Chitin: A biological approach to this material

 The armored walkers

stag-beetle-383984Exoskeleton has played a major role in the triumph of arthropods on land and in the seas. I won’t list the benefits of this kind of protective armor, not only against impacts, but in many others scenarios as dehydration, chemical and physical attacks, communication, migration…(I’m listing, am I?)

But seriously, if you are that size, that’s probably one of the best suits you can be in. Along the introduction to this Biopolymers series we have seen that this kind of long molecules can create very extensive chains. It’s not hard to understand then the easiness nature find creating long chitinous fibers, composed of several polymeric threads, that can be integrated conforming a quite tough and flexible material.

In insects and crustaceans cuticle, this chitin fibers run parallel through each layer of material, but with different directions from one layer to another, creating a very resilient frame. This kind of use for fibers, arranged in different directions trough several layers of material, can be found in natural and human made composites, being the hardness and elasticity of this design very well known.

crustaceans exoskeleton1
Structural levels in crustaceans (H. americus). Image: author’s edition of the picture taken from the D. Raabe et al’ paper in Acta Materialia [1]

Actually, this chitin framework constitutes only a scaffold for a surely complex exoskeleton.  Insects add other proteins and molecules like quinones to the mix, to harden this composite and create sclerotin [2]. Or others of a completely different nature if a much more flexible or even elastic material is needed, i.e. in the legs’ joints.

Crustaceans count on the salts diluted in the water and have incorporated a mineral component which is calcium carbonate to this skeleton. That way, and depending of the mineralization rate which can reach an amazing 95% in some cases, you can find really shielded animals whose aspect resemble more a rock than an animal.

Chitin is also present in other lifeforms like cephalopods, mollusc, and even in the cell walls of fungi. But I think that, for now, we have a good bio-perspective and we can continue with our egocentric human-perspective.

Then, considering that chitin is estimated to be the most abundant natural amino polysaccharide produced by nature, almost as much as the cellulose produced by the vegetable world [3]: What can we do with this wasted resource?.

Remember that food industry is already capturing and farming shrimps by millions of tons each year (almost 7 million tons in 2010 according to Wikipedia). Sorry about that crustaceans of the world: you look cute but you taste better.

In fact, the main industrial resource for obtaining that biomaterial is the above mentioned crustaceans captured or farmed by this food industry.

Fortunately, scientific community have been working with chitin for many years now, since Albert Hofmann determined it’s chemical structure in 1929 (the same guy that synthesized LSD for the first time, random fact of the day).

So, the next Biopolymers entry will bring the technological view of this biomaterial with what I think are several unexpected applications. See you there!

References:

[1] D. Raabe, C. Sachs, P. Romano. The crustacean exoskeleton as an exampe of a structurally and mechanically graded biological nanocomposite material. Acta Materialia 2005; 53: 4281-4292

[2] R. H. Hackman. Hardening and Darkening of the cuticle. Chemistry of Insect Cuticle. 1952; 54: 371-377

[3] Majeti N.V. Ravi Kumar. A review of chitin and chitosan applications. Reactive & Functional Polymers. 2000; 46:  1–27

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2 thoughts on “Chitin: A biological approach to this material

    1. You are not alone! I thought the same until I started reading about this material. It seems so weird at a first moment. It’s the soft caterpillar “skin” the one that contain more chitin, and not the hard beetle carapaces we all think about when we hear that word. Thank you for your comment!

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