title: The effect of static stretch on elastin degradation in arteries.
abstract: Previously we have shown that gradual changes in the structure of elastin during an elastase treatment can lead to important transition stages in the mechanical behavior of arteries. However, in vivo arteries are constantly being loaded due to systolic and diastolic pressures and so understanding the effects of loading on the enzymatic degradation of elastin in arteries is important. With biaxial tensile testing, we measured the mechanical behavior of porcine thoracic aortas digested with a mild solution of purified elastase (5 U/mL) in the presence of a static stretch. Arterial mechanical properties and biochemical composition were analyzed to assess the effects of mechanical stretch on elastin degradation. As elastin is being removed, the dimensions of the artery increase by more than 20% in both the longitude and circumference directions. Elastin assays indicate a faster rate of degradation when stretch was present during the digestion. A simple exponential decay fitting confirms the time constant for digestion with stretch (0.11 ± 0.04 h(-1)) is almost twice that of digestion without stretch (0.069 ± 0.028 h(-1)). The transition from J-shaped to S-shaped stress vs. strain behavior in the longitudinal direction generally occurs when elastin content is reduced by about 60%. Multiphoton image analysis confirms the removal/fragmentation of elastin and also shows that the collagen fibers are closely intertwined with the elastin lamellae in the medial layer. After removal of elastin, the collagen fibers are no longer constrained and become disordered. Release of amorphous elastin during the fragmentation of the lamellae layers is observed and provides insights into the process of elastin degradation. Overall this study reveals several interesting microstructural changes in the extracellular matrix that could explain the resulting mechanical behavior of arteries with elastin degradation.
authors.affiliation: Department of Mechanical Engineering, Boston University, Boston, Massachusetts, United States of America.
authors.forename: Ming-Jay
authors.initials: MJ
authors.lastname: Chow
authors.affiliation: Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, Cambridge, Massachusetts, United States of America ; Graduate School of Nanoscience and Technology (WCU), Korea Advanced Institute of Science and Technology, Daejeon, Korea.
authors.forename: Myunghwan
authors.initials: M
authors.lastname: Choi
authors.affiliation: Wellman Center for Photomedicine, Harvard Medical School and Massachusetts General Hospital, Cambridge, Massachusetts, United States of America.
authors.forename: Seok Hyun
authors.initials: SH
authors.lastname: Yun
authors.affiliation: Department of Mechanical Engineering, Boston University, Boston, Massachusetts, United States of America ; Department of Biomedical Engineering, Boston University, Boston, Massachusetts, United States of America.
authors.forename: Yanhang
authors.initials: Y
authors.lastname: Zhang
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000378:metabolism*; D001696:Biomechanical Phenomena / Q000502:physiology; D004548:Elasticity; D004549:Elastin / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism*; D008954:Models, Biological; D010196:Pancreatic Elastase / Q000378:metabolism*; D013314:Stress, Mechanical; D013552:Swine
chemical_list: D004549:Elastin; D010196:Pancreatic Elastase