Analysis of mammalian connective tissue: relationship between hierarchical structures and mechanical properties.

It is widely accepted that the mechanical properties of implants must match those of the surrounding connective tissue to prevent stress concentration and premature failure. The purpose of this paper is to review the structure-mechanical property relationships that exist for connective tissue. The mechanical properties of connective tissue depend on the content of collagen, elastic tissue, and proteoglycans, as well as the geometric arrangement of the fibrous components, age, and location of the specimen. To a first approximation the geometry and loading pattern of the collagen networks in these tissues dominate the mechanical response at high strains. The behavior of the elastic fiber networks dominate the low-strain mechanical response in tissues where energy and shape recovery are critical. Proteoglycans are involved in resisting tissue compressive forces. Since the stiffness of connective tissue increases with age, it is necessary to attempt to match this property by designing implants that have similar behaviors to insure that stress concentration does not occur at the interface between the implant and host.