. Many metal alloys have been developed that have the ability to bend and then snap back into place when energy is applied.
Unlike reversible polymers, energy must be directly applied within a larger mass of substance, which is where a fiber-optic network would come into play. Much like the nanotube example above, this fiber-optic network would be activated when the “cable” was breached, and a laser light would be sent to that location to provide the heat. At that point, the shape-memory material would snap back into its original place, undoing the stress, strain, or damage it had just suffered.
Self-Healing Materials in the Future?
In a little over a decade, self-healing materials have gone from concept to reality, and the long-term benefits that it can have on countries, economies, and individual people is practically limitless. Imagine bridges that never break, cars that re-do their own paint jobs, and planes that fix microscopic cracks in their fuselage, avoiding things like this.
Self-healing materials are still quite costly and their widespread use is still hampered by their availability, but things are moving forward every day. New combinations of these self-healing approaches are being tried, such as mixing gelled microcapsules with the shape-memory approach, producing flexible, durable, and long-lasting materials that will significantly increase the safety and longevity of materials across the world.
So in answer to the original query of this article, it’s not a matter of if they will change the world, but only when!