Fibre reinforcing by collagen in cartilage and soft connective tissues

Mechanical support in animals is performed by connective tissues. The soft tissues consist of collagen fibres embedded in a highly hydrated proteoglycan gel. By considering them as fibrous composite materials, a unifying theme can be found to explain their mechanical behaviour in terms of their structure and composition. Interactions between fibres and matrix are essential to their functioning in this way. Calculations are made of the maximum stress transfer per D-period required to enable collagen fibres of a given axial ratio to provide effective reinforcing. Weak non-specific interactions are shown to be sufficient. A mechanical function is proposed for type X collagen in the epiphyseal growth plate on the basis that it modifies and supplements the properties of the type II fibrils. This provides extra reinforcing and, hence, a greater stiffness to the cartilage to compensate for the reduced amount of extracellular matrix.