Collagen fibrils mechanical properties

Parry, D. A. D., Barnes, G. R. G., and Craig, A. S. (1978). A comparison of the size distribution of collagen fibrils in connective tissues as a function of age and a possible relationship between fibril size distribution and mechanical properties. Proc. Roy. Soc. Lond. B. 203, 305-321. 

Figure 7.9. Relationship between mechanical properties and fibril length (L) for self-assembled collagen fibers. Plot of UTS (A) and elastic slope (B) versus L in im for self-assembled type I collagen fibers stretched in tension at strain rate of 50%/min. Points with fibril lengths less than 20 pm are for uncrosslinked self-assembled type I collagen fibers and the points above 20 pm are for crosslinked fibers. The correlation coefficient for the best fit line is given by R2.

The importance of lysyl hydroxylation is seen in patients with the type VI variant of Ehlers-Danlos syndrome (Table 25-5). The collagen in these individuals has a decreased fibril diameter and profound changes in mechanical properties. Skin fibroblasts show virtually no lysyl hydroxylase activity. Furthermore, hydroxylysine formation can be severely affected in some tissues, mildly affected in others, and unaffected in still others (e.g., cartilage). These observations suggest the presence of tissue-specific lysyl hydroxylases. 

Figure 3 Proposed interactions between mechanical strain, proteoglycans (PGs), and transforming growth factor (TGF)-P in the extracellular environment of the airway wall. Excessive mechanical strain stimulates fibroblasts to increase PG secretion and deposition. The altered viscoelastic properties of the matrix subsequently modulate transmission of the mechanical signal to the airway structural cell and, thereby, protect the cell from mechanical strain-induced injury. In addition, increases in decorin may result in enhanced binding of TGF-P and thereby influence the effects of this cytokine on the fibroblast. Finally, changes in small PGs, such as decorin and lumican, may affect formation of collagen fibrils. CS, chondroitin sulfate HA, hyaluronic acid.

A basic building block of the bone is the mineralized collagen fibril. With various percentages of mineralization, different types of bones have specialized properties for their own purposes. As with other biomaterials, the atomistic mechanical properties of its basic constitutive units are strongly correlated with their chemical bond network induced by their structural stability, and their reactivity during deformation and fracture. 

Because the mineral has higher modulus than the collagen molecules, it is commonly believed that the presence of HAP is important to the stiffness of bone [81, 82]. The mechanical and failure properties of bone depend on the relative amount of the mineral deposited in the collagen fibrils [83, 84]. From tests on various bone samples of mammals, it is known that the Young s modulus of the mineralized-collagen fibrils increases linearly with the mineral contents [81]. 

Holmes, D.F. Gilpin, C.J. Baldock, C. Ziese, U. Koster, A.J. Kadler, K.E. Comeal collagen fibril structure in three dimensions Structural insights into fibril assembly, mechanical properties, and tissue organization. Proc. Natl. Acad. Sci. U. S. A. 2001, 08 (13), 7307-7312. 

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