Increased Disarray of Extracellular Matrix Collagen-I Fiber Network and Compromised Biomechanics in Aortae From Marfan-Syndrome Mice Assessed Through Combined Opto-Biomechatronics.

Fibrillin‑1 (FBN1) mutations lead to extracellular matrix (ECM) defects with progressive aortic dilation in Marfan's syndrome (MFS). MFS thoracic aortas have increased stiffness, but how visco-elastic and microstructural abnormalities affect in vivo hemodynamics remains inconclusive. We applied ex vivo uniaxial visco-elasticity stress-relaxation testing and simultaneous 3D collagen Second Harmonic Generation (SHG) imaging to MFS and wt littermate linearized aortic strips with in vivo vascular function. MFS mouse (Fbn1mgR/mgR) aortas were stiffer and more viscous. SHG imaging revealed MFS ECM disorganization at rest and stronger collagen-alignment strain response than wt strips, indicating greater fibrillar straightening capacity. in vivo, MFS mice developed early, progressive aortic dilation. Pulse wave velocity was elevated in young MFS mice pre-dilation but declined as aneurysms formed. Female MFS aortic peak pressure and velocity were normal, but reduced in MFS-males vs. wt. Ex vivo perfused wt carotid arteries were highly compliant. Female MFS carotids were stiffer, had reduced radial strain, a right‑shifted pressure-strain curve and minimal wall‑thickness changes. MFS carotids did not recover baseline diameter after perfusion, indicating impaired visco-elastic recoil. We demonstrate early visco-elastic MFS aortic dysfunction and ECM disorder. Mechanistically, the larger collagen-straightening capacity in MFS cannot compensate for the increased visco-elasticity during a beat-to-beat cycle.