Bone as a Collagen-hydroxyapatite Composite and its Repair

The principal structural tissue of the skeletal system is bone which used to carry major loads in an enormous variety of vertebrate animals. To fulfil this role, nature has devised an extremely interesting ceramic composite whose components are primarily collagen and hydroxyapatite, but whose complex structure contains a wealth of mechanically relevant detail. Its mechanical properties depend on each of these aspects of composition and structure. Lamellar and fibre-matrix interfaces limit the growth of cracks and fatigue damage. Through the actions of remodelling by cells, bone's composite structure repairs fatigue damage and continuously adapts to changes in mechanical usage. When a bone suffers a trauma such as physical damage or surgery, a temporary mechanical support is often desired to allow the use of the bone while natural healing occurs. Besides use of bone grafting, bioactive biomaterials are gaining popularity for bone replacements. These biomaterials form a strong interfacial bond with living tissues, both bone and soft connective tissues and has elastic modulus that is very similar to bone. Bioactive implants thus provide a better means for assisting the body in its repair process. © Society for Biomaterials and Artificial Organs (India), 20080327-16.