Effect of elastin digestion on the quasi-static tensile response of medial collateral ligament

Abstract

Elastin is a structural protein that provides resilience to biological tissues. We examined the contributions of elastin to the quasi-static tensile response of porcine medial collateral ligament through targeted disruption of the elastin network with pancreatic elastase. Elastase concentration and treatment time were varied to determine a dose response. Whereas elastin content decreased with increasing elastase concentration and treatment time, the change in peak stress after cyclic loading reached a plateau above 1 U/ml elastase and 6 hr treatment. For specimens treated with 2 U/ml elastase for 6 hr, elastin content decreased approximately 35%. Mean peak tissue strain after cyclic loading (4.8%, p≥0.300), modulus (275 MPa, p≥0.114) and hysteresis (20%, p≥0.553) were unaffected by elastase digestion, but stress decreased significantly after treatment (up to 2 MPa, p≤0.049). Elastin degradation had no effect on failure properties, but tissue lengthened under the same pre-stress. Stiffness in the linear region was unaffected by elastase digestion, suggesting that enzyme treatment did not disrupt collagen. These results demonstrate that elastin primarily functions in the toe region of the stress-strain curve, yet contributes load support in the linear region. The increase in length after elastase digestion suggests that elastin may pre-stress and stabilize collagen crimp in ligaments.

Elastin governs the mechanical response of medial collateral ligament under shear and transverse tensile loading

“…Porcine MCL was chosen as it is a readily available planar ligament that is large enough to allow isolation of multiple rectangular test specimens, and its native material properties are similar to human MCL [5, 11]. The tissue was thawed and the ligament was fine dissected to remove overlying fascia.…”

“…We recently examined the role of elastin in ligament mechanics via selective degradation with elastase [9] and found that elastin provided a disproportionately high contribution during uniaxial tensile deformation along the primary collagen axis. Although elastin constituted only 4% of the tissue dry weight, it supported up to 30% of tensile stress under uniaxial strain [5]. In addition, elastin is localized between and along collagen fibers in cruciate ligaments [10].…”

Tendon injury and repair – A perspective on the basic mechanisms of tendon disease and future clinical therapy

“…Proteomic screening studies have suggested that collagen Type VI may be an important component of the tendon ECM [64], being a pericellular matrix protein that plays a role in collagen fibrillogenesis [65]. Beyond the fibrillar collagens, elastin is a fibrillar glycoprotein contributing 1-2% of tendon dry mass that plays a role in recoil of the matrix after repetitive mechanical loading [66]. Binding the fibrillar matrix are numerous FACITs (fibril-associated collagens with interrupted triple helices) that regulate interactions between the fibrillar matrix and other ECM molecules.…”

The (dys)functional extracellular matrix

“…3A) [53]. While collagen is generally thought to be the main mechanical element in tendons, removal of non-collagenous molecules, such as elastin or glycosaminoglycans, reduces the whole tendon mechanical response, emphasizing their role in development, homeostasis, and load transfer [54–56]. …”