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 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 propagation of intramural delamination. Across experiments, injection pressure-volume curves exhibited nonlinear responses with pressure peaks followed by stepwise pressure drops, suggesting progressive micro-delamination events within the medial lamellar network. Increasing axial stretch elevated peak injection pressure and promoted 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 because of increased hydraulic resistance. Synchrotron imaging revealed the transition from intralamellar fluid permeation and wall swelling to formation of a fluid-filled delamination cavity. These results support a mechanistic framework in which pressurized fluid within the aortic media behaves as a hydraulic fracture process in a layered poroelastic tissue governed by the balance between fluid pressurization, wall loading, and interlamellar strength. The findings provide insight into the biomechanical conditions contributing to initiation and propagation of aortic dissection.