A self-healing material is an artificial material that can repair itself automatically without any assistance or contribution from a human. Self-healing polymers are one of the first types of self-healing materials to be reported in 2001 by researchers at the University of Illinois . There have been many self-healing materials that have since been developed by scientists all over the globe.
There are a variety of ways in which self-healing polymers work. One method is the solid material has a capsule that contains a healing agent, which could be an adhesive or another type of chemical, embedded within it. When the solid material cracks upon damage, the embedded capsule breaks open and releases the healing agent which flows to the region of damage and fixes the solid material back together through some chemical processes and reactions. A chemical catalyst is usually used to ensure the reaction occurs rapidly and under different conditions. However, there are some disadvantages of having embedded capsules. They can disrupt the overall structure of the material which can, ironically, make it weak. Another important disadvantage is that it can only repair itself once and so there is no real long-term solution as damage may occur again .
Hence scientists have looked elsewhere for inspiration in developing self-healing materials, the human body. Specifically, the human body’s vascular system, which consists of tube-like blood vessels that pump more blood to areas which are in need of oxygen and nutrients for growth and repair . Many self-healing materials have been designed in a way that consists of many small, thin tubes that pump the healing agent across the material. When the material has been damaged at a certain region, more of the healing agent is pumped to the damaged region due to the pressure released upon cracking .
Other methods to develop these exciting materials include the use of shape-memory materials and reversible polymers, which are involve more complexed and technical processes.
Self-healing polymers have shown a wide variety of uses in paints and also mobile-phone cases that can repair itself when it is damaged, opening the doors to many business opportunities. Scientists at the University of Reading’s Department of Chemistry have collaborated with Engineers at Oxford University to deliver ground-breaking research of self-healing polymers. They have developed an adhesive that functions with an elastic polymer and can repair itself at body temperature which has opened the door to biomedical applications such as artificial skin or wound dressings . As Professor Wayne Hayes of the University of Reading explains: ‘If we cut ourselves we have to apply a plaster and after a period of time, that plaster starts to fail, its stickiness wears off, it gets damaged – you have to pull that plaster off a damaged part of skin, which is a very painful process’. He also goes on to explain: ‘One of the key targets for our research was to develop materials that could automatically heal when damaged. In particular, we were interested in materials that could heal at 37°C – body temperature – to maintain protective barriers’ . Strips of the polyurethane material was seen to flow back together 60 minutes after being cut with a razor. Moreover, the polymer had also showcased its self-healing ability when tested on pig skin and its mechanical stability under physiological conditions has paved the way to many uses in medicine. The fact that the healing process occurs efficiently at body temperature has inspired material chemists to hail the research as ‘beautiful’ .