Controlled intramural fluid injection to quantify propensity to thoracic aortic dissection.

Dissection of the thoracic aorta includes delamination of medial lamellae and permeation of blood within the media. Quantifying how biaxial loading of a vulnerable wall and fluid mechanics interact to drive dissection remains a central challenge. Here we combine controlled distension-extension testing of intact porcine descending thoracic aortas with forced intramural fluid injection to investigate how axial stretch, injection rate, and needle gauge modulate the initiation and propagation of intramural delamination. Across experiments, injection pressure-volume curves exhibited nonlinear responses characterized by pressure peaks followed by stepwise pressure drops, suggesting progressive micro-delamination events within the medial lamellar networks. Increasing axial stretch significantly elevated peak injection pressure and promoted preferential axial propagation of the permeation / delamination front. Higher injection rates induced abrupt lamellar separation and larger dissected areas, whereas smaller needle gauges generated higher upstream pressures due to increased hydraulic resistance. Synchrotron imaging revealed the microstructural transition from intralamellar fluid permeation and wall swelling to the formation of a large fluid-filled delamination cavity. These results support a mechanistic framework in which the introduction of pressurized fluid within the aortic media behaves as a hydraulic fracture process in a layered poroelastic tissue, governed by balance across fluid pressurization, wall loading, and interlamellar strength. The findings provide quantitative insight into the biomechanical conditions that contribute to the initiation and propagation of aortic dissection.