It is fibre orientation and laminar structure which takes bone the crucial step from embryonic, woven bone to the order and strength of compact bone. The metabolic unit of compact bone is the osteon, a rod with concentric laminations, like the layers of a leek. The collagen fibres run in a concentric direction around each lamination and in a longitudinal direction down the length of the osteon. Down the middle runs a bundle of blood vessels which provides the transport and energy required for the regular replacement of bone in the osteon. The osteons are packed together into compact laminated bone and aligned along the length of a thick tube which makes up the shaft of long bones.
Synthetic composites follow the same rule of fibre orientation as bone does.
The steel fibres of reinforced concrete can be seen sticking out of the ground on building sites, before the concrete is poured around them. A more sophisticated arrangements of fibres in a composite can be found in the drive shaft which links the tail rotor of a helicopter with the motor. The shaft must be long and thin but not whip or wobble. Teeth are composites of enamel and dentine and each of these material is itself a composite. Enamel consists almost entirely of hydroxyapatite crystals but there is a regular alignment of the crystals within each enamel prism.