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

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 1U/ml elastase and 6h treatment. For specimens treated with 2U/ml elastase for 6h, elastin content decreased approximately 35%. Mean peak tissue strain after cyclic loading (4.8%, p0.300), modulus (275MPa, p0.114) and hysteresis (20%, p0.553) were unaffected by elastase digestion, but stress decreased significantly after treatment (up to 2MPa, p0.049). 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. (c) 2013 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 31:1226-1233, 2013