Chitin is a very strong polysaccharide with a long-chain that plays an important role in the structure of several organisms. It has a molecular formula of (C8H1305N)n which has been discovered for the first time by Swiss scientist Albert Hofmann in 1929.
It is the key structural component of the cell walls of all types of insects and crustaceans, as well as most fungi and arthropods in general. Other hard parts of these creatures are also made of chitin, some examples include the bird-like beaks of octopus and squids, as well as the teeth (known as radula) of mollusks. More advanced life forms, like reptiles, birds and all mammals including humans, use keratin instead as the main structural building block. However, chitin is even stronger than keratin and the hard shell of some creatures like crustaceans is made of a combination of these two compounds.
Scientists believe that chitin is very old and appeared for the first time one billion years ago. In the initial process of evolution, the first primitive types of single cell fungi separated from the earliest forms of unicellular life. The chitin-based walls of these fungi made them the best protected of all single-cell creatures and ensured their long-term survival. Fungi are actually more closely related to animals than to plants, even if this is not very obvious and few people are aware of it. They were the most widespread form of life until a mass extinction at the end of Permian almost obliterated them. They still exist today, in their old role as decomposers of organic matter.
Chitin is rarely found on its own in nature, almost always being combined with other molecules in order to produce strong materials. Pure chitin is transparent and flexible but at the same time very durable and tough. Arthropods use chitin in the external skeleton only as a component mixed with other substances, the most common end product being sclerotin, a matrix of proteins. External shells of molluscs and crustaceans are even stronger, being built from a combination of chitin and calcium carbonate. This composite is superior to both pure compounds, being a lot stronger than chitin and doesn't break easily like calcium carbonate. These different composite materials have various qualities, depending on their usage, which is obvious if you compare the flexible body of a caterpillar (normal chitin) with the tough exoskeleton of a beetle (mostly made of sclerotin).
Chitin has an innovative usage in the wings of butterflies, where its photonic crystals are built as layers of gyroids. Butterflies use them to communicate with one another and send various signals, by showing vivid iridescent colors on their wings.
Another special form of chitin is found on the scarab beetles of the Cyphochilus genus. The scales on their bodies are perfectly white, even more so that milk. This color is achieved by the structure of the chitin that makes up the scales. They actually consist of numerous chitin filaments, extremely thin but very densely grouped. They have various shapes and sizes but don't follow a particular order, which allows them to scatter light. All colors are deflected and become invisible, what remains is the pure white nuance.
Protopolybia chartergoides and other species from the social wasps' family use chitin to protect their nests building some kind of balloon on top of it. The wasps produce the material in their mouths, most of it being chitin.
Arthropods actually build their external skeletons out of a very resilient protein network that includes chitin, rather than the pure substance. Combined chitin tends to be much more durable than the pure one, but also rigid and less flexible, as observed by comparing the chitin skin of caterpillars with the hard shell of beetles. Some mollusks and crustaceans use chitin in a different way, by combining it with calcium carbonate to produce a very strong shell.
One of the most interesting uses of chitin is in the body of arthropods. Since they are among the most numerous and diverse forms of life on Earth and millions of distinct species have been discovered so far, it is obvious that chitin is a very good evolutionary choice as a structural building block in the animal world. The external skeletons of arthropods are mostly made of chitin but they grow in a unique way. They don't just increase in size, like the bodies of most animals. Actually, when the creature becomes too big and doesn't fit in its current shell, it discards it completely and grows an entirely new one. This process is named molting and happens very fast, in an accelerated growth that doesn't last more than one hour. This is the maximum time until the new exoskeleton becomes too strong to grow any further. The process is repeated every time it's needed until the arthropod eventually dies.
Chitin has an amazing quality: it can bond with living human and animal tissues. This compatibility makes it potentially very valuable in the treatment of wounds, as it could greatly increase their rate of healing. For the same reason, it could provide a breakthrough in the care of people with burns. Mixing chitin to make it acidic greatly increases its effectiveness, vastly reducing the healing time of burns. Applying this solution on a third degree burn can cure it completely after just a couple of days.
Other experiments have revealed that it boosts the overall process of healing, when used on bandages or directly on wounds. The same mechanism can maintain a high activity of the human immune system, even during times of severe stress or aggressive medication.
Chitin, along with chitosan and some other of its derived compounds, is thought to provide a wide range of beneficial effects. The most important effect is the antioxidant one but it also reduces tension, regulates cholesterol, balances blood sugar treating diabetes, reduces inflammation, works as an anticoagulant and antimicrobial and also kills tumours and cancer cells. At the same time, chitin and its derivatives regulate and improve the way our body works, tuning many of our built-in mechanisms, which can be useful against many chronic diseases.
The antioxidant effect of chitin and other derivatives neutralizes the dangerous free radicals both in vivo and in vitro. This makes them a very prized ingredient in food supplements because not only they provide health benefits but actually increase the life of the products themselves by delaying their decay.
Chitin can also be an excellent material of choice for the production of surgical thread. It is very strong and flexible, as well as being biodegradable, so it will disappear by itself by the time the wound closes. In addition, the intriguing healing properties already mentioned above mean that it could accelerate the rate of healing from inside the wound.
High doses of chitin can have a negative effect. Some jobs, like seafood processing, lead to inhaling large quantities of chitin. It has been proven that workers in such sectors have a high rate of asthma. Modern studies trying to understand why this happens have discovered that chitin actually plays a role in human allergies. Tests on animals have found that rodents increase the level of innate immune cells and develop an allergic response.
Chitin can also have several industrial uses. Because it combines well with other molecules, it serves for example as a binding agent in glue, as well as dyes and fabrics. It can also be used in the production of ion-exchange media and separation membranes for industrial purposes. Along with its derivative chitosan, it is employed in the paper industry to change its size and increase its strength. The newest research breakthroughs have found a way to manufacture from chitosan a revolutionary material similar to biodegradable plastic. Three-dimensional bio-printing can also turn it into a foundation for artificial human tissues engineered in labs. The structural strength of chitin makes it useful in the food industry as a stabilizing additive or an edible layer of film.