Arthropod cuticle: A natural composite shell system

The cuticle of arthropods (jointed-limb animals), and especially of insects is, by biological standards, a relatively simple composite. It is a single external layer of material forming the skeleton and many sense organs. The fibrous phase is crystalline chitin making nanofibrils of about 3 nm diameter, a few hundreds of nanometers long and a modulus probably in excess of 150 GPa. At least two surfaces of the nanofibril can have silk-like protein attached through specific H-bonds; the rest of the protein is globular. The protein matrix stiffens through dehydration controlled by the introduction of hydrophobic phenolics. Crustacea add up to 40% calcium salts. The stiffness of cuticle can range from tens of GPa to 1 kPa. It can be hardened by the addition of Zn or Mn. It can form springs and change its stiffness and plasticity under the control of the animal. © 2002 Elsevier Science Ltd. All rights reserved.