ROLE OF COLLAGEN IN ELASTIC PROPERTIES OF CALCIFIED TISSUES

Bony tissues, considered as a two phase composite system of HAP (hydroxyapatite) and collagen, are described as a family of Ruess solids where the soft matrix becomes stiffer as the hard filler is added until a maximum elastic modulus is reached. Polymeric elastic moduli increase with cross linking density and shortening of maximum cross link length in macromolecules. In some polymers like epoxy these are strongly affected by the solid filter. Close similarity is found between HAP-collagen and FAP-epoxy (fluorapatite-epoxy). The concept is supported from evidence found in chemistry, physical properties, hierarchical structure and mineralization characteristics of collagen. It is postulated that increased cross linking density is associated with increased HAP content and the HAp crystallites provide rigid bases for shortened links to stiffen the composite by reversible enzyme directed processes.