Tissue mechanics.

Great info.

Also:

One fundamental property of living tissues is their ability of adaptation to environment because cells are always exposed to mechanical stresses related to environment or to movement (i.e. external pressure, blood flow, pressure on bone or cartilage related to walking, …). Today it’s generally accepted that these mechanical forces can modify the biological behaviour of cells by affecting their metabolism, secretion of autocrin factors, phenotype, etc …

The modifications induced by mechanical factors are now considered as determinant to the comprehension of some patho-physiological processes (i.e. : atherosclerosis, thrombosis, arthrosis, …).

Drs. J.F. Stoltz and X. Wang, Chairmen
Euromech Colloquium N°420, Mechanobiology of Cells and Tissues, April 24-26, 2001, Nancy, France.

A highlight from link 1:

Immoblization of a joint for a long period of time leads to significant changes in joint structure and function, including decreased range of motion for the joint. The affects of both ligaments and tendons can be severe. Woo et al. studied rabbit knees in the following experimental groups:

1. 9 weeks immobilization
2. 12 weeks immobilization
3. 9 weeks immobilization, then 9 weeks active
4. 12 weeks immoblization, then 9 weeks active

9 weeks of immoblization led to a 69% decrease in ultimate load and an 82% decrease in energy to failure. After 12 weeks of immoblization led to a 71% decrease in ultimate load. Affects on the stress strain curve from Woo are shown below:

If the rabbits became active, there was an increase in stiffness and strength almost back to the level of controls.

Corresponding to the reduction in mechanical properties, there is a reduction in the ligament structure. During immobilization, the cross sectional area of the ACL is reduced. This implies a loss of collagen fibrils as well as a loss of glycosaminoglycans that form the ground substance of the ligament. In addition, the may be alterations in collagen fibril orientation that reduce properties. Upon remoblization, it appears that the mechanical properties of the ligament are gained back first, followed by the structural properties. This indicates that structural loss at the ligament insertion site may take longer to be removed that changes in ligament substance.