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Structure and behavior 11

of collagen ﬁbers

2
1
Frederick H. Silver , Michael Jaffe , Ruchit G. Shah 1
1
Rutgers, The State University of New Jersey, Piscataway, NJ, United States;
2
NJIT, University Heights, NJ, United States
11.1 Introduction

Collagen ﬁbers form the basic structural components of the extracellular matrix (ECM)
of vertebrates that serve to store elastic energy during muscular deformation, transmit
stored energy into joint movement, and transfer excess energy from the joint back to
the attached muscles for dissipation (Silver and Landis, 2008). They also act as mecha-
notransducers by transferring stress borne by the musculoskeleton to the attached cells
in order to regulate tissue metabolism, either up or down, as a result of changes in
mechanical loading (Silver, 2006). Finally, they prevent premature mechanical failure
of tissues and limit deformation of most ECMs and organs (Dunn and Silver, 1983).
Therefore, the collagen ﬁber structure is intimately related to energy storage, transmis-
sion and dissipation, and premature mechanical failure of tissues.
Collagen ﬁbers are composed of collagen triple-helical molecules that are derived
from one or more of the 28 collagen types that compose the collagen family (Ricard-
Blum, 2011). The collagen family is composed of collagen subfamilies including
ﬁbril-forming collagens, beaded ﬁlaments, anchoring ﬁbrils, and networks. Most
collagen ﬁbrils are composites since they are made up of more than one collagen
type such as tendon (types I, II, and V), cartilage (types II, IX, and XI), skin (types
I and III), and cornea (types I, III, and V). In addition, other noncollagenous
macromolecules are attached to collagen ﬁbrils that are involved in ﬁbril formation
(proteoglycans), cell-collagen interactions (ﬁbronectin), and mechanotransduction
(integrins) (Ricard-Blum, 2011).

11.2 Collagen molecular structure

The chemical description of collagen is a protein containing three polypeptide chains,
each of which is composed of one or more regions containing the sequence Gly-X-Y,
where X and Y can be any other amino acid residue but is commonly proline and hy-
droxyproline, respectively. This three-chained molecule forms a right-handed triple
helical structure containing glycine residues buried at the center of the cylindrical
molecule and is synthesized in a longer precursor form termed procollagen (see
Fig. 11.1). The most abundant subfamily is the ﬁbrillar collagens of which type I

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