title: Variations of dissection properties and mass fractions with thrombus age in human abdominal aortic aneurysms.
abstract: BACKGROUND
  Thrombus ages, defined as four relative age phases, are related to different compositions of the intraluminal thrombus (ILT) in the abdominal aortic aneurysm (AAA) (Tong et al., 2011b). Experimental studies indicate a correlation between the relative thrombus age and the strength of the thrombus-covered wall.
  
  
  METHODS
  On 32 AAA samples we performed peeling tests with the aim to dissect the material (i) through the ILT thickness, (ii) within the individual ILT layers and (iii) within the aneurysm wall underneath the thrombus by using two extension rates (1mm/min, 1mm/s). Histological investigations and mass fraction analysis were performed to characterize the dissected morphology, to determine the relative thrombus age, and to quantify dry weight percentages of elastin and collagen in the AAA wall.
  
  
  RESULTS
  A remarkably lower dissection energy was needed to dissect within the individual ILT layers and through the thicknesses of old thrombi. With increasing ILT age the dissection energy of the underlying intima-media composite continuously decreased and the anisotropic dissection properties for that composite vanished. The quantified dissection properties were rate dependent for both tissue types (ILT and wall). Histology showed that single fibrin fibers or smaller protein clots within the ILT generate smooth dissected surfaces during the peeling. There was a notable decrease in mass fraction of elastin within the thrombus-covered intima-media composite with ILT age, whereas no significant change was found for that of collagen.
  
  
  CONCLUSIONS
  These findings suggest that intraluminal thrombus aging leads to a higher propensity of dissection for the ILT and the intima-media composite of the aneurysmal wall.
authors.affiliation: Graz University of Technology, Institute of Biomechanics, Graz, Austria.
authors.forename: J
authors.initials: J
authors.lastname: Tong
authors.affiliation: Medical University of Graz, Clinical Department of Vascular Surgery, Graz, Austria.
authors.forename: T
authors.initials: T
authors.lastname: Cohnert
authors.affiliation: Medical University of Graz, Institute of Pathology, Graz, Austria.
authors.forename: P
authors.initials: P
authors.lastname: Regitnig
authors.affiliation: Medical University of Graz, Institute of Pathology, Graz, Austria; Medical University of Graz, Center of Medical Research, Graz, Austria.
authors.forename: J
authors.initials: J
authors.lastname: Kohlbacher
authors.affiliation: Medical University of Graz, Institute of Pathology, Graz, Austria; Medical University of Graz, Center of Medical Research, Graz, Austria; ACIB GmbH, Graz, Austria.
authors.forename: R
authors.initials: R
authors.lastname: Birner-Gruenberger
authors.affiliation: Graz University of Technology, Institute of Biomechanics, Graz, Austria.
authors.forename: A J
authors.initials: AJ
authors.lastname: Schriefl
authors.affiliation: Graz University of Technology, Institute of Biomechanics, Graz, Austria.
authors.forename: G
authors.initials: G
authors.lastname: Sommer
authors.affiliation: Graz University of Technology, Institute of Biomechanics, Graz, Austria; Royal Institute of Technology (KTH), Department of Solid Mechanics, Stockholm, Sweden. Electronic address: holzapfel@tugraz.at.
authors.forename: G A
authors.initials: GA
authors.lastname: Holzapfel
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000784:Aortic Dissection / Q000473:pathology*; D001012:Aorta, Abdominal / Q000033:anatomy & histology / Q000473:pathology*; D017544:Aortic Aneurysm, Abdominal / Q000473:pathology*; D003094:Collagen / Q000032:analysis; D004549:Elastin / Q000032:analysis; D004730:Endothelium, Vascular / Q000473:pathology*; D005337:Fibrin / Q000032:analysis; D006801:Humans; D008875:Middle Aged; D011312:Pressure; D013927:Thrombosis / Q000473:pathology*
chemical_list: D005337:Fibrin; D003094:Collagen; D004549:Elastin
keywords: Dissection; Intraluminal thrombus; Mass fraction; Thrombus age; Thrombus-covered wall