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. (C) 2002 Elsevier Science Ltd. All rights reserved.