A structural finite element model for lamellar unit of aortic media indicates heterogeneous stress field after collagen recruitment.
Incorporation of collagen structural information into the study of biomechanical behavior of ascending thoracic aortic (ATA) wall tissue should provide better insight into the pathophysiology of ATA. Structurally motivated constitutive models that include fiber dispersion and recruitment can successfully capture overall mechanical response of the arterial wall tissue. However, these models cannot examine local microarchitectural features of the collagen network, such as the effect of fiber disruptions and interaction between fibrous and non-fibrous components, which may influence emergent biomechanical properties of the tissue. Motivated by this need, we developed a finite element based three-dimensional structural model of the lamellar units of the ATA media that directly incorporates the collagen fiber microarchitecture. The fiber architecture was computer generated utilizing network features, namely fiber orientation distribution, intersection density and areal concentration, obtained from image analysis of multiphoton microscopy images taken from human aneurysmal ascending thoracic aortic media specimens with bicuspid aortic valve (BAV) phenotype. Our model reproduces the typical J-shaped constitutive response of the aortic wall tissue. We found that the stress state in the non-fibrous matrix was homogeneous until the collagen fibers were recruited, but became highly heterogeneous after that event. The degree of heterogeneity was dependent upon local network architecture with high stresses observed near disrupted fibers. The magnitude of non-fibrous matrix stress at higher stretch levels was negatively correlated with local fiber density. The localized stress concentrations, elucidated by this model, may be a factor in the degenerative changes in aneurysmal ATA tissue.
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States.
James R
JR
Thunes
Mechanical and Industrial Engineering Department, Indian Institute of Technology Roorkee, Roorkee, India.
Siladitya
S
Pal
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States.
Ronald N
RN
Fortunato
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; Department of Cardiothoracic Surgery, University of Pittsburgh, Pittsburgh, PA, United States; Department of Surgery, University of Pittsburgh, Pittsburgh, PA, United States; Center for Vascular Remodeling and Regeneration, University of Pittsburgh, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, United States.
Julie A
JA
Phillippi
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; Department of Cardiothoracic Surgery, University of Pittsburgh, Pittsburgh, PA, United States; Department of Surgery, University of Pittsburgh, Pittsburgh, PA, United States; Center for Vascular Remodeling and Regeneration, University of Pittsburgh, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, United States.
Thomas G
TG
Gleason
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States; Department of Cardiothoracic Surgery, University of Pittsburgh, Pittsburgh, PA, United States; Department of Surgery, University of Pittsburgh, Pittsburgh, PA, United States; Center for Vascular Remodeling and Regeneration, University of Pittsburgh, Pittsburgh, PA, United States; McGowan Institute for Regenerative Medicine, University of Pittsburgh, Pittsburgh, PA, United States.
David A
DA
Vorp
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States. Electronic address: spm54@pitt.edu.
Spandan
S
Maiti
D001013:Aorta, Thoracic / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D017545:Aortic Aneurysm, Thoracic / Q000378:metabolism / Q000473:pathology; D003094:Collagen / Q000378:metabolism*; D005109:Extracellular Matrix / Q000378:metabolism; D020342:Finite Element Analysis; D006801:Humans; D013314:Stress, Mechanical; D017540:Tunica Media / Q000166:cytology / Q000378:metabolism* / Q000473:pathology
D003094:Collagen