title: Biomechanical properties of the thoracic aneurysmal wall: differences between bicuspid aortic valve and tricuspid aortic valve patients.
abstract: BACKGROUND
  The prevalence for thoracic aortic aneurysms (TAAs) is significantly increased in patients with a bicuspid aortic valve (BAV) compared with patients who have a normal tricuspid aortic valve (TAV). TAA rupture is a life-threatening event, and biomechanics-based simulations of the aorta may help to disentangle the molecular mechanism behind its development and progression. The present study used polarized microscopy and macroscopic in vitro tensile testing to explore collagen organization and mechanical properties of TAA wall specimens from BAV and TAV patients.
  
  
  METHODS
  Circumferential sections of aneurysmal aortic tissue from BAV and TAV patients were obtained during elective operations. The distribution of collagen orientation was captured by a Bingham distribution, and finite element models were used to estimate constitutive model parameters from experimental load-displacement curves.
  
  
  RESULTS
  Collagen orientation was almost identical in BAV and TAV patients, with a highest probability of alignment along the circumferential direction. The strength was almost two times higher in BAV samples (0.834 MPa) than in TAV samples (0.443 MPa; p<0.001). The collagen-related stiffness (Cf) was significantly increased in BAV compared with TAV patients (Cf=7.45 MPa vs 3.40 MPa; p=0.003), whereas the elastin-related stiffness was similar in both groups. A trend toward a decreased wall thickness was seen in BAV patients (p=0.058).
  
  
  CONCLUSIONS
  The aneurysmal aortas of BAV patients show a higher macroscopic strength, mainly due to an increased collagen-related stiffness, compared with TAV patients. The increased wall stiffness in BAV patients may contribute to the higher prevalence for TAAs in this group.
authors.affiliation: KTH Solid Mechanics, School of Engineering Sciences, Royal Institute of Technology (KTH), Stockholm, Sweden.
authors.forename: Caroline
authors.initials: C
authors.lastname: Forsell
authors.affiliation: Atherosclerosis Research Unit, Center for Molecular Medicine, Department of Medicine, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Hanna M
authors.initials: HM
authors.lastname: Björck
authors.affiliation: Atherosclerosis Research Unit, Center for Molecular Medicine, Department of Medicine, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Per
authors.initials: P
authors.lastname: Eriksson
authors.affiliation: Cardiothoracic Surgical Unit, Department of Molecular Medicine and Surgery, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Franco-Cereceda
authors.affiliation: KTH Solid Mechanics, School of Engineering Sciences, Royal Institute of Technology (KTH), Stockholm, Sweden. Electronic address: gasser@kth.se.
authors.forename: T Christian
authors.initials: TC
authors.lastname: Gasser
mesh_terms: D000368:Aged; D017545:Aortic Aneurysm, Thoracic / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D001021:Aortic Valve / Q000002:abnormalities* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D000082882:Bicuspid Aortic Valve Disease; D001696:Biomechanical Phenomena; D003094:Collagen / Q000502:physiology*; D005260:Female; D020342:Finite Element Analysis; D006349:Heart Valve Diseases / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D013718:Tensile Strength / Q000502:physiology*; D014261:Tricuspid Valve / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*
chemical_list: D003094:Collagen