Biomedical Engineering Reference
In-Depth Information
Fig. 5.5 Collagen and elastin: a Collagen triple helix (Israel Institute of Technology 2009),
b collagen is a triple helix formed by three extended protein chains wrapping around each another
(bottom). Many rodlike collagen molecules are cross-linked together in the extracellular space to
form unextendable collagen fibrils (top) that have the tensile strength of steel. The striping on the
collagen fibril is caused by the regular repeating arrangement of the collagen molecules within
the fibril, c elastin polypeptide chains are cross-linked together to form rubberlike, elastic fibers.
Each elastin molecule uncoils into a more extended conformation when the fiber is stretched and
recoils spontaneously, as soon as the stretching force is relaxed (Alberts et al. 2009)
Fig. 5.6 Elastin a in a muscular artery (elastin stain) (Israel Institute of Technology 2009), b in
alveoli (orcein stain) (Israel Institute of Technology 2009), c Bundles of collagen fibres wrapped
with elastin fibres from (Schäffler et al. 1995)
interconnected by hydrogen bonds, are entangled, constituting a right-orientated
super-helix, building a 3D network of fibrils. The winding (similar to rope fibres) is
responsible for the collagen fibre's tensile strength, which can carry loads ten
thousand-fold its own weight. Under loading, the threadlike windings of the fibrils
stretch, reducing their diameter. In this initial phase, collagen is relatively
stretchable. While the diameter of the winded polypeptide chains decreases,
stiffness and resistance against further deformation increases (Gordon 1989).
