Strain-Rate Sensitive Mechanical Properties of Tendon Fascicles From Mice With Genetically Engineered Alterations in Collagen and Decorin

Abstract

Tendons have complex mechanical behaviors that are nonlinear and time dependent. It is widely held that these behaviors are provided by the tissue composition and structure. It is generally thought that type I collagen provides the primary elastic strength to tendon while proteoglycans, such as decorin, play a role in failure and viscoelastic properties. This study sought to quantify such structure-function relationships by comparing tendon mechanical properties between normal mice and mice genetically engineered for altered type I collagen content and absence of decorin. Uniaxial tensile ramp to failure experiments were performed on tail tendon fascicles at two strain rates, 0.5%/s and 50%/s. Mutations in type I collagen led to reduced failure load and stiffness with no changes in failure stress, modulus or strain rate sensitivity. Fascicles without decorin had similar elastic properties to normal fascicles, but reduced strain rate sensitivity. Fascicles from immature mice, with increased decorin content compared to adult fascicles, had inferior elastic properties but higher strain rate sensitivity. These results showed that tendon viscoelasticity is affected by decorin content but not by collagen alterations. This study provides quantitative evidence for structure-function relationships in tendon, including the role of proteoglycan in viscoelasticity.

Matrix and gene expression in the rat cranial base growth plate

“…Within these constraints, the present data represent the first identification of the expression of cartilageand bone-related genes and matrix molecules in the CBGP. Consistent with several recent reports (Elliott et al 2003;Chen et al 2004;Robinson et al 2004), decorin appears to be involved in mechanotransduction and to have important roles during both normal development and upon mechanical modulation of chondral growth and development. Nonetheless, additional work is warranted to demonstrate the role of decorin in mechanotransduction pathways.…”

“…A catabolic fragment of decorin, named decorunt, lacks the binding affinity to type I collagen (Carrino et al 2003). Tail tendons demonstrate larger and faster stress relaxation properties in decorin knockout mice (Elliott et al 2003;Robinson et al 2004). Annulus fibrosus cells encapsulated in alginate gel increase their decorin mRNA expression upon unconfined compression (Chen et al 2004), although cells of the meniscus decrease their decorin mRNA expression upon both static and dynamic compressions (Upton et al 2003).…”

Evidence against proteoglycan mediated collagen fibril load transmission and dynamic viscoelasticity in tendon

“…This viscoelastic behavior has been directly associated with tissue water content (Chimich et al, 1992;Haut and Haut, 1997;Lam et al, 1993;Mijailovich et al, 1994;Woo et al, 1993) and the highly hydrophilic tendon PGs have been hypothesized to regulate tissue hydration and viscoelastic frictional losses associated with fluid flow through the solid matrix (Elliott et al, 2003;Haut, 1985;Screen et al, 2006). Again, available experimental evidence yields a convoluted picture, with support from experiments showing that enzymatic disruption of PGs side-chains reduces viscoelastic effects in tendon and palmer aponeuroses (Millesi et al, 1995) and that tendons from decorin knock-out mice show reduced strain-rate sensitivity (Robinson et al, 2004), but with other experiments indicating increased rates of stress relaxation in the same mice (Elliott et al, 2003).…”

“…There is some evidence that sulfated GAGs play a role in quasi-static tendon mechanics (Cribb and Scott, 1995;Liao and Vesely, 2007;Redaelli et al, 2003), while other studies indicate that this may not be true (Lujan et al, 2007a;Millesi et al, 1995;Rigozzi et al, 2009). Some researchers have proposed that GAGs might rather influence dynamic viscoelastic tissue properties (Elliott et al, 2003;Lujan et al, 2007a;Robinson et al, 2004;Screen et al, 2005), but this also remains to be conclusively established. The current study thus tried to clarify the mechanical role, if any, of SLRP GAG side-chains in regulating tensile mechanical properties of tendon through carefully controlled experiments using a well characterized experimental model for investigating tendon structure-function (Derwin and Soslowsky, 1999).…”

“…Decorin has been identified as a critical factor in the structural organization and development of the tissue (Birk et al, 1995;Reed and Iozzo, 2002;Zhang et al, 2006) as well as a promoter of nutrient diffusion (Koob and Summers, 2002). In addition to aiding in the bearing of compressive loads (as hydrophilic molecules that attract water), it has also been suggested that decorin may play a direct role in the support of tensile loads (Cribb and Scott, 1995;Hedbom and Heinegard, 1993;Korhonen et al, 2003;Liao and Vesely, 2007;Robinson et al, 2005;Robinson et al, 2004;Ruggeri A., 1984;Scott, 1986).…”