Chemistry of fibrous composites

In living systems, fibrous composites (defined in Section 1.3d) behave like fibreglass and consist of stiff fibres embedded in a pliable matrix. Their chemistry is dominated by polysaccharides and proteins, both of which are polymers. The chemistry of both the fibrous and the matrix parts of these composites is variable. The following are some examples of the chemical variety, and all possible combinations can occur:

1. (1)Polysaccharide fibres in a polysaccharide matrix. Examples include plant cell walls (Neville et al., 1976).

2. (2)Polysaccharide fibres in a protein matrix, such as cuticles of insects, crabs, and other arthropods (Neville, 1975a; Bouligand, 1965), and tests of tunicate sea squirts (Gubb, 1975).

3. (3)Protein fibres in a polysaccharide matrix, such as eelworm cyst (Shepherd et al., 1972), chicken cornea (Coulombre & Coulombre, 1975), human bone (Giraud-Guille, 1988), and basement lamella (Kefalides et al., 1979). Vertebrate extracellular matrix is not included in detail in this book, as it is already the subject of numerous works (Hay, 1981; Trelstad, 1984; Bard, 1990).

4. (4)Protein fibres in a protein matrix, such as fish eggshells (Grierson & Neville, 1981), butterfly and moth eggshells (Smith et al., 1971), and praying mantis eggcase (Neville & Luke, 1971b).

Examples of polymers which form the fibrous component of composites include the polysaccharides cellulose and chitin and the protein collagen. Matrix components include the polysaccharides hyaluronic acid and hemicellulose and the protein rubber resilin. There is a tendency to consider hyaluronic acid as a molecule characteristic of vertebrate materials.