Mechanical and structural contributions of elastin and collagen fibers to interlamellar bonding in the arterial wall.

The artery relies on interlamellar structural components, mainly elastin and collagen fibers, for maintaining its integrity and resisting dissection propagation. In this study, the contribution of arterial elastin and collagen fibers to interlamellar bonding was studied through mechanical testing, multiphoton imaging and finite element modeling. Steady-state peeling experiments were performed on porcine aortic media and the purified elastin network in the circumferential (Circ) and longitudinal (Long) directions. The peeling force and energy release rate associated with mode-I failure are much higher for aortic media than for the elastin network. Also, longitudinal peeling exhibits a higher energy release rate and strength than circumferential peeling for both the aortic media and elastin. Multiphoton imaging shows the recruitment of both elastin and collagen fibers within the interlamellar space and points to in-plane anisotropy of fiber distributions as a potential mechanism for the direction-dependent phenomena of peeling tests. Three-dimensional finite element models based on cohesive zone model (CZM) of fracture were created to simulate the peeling tests with the interlamellar energy release rate and separation distance at damage initiation obtained directly from peeling test. Our experimental results show that the separation distance at damage initiation is 80 μm for aortic media and 40 μm for elastin. The damage initiation stress was estimated from the model for aortic media (Circ: 60 kPa; Long: 95 kPa) and elastin (Circ: 9 kPa; Long: 14 kPa). The interlamellar separation distance at complete failure was estimated to be 3 - 4 mm for both media and elastin. Furthermore, elastin and collagen fibers both play an important role in bonding of the arterial wall, while collagen has a higher contribution than elastin to interlamellar stiffness, strength and toughness. These results on microstructural interlamellar failure shed light on the pathological development and progression of aortic dissection.